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NOTE:- Jan 2013 - UK MOT testing requirments state for a tricycle - only 1 wheel required to have mechaincal parking brake - this can be either front or Rear.

Trike builders guide JP7 builders guide trike design build
JP7 builders guide trike design build Although these are guides, the author does not advise anyone to actually build or even consider building such devices. Read, but do not act upon this information. Everyone should just live a quiet, pastoral life because the dogs of law lie around every corner. I have no wish to be closed down like other useful websites from threats by parasitic lawyers. (As lawyers get rich, society gets poorer.)

Always try to improve society rather than just take from it. Until then, lawyer stuff. Copying, duplication or transmission of this material whole or in part is not permitted without the written permission of the author. The contents of this text are for illustrative purposes only, and available here to view, for those who wish to buy a copy and support the research. Those using this information do so entirely at their own risk. Errors and omissions excepted. Contents subject to change without notice. All material herein is subject to copyright, patent and other intellectual property rights. All rights reserved. Copyright (C) J.Partridge. 1999. 2003.
Have a nice (lawyer free) day.

In March 2006, this web page has been copied and printed, then sold on E bay without my permission. Such is the modern world, at least I know that this web page as a book is worth 20 quid plus a fiver for postage, so perhaps I should start publishing it for a tenner, plus a fiver for postage - any takers ? - Of course not, why pay for something that's free. If someone tries to sell my work again, I'll may get annoyed and even consider putting one of those awful parasitic lawyers on the offenders arse.
If you are going to print this out, (for personal use only !) then at least check out 'Printers' on my web site for cost effective inkjet printing, so it need only cost you a few quid to print out. On my word processor it works out to 150 pages, or 100,000 words and that's without the piccies, so you may wish to set the browser text to small or smaller and test with a few pages before printing from a web page. It takes all sorts I suppose. Have a nice, lawyer free day. :)

This text is available to view as there are not enough high quality trikes out there. If you like the text, please offer feedback as this helps me to refine the contents.
Lots of other bike and trike stuff via the website at
Being long term unemployed motorcycle mechanic, technology and science teacher, marine and nuclear engineer, B.Sc, B.Ed. and draughtsman, I'd like a job please.

Please consider this monograph a bit of a C.V.

Feel free to email.


A Builders Guide To Trike Design.
J.Partridge. B.Sc., B.Ed. Gizzajob.
Version 1j. April 2006.
Because of a plague of litigious lawyers in Britain today, nobody should read this,
nor ever attempt to act upon the following information.

Index for trikes.
Chassis design.
The engine I.
Frame design I.
Engines II.
Transverse engines.
Frame design II.
Bike frames.
Front ends.
Steering head.
Building the frame.
A build sequence.
Parking brake.
Fuel system.
Fuel injection.
Radiators and aerodynamics.
Engine adaptations.
Other bits.
Load carrying.
Keeping it tidy.
Non destructive testing.
Destructive testing.
Final Testing.
Basic tool kit.
Basic materials check list.
Invalid bikers.
Useful info sources.
This monograph is a bit long. Don't try reading it all in one go, (I wouldn't.)
I'd recommend a skim through, then properly read each section when you need it.

I've kept it down to just the basic stuff, plus some of the more interesting bits and bobs. There is almost no arithmetic and certainly no maths, leaving you to gauge trike structural and handling requirements by using common sense and non arithmetic geometry assessments and other ways to make your trike handle better from the design stage onwards and also make it safer. If anyone wants the maths, physics and geometry stuff to be added, just ask !
For the wiring, well that's another (42,000 word) story, also freely available on my website.

I help design and build trikes, from mini's to V12 fuel injected trikes. These trikes can out-handle rally cars on corners, and Jags on the straight. I build custom trikes and trike modification kits to order, if local, see appendix. If you want to build the worlds ultimate trike and do it on a sensible budget, just ask. I'm unemployed, so feel free to employ my services.

NOTE: The following is based upon personal experience and is for guidance only. No-one should try building such machines without reasonable abilities and know that injuries can ensue from the materials, tools and from riding of machines. Those using this information do so entirely at their own risk. Fully understand the implications and dangers before building, testing and riding.

This monograph is aimed at those who wish to learn from a hands-on approach using commonly available technology. The intention is to make trike design and manufacture available for all.
This is not a 'stick part A to part B' type of guide, neither is it a 'how I built a trike' guide.
It is exactly what it's called. -
A Builders Guide To Trike Design.

Attention is drawn to the fact that there are a few other reference works explaining the technical and theoretical application of similar machines, mainly regarding on single front wheel - dual rear wheel stability.
This monograph is how to design and build a trike is a full process, from initial idea to final testing and beyond. You will be expected to use YOUR brains to design and build and test YOUR dream trike. This monograph should hopefully keep you on the right path, and hopefully help you build a much better trike. If you are prepared to learn, and want a better trike, welcome.

When building a trike, remember that it's all been done before, from children's trikes, through VW trike's to V12 monsters and beyond. What is important is getting it right.
Getting it right is not simple, but neither is it unduly difficult, as many home builders can manage excellent machines without expense. Yet far too many trikes start off as a good idea, but often suffer with poor design if any, with bits bodged on as and when needed. Some trikes that are road legal simply frighten most people; we all know what we are talking about.
I often get people emailing me asking for advice after an expert has built them a trike and it handles appallingly because it is of such bad design.
In some of these photos I see excellent welding, new tubing and a big workshop, but although the mechanic is working to their best, it simply is not enough. A good mechanic is all to often not a chassis designer, the ability to design a trike is desperately in need of more than just simple mechanic work.
I realise that most who build trikes are not engineers nor perfectionists, but usually know that a better trike is possible, hence this monograph, to help them look a little further towards a better trike.
It is the common failure to develop the fundamental machine in the initial stages is usually the main reason why so many potentially good trike concepts remain less than perfect. Read on.

Designing a trike is not just a case of building the nearest idea that will work. Anyone can design a simple cardboard box, and many trikes look like they are thrown together rather then designed. Take your time to think first, only then can you build.
This monograph does not want the reader to follow like a sheep, as this simply limits the readers boundaries. This monograph is a means to help develop the initial idea for a dream machine, and then to build and refine it.

". . . you won't have a future if you don't make one for yourself.
It is as simple as that.
If you accept the forms that be, then you are doomed,
to your own ultimate blandness."
- John Lydon. (Sex Pistols.)
It is possible to make a simple trike such as welding a Austin Metro subframe to a bike frame or a couple of scaffold poles, or fixing forks on the front of a VW with a bit of box-section, but a triker's life should be far more exciting. To make life more interesting and to highlight what this can involve, the following is based on a car engined trike with a frame designed from scratch, with bike framed trikes also considered. This describes a path through the design stage, the building jungle and traps, to testing a working machine. From this, the sculpting and other options are then discussed.

This monograph is aimed mainly at designing the larger, car-engined trike and is based on first hand experience building trikes which out-handle sports cars in the bendy bits of the road. The processes are not expensive. Many excellent machines are built on a small budget and good wits.

Each trike will be different to what is described herein, but the guides and suggestions will be applicable to all. It's assumed that the reader is able to rebuild an engine and know the basics of transmission and suspensions. If not, the workshop manual of the donor machine will help.

For first timers, it's best to build to a budget at first, then to decide if to modify, elaborate or simply try again.

A budget trike can also be a work of art without compromise, if based on a fairly sensible (and surprisingly cheap) car engine. The cost of creating a well-built trike need not be expensive, thereby allowing for a few tries or major modifications before the final form is acceptable. The processes described herein are all fairly cheap and can enable a good working trike to a sensible budget.
Even if the first attempt does not work well, rebuilding a frame is not as bad as it may seem, as a total rebuild does not require making new steering head, gearchange nor a host of other re-usable components, leaving just the frame tubes to be re-designed.
Flourishes can be added later, such as a full engine rebuild, better wheels, seats and paint. This should be done preferably once the basics are refined to a level where it stonks around corners, stops on a sixpence and performs reliably.

The basic costs are a decent welder or paying for the services of a professional welder, the cost of an almost complete donor vehicle, usually a car and also the steel tubing. See check list at end. Tools are minimal, but an angle grinder and a good engineers vice mounted on a strong workbench make for a much easier life and are always worth the cost.
The only high costs are having the steering head, spindle and slab yokes made professionally, although even these can be circumvented as described later.
Both the donor vehicle and stock metal tubing are surprisingly cheap.
The biggest cost is time and effort. Time and effort lead to good design, accuracy and good handling.

This monograph is long and I doubt if anyone will follow all the possibilities, but even if just a few aspects mentioned herein are of use, then I hope it can lead to a better trike.

Getting your ideas together.
When ideas grow, they rarely stop and they will give a vast choice of ways to do things, from the simplest nut and bolt to the overall look of the machine.
Some people may find drawing difficult, so begin by copying pics from magazines to start the ideas rolling. Buy an A3 sketch book, a decent 2B pencil and eraser. The reader will be surprised just how fast the pages will fill up with ideas, usually rough sketches at first. Well considered ideas are the difference between a second rate machine and a trike to be proud of.
If your drawings are terrible, do them anyway and if, like many of us who failed play school hand painting, and you're embarrassed, then keep them to yourself. Your ideas are what you need, not good art.
Your ideas will change, perhaps as your wife and kids hassle you for better seating, while you prefer sleeker styling, meaner look. There are a thousand and one other needs, such as where to put the shopping. Yes, trikes are often used as day to day transport for shopping and to take the kids to school.
When the rough outline gets close, follow up with simple plan and side sketches to decide how the engine, kids, shopping and macho image will eventually fit into your design. This takes time and many a good cuppa or beer, usually over many weeks or months.

A trike by it's very nature is a lifestyle statement, but this alone should not be seen as justification for a second rate machine. If making a lifestyle statement, be it high tech, post-apocalyptic in style, or a sculptured art form on wheels in the Italian style, then make it a superb example. Do not accept second rate.

All good trikes start with a clean sheet of A4 paper and a pencil. After dozens of sheets, the design will flourish and evolve far beyond the original concept.

For those with garage or other floor space and enthusiasm, buy a roll of pain wall paper, often known as lining paper. Join two ten foot lengths together with a little glue to give a large sheet to draw the machine full size in side view, which can be rolled up when not in use or pinned to a dry garage wall. A full-size side view is important. This will greatly help getting much of the design right, including the weight balance, centre of gravity, rider seating, deciding the vertical forces and the frame design. A full-size side drawing is also very important to ensure the side view styling will be as good as possible.
The other side of the paper can contain most of half a plan view. As lining paper is cheap, simply use more paper for the plan. For those with dedicated garage space, then the basic machine can be drawn roughly full size in chalk upon the floor, modified with a damp cloth as the design progresses.
Drawing full size gives the best chance for the fundamental design and overall styling to be refined. This saves time and money, by allowing the engine layout and seating to be thought through and refined before purchasing anything. Always note that full size drawing do not always look the same as what you imagine. Stand next to an ordinary car and imagine that if you drew this on the wall, it would look to small to get into. For this reason you will also be drawing full size shapes of the rider and passengers. If drawing on the lining paper or on floor, then time to sit down and draw some outlines. Welcome to ergonomics.
Decent centre lines can be painted on the most level part of the garage floor, allowing the chalk ideas to be regularly re-developed. A taught string accompanied by two strips of masking tape each side followed by a narrow line of paint. For those who seek total accuracy in poorly painted lines, accurate scribe lines can be made in the paint with a knife blade.

Eventually an idealised layout must be decided. If deciding to build around a specific engine, then that is OK. Trikes can be built engine first, or style first. But there is no need to decide on a specific engine before designing the trike, as there is a vast choice of engine layouts available for fitting into almost any trike design.

The next step is to draw a trike and a stick man on your sketch pad.
It does not have to be accurate, simply measure the probable wheel diameters, relative to the stick man, e.g, wheels up to the knee. Check by standing next to the potential choices of donor car, to find how far up the leg the wheel is, then place the feet toe to heel across the front or back to get the overall width across the wheels. Welcome to research.
To make a scale drawing, measure your height, divide by four or whatever is usable to get a scale drawing of the wheel arrangement and a man which roughly fits the page. Make a note of the scale on the page.
Then measure the outside width of the driven wheels of the potential donor vehicle and make a basic plan view using this wheel width and centre line. (Plan view is looking down from above.)
If a scale drawing is too much hassle, simply use approximate drawings.

Before buying a donor vehicle, buy the workshop manual and sketch or trace the engine and wheels onto the pad first. Do this in side and plan views. The intention is to get a general shape of the engine to see where any awkward problems may arise. Once these drawings are reasonable, draw the lines much bolder. Now use this general arrangement of engine and wheels to slide under the pages to help make many more drawings. With side and plan views of the engine and wheels, then this easy drawing system will allow a large number of designs to be easily created. It is not unknown for two or three different engines to be drawn allowing a better range of options for the final design.
It is now much easier to make many drawings of the machine in various forms, styles and passenger layouts. Usually done at work or while watching TV, and may probably become more interesting for all the family. If the kiddies want a parasol top or twin rocket launchers, then at least they are becoming part of the design process and may soon grow up to learn a lot faster about design, technology and style than other kids.
The design associate involved with taking the kids to school and the shopping will be much more dedicated in certain concerns, such as a cool luggage compartment so the ice cream does not melt above the exhaust on the way home from shopping.
Even a family friendly trike can still be an intimidating machine to other road users, or an art form, often both.
Design many times, to build the best once.

Study the workshop manuals or actual machines.
Many engines in the front of cars can be moved rearwards in a trike. This applies to both in line and transverse engines. Decide how much further to the rear the engine can be moved to give better overall trike balance. The typical front wheel drive transverse engine, wheels and transmission can be positioned to the rear as one lump. A traditional in-line car engine can shorten the prop shaft.
Draw the various options to slide under the sheet until the engine can be repositioned until ideal, or to see where it can and cannot go. The stick man rider and passengers will compete with the engine for room, but a good accommodation of all should ensue.
As time progresses, there will gradually develop a need to have an engine with perhaps a specific shape, layout, mounting, gearchange or braking system. The range of possible proportions and layout is priceless knowledge.

As the ideas gradually fall into place like a jigsaw puzzle, the choice of engine will become more defined. This is where paper simply saves so much hassle later - the process of creating a better design from the start. There are many trikes which suffer from the outset from using less than ideal layouts. Only the reader will know whether the choices will work well and also look good later.

By having a basic drawing of the engine and rear wheel layouts over which to trace, it is possible to draw up many different chassis designs. The front wheel can now be positioned wherever it will give good style and balance with a decent turning circle. The stick man will give overall scale, which is very important to get the ergonomics and all-round proportions and the styling close to the real thing.

When building any trike, get the basics right and many of the details well-sorted before the hard work starts, so there will be fewer hassles, possibly none. Make sure it's fun, a trike made with loads of hassles from the outset will always be second best. The best way to eliminate most hassles is to get it right before starting the hard work or spending money. The reader may not know the problems, so drawing will help highlight the many ways a dream trike can become a nightmare, and so prevent problems later. Brain work done in the first few months will save more than three times the effort later - guaranteed.

By taking time in the early stages and constantly refining the design, the builder will enjoy watching the original ideas grow and flourish on the paper. By gradually working though the design, finding better or easier alternatives or work-arounds for major problems, the processes will develop fewer hassles, and finally design an effective machine, perhaps the trike to beat all other trikes. Engine choices may change and refine, seating will get better, and overall profile will gradually evolve towards the perfect shape and form.

Should your kids one day point at an Italian sports car and decide the cut lines are 'totally incongruous', then smirk quietly and consider becoming a design and technology teacher.

Typical problems.
I have received many requests, from email land. Here is a typical example from across the pond. We all learn from our mistakes.
So while reading this, do not just make something different, but also take plenty of time to understand the fundamental design needs so that your designs will not cause problems.
This is where paper and pencil come into their own.
The pen is always mightier than the welder.
Time and a cuppa tea cost nothing - so use it to your advantage.
Here is a Yamaha 1100 V twin modified into a trike. The owner had many problems with it and emailed me as the mechanic seemed less than happy to solve them.
I suspect this builder had no pipe bender, and although this is not vital, it does help produce a nicer machine.
So please, please, please use the paper and pencil before anything else, as it solves so many problems and always makes for a happier trike and a happier mechanic.

There are superb welds, but some classic potential trike problems. The arrow points towards the white mark on the rear wheel showing that accuracy is probably good and that the basics are understood, needing just a little initial thought prior to making a much better design.

The Yamaha 1100 front end was standard right back to the swing arm.
Because it was a shaft drive, a ford rear end was used and there is nothing wrong with this. Both very reasonable choices.
What was wrong was the serious lack of forethought.
The propeller shaft from the engine to the diff was left at its original length, and therefore the rear end was too far to the rear that it put nearly the weight over the front wheel and it became atrociously heavy and possibly dangerous.
A possible solution: As this is a fixed rear differential, then there is no need whatsoever for a long propeller shaft, and even a sliding spline link need only slide a millimetre or so, to allow for chassis flexing and engine fitting play.
Therefore cutting down a prop shaft needs only the grinding of the weld and sawing the tube much shorter, then welding the end accurately with a set square and file. Then spin and balance between a couple of spikes, or with the wheels off. Prop shaft end pieces are usually fitted in the tube with a stepped machined face, so are fairly easy to fit. Because the prop shaft is much shorter, balancing it is also easier.
I suspect the prop shaft length and inability to solve it from the outset led to most of the heavy front end problems.

With the short prop shaft, the overall balance of the machine is far better, much less weight is placed over the front wheel, preferably a similar load to that of the original machine, although now having a purely vertical alignment, the steering will of course be harder, - as leaning a bike, and with round profile tyres, makes bikes easier to use.
Nevertheless, this trike with a very short prop shaft would be far closer to a good trike.
But there is much more to be done before I could live with this trike chassis.

Secondary solutions.
The width at the rear was atrocious, and although used in lard land across the pond, I still believe that lithe trikes are better. Therefore I would shorten the left shaft from the diff to the wheel axles, buy cutting, shortening then sleeveing and balancing, to bring the rear wheels in about 20 percent closer. I would also check if there were any mass dampers on the original wheel prop shafts.
This would also align the diff to line up with the bike shaft output. Then make sure both wishbones are identical, but the diff offset to one side in the frame a little to optimise the diff alignment, and reduce overall width of the machine. The wishbones would be a little narrower, and would allow a stronger central frame. The minor offset of this fixed mass could be offset by placing the battery appropriately so the axle loadings are well balanced.

The ford diff has fine set of six bolts on the output of the diff, and to this I would contemplate fitting motorcycle discs outboard of the diff, so that I could use wire or there spoke wheels with a very light, clean and open look.

There is also no cross piece between the lower rear wishbone mounts, so this part of the frame is prone to spread dangerously under load and will cause steering problems but welding one would permanently prevent the diff being removed, while a bolted version would place undue stress on bolts unless well designed. I would weld the lower tubes and employ an upper, bolted tube in compression for easier removal of the differential.

The wishbones could be a lot sexier, and they also looked identical in length for upper and lower, units, which is another wasted opportunity. The wishbones have no triangulation, so under power, they will want to bend forward along the horizontal plane as an unstable four bar linkage. For this reason, wishbones are usually triangular. These will need a triangulation tube to change them from a rectangle to a rectangle made of two triangles. as the main forces are accelerating, then I'd place the triangulation tubes from outer rest to inner front as compression is always the best way to resolve force in short tubes which do not have large welds.
I would have made the lower wishbone extended triangular, with the extended front tube to take the acceleration and braking loads, thus making the upper wishbone lighter and leaner for easier passenger room.

The shocks in this example are poorly placed and offset. The vertical shocks, just under the arrow are not the happiest of items.
If needing a low profile for perhaps a top rack or seats, then two lighter shocks on each side is preferable to maintain balance, although it would look much nicer to take the opportunity to use Formula one technology and fit compression struts to shocks mounted horizontally above the differential. This would also allow the shocks to be adjusted in leverage to match the rear axle loadings and also allow the horrible upper structure to be removed to leave clean lines.

The superstructure is also most likely to push up and bend if not supported with a stay tube from the present upper shock mount to a point on the lower tubes, preferably near the diff to prevent bending.
The best solution is to mount two small motorcycle shocks either side of the lower wishbone outer pivot and have these shocks either side of the prop shaft to a low upper mounting. Such shocks are often available from 125 and 250cc bikes, - so choose a commonly scrapped bike for donor parts. A simple rear end would be to place the shocks on the upper of the axle housings and fit a small triangular arrangement to the frame over the differential should it be needed.
(I have shown this picture a second time, to save the reader from having to scroll up and down, and takes no extra room on my website.)

Rebuild option:
First, shorten the prop shaft as much as possible. Then cut the frame tubes beside the original bike frame and move the whole forward to the optimum new prop shaft length and alignment. The width of the bike frame will allow a slightly offset differential. Then shorten one shaft and build this side wishbone first, then make a symmetrical copy for the other side.
Then position the shocks close to the prop shafts to decide the shock loading, and mount accordingly, to allow supple suspension.

Because the new frame tubes do not reach up far onto the frame, then there is a natural tendency for the upper rear tubes to bend the frame tubes inwards, This would be reduced with a shorter frame, but must be checked nevertheless. This should be checked under a load of sandbags, and see if the rear engine bolts are tight. If so, then I'd recommend that the upper tubes are welded higher, by making a bend in them - and then at the bends, adding a triangulating tube down to the bottom tubes where they meet the lower bike frame.

Although this trike is not finished, there is no lateral triangulation in this frame. As a trike does not lean, there is a far higher lateral, sideways loading on the frame, and this frame most definitely needs a triangulation in the horizontal plane. Therefore a tube on both the upper and lower sections between bike and diff will be needed. By making them the same looking downwards, the side loads will be even, but if placing one as a X cross to the other, then there is a chance for a torsion twisting if the vertical load is too large. So keep it simple and symmetrical for best handling.

Here is a nice example of a trike rear end.
The axles took MacPherson struts, but have been beautifully crafted to take adjustable upper wishbones.

This is a nicely done rear end, although a little heavily built because it's a chain drive GSX, it also has adjustable inner links to adjust the camber and resolve the acceleration and braking forces well. The shocks just miss the prop shaft for a neat arrangement with an almost central shock force resolution under compression, thus improving handling when cornering. I would implore all trike builders to contemplate a few similarly neat arrangements, and even the simple 3D graphic below, shows what is possible with sketching before turning to metal.

Apart from the whole assembly being closer ands mentioned, the bottom wishbones would be pivoted from the front of the frame to assist acceleration and braking forces more safely into the frame. I would use rubber bushes here, either from a small car or from a 250cc bike swing arm.
The rear shocks are neater and far more strongly supported and may be closer to the original Yamaha shock angles, but if not, then I would simply use car shocks from the donor rear end if the rear was a little soft in compliance. The triangulation would be done to enable the differential to be removed, probably by using a few spacers on the through bolts holding it in place, so the rear end is well triangulated for resistance to flexing.

Adding an anti roll bar would be simple, with just a couple of U brackets and rubber sleeves to take a standard car anti roll bar, and bolt the ends in rubber, in U clamps near the base of the axles, near the shocks.

This is not complex and is a typical and just plain 'old standard arrangement found in trikes and kit cars. - Just look and learn.

The original car rear end uses discs, so parking brake may be a pain. I'd consider adding a parking brake by fitting a small motorcycle disc on the propshaft flange where it enters the ford diff and mounting a simple mechanical or hydraulic brake calliper onto this, restrained by a bracket on the frame such that any excessive braking forced are resolved parallel to the disc to prevent distortion. A drum brake is also possible for an easier life, - but make sure it is a bike rear brake, as this allows the brake to be applied forward and in reverse, whereas some brakes have twin leading shoes and only work well in one direction.

Other notes.
In this particular case, the owner said the trike handles very poorly and pulled to one side. After emails, it transpired the forks were out of alignment, and presumably need straightening or the front end was not aligned accurately in the vertical plane. Many people use a tape measure between the centres of the wheels and the steering head, but fail to check the steering head is vertical relative to the rear wheels.
Other potential problems could have been sticking rear brakes or uneven wishbones, or incorrectly aligned rear wheels with perhaps toe out or non symmetrical alignment.
The owner also said the trike was hard to steer. I recommended shortening the prop shaft and rear frame first, to take some of the load off the front wheel. Then if this was not enough, the trying a little toe - in to see how it feels, and if this was not enough, then slotting the upper yoke central hole slightly then shimming it forwards slightly to reduce the amount of trail, which should make the handling more skittery, but as it was too heavy, then this should eventually reach a happy medium,- but ONLY after careful high speed tests and possible use of a steering damper if any signs of potential problems occur.

This trike rear end could be totally rebuilt over a weekend using the same items, plus a hacksaw, welder, tape measure and some thought.
If the mechanic is reading this, please do not be offended, as I have seen much worse. - You will find that shortening prop shafts is quite straightforward, and then much of the rest should fall into place. I would also consider using the donor Ford rear suspension wishbones and also the ford handbrake and hydraulic linkages for an easier life.

Chassis design.
From the outset it is necessary to get the handling right. This is theoretically imperfect for a single front wheel. But all the theory and science to the contrary has not managed to make itself apparent on many a good handling trike - so it can be done. The theory and trike riders who like power drifts do not always agree. The main problems are weight balance, decent rake and trail, good wheel alignment and overall set-up.
Chassis design will always be dependant upon the engine, causing the design to require certain engine mounts and the way the transmission and wheels were manufactured relative to the engine.
Weight balance is a moot point on trikes, but for general awareness, the following can be considered.
With equal weight on each of the three identical wheels, basically, neither wheel will want to break away first, for ideal grip. Unfortunately most trikes have wider rear tyres and a narrower tyre at the front. Worse still, when cornering, the outside wheel will become loaded, while the inner gets light. Worse still, such rear tyres have a flat profile, while the front is probably a partially rounded section because of action of the use of forks, with their large rake angle compared to cars. On a heavy loaded front wheel, the traditional motorcycle fork leg suspension may often be close to its limits (unless specially designed). When cornering, the inside rear wheel unweights dependant upon cornering forces, and will allow the inside wheel to break away first, causing slippage in the differential. Never rely on rear wheel break-away before the front as a good idea. It is not.
From this you will realise that too many trike tyre choices have more to do with style than engineering. But good style can still include responsible or even superb engineering choices. The engineering choices of balance and traction while cornering or braking are notorious on trikes, so always do yourself a favour; consider the better choices from the outset. If worried bout imbalanced wheel sizes and loads and footprints, then just consider how much weight is on each while stationary, then decide if it is ridiculous or adequate or good. While cornering, consider the wheel loads and how they will or will not help the tyres in doing their job. Also while braking, the loads on the tyres will need some reasonable choice. As this part of the design process is likely to cause worry, the process is described in more detail later, but please do not worry too much at this stage, just make sure it looks reasonable and not too stupid, unless a purely show trike. For road use then simple common sense is usually acceptable.

Ride as many trikes as possible. If not, ask all owners how they handle, especially around corners. Always take the opportunity to study the way the various trikes handle to check what is happening at the boundaries of the ride envelope, then ride within a safety margin. Get to know the break away signs and refine the riding reactions necessary to control them. See testing later. Unless the trike balance is based on another good handling trike, then take care and consider the weight distribution carefully.
I have yet to ride a truly decent trike, or at least one that comes up to my standards of handling, although I have ridden a few that are very close. (Thanks Spike !) But these are rare and most trikes are just plain appalling. - I just had to write this monograph.

Do not get overly worried, as many trikes have terrible weight balance yet are quite adequate for most purposes of daily transport. If building a better machine, consider that, although most cars, including factory rally cars, they often have the engine in the front and the driver too, with a lightly loaded rear, yet they still handle fairly well. For a much better approach, formula one cars usually prefer a mid engined design, with weight distribution between 45/55 to 40/60 percent front/rear. This is not possible on trikes, but a mid mounted engine greatly helps.

For a single front tyre, aim for around equal load on each wheel, giving about a third of the weight on each wheel. Then adjust to match the front wheel size. If it's a light, custom front wheel, then reduce the weight on the wheel more than if the front wheel is a car wheel. In the worst case such as a VW trike, with the engine hanging out the rear, this may even require front weights. At the other extreme, this may not be possible with a Jag V12 trike without serious modifications and a strong front end.
Sensible engine choice and overall layout of engine, wheels and riders is going to pay dividends later. Aiming close to a sensible weight balance is unlikely to do any harm.

The engine.
Making trikes with bike engines and frames is a doddle.
If you want to use a bike engine but make a new frame, then car chassis design applies.
But the bottom line is that using car engines is the best way for maximum stonk for minimum pennies, and is the main way described in this monograph, as there are many more variations with car engines than with motorcycle engines. The only hassle with motorcycle engines and frames is fitting a differential and rear axle(s), as described later.
Note: Do not use a car engine with a narrow power band, as changing gear on a trike is not so well controlled as in a car. Choose an engine with a wide power band, so you don't have to change gear while diving in to a fast corner, where removing your hand from the handlebars can lead to poor control.
Only use fiery engines if they have an automatic transmission or have electronic 'paddle' gear changes.

When it comes to car engines, most trike builders begin knowing little about car engines. This is not surprising, as nearly all trikers are bikers and most car engines are boring.

Welcome to the wide and wonderful world of the infernal combustion engine.

Car engines are a wide world of inline fours and sixes (mainly boring cars, with a few exceptions), transverse fours and fives, yes, fives!, V6 and V12's. (Transverse Lambo V12s are rare.) Flat fours and sixes (VW's Porches, Subaru, Alfa Romeo), Vee and flat twelves, inline V6, V8's, V12's and a whole lot more.
If it's not there, then bikes can furnish V twins, fours, transverse, 2,3,4's and sixes. If looking long enough, the builder will be spoilt for choice.
The local newspaper adverts and scrapyards are ready to offer some serious metal. Start by looking at the cheap cars section in papers, as many excellent donor vehicles, usually with rusted chassis, are available for spares or for next to nothing.

When starting your hunt for the engine, go for the whole package, in both design and in building. The prime concern for a trike is overall layout of engine and transmission relative to the wheels and overall weight balance.
Scrapyardin' used to be a traditional British hunting sport. Today, due burEUocracy, there are few old-style scrap yards which will allow builders to scramble over their stock. This is a great shame, for inspiration always comes from looking. When up to the ears in rusty, bent and twisted metal, one always spots a new idea, a little jem, a new concept or design possibility. Occasionally one will spot a worthy machine, from which inspiration can flow in torrents.

Before going to the local scrapyards, stroll off to your local library, if there is still one. Sit close to the workshop manuals and similar vehicle publications. Work through them, study the layouts, their possible options etc. Always take the sketch pad for notes, tracing paper or some cash for the photocopier. If you have a digital camera, then use it to good effect. The author is occasionally found in various sections of libraries reading and often clicking away. Even if the ideal engine is not found, at least what to avoid will be learnt the easier way. Most trikes can be built on a tight budget, so knowing the basics with simple research is a good way to save money, time and effort it works every time.

There are two main forms of car engines as used in trikes, either with the engine between the riders legs at the front, or hidden at the rear, between the rear wheels.

Once a general idea is created using your preferred form and layout of engine and transmission, check out and find the local friendly scrap yards. If scrap yards are not local, or are less than their normal friendly type, then get to know engines by simply looking under as many bonnets (hoods) as possible, as there is no substitute for seeing the real thing first. This will lead to a working knowledge of what engines are good, bad or indifferent. The best alternative is to help out in a garage, or preferably a large scrapyard for a few days, especially if unemployed, ideally in exchange for a donor machine. Just ask, you may be pleasantly surprised. Make sure you turn up in tough clothes and boots, be honest with them and leave your phone number, they may get a rush of vehicles and need some help soon, possibly during the new car registration season. Not only will you get a cheap motor, you will also know how machines are actually held together and work. If you get this lucky, take notes and always stroll around during your lunch break.
In whatever way is available, helping out always helps to understand the underlying engineering and makes for a good, short and very effective apprenticeship.

Although weight balance is poor, engines like old VW's are easy for trikes, as the engine, gears, final drive and suspension are all in one lump and set up ready for use. Even the gearchange is a doddle.
Never take the easy option - you will have to ride it.

Some engines can be very difficult. What looks simple may have major design flaws. Look, think, then buy. Be prepared to scrap the engine if a better design is found, as there will be a lot of time and effort put into building a good trike. When done properly, the trike may be kept for decades, so if a better design of engine turns up, be prepared to go for gold. The best is to spend time getting the ideal 'generic' engine and transmission from the outset, so time and effort spent choosing the best donor vehicle is never wasted. It need not be an expensive version donor vehicle at this stage, as the better engine can be fitted later, possibly the later turbocharged version if the trike handles well enough.

If buying a V8 off a friend because it's going cheap, you may be going about this the wrong way.

Heavy engines at the front tend to understeer.
Engines at the rear tend to oversteer.
Engines with too much weight behind the rear wheels such as VW's can have you pulling wheelies in second gear every time you pull away. Great the first few times, but when you get annoyed doing it every day, you may think differently. Engines with iron cylinder blocks are heavy.
Engines with dubious reliability or poor spares backup should always be steered clear of.

Here is the crankcase of a Porsche V8 engine, from the front engined versions which have a terrible reputation for reliability, (Because the yuppies drive them in to the ground without bothering with servicing) and so often get sold for pennies. A car for spares for 500 quid and a runner for 1,000 to 1,500 quid. This includes matched transmission, serious brakes and all the other bits, including the badge and key fob.
Such machines give the trike builder many excellent starting points, not only in engine, but transmission and most important of all, a low slung engine and plenty of serious stonk.
Note the engine is unlike some V8's; It is perfectly balanced, eight cylinders in 90 degree format, just like having 4 Ducatis,- that'll do nicely !
For this engine, a low, all alloy and more racing character would be inherent in the design, more than any aftermarket custom catalogue could ever hope to achieve. Built properly, it can also be very reliable.
See also sketch of Porsche V8 transmission for a complete, well balanced, and nicely overpowered trike design.

I am not advocating the Porsche as the only choice, far from it, but for bang per buck you can not only get excellent power, handling, but also a posing key fob too, simply by careful choices from the outset. It all boils down to choosing the best donor car or bike for you.
You simply cannot buy the fundamentals of a real custom machine from catalogues, no matter how much you spend. You may end up with an overpriced Harley motor and semi cute frame, but they all eventually look the same from a distance.
So please think about going for gold, not spending cash like a drug dealer looking for another Hardly Maybesome.

Another good choice is the Citroen 2CV, 600 twin engine. This is at the economy end of the engine world, but is a superb example of having an almost ideal trike engine. The weight is forward of the rear axle and very low, with inboard rear brakes and can be built with a rear suspension design similar to formula one. Only the upwards exhausts are a minor problem. This makes a superb two or three seat trike for general use at normal speeds. I see these motors being relentlessly thrashed across France and they are simply indestructible and I consoider them far more reliable than Porches.

For most of us, the classic choice is the bog-standard transverse front wheel drive, four cylinder water-cooled car engine and transmission. These are often available for free.
The whole engine and transmission and wheels can be moved to the rear of a trike design for minimal hassle. Only the gearchange and rear passenger seating may be problematic, so check first for the best design choices. See later.

These are just three of many very different yet good possibilities: Always decide what you want as your trike.

To repeat; Do lots of homework, then enjoy the pleasure of knowing you have the best design route towards your version of perfection. Take your time and use some imagination to get the engine, transmission and wheels with the perfect shape and layout. Searching library, scrapyards, garages and workshops is the best way to see how engines, transmissions and suspensions are arranged. Take your time - as the more you know, the more you will understand how to build your ideal machine, and the fewer the hassles.

When a good choice is made, search the local ads for a suitable and cheap test failure, and always get a receipt and the documentation. Don't get fobbed off with excuses.
No documentation - no purchase.
It may be necessary to place an advert for an unusual machine. If all else fails, then it's the scrapyard again. With a little common sense, you may wish to search for a specific machine in a special way, such as old four wheel drive Subarus which are often left neglected by farmers, so go a huntin' and ask around. I know of two Subarus in North Wales. They just need me and a customer needing a trike, to make them happy again.

Wherever possible, ensure the engine, suspension and ancillaries are all from a single donor machine so it all fits together and works properly. Ideally the donor machine should have failed for something which is not needed on a trike, such as rusty bodywork. Ideally the engine should run and the whole machine may often be driven back.

An ideal trike would have the engine, transmission and final drive in one unit to minimise alignment problems and with the weight forward of the rear wheels. There are quite a few almost perfect engines out there, but in the real world, no engine will be perfect for every aspect of trike design.

In an ideal world, a donor vehicle will be a serious crunch job, preferably with no blood or body parts in the driver area, with only 10 miles on the clock and no real damage to the parts required. As these types of machines are soon stripped for spares, keep your wits about you and carry cash when visiting.
For beginners, it is far better to build with an older version at first, then keep an eye out for a pristine engine later.

Decide how these strange engine and transmission shapes will fit into your design.
Have a good long look at anything promising, then chat to the guys in the garage trade and scrapyards. Tell them what you want and they will tell you if it's a dog or a doozie. If you don't see your dream machine, they can often tell you where to start looking, and what at engines are going to be close to what you need.
For example, if intending to use an Alfa, ask the Alfa garage what problems are common. Don't ask the salesman. If you want the truth, go around the back and ask the mechanic. A good scrap yard should be able to advise you if you know what to ask. Do your homework first, and think up just three best questions to ask them. Any more then three and like most mechanics, they will want to get back to work, unless it's a ciggie break.

You may not be buying the donor machine from the scrap yard, but you will probably find them very useful later on, for larger wheels, exhaust bits, special tail lights, and a host of other componentry. Scrap yards are often required to write off vehicles, you may not be able to get the paperwork from them, requiring the builder to get a new identity for the machine, so receipts are a must.
So always preferably privately buy a rough but legal donor vehicle for its identity.
Your ideal engine and suspension layout is out there somewhere, you just have to hunt it down.

For example, an Alfa Romeo engine unit lay in a corner of a local scrapyard. I had never noticed these engines before, but it had promise, the 1500 OHC flat four engine lay forward of the rear wheels, with the engine, gearbox and final drive in one unit. It even had the luxury of inboard ventilated discs on the gearbox output shafts, to allow wire wheels for a very clean look. A few faults would need working around including the total lack of carbs, gear linkage and engine mountings. As the bulk of the problems will be in design and preparation, this is a good example for designing and making a trike.
As the machine did not have a body shell around it, a search for a second donor machine was immediately begun. This was eventually found, so that by the time the chassis was built around the first engine, a second, running engine was ready for transplant, complete with all the ancillaries - no need for an engine rebuild, or excessive new wiring etc. As the Alfa is popular with junkyard racing, a totalled, barely running but 'complete' machine was almost free, but needed a few spares to look nice, and a very serious service.
The Alfa unit is in many ways similar to a VW, except it points the right way, forward, with the engine weight forward of the rear axles. In style, the Alfa is a poor man's Ferrari, as the rocker covers will polish up nicely and sit either side of the rider, with the Alfa Romeo logo in resplendent polished alloy. In ease of build, it is similar to a VW, because the engine, gearbox and differential are one piece, even better as the brakes are inboard ventilated discs. Being water cooled it was quieter and would allow a lower body shell and allow alternative radiator layouts.

To make life easy, make sure you get any subframes, suspension, gear linkages, clutch and brake cylinders, wheels, propshafts, carbs, water gauge, electric ignition, and everything else you need. Buy it all the same time as one car, so they work properly, it's also much cheaper than buying separately.
Where possible, fire up the engine and check for a good motor. A crash damaged or badly rusted vehicle is the best bet for a good engine, as its unlikely that the engine has caused the machine to be scrapped. For rust, Italian cars are excellent, as they have alloy, fiery, twin cam engines, but may be atrocious for spares - so check.

Don't choose an engine you cannot get or afford parts for.
Before paying out a large amount of money for a donor vehicle, first try buying a cheap, but unusual new spare part for the engine. If you can't get or afford it, think twice.
If it's your dream engine, be prepared to build up your own spares supply from scrap donor vehicles.
A friend has a Citroen SM car, with its Maserati V6 engine with everything polished, even the con rods, a superb classic car, but a totally irresponsible choice for a trike.

If, like most sensible builders, you choose a common donor car, you will enjoy buying a new set of brake discs and pads for less than the cost of a set of motorcycle brake pads. Even a new set of four alloy wheels with new tyres can cost less than a big bike tyre, and the scrap yards are full of excellent items at exceptionally happy prices. It can truly be surprisingly cheap to build a very good trike to a high spec, when based on a typical donor car.

Clean, check and run the engine, if you find any serious damage or noises, forget it.
For a front wheel drive, where possible, get the scrap dealer to grind out the engine complete with engine mounting brackets and such like. Preferably get the whole engine bay, right back to include the dashboard and steering, you will then have all the necessary wiring and mountings. If rear wheel drive, get the whole machine.
The better choice is to buy the whole machine, run the engine and fettle it, then preserve it carefully. Most scrap yards will deliver a wreck to your door. (An unusual experience, it's usually the other way around.) Such machines can be found locally for pennies, usually MOT failures with mostly rust problems.
The best way is to search the papers for a cheap car and drive it home. If there is no paperwork, or you cannot drive it, don't buy it.

Once you have got it all back home, there is often only room in a garage or garden for either the donor vehicle or the trike. Do not worry. In such cases, metamorphosis gradually removes the unnecessary parts until the core remains still intact - engine, transmission and suspension. Then the trike begins to grows in it's place.

First of all, give the whole donor vehicle a good clean, scrub the engine and hose off the crud. Check the engine and transmission works again and to dry it out thoroughly.
The machine will gradually transform until the engine and transmission sits precariously on the core donor chassis, supported on wood blocks and wedges. The wiring loom ends up hanging up in the roof space held loosely in place wrapped around the attached dashboard like a demented python. Likewise brake plumbing and other bits.
Do not throw anything remotely relevant away.
If in doubt, keep it in poly bags in the garden (not next to the trash) or tucked away in the garage roof space.
At all stages, you will be prone to loosing an important lug, bracket, clip or other component. It always happens and will always happen, so protect yourself from such annoying hassles from the outset. Refit all nuts, bolts and brackets back where they came immediately after disassembly and carefully bag all the rest.

Some of the things which can be easily lost are important dimensions.
Before touching a spanner, (wrench), make a permanent note of the outside width of the driven wheels of a transverse engine. This allows the transmission shafts to be properly aligned later. It is also important to measure the distance of the engine / clutch housing face to the nearest wheel. To prevent later drive shaft and suspension inaccuracies, do not replace these wheels until the chassis is built. Also measure the ground clearance of the sump, so the engine will be blocked and positioned correctly for standard suspension set-ups.
Keep the original car speedo that probably works off the gearbox to calibrate any new speedo. Same goes for the tacho. Keep the seats for foam and complete seats for total passenger retainment systems. Seat belts too. Consider flowery pattern seat coverings as patterns for remaking any passenger seats in vinyl or leather. Tail lights, side lights, boot (trunk) lid and its lock, ignition switch, steering linkage, handbrake lever and all the brake bits, both front and rear, all into polythene bags and free from dust, rain or from getting lost.
If you use an automatic transmission, check if setting up the system will need special access to certain parts of the transmission housing. If in doubt, keep it intact as much as possible.
Never use an angle grinder until having removed all the wiring and hydraulics, as it is possible to cut through something useful such as a brake pipe or tail light wiring.

The traditional way to compact a car shell is to remove the roof, and use it to stow all the parts as the shell is gradually cut into chunks. Either by use of a traditional two handed battle axe and heavy boots, (Viking heritage of real bikers) or the newer method of angle grinder and saw.
The petrol 8 inch angle grinder is now affordable for those who are not afraid to loose their arms and legs.
But if on a very serious budget, or suffering wallet attack, then buy a cheap 4.5 inch angle grinder and a few cutting discs. ALWAYS buy goggles and gloves at the same time. Then use them.
I hang my safety equipment on the grinder, so I have to remove them before use, - it works for me - it can work for you.
Continue until just the floor pan is left, into which all else can be dumped and tied down for transport by trailer to the local recycling centre.

It is extremely common to have to change a few bits as the design is refined. So keep friendly with the scrap dealers, they will probably have a later model, possibly with turbocharger, as these are harder to find in local adverts, often having been wrapped around a lamp post.

Car electrics are simple, as the modern alternator is self contained, with a regulated DC 13.8 volt output to charge the 12 volt battery and even a warning light connection which can be ignored if you feel lucky. The rest can be just as simple as you wish.
If you don't like electronic ignition, or if it fails, you can often replace it with the older contact breaker system of earlier models if you know their history. Choose your engine carefully, as many car engines have surprisingly long pedigrees. Again, talk to the trade to make life easier. Always buy the workshop manual before buying a donor vehicle, as money spent on this may save you much money later. Read fully and if all is OK, you have the manual. If not what you want, you have only lost the cost of a manual.
If the engine does not have electronic ignition, then you can make your own, using old bike pulsers and CDI units with integral electronic advance curves, which use the standard motorcycle dual HT lead coils, which work just as well with 4 cylinder car engines. alternatively you can use parts from other car engines with a similar basic layout, as they are nearly all the same in their basic formats. See making your own CDI systems on my website.

The final engine choice will be narrowed down to an ideal, specific engine during the design process. Often, part way into a project, a completely different engine may be chosen which may improve the design by leaps and bounds.

Considerations for types of trike frame layouts.
As most car engines are ugly, expect to hide them. Notable exceptions, most early V12's. Later V12's are over-sanitised and 'plasticised' into amorphous corporate blobs without a soul, ideal for accountants, but not for bikers.
The standard VW engine will give an unwanted rear overhang, but is easy to weld up a frame.
The Austin Mini gives a very nice handling machine and is quite easy, just an engine on a sub frame. It doesn't get much easier to get the basics right, except in plastic model kits. It's only hassle is a parking brake and for some, the gearchange. If you have been paying attention, then I've already mentioned earlier, three good choices.

The transverse engine. (Across the frame).
From (real) Minis to Lamborghini Miura V12.
The basic engine is the mid engine transverse four, plus the occasional five and six cylinders and the vast range of clones. Transverse V12s are very rare.
Often a good, well balanced, honest set-up, such as exemplified by the European classic later Ford Escorts. Some engines have the transmission exiting to the rear if the engine unit, while a few others have the engine behind the transmission output. The latter is better for trikes if carrying passengers very low.
Most of these usually employ McPherson struts which may need widely placed tubing over the top of the engine. Therefore it may be preferable to design for the engine to be removed from rear. The top of these suspension struts can be resolved without upsetting passenger room, as most of the braking and accelerating forces are taken by the bottom radius arm / anti roll bar, which should be kept as is. This set-up applies to most common machines.
The McPherson strut can be cut down into a more traditional suspension setting, made using the bottom parts of the McPherson strut, to allow a much neater and lower design, more in common with formula one.

Like the mini, the gearchange and parking brake will be the biggest hassles, so do your homework. (See gearchange and brakes later.)
The transverse engine is good for weight balance, allowing the trike to have most of the weight just forward or to the rear of the rear wheels, and an open book for the front end. If choosing a transverse engine layout as used on most front wheel drive cars, then for ease of adaptation, always choose a design with the gear linkage on the top of the gearbox. Unlike the real mini, the engine and transmission is not usually on a sub frame, so it may be preferable to keep some relevant parts of the chassis interface to weld to the trike frame tubes.

The front engine in-line. From Moggie Thou (A series) to Jag V12.
There are always problems with heavy front ends, so always expect to design with a shortened prop shaft to move the engine to the rear to improve axle loadings. Always keep the prop shaft sliding spline. Do not allow dangerous angles on the universal joints at each end of the prop shaft. Check the differential movement of a solid rear axle and use a Panhard rod where needed. Radius arms will usually be needed and are part of the donor machine.
Independent rear suspensions are usually far better.
The larger engines will cause a heavy front end, and may demand a car front wheel, so expect to build a heavyweight front end.
The frame will need to support the engine and will probably need to be a variation of four heavy tubes. Two over the top of the engine to the steering head, the other from the steering head, around or below the engine to take the engine mountings. A massive version of the Norton Featherbed works well if a tube bender is hired. Box section tubing makes an alternative and is very strong per unit weight but square section tubing is rarely stylish unless it's done well. If suitable rectangular section tubing is available, a wrap around design is possible using single box beams, or variations on multiple tubing.
The rear axle from a donor van may use leaf springs, so the trike will require longer lower main frame tubes, but simply replace with alternatives from the saloon variant. If the prop shaft is very short, it is better to discard leaf spring set-up and use radius arms to maintain good angles on the prop shaft as the rear axle moves up and down, and to reduce excessive frame overhang at the rear.

There are a few decent rear ends, with notable mention in dispatches for Jaguar's definitive limited slip differential / independent drive shaft set-up. As rear ends are rarely seen, standard components usually suffice. Solid rear axles are not as good as independent rear suspensions, so choose carefully and be prepared to mix engine and transmission.
Check the gearing. As most cars use very similar diameter wheels and fourth gear is usually direct drive and if engine revs are similar, then gearing hassles will often be minimal. Adjust gearing with van, saloon, or other gearbox and differential ratios, or other rear axle units, or more simply with smaller or larger diameter wheels and tyres. Always check first gear is sensible and will not cause clutch slip. As most cars are similar, gearing may not be much of a problem, but always check first.

If using a jet engine, (extreme show customs only), ensure the exhaust is deflected for zero back pressure and with even, positive down forces. (Vent exhaust to the sky.) Do not allow the exhaust to be deflected such that wheelies are produced, (unless for show) so keep the rear wheels just behind any acting point of exhaust pressure.
For 'general' use or close to crowds, do not expect pure thrust for power, as other road users do not like scorched front grilles. In such cases, use helicopter transmission set-ups, to use the power take off turbine and gearing to drive a modified car transmission. Gears may not be needed, but a clutch is important. You may need an intermediate gearbox with oil cooler. You will most definitely need large fuel tanks and also damn good brakes, as reverse thrust is not acceptable nor practical. The exhaust may need decent heat and sound shielding.
The intake will need a large screen air filter for road use, which is impractical, so the intake area may need to be enclosed in a large box, covered with coarse cloth as a basic filter. This will help prevent large particle debris from entering, which is much more common on surface machines. (Most jet engines work in clean air away from the ground, and can handle a bird strike or two.) Alternatively, the intakes could be designed to take 'clean' air from ahead of any wheel turbulence. A large concertina stack of many car air filters may help, but is normally unnecessary except in sandy or gritty countries.
Gas turbines are very light and powerful, so don't go stupid and get something totally unmanageable. Gas turbines are designed to burn fuel like paraffin, so don't expect to fill up at petrol stations on the way to the shows. Do not choose turbines which need excessive start up procedures or equipment. Get all ancillary equipment including any necessary ground crew support kit and installation and service manuals. Choose an engine with a low number of hours since its last rebuild or expect to have expensive services by officially approved turbine engineers.
Turbines like to work for hours when up to working temperature, so any stop-start use is likely to reduce the hours between services. Ensure access is good enough for regular visual checks of blades. Always retain and use the number of hours run counter and keep all documentation, especially the maintenance log. Spares will need to be via specialist dealers. Be prepared to use 24 volt and exotic electric starting systems.
When a car engine goes bang, usually just the con rod appears out of the sump. When a jet engine goes bang, there can be a massive amount of turbine flying in all directions, so inspect and maintain regularly, and build a serious steel or aramid guard around the areas of the most vulnerable blade paths, especially near passengers. These are not toys.

A sensible alternative to a jet engine is a multiple rotor wankel. (Mazda)
They are small, powerful, light, uncomplex and very smooth. Do not expect to tune or modify the engine. Exhausts will get very hot. They drink fuel and will need larger fuel tanks, an oil tank and need better brakes, but well worth the effort for an extremely low, extremely serious trike. The RX8 offers 200+HP from a very small package.

Whatever the donor vehicle choice, always keep the receipts for the parts and get all documentation. This will show the official inspector that it's not stolen. It may even still have a 'valid' road legal status.

Other aspects of engines includes noise.
Anyone who has heard a large Detroit lump fire up, will never forget the sheer thrill of burbling excess of cubic inches. A V12 on song is sheer poetry of engineering, while a wankel rotary makes its own strange music. Playing with noises requires getting the exhaust correct and tuned in and may not always be legal, so always make sure there is also room for a legal exhaust system or a butterfly valve in the pipe.

Style of engine is very dependant upon two main facts. Status and aesthetics. For some, it may be possible to get away with an amorphous blob or ugly engine if it has the right badge. Many high status engines are ugly, but to be truly perfect, an engine must look good.
Looking good for a front engined trike, the engine must be alloy, at least a V six, so the pipes look good, and with decent rocker covers. This must then be backed up with crankcases and heads which will also look the part. An iron block with oil and fuel pumps sticking out is not perfect. A sleek alloy lump, clean, neat and devoid of plumbing and wires will always polish up and look the part - light and powerful.
There is a Rolls Royce Merlin engine in the Imperial War museum in London in a glass case. It has style, clean looks, perfectly detailed and finished components, a magnificent number of oval exhausts and a superb name resplendent on the rocker covers. It is also nice to know that these engines are still thrashed regularly in the USA in air days and spare parts are still easy to get. If you ever get the chance to look inside one of these engines, the highly polished camshafts and other components will leave a lasting memory. Trikes too, can choose from a similar array of much more appropriate, yet equally resplendent engines. In the real world, there is still an excellent range of engines for day to day triking.

Unfortunately, engines also require air filters and other items, if only to reduce the intake roar and prevent excess wear. Therefore make ancillary items either hidden as much as possible by mounting the air filter under the seat and using subtle ducting, or a rethink to make them part of the overall style.

Here's a few pointers to engines of note.
Please note that the engine descriptions in this monograph are as used in a trike, not as used in the donor vehicle.
No apologies for aiming high. No apologies for leaving out many also-rans. No apologies for comments. When choosing an engine, only the builder can call the shots.

Rear engine in line. (Engine behind the wheels.)
Older VW's and 'real' Porsches - don't bother unless you like wheelies.

Mid engine inline. (Engine just in front of rear wheels.)
Subaru flat fours, good trike material and ideal for powered trailers.
Some Alfas.
Citroen SM with dated V6 Maserati engine, be prepared to get lost in the plumbing.
Ferrari flat twelve's, - mmmm, nice, but perhaps just a little too pretentious?
For low budgets Citroen 2CV and '4CV'. If disabled, get the version with automatic clutch. 2CV's are thrashed mercilessly across France on a daily basis and seem to last forever.

Front engine in line. (All must have a suitable prop shaft to shorten.)
Model T Ford - don't even think it, or I will personally perform your lobotomy.
Porsche water cooled V8. A fine piece of metal, low and light for the power. Well worth a look, but don't expect to get a genuine workshop manual. A surprising number of automatics available, and very cheap too.
Jaguar V12's. Sheer music, but how far will a tankful get you? (It still works every time for me.)
Rover and American V8's - join the clan.
Mazda wankels. Surprise yourself - get really low for stonkin' around corners. For high power, compact engines, the latest RX8 Wankel (1300cc) offers 200+HP.
Gas turbine jets. (Usually from helicopters. You will have serious hassles becoming road legal, but Frank Bell and Spen King at Rover Cars managed it - see UK registration number JET1! and others too, including G.M.) Best kept for show use only.

Mid engine transverse.
Honda and other micro vans and cars, 550cc, 'er, well guv, it's a trainer trike for the kiddies'.
Ferrari transverse V sixes - its just gotta be done. Rich punters please call the author.
Lamborghini Miura V12 - prepare to be lynched by owners club.

Front engine transverse.
The ubiquitous and all round favourite - Alex Issigoniss's most excellent Mini. (Not the lardy Brazilian BMW motor)
Ford Escorts and almost every common car - It will get you to work every day.
V sixes from various manufacturers now available and coming to a scrap yard near you soon.

Front engine transverse. - Bikes.
Bike based trikes: Mopeds to Harleys to 'busas upwards. Engines and frames as supplied. Mopeds only suitable for kiddies.

Other engines.
Honda Gold wings seem a waste of time when equally large car engines are available for much less cash and already have the dual rear wheel drive totally sorted. Cars also offer turbo options, tuning mods and such like for much more affordable pennies.

Although mainly for show use, there is no reason not to use a dual engined machine. This will require an extra wide double differential set-up, but quite feasible and usable with limited slip differentials. Consider differential mods or differential locks should one engine fail. Other set-ups also possible.

For reliability and ease of build, keep the engine and transmission as standard as possible.

Chassis considerations.
Having chosen your dream engine, time to design a trike to fit around it.
It is assumed that if wishing to build a particular type of machine, the reader will have hopefully ridden a number of similar trikes and also thought seriously about the engine.

The first thing that may come to mind when riding the average trike is the awful control, especially the clutch and gearchange. For some, the experience may end abruptly as reverse is found to be hiding yet again. This is often soon followed by the awful wallowing around corners as passengers and luggage struggle to remain with the machine.

When designing trikes, especially those requiring the subjective needs of usability and good handling, then the designer should begin with a fierce approach to the prime purpose, only ameliorating the form to fit the real world.

Sukoi's Fulcrum, possibly the worlds finest air superiority aircraft, began with the Russian designers just creating the most perfect wing. Only then were added engines, nose and controls to see how much the ideal wing was compromised. (The Americans still cannot do a 360 loop while travelling forwards like the Sukoi's. Perfection does not equate to dollars.)

This is an excellent way to build a trike, beginning with perfect weight distribution and a low centre of gravity. Then compromise the design with the best engine layout to fit, plus rider and secondary components which will minimise any compromise of the potential ride envelope.
Finally, the testing and refining the fundamental structure will help ensure the best overall design is possible.

Know and understand exactly what is wanted: Good handling, good control, safe and comfortable passengers, reliability. A trike that truly can be enjoyed every day.

The first step is to know the dimensions with which to work. Dimensions are in three forms, the fixed, the dependant and the free. Knowing the difference enables the process to develop in a fairly logical manner.
Fixed. The fixed dimensions are those which due to their nature cannot be changed: The sizes, shapes and weights of the rider and standard components such as engine, wheels and transmission. Even these may need modification before a final design is made. (I often modify engines). Decide if the machine is for various rider sizes and which size of wheels etc. It is the fixed dimensions which give us generic forms. Once these 'unchangeable' dimensions are decided, they become the starting point of the design process.

Dependant. These semi-variables are decided by the design as it forms, rather than by a totally free path. This includes the wheelbase and ground clearance which can change within specific limits set by engineering constraints. Spend much time thinking about the variables, as this is where the underlying parameters of a good design are created. For trikes, such as the possible propshaft shortening for adjusting overall weight balance.

Free. The free variables which must be created in the mind are the overall shape, colour, seat style and form and the many small styling options which make a machine a whole and competent device, a complete mess, or a work of art.

The best way to design a machine is to tie down all possible fixed dimensions and optimise their arrangement to create the best basic form. It's often referred to as 'juggling the bits'. Initially rough sketches on paper at first to assess the overall style before buying anything, then subsequently more accurately to scale or full size on paper once the main contenders are chosen, then finally in full size on the garage floor. Once the fixed dimensions are sorted, (usually engine transmission and rear wheels) the dependant variables will often fall naturally into place. Finally the builder can begin to mould them together to create the best possible design, as seen in the eyes of the designer. The reader may not consider themself a designer, but this is a genuine hands on design process.

Computers. (It had to happen. If galled or vexed, then skip to 'The most important design skill is being able to use paper and pencil.')
If preferring to use a drawing package on computer, then simulate the paper process. Although computers are superb for refinement, they cannot replace the paper and pencil stage. Neither is there a substitute to handling full size components and the true feedback they always give.
Computers have the advantage of allowing the designer to model the design and view it from all angles, to see faults and places of refinement. Both paper and computers have their uses, and both should be used where appropriate.
A note before buying expensive CAD packages. Although dimensionally based drafting packages are the seemingly natural choice for designers of engineering projects, they do not have the flexibility of 3D packages such as Newtek's superb Lightwave, which has enabled many fine machines to be developed and refined. Two industry standard CAD drafting packages with university training were rarely used by the author in preference to Lightwave. As the trike is basic engineering, the design can be seen primarily as an art form.
Fundamental engineering is easily accomplished with or without a computer, but the overall final form, shape, style, colours and final detailing of the trike are usually more important, and more easily accomplished is it can be studied on a 3D software, or on a clay model.
The last paragraph may be controversial, as many designers will offer the standard reply that building a mechanical design requires mechanical drawing software. This is often a trap, as the actual design is never done on the computer, but with common sense.
Computers do not design trikes, - people do.
Sketching a frame tube on a full size or scale drawing on paper or screen is quite good enough for most purposes.
A trike is not an oil rig or aircraft and therefore does not need a set of working drawings. Even if a design is to be mass produced, a simple jig from the original machine often suffices at this level of engineering. Therefore do not get sidetracked by having to spend many hours making technical drawings. As a draughtsman from the marine, military, nuclear and electrical industry, the author does not see any need to waste time where true design should be done more productively elsewhere in the design process. Trikes are a fairly basic engineering structure, aiming, in most cases, to be an art form. Treat them as such.
Art forms develop nicely with 3D visualisations from all aspects and Lightwave does this extremely well. Understand what is being created and use the tools available in an appropriate and useful manner. Do not waste time on computing if it's not needed.
3D modelling (computer or clay) can greatly help refine an idea, especially overall styling or where components may come into conflict, such as exhaust runs through frame tubing, steering linkages or items which move relative to each other. Inverse kinematics is useful for refining complex steering and suspension systems or particularly evil gearchange routings.
If very keen, exporting work between various packages such as drafting and finite element analysis should also be checked prior to purchase. Data transfer is particularly important due to the steep learning curves of some packages, should the reader wish to become deeply involved in the design process. Therefore always carry floppy with a test piece, to see if it transfers easily and correctly. The test piece can be generated on the first item to be tested.

The most important skill is being able to use paper and pencil.
This works perfectly well for most people and it still remains the definitive design process for innovation.

If using a computer or on a good 'ole paper sketch pad, begin by roughly modelling the three best choices of engines, transmission, wheels, front end plus riders. The engine, wheels and rider can then be positioned relative to each other, until a refined layout is accomplished. This is the same as laying parts out in the garage with chalk, or sketching on paper. The advantage of using a 3D package is that the various virtual engines can be easily tested and adjusted for looks and fitment, then seen from all angles for the best possible layout. For basic assessment, the virtual 3D components need not be much more than a dimensionally accurate box for the engine, and simple extruded cylinders for clutch and gearbox, wheels and such like. Then the overall weight distribution can be calculated on paper once the basic design is optimised.

Designing a frame.
A frame does not appear from nowhere. It grows from the requirements placed upon it.
The requirements are many, from the fixed dimensions of engine mounts and suspension set-ups, to the overall structural shape and its styling requirements. This means understanding the way the frame must work, and the many parts it has to contain and control.
A good frame is not designed overnight. If you take this seriously you will (must) be constantly changing the design and refining it.
Every second spent refining the design will reduce the amount of grief when building.
This will also save you from having to ride a less than perfect trike in the years to come.
At this stage, you will have begun drawing sketches to get your head tuned in to what you want, and have a good idea of where you are going.
If you get stuck, email your ideas and no more than two small, jpeg compressed sketches to me for a free assessment and a few hints. I do not expect works of art.
The structural part of the frame is the most important and is designed first. This will decide how you will mount the suspension, wheels and steering. The engine mounting will also demand certain requirements of the chassis.
The non-stuctural parts will be added later, such as the seats and radiator mountings etc.

The following is what you need to understand your design more closely.

It is assumed the drawing stage will have helped decide the best engine and the other main components such as rear axle.
Start off with a rough assembling of the engine, wheels etc. on the garage floor or perhaps on a garden patio, or simply on three levelled concrete slabs in the garden. This will highlight any possible problems and to help get your ideas growing.
Clear the scene and block the basic engine, transmission and rear wheels in a working position using wooden blocks etc. Use original dimensions, so the assembly is as it was for the original donor machine, to ensure maximum accuracy and reliability.
Then juggle the bits around to find the best layout. Measure the static ride height of the engine (ground to sump) before removing the car bits or wheels. Wherever possible, keep all the transmission and other heavy stuff intact as one.

For front engined trikes, do not modify the prop shaft to the rear differential until after deciding the final positions of the components. The prop-shaft need not be positioned in place at this stage, just leave sufficient room. Most other parts should be arranged as the manufacturer intended and has been tested for many years. Use of standard parts and dimensions are central to long term reliability. Get plenty of scrap wood or other packing and use simple wooden wedges where necessary for perfect positioning. Likewise wheel blocks. Do not unnecessarily compromise the ideal positions of the items. Position the front wheel if possible, resting the forks against an old chair or strung from the roof.

On transverse engines, there is often little to do. On front engined trikes, the engine should be moved backwards enough to give good weight balance and ensure a shortened propshaft works well, yet still allow room for the riders. It may take days or weeks to decide the best weight distribution.

Take your time laying out the bits.
Adjust, look, contemplate.
Then repeat many times, then cover with a cloth and walk away for a week while you do some styling and detail design. When you look at your last layout after a week, you may get a better feel for its overall layout and balance with fresh eyes.

Check what can be rearranged to improve your options, both for aesthetics and for engineering purposes.
Engine parts which stick out or look ugly should come under closer scrutiny. An alternator can be repositioned using longer or shorter V belts, or an awkwardly positioned mechanical fuel pump which could be replaced with an electric fuel pump somewhere else. See fuel later. On front engined machines, the radiator can be removed from the front of the engine to clean up this area and make the machine look leaner. See Cooling later.
Carbs can be shuffled around, perhaps by simply cutting and re-positioning their inlet tract. If very lucky, simply bolting back to front or from side to side on flat fours may suffice, perhaps with just a little re-porting of the inlet tract to ensure a smooth flow. Keep the carbs level as intended and ensure all linkages are retained.
Some engines use an iron exhaust header. This can often be replaced for cosmetic purposes by the four into two into one from the sports version. Leave the rear half of the exhaust system for later.

If the shocks are not mounted on a sub frame or similar, allow for ground clearance by measuring the movement of the suspension. Do not trust the amount of dirt wiped off the suspension chromed central shaft. The trike should have reasonable ground clearance on full compression. A basic comparison with the shock movement and the ground clearance will often suffice. For simplicity and reliability, or if in doubt, use the same ground clearance as the donor machine.

For a low, better handling machine, you may wish to go for stiffer suspension, lower the ground clearance a little and add a little more rubber to the bump stops, but first check the local roads for speed bumps.
For very low trikes, consider a sump guard with a firm rubber block interface between guard and sump. The sump guard should be both curved up and strongly supported at the front. This should allow a little high speed skiing with bottomed suspension on less than perfect roads and hump back bridges, (the ones with sump marks on the road either side of the brow) such as Postbridge, Devon.

For a nice, low, forward mounted engined trike, consider the 2CV for a well balanced design with excellent economy. Or perhaps a V8 water cooled Porches and similar designs which have a nice low engine, with a 90 degree vee bank for perfect engine balance and many being available in automatic versions. The five litres of stonk should do quite nicely. The Porsche engine can be repositioned nicely much closer to the rear by minimising the high speed prop shaft between clutch and rear mounted gearbox. Seating may be problematic and require a little juggling.
In some cases where the gearbox is on the differential, a high speed prop shaft similar to a water cooled Porsche is used. The drawing shows that the distance between engine and transmission is up to the builder and a little imagination. From a couple of feet to a couple of inches or as one lump. Likewise the gearchange is an open book.

If you can match the shaft gearbox splines in a safe manner to a suitable clutch plate and match the flywheel starter ring to the starter motor, (by machining the flywheel to take the correct starter ring) then it is often possible to use an intermediate mounting plate between the back of the engine and the transmission bell housing. A classic example is fitting a Ford Pinto engine to a VW transmission unit.
This is a Ford Pinto motor using a large sheet of steel to mount the VW transmission, a very popular arrangement for dune buggies.

If you want such an engine extremely close to the rear diff of a design with independent rear suspension, then you can mount the diff on the back of the engine, using intermediate struts or brackets, but make sure the engine and diff are rubber mounted. The engine mounted to allow torsional rotation and any vertical and sideways vibration, and also allow the diff to take and resolve the torsion from driving the wheels.

For those who want to get rid of the seating problems associated with upright shock units, consider the suspension of some smaller, older Renaults which use suspension arms in conjunction with torsion bars to give a very low mounted suspension set-up. The torsion bar mountings can be tweaked to get adjustable spring forces with minimal hassle. Alternative top ends to the tall McPherson struts are mentioned later for very nice chassis.

5,000cc Porsche engines are not compatible with small car suspension components. Never apply the power of large engines through ordinary components. Always use parts that are appropriate for the purpose.

If making an open design of trike without a covering or shell, then try not to use large sections of the cars chassis, such as the areas around the shock supports or around the engine mounts which will usually look ugly. These areas may be kept until the frame is aligned, and then removed, possibly keeping just a small part of the old mountings and brackets for ease of manufacture of some important fittings.

Most modern cars have the same layout as the Real Mini which started it all back in 1959. On the mini, the whole engine, drive and wheels can be assembled as one system as found on the original vehicle, using Alex Issigonis's most excellent sub frame.

Today, the extremely common suspension mounting on front wheel drive transverse engines is the McPherson strut. These often mount directly into the cars body shell, so upper mountings will have to be built into the trike frame. An alternative is to chop off the top of the strut and use the mounting hole in the axle to mount an upper wishbone. Note that in the picture, the upper suspension pivot bush joint is threaded into the upper wishbone, allowing the vertical alignment of the wheel to be adjusted for optimum handling during testing.

Either side of the transverse engine's differential exit the propshafts, with their appropriate spline positions. Some splines are part of the wheel axle unit. Splines are the way the shafts allow for the changing distance between the differential housing and the wheel axle. At rest, splines should be positioned so they can be slid in, to shorten the shaft as the wheel goes over a bump. They are usually hidden under a rubber concertina boot and must be correctly positioned. If an anti-roll bar is used, then this often statically aligns the width of the items correctly, but make sure the centre line of the engine and the roll bar are marked prior to removal, so all will align correctly. Again, use original dimensions if in doubt. If a crunchy donor car, then be careful. This is best done by measuring the gap between the inside of each wheel to a datum point on the engine, such as the clutch housing to engine face. If the wheels are to be changed, then align with standard wheels first, or else measure to a retained component such as the hub carrier bottom pivot. Then remove the shocks and physically move the wheels up and down to check the prop shaft splines work as intended and do not suffer from tight spots.

The radius arms will need to mount to strong parts of the frame, forward from the hubs to a point on the intended chassis and in a manner that allows them to control the rear suspension. In many cases, radius arms are often the same item as the anti roll bar.
The wheels will also be positioned either side of the vehicle by a bottom wishbone or arm, which is there to take the sideways loads from the wheel into the frame. Again the position will be dependant upon the correct position of the prop shaft splines. Where these bottom support arms will eventually mount on the trike, the frame will want to flex out, so cross support will be required between the trikes lower frame rails to prevent spreading.

The wheels are positioned to lie vertically. Allow the position of the upper cross member to support the tops of the two suspension units. The whole weight of the rear of the trike will be supported on the tops of the spring units, so distortion of the shock unit springs depends upon the weight placed upon them at this major structural part of the chassis. If used, the top of McPherson struts must also be constrained from slight fore and aft movement. Triangulation is a nice word.
Where torsion bar suspension springs are used, (Renault 4 etc) the fixed ends must be clamped securely, as the whole weight of the rear of the trike is acting at these very highly stressed points. Make these mountings strong, as a lot of torque is developed at the ends. The trike frame torque arm mountings can be adjustable to allow for slight adjustment in the amount of torsion used, to give slightly heavier or softer suspension spring rate. Although torsion bars don't look like springs, they are indeed springs, they just happen to look like bars. They support the whole load of the machine. Read the manual to check the amount of preload required. See also primary testing, later.

McPherson struts. Double check the prop shaft splines are in the correct position relative to the engine and wheels with the machine at rest. Then temporarily brace the tops of McPherson struts using a plank and blocks of wood across the engine etc. The McPherson strut spring rates are normally set to take the weight of the engine plus half the weight of two car occupants, so the spring rates are fairly close to ideal for a two or three seat trike.

Trikes tend to have a poor time with differentials. This is because they were never designed to use chain drives and too many trike riders fail to spend enough time designing the differential and its many problem areas.
You can build the worlds nicest trike, but if the differential is not sorted, neither is the trike.
The differential takes the power from the prop shaft or rear sprocket, and turns it through a right angle to drive the wheels on each side. It also modifies the gearing by about 3:1.
Differentials also allow both wheels to rotate at different speeds when cornering, hence their name.

For trikes with bike engines at the front which have to adapt differentials, then there are usually two types of rear axles available: The basic, old style is a one piece differential / axle unit. The other uses independent rear suspension with a differential fixed on the chassis and separate drive shafts to the wheels.
The solid rear axle is not a superb solution, as it is heavy and offers poor suspension movement. But it is much easier to fit, often needing just radius arms, spring mountings and a Panhard rod.

The independent form of rear drive from the differential is far superior, but more complex. The radius arms in the picture keeps the fore and aft position correct, especially under acceleration and braking.
The Panhard rod on the top of the solid axle prevents it from moving left or right, while still being able to move vertically.

With a front car - engined trike, the propshaft between the gearbox and differential must first be laid out and the engine then adjusted for best position allowing for prop shaft mods. For solid rear diff / axle units, the propshaft gearbox output should be level with mid point of the rear axle up and down movement, to ensure the prop shaft splines will suffer minimal sliding. This is controlled by the radius arms.

Once piece rear axles.
If the one piece axle unit with the differential, it may use leaf springs as standard and these are usually replaced with radius arms for styling purposes. Leaf springs require longer and lower main frame tubes. If the prop shaft is very short, it is better to discard leaf spring set-up and use radius arms and coil springs to maintain good angles on the prop shaft as the rear axle moves up and down. The leaf springs act as radius arms, so build or use radius arms which are similar to this movement and which pivot at the front either side of the front of the central prop shaft. This will require minor modifications of the mounting brackets on the axle, although the shock units can remain essentially as fitted. Leaf springs are not a good idea for trikes, and is often easily replaced by using the saloon version of the donor vehicle which often uses radius arms.
For basic trike designs, there is not always a need to change anything unless necessary, as most suspension designs are specific to the donor machine and are often used as the manufacturer intended.

When using front mounted engines it is common to cut down the prop shaft to get the engine weight more to the rear. With once piece diff / axle units, this will require positioning or modifying the radius arms to closely follow the arc of the prop shaft. Ideally, the front of the radius arms will be pivot approximately either side of the gearbox output universal joint. The prop shaft spline will allow the radius arm pivots to be positioned aft of the universal joint, so overall accuracy can be reasonable rather than perfect.

Independent rear suspension.
Independent suspension offers better handling, better control over some adjustments during building but is more complex to fit. Because the central diff housing is on the frame, the frame also requires suspension arm pivots and spring mountings to be positioned relative to the differential housing and it's drive shafts.
For independent rear suspension, the differential housing is fixed on the frame, so the prop shaft only needs a little flexibility in alignment and length for the movement in the engine mountings, and thus can be a lot shorter if required.

Chain drive and differentials.
If the engine has a chain drive, such as for many motorcycle engines, then fitting a rear sprocket to the differential will be the biggest problem.
Sprocket ratios must be adjusted to match the diameter of the new rear wheels. If the new wheels are the same outside diameter as the original bike tyre, then the standard sprockets will often suffice.
The rear sprocket should be mounted onto the differential crownwheel, in place of the original gear ring. This usually requires a sprocket with a fairly large hole in the centre, which can be machined or ground away by powered hand tools. It is always better to choose the sprocket nearest to the proposed requirements; Some aftermartket suppliers have excellent sprocket guides in their catalogues, complete with dimensions. If a standard is close, then preferably machine the crown wheel mounting to match the sprocket for easy replacement of this high-wear component. Always get a few spare sprockets.

If there is not enough room in the housing of a solid rear axle unit to clear the chain and sprocket, simply build up a set of at least four wrap-around cross braces to support the outside of the differential housing, which will then allow the differential housing to be gently trimmed back to clear the chain and sprocket without loosing shaft alignment. These could be strong, long, curved tubes to support both sides of the differential unit. Before cuting the diff hosing, fit and weld up the bearings, and when cross braced, remove just enough to clear the chain and sprocket. The open area can now be built up with a light sheet metal or fibreglass GRP shell to help protect the differential bearings and the chain entry and exit points. Make sure the chain and the sprocket can be easily replaced.
If replacing the sprocket is particularly difficult, and if it is not transmitting too much power, and if it is mounted on at least four bolts, then the sprocket can be bisected with a hacksaw and mounted as two halves to fit into the standard axle housing.

If you think that running a rear differential without its hypoid gear oil is likely to lead to extreme wear, fear not. The gear oil is to overcome the high shear force between the prop shaft pinion gear and the crownwheel. the rest of the differential does not need this and the main axle bearings holding the core of the diff do less work than the wheel axles which run in grease, so greasing these is plenty enough in most cases. The central star gears do very little work and then only in corners and at relatively low revs, so can be lubricated by chain lube or drip feed.

If using a one-piece, solid rear axle, then the sprocket alignment will be badly offset from the centreline: One side of the rear axle may need to be cut and shortened using high class engineering techniques. Alternatively the bike engine can be moved slightly to one side, or the sprocket on the diff can be spaced out by half an inch and also one of the road wheels spaced out to give a reasonably even rear wheel spacing or usually a mixture of all three to get the wheels evenly spaced. It is for this reason that it is recommend to use independent rear suspension for chain driven bike engines.

With independent rear suspension, the differential is mounted as part of the frame, with the independent drive shafts exiting to left and right. Because the differential is mounted to the frame, then much of the unit can be rebuilt for trike use.

A design example.
This is just one example of making your own engineering solutions.
It is not simple DIY, but needs a reasonably high degree of engineering skill, rather than expensive engineering machine shop solutions. Done badly, it can be very dangerous.
First of all, the differential can be removed from a modern car such as an Escort Mk 3 or 4 and mounted into its own metal cradle sub- frame supported from the bike swing arm pivots and shock mounts.
The Escort diff is mounted on taper rollers which are preloaded axially by large belville washers, so a simplified housing is possible, without any need for shimming the bearings.
Start by machining the diff centre to take a standard bike sprocket of the same size as the original, if the bike rear wheel and the trike rear wheels are of a very similar outside diameter. Adjust the sprocket ratios if the rear wheel diameters are different.
To mount the bare differential assembly in the fixed sub frame, make shouldered steel rings or cups to take the diff bearings. These can be mounted on the left and right sub frames, such that the halves can be bolted together to make a well mounted differential unit on the bike frame.
Such bearing cups can be made by steel tube, split to fit and welded to be a snug fit. Then an end plate added which has a hole just big enough for the prop shaft to fit through.
Measure the width of the assembled diff and bearings, then add two thirds of the width of the belville washers, so that some compression is available when the left and right sub frames are bolted together. This will give the final width of the differential housing in the sub frame. As such a sub frame is usually a symmetrical pair of left and right hand brackets, then the differential can be positioned between them and these are easily bolted together with spacers to ensure the correct width for the differential to about 1 mm tolerance in width. This will compress the belville washers enough to hold the main bearings in place. This makes for a very simple and easy design.
It is then possible to add extra support for rubber seals on the outsides of the taper rollers to prevent oil loss.
The sprocket is mounted in the place of the large crown wheel and the sub frame is then adjusted for prefect chain alignment and cross braces used for final alignment.

Chain adjustment will be needed, and the whole diff assembly can be slid backwards on slotted mounting bolt holes and kept with adjusting bolts , similar to those used for a bike rear axle. An alternative is to use a rigid sub frame on the bike frame, and to use a slipper tensioner on the bottom run of the chain. The slipper tensioner is the easier option, as the chain does not need much slack, (unlike bikes with swung arms or if using solid rear axles). Always set up the engine and rear sprockets alignment with a NEW chain.

The diff will be open to the rain, but snug fitting plastic bearing covers, possibly with felt seals will allow grease nipples to be used to maintain reliable bearings.

The spinning differential body which holds the sun gears can be easily covered in fibreglass and a small screw hole used to fill this with about half a pint of hypoid gear oil.
The donor car drive shafts are not the same length, so the designer can decide which to use, perhaps choosing the shorter props shafts if living in a congested city, or the longer ones if living in the wide open plains. If the diff is heavily offset, then use the prop shafts to advantage.

The Escort wheel axles can then be mounted using their bottom radius arms. The standard Mac Pherson strut is either mounted to a upper bike frame assembly, or cut flush with the cast axle unit and a mounting built to take an upper wishbone with separate shock absorber. See later.

Fully enclosed chains are possible.
A few larger machines use rubber tubes for the purpose which can be modified to fit. By using a fully enclosed chain, the differential oil will reduce chain wear, although it may be messy at the front sprocket area. If too messy, simply allow room to regularly use spray-on chain lube on the differential and chain, possibly with aftermarket automatic chain oilers to lubricate the differential bearings and another automatic oiler for the chain.
Alternatively fit a pan to catch the oil as it flings off the front sprocket and include a small return pipe back to the diff housing.

Differentials are not pressurised, so a simple fibreglass covering is that's needed to retain most of the oil. Where the sprocket reaches the lowest part of the differential, splashing is guaranteed and the oil level will not last very long unless well sealed. Scrapers and splash deflectors will help retain oil. The best compromise is to enclose as much as possible and use dual automatic oilers: one for the chain and one for the differential.
For long term reliability of solid full width rear axle units, the outer wheel bearings should be given a metal shield and well greased via a grease nipple.
The chain can run easily in rubber tubes or nylon lined alloy or steel tubes bolted to the differential. This will keep much of the lubrication in place. If a lot of oil is carried along the upper run, then an oil drain cup arrangement can be incorporated into the lower front of the lower chain tube around the sprocket to drain excess back to the differential via lower run. This is not perfect, but every little bit helps. For those who cover many miles but don't want to keep toping up the differential, the ideal is to fully seal the whole, including the front sprocket. The heavy oil used in differentials is there for the hypoid gears, which are replaced by chain and sprocket, so a lighter oil is possible for splash lubrication. The inner sun gears of the differential unit may wear a little more, so always ensure any oil drip feed is to these as well, should oil loss be a problem.

Engines with chain drive will need to align the engine sprocket to the differential, wheels and the suspension to match the final drive alignment. On some rare occasions, this may require shortening of one side of the axle unit, or offsetting the engine in a custom trike frame.
Shortening one side of the rear axle unit will help position an axle into reasonable alignment to the centreline of the machine. Independent suspension rear ends make this a little easier.
Fewer problems apply to a prop shaft between engine and differential, as the shaft will allow the engine and the rear wheels to be retained centrally in the frame, with the misalignment taken up by the prop shaft universal couplings.

To stop a one piece differential / axle unit from moving left or right, a Panhard rod is often used which is about two thirds the length of the axle - or preferably longer. The rod is positioned on one end of the differential unit, the other end mounted on the frame and kept as horizontal as possible at mid point of movement. The Panhard rod is usually on rubber bushed to allow the axle to move up and down without leaving the centre line of the trike. The Panhard rod should be taken from a similar car, as it must not buckle under severe cornering forces. The fixed pivot on the frame should be positioned at mid point of the suspension movement, so it will keep the rear axle centrally positioned across its whole movement.

Leaf springs and other types of suspension have been used in the past, but the standard concentric damper/spring unit seems here to stay. They can be separated for ease of development, but are not usually worth the extra effort. Leaf springs can keep spring height really low, eliminate panhard rods and also prevent one piece rear axle/differential units from rotating, but will need a wide, lower frame with more rear extension which can compromise a clean design.
When used merely as a spring, leaf springs need not be positioned fore and aft, but a single, evenly balanced leaf spring mounted across the frame can spread the load to both rear wheels. It can be further refined if an adaptable mounting is used.

There are many types of rear drives and axles which are indirectly joined to the frame using a variety of methods, so check you know how your choice of axle works and whether it will fit and integrate well in the design of trike.
A rigid rear end is not worth considering.

Independent rear suspension is the better design for trikes, as the system has lighter unsprung mass, should handle much better, allows constant chain tension with easier full enclosure. The wheel bearings of independent suspension are sealed and the differential unit can be modified to fit within the removed swing arm area for standard bike frames. It must still be capable of adjusting the distance between the sprockets for chain wear, but suspension movement need not be considered between the sprockets, so perfect chain tension is possible.

With many front mounted car engines, the drive is usually a prop shaft.
When shortening propshafts, always mark the alignment of the ends first and only modify just one end, preferably where there are most balance weights. Please note that the positions of the universal coupling pivots are symmetrically aligned, so note and check it is replaced in the same alignment. Then cut and check the end is accurate by a set square so the end piece fits accurately. Reassemble using the marks and tack weld, then make sure the shaft runs true initially, by rotating them between centres. Nothing fancy is needed to make a basic check, just two thin spikes to fit into the central centring pilot drill holes usually machined in the ends of each unit. Adjust for minimum friction, then spin and adjust the bare shaft until it balances. To spin fast, place a spike in an electric drill and use a rubber flange on the spike to turn the shaft. If the shaft is not balanced, vibration may trash the couplings. For the final test, block the axles, remove the wheels and run the engine in top gear to check the propshaft in situ. Very gently applying a marker pen to a clean, rotating shaft may show up the high spots requiring modification. Weld on sheet steel weights opposite, then grind down the weights until vibration is eliminated. When true, fully weld the weights in position and check again.

General considerations.
At this stage the machine is not being built, simply working through the many requirements before figuring out where all the frame tubes will go to best effect: It's called refining the engineering layout.

Careful consideration of the intended design will reduce the frame tube count. A common example is a cross-tube doubling as the seat backrest. If a McPherson strut cross-tube is positioned just a little behind and below the strut mounting plates, then this will allow the passengers to recline more comfortably. Not all suspensions will allow this, whereas a few unusual suspensions will allow almost anything, and triangulation can overcome most problems.
If something gets in the way, consider redesigning or using a different component, so the trike will be as uncompromised as is sensibly suitable.
The classic Jaguar differential and suspension rear end is a classic example which allows almost total design freedom.

Once the general structure for the frame is decided, start designing how the parts will fit in, on and around the frame. The suspension, engine and transmission mountings are often fixed, so how the frame must fit to these is a first priority. Having the donor components in place will always help, especially with the old engine and suspension lugs, brackets etc.

Carefully sit between the bits to finalise where the rider and passengers can sit, and where the frame can and cannot go. This in turn will decide the position of the gearchange, footrests etc. Adding riders will increase the load on each wheel, so make sure the axle loadings will be sensible and fairly even when the trike is eventually ready to roll. Begin to get a feel of where is the best place for the front wheel. - Just because you have placed a concrete paving slab in the front of the assembly for the front wheel, does not mean this is where the wheel will eventually go, so place two or three pacing slabs to allow you to vary the front wheel position as you refine the overall balance of the machine.

The frame itself will be most important, but must also take into account the purpose of the machine when building a trike for people. Far too many trike passenger seats are 'sit up and beg' designs.
Do not accept a second rate design. Trikes should be fun for all. A frail 85 yr old lady found some trikes to be extremely comfortable; easy to get in and out, and very comfy too.

Always take the occasional ten minutes to think of the weight on the whole machine. Stand back and simply look, then contemplate the weights and loads. Just stand and look, with a cuppa or a beer, not just for a few seconds, but as long as it takes to grasp the overall feel of the machine as it develops in the early stages.
Ensure approximately a quarter to a third of the weight is on the front wheel, with one rider. Preferably the same with passengers, which requires they should sit over the centre of gravity of the machine. If you have the car seats, simply sit, relax, look at the bits laid out. Allow the mind to do what great artists have been enjoying for hundreds of years - free thought - nothing forced, nothing directed. This should take at least one hot cup of tea to contemplate, or a beer etc. Preferably a long, relaxing afternoon.
Keep the notepad handy and make notes before the best thoughts are forgotten.
When loaded with passengers, try not to have too much extra load on the front wheel, as the rear end is invariably the main load carrying area. On heavy front ends, keeping the extra loads to the rear will help with the steering and manoeuvring in car parks etc.

By mounting the passengers just in front of the rear wheels, the overall load on the three wheels will remain optimised for better handling with and without passengers. This also allows the passengers to sit low and more comfortably, nestled between suspension and frame. Being lower, the centre of gravity will be less prone to roll the trike, so the machine will handle much better, improving handling and comfort, especially around corners. Another major advantage with low riders, is that aerodynamic drag can be reduced, allowing a higher top speed and the passengers will get less wind and rain buffeting, - very important on long journeys.

For those with many kids, consider the old USA design, where the boot (trunk) would open to become an extra pair of seats, with the boot lid folding backwards to become the backrest. Occasionally referred to as a 'rumble seat'. Many modern versions of this are possible. A couple of recessed foot steps, aircraft style, will assist their entry and add a little extra style.

It may be necessary to take the design process a stage further.

Although most trikes will be quite good using standard components as intended by the manufacturer, and some atrocious machines still get used daily, it is nice to be able to see the underlying design when looking at the machine laid out before ones eyes. Therefore, a little theory will help develop the plot and improve the possibilities.
As a general rule, it is often advised that the centre of gravity of a three wheeler should not exceed thirty five prevent of the distance from the two rear wheels towards the front wheel. That is to say, the overall weight of trike and rider(s) should be closer to the two rear wheels.

If making or modifying engine layout or suspension, consider the following.

Steering and Balance.
I have ridden various trikes and hate those that don't handle, as there are far too many out there which are absolutely appalling.
Some trikes have out performed sports cars in the twisty bits.
That's not to say all trikes can be superb handling machines, but there really is no excuse for a poor handling trike.
Trikes can turn better than some cars - if well designed. This is for many reasons, mainly lower mass and how this mass is positioned relative to the wheels.
With good balance, a traditional single front wheeled vehicle will tend to oversteer; that is to say, it tends to turn further into the corner than required. If the single wheel was at the rear, it would tend to understeer, which is usually considered safer for ordinary drivers and for example, usually the safe set-up when handed LeMans car to try if new to the racing game.
When cornering with a single front wheel, where oversteer is a problem, then accelerating out of a corner tends to work better, but braking into a corner tends to de-stabalise a trike. This is reversed for a rear single wheel.
This is not a perfect description, as it also depends upon whether the weight of the engine is at the front or at the rear of the trike.

Unfortunately for a single front wheel, the forces involved in braking are higher than accelerating, so making sure the ability for a trike to brake when in a corner must be very carefully considered. When further compromised with a narrow front tyre, with a round profile which tends to limit braking ability, then problems can accrue. Hence, like a bike, brake in a straight line before the bend and accelerate out, unless it is poorly balanced.

When cornering, the designer must realise that if sufficient traction so the wheels do not slide, then the weight distribution of the trike will determine how it handles. When turning a corner, you are moving heavy loads such as the engine and riders around a corner. The heavy bits will either tend towards the rear or front of the trike. Making them go around corners happily will depend how they relate to the wheel positions.

The more the centre of gravity is towards the front of the machine, the greater the tendency to understeer; it will tend to move towards the outside kerb.
The greater the centre of gravity is to the rear, the greater the tendency to overtseer; it will want to tuck into the turn and is usually the more dangerous option. (If you are ever offered a test ride of a very high performance machine such as a race Ferrari, then the mechanics will usually set up the steering to understeer, so you don't get into too many problems on the test track.)

When considering the overall way your machine will behave, it is not the way the steering works, but the way the masses act in relation to the wheels. Getting the mass central to the wheels will help the trike handle well in corners, even when accelerating and braking heavily.
If making a stonking brute for serious thrashing, then it will be difficult to minimise understeer if using a V12 at the front, unless a long wheelbase can keep the engine unbelievably close to the rear.

With a poorly handling trike, perhaps for show use, then there are suspension and geometry tricks to ameliorate the suspension and steering to reduce the effects of imperfect weight distribution.

Now a short guide to what you should be looking at when considering the overall layout of your trike.

Heave up and down.
Stiffer suspension makes handling better, but gives a harsher ride. Therefore trike comfort is dependant upon many factors. If standard components are retained and are in good condition, most problems from suspension bounce and rebound etc will be fairly acceptable. When changing to different wheels or suspension arms and links, the dynamics may alter, but the natural frequencies of most standard and slightly modified suspension systems are usually within acceptable limits.
Most acceptable systems allow the springs to compress about ten to fifteen percent in normal riding conditions. If the springs do not do so, choose lighter springs, or re-position these items until they act so. This slight initial compression is to allow the suspension to already be in an active state, allowing both up and down movement so the wheels can comply with all normal road irregularities. If the springs did not compress slightly under normal conditions, they may act as a stiff block until a large bump is encountered, and this means a very harsh ride and far inferior handling.
For a lightly loaded rear end of a front engined trike, the weight of a couple of passengers will compress the suspension further, which may cause problems of a light rear end, such as a trike with the engine at the front. For this problem, use springs and dampers from a similar situation, such as from the rear a light family car which also has a front engine.
When using a front engined car engine and suspension, placed to the rear of a trike, the load is fairly close to standard. In practice, this rarely needs much, if any adjustment.
Next time you are beside a car, push down on a front wing, and also on a rear wing, to see how it reacts and behaves and try to get your trike to be in the same ball park. Decide if the engine mass affects the movement appreciably. Get to know what is happening, so you can also check this against your trike as it's being built. If possible, do the same on a real sports car.

The amount of sprung to unsprung mass is more important on a lightweight trike. On a heavy machine, the greater mass usually absorbs the forces of maintaining the wheels in contact with the road. Trikes are usually much lighter. The unsprung mass of the wheel, tyre and half the suspension is going to have a larger, negative effect on a lighter chassis. It is best to keep such weight low, such as inboard discs, alloy wheels and such like wherever possible. This is especially important if aiming for a good handling, comfortable, lightweight machine. This is further refined by adjusting the damping rates to suit. Where the shock unit is rebuildable, this may require changing the damper fluid to get better results.
Do not get overly cautious as the spring rates often do not need to be changed if they compress a little at normal static road loadings.

Pitch fore and aft.
Fore and aft pitching is a problem for many trikes, especially those with tall, front engines while braking, where the nose of the trike dips down. This causes minor problems with geometry and suspension. Antidive is a secondary solution, but it is better not to have the problem, or at least to ameliorate it from the outset.
Therefore it is important to keep the centre of gravity low and nicely positioned between the front and rear wheels to reduce most pitching problems. Poorly designed trikes with this problem can be greatly improved with leading link suspension systems or hub centre steering.
It is not just the suspension which causes comfort problems. The classic VW engine hanging out the rear will give rise to wheeling tendencies, especially if a fierce clutch linkage is used.

Yaw side to side.
The ability to quickly set a trike up into a turn from a straight line is much faster than most cars. The ability for the heading to change, - that is to point to left or right faster, is called the yaw response time. With lower mass and reasonable road holding, the trike can have a great advantage. As steering involves the front wheel, a single front wheel trike is not as good as the two wheels front, one wheel back version, but the conventional trike still remains a good contender in the cornering game.
The trikes lower mass enables the forces available to redirect a trike to be more responsive. The polar moment of inertia (force to move a mass through an arc) can be lower on a trike than a car, hence cornering is greater fun. Polar moment of inertia can be considered as a 'dumb bell', as used in weight lifting. If the weights (mass) are at the ends, turning it is difficult. If the mass was in the middle, if would be easier to turn.
The best polar moment of inertia is if the centre of gravity of the whole mass is positioned fairly central with the wheels relative to a sensible wheelbase. A front engined trike such as a V12, will have more of a dumb bell action: Whereas a mid engined trike with the engine and passengers just forward of the rear wheels will be very nicely balanced and allow the steering forces to turn the machine much easier and will be a lot more fun on twisty Dartmoor roads.

When cornering, there will be a rolling action towards the outside of the turn. The mass of the trike further above the ground will cause greater roll. Roll works in harmony with the suspension set-up, but the lower the mass is to the ground, (low centre of gravity) the less the roll and the more effective and subtle the suspension can be.
From a safety aspect, there is less chance to roll-over if the centre of gravity is low. In plan view (looking down from above), draw a triangle between front and rear wheels. The closer the centre of gravity is to the centre of this triangle when seen in plan view, the less the roll effect. Unfortunately this can be improved by moving the centre of centre of gravity rearwards, by positioning the heavy bits to the rear, but not always at the expense of poor weight balance required of a small front tyre. Therefore in some cases, it is better to get the best polar moment of inertia and accept a little more roll. To do this, get the centre of gravity proportionally between front and rear axles in such a position that the heavy bits are acting fairly evenly on all wheels, then adjust for the choice of front tyre.
The use of an anti roll bar is designed such that some of the forces involved when cornering are transferred from the inside suspension to the outside suspension, to limit the amount of roll. Roll bars are common on most modern vehicles and should be employed on trikes and always on taller trikes using motorcycle frames.

Camber angle.
When seen from the front, if a rear wheel leans outwards at the top, it has a positive camber angle. Leaning in at the top is negative camber.
One piece rear axles cannot be modified.
Independent rear suspension can be adjusted for camber, and usually have a longer lower wishbone than the top wishbone to enable the camber to change as the suspension compresses, or use McPherson struts or similar.
In normal use, the wheel should be vertical or have a slightly positive camber, sitting square in the ground and ideally positioned for straight driving. When cornering and the suspension compresses, then the outside wheel should ideally become slightly negative in camber, to keep the outside of the tyre fairly normal with the road and to help reduce tyre wear and maximise grip.

Centre of gravity.
A lot of the above has mentioned the centre of gravity. To find the centre of gravity of an item, simply hang it from a point and draw a line vertically down from pivot. Then do so from another point. Where they meet is the centre of gravity. For a piece of unusually shaped card, use a pin through the item, and draw a vertical line down from the pin, then a different point on the card, hang and draw another line. Where they cross is the centre of gravity, where it should balance perfectly well. Unfortunately for a trike, this is not so easy.
As the trike has not been built yet, is impossible at this stage, only an approximation can be done. The further the engine and riders are to the rear, the further the centre of gravity is to the rear. Likewise for the height of the components off the road surface. This is then modified during test riding.

Will it want to Roll or Skid ?
As a general rule, it is possible to find out approximately if a machine is going to roll or skid first. This is important to those who are going to thrash their machines along British country roads and Alpine passes.
As this is an early stage of the design, then general approximations to overall weight balance of the trike can be made.
With all the parts arranged on the garage floor, weigh them and work out the amount of each load on each axle. If the engine is half way between front and rear wheels, then half will be on the front wheel and half the weight split between the rear wheels. Mark it on a piece of paper, to add up all the basic weights on the trike. Do likewise for all the other bits including riders. Then work out roughly where all this mass will be along the centreline of the trike. Mark this guess of the centre of gravity on the floor as 'X'.
Next draw a line between front and a rear wheel, to go though the middle of the tyre contact patch where they touch the ground.
Now make a reasonable guess of the height of the centre of gravity above the ground. This can be guessed by averaging the centre of gravity of the engine, riders etc, to get a rough idea of the whole machine with riders etc. It may be a few feet above the ground for an average machine, perhaps more, hopefully less.
The final step is to draw a circle on the floor, using point X as the centre. Draw a circle with a radius the same as the height of the centre of gravity. (in this example, two feet radius to give a circle four feet in diameter.) If the circle goes outside a line drawn between the wheels, it will tend to roll, but if inside, it is more likely to skid. The further the circle is inside the line between the wheels, the safer the machine will be, tending to skid rather than roll over.
See also how to check the centre of gravity of the basic rolling chassis, later.

Tyre adhesion will also effect the roll / slide situation. Modern tyres often have the ability to retain friction with the road up to eighty percent of their load. This will vary with roll, etc. and if problems occur, then simply use less efficient tyres to allow the tyres to slide before rolling the trike over. Tyre pressures will also affect this situation slightly.
In some conditions, the inner wheel may tend to loose adhesion before the outer, due to the lighter load causing it to lift off the road, and the diff will then transfer little or no power, causing the trike to slow. Loosing power in this manner is dangerous. This usually causes a line change, and can be considered a desperate warning just before things get seriously out of control. If considering such problems because you are a serious thrasher, then seriously consider limited slip differentials as used in some Jag and Porsche rear systems and ideal for over powered trikes.

Refining the basic layout.
Once the centre of gravity requirements for a trike are well considered and then refined, then the suspension can be used to improve the plot, usually by optimising the engine position and keeping the load low.

The tyres are the main point of control with the road. The way tyres are controlled is by the suspension. This means the load is carried by the springs, the damping control by the dampers, and the way it moves (the geometry) by the suspension arms and rods etc. The way the suspension moves can be designed or modified such that the wheel moves in a positive manner, to control and augment the natural steering of the trike.
When cornering, the outside wheel takes most of the weight and the spring compresses, lowering part the trike. The design should be such that the suspension can keep the wheel level when cornering. This is usually done by using uneven suspension arms to control the wheel alignment as the suspension moves. An anti roll bar can be used to reduce the roll of the chassis.

When cornering, the suspension moves as the trike rolls, and when seen from the front, the position from which the wheel seems to arc is called the reaction point. If a line is drawn between the reaction point and the road contact point on the tyre, then the place it crosses the centreline of the machine is called the roll centre. The roll centre should be as low as possible for trikes.

McPherson struts usually work in a similar manner, but as they are from the front of the donor machine and therefore used for steering, the centre line of the strut is also designed as the steering axis. This axis may not be directly in line with the centre of the tyre contact point, causing the steering under the strut to want to pull the wheel off line. As this is normally on a two wheel set-up on both donor and on a trike, the effect of both sides is evened out. When the machine corners, the more heavily weighted side has greater effect, which should be designed to act in a positive way. Placing the engine and suspensions systems of a front wheel drive car to the rear, as in a trike, these actions will remain in play. But what is good for the front of a car is not always the best for the rear of a trike. Normally this is not of much importance, but on powerful machines such minor imperfections should be recognised, if handling becomes problematic.

In general, a lot of theory can be applied, but not always necessary, but a basic understanding helps.
The standard components of most cars are usually quite acceptable for most trikes, but can always be improved. The tyre sizes, aspect ratios and pressures will also affect the steering. Within sensible limits, many items can be adjusted to refine a machine.

Getting the balance right is not easy, and often best assessed by riding as many trikes as possible.
Test ride while understanding what exactly what a test session is looking for. Write the parameters on a piece of paper and choose road conditions to test each one. In an ideal world it is preferable to have a few different types of trikes available for back to back testing. With a single test machine, simply set standards high and expect the best, whereupon the problems will often be seen more easily.
Bear in mind the understeer or oversteer, suspension, roll, dive, braking around corners, pulling away uphill, steering stability or twitchiness and the general ability to be thrashed through twisty roads. If the test session is short, it is best done in an unused, large carpark, so the limits of roll or slide may also be assessed, with plenty of room for a safety run off.
Take time to assess the various requirements, noting each in turn, then understanding how they will all work in best possible harmony.
Have a general look at the machine before riding it. Start by pressing down on the rear suspension to see how stiff or soft it is. Guess the centre of gravity. Then make a guess as to how you think it will handle. Then ride it. Afterwards, decide if your guess was correct and modify your thinking to suit. You will probably want to look again at the machine to see why it handles thus.

No machine will be perfect, but another refining stage is to get the many conflicting aspects of the design sorted into the best compromise as possible from the outset, then by gradual steps, improve the design by various means.

Having the facilities to make complex engineering parts from scratch is great, but few have such luxuries. Searching out parts and ideas from other vehicles, already built, or closely manufactured to the intended purpose will save a lot of work. This will also give greater reliability and make parts replacement so much easier.
There are perfectly good solutions to most problems somewhere in other vehicles, or perhaps in divers other machines, so keep eyes open and use imagination. It should all fall in place with a little time and effort.
When starting to use parts from many machines, use a permanent paint marker pen to ensure the make, model and year of the donor vehicle is permanently on the item. This way it is possible to replace or repair with minimal hassle. It is easy to forget much about the components, so make life easier from the start with a simple parts list.
Never modify a standard component such as engine mount or prop shaft until the last moment, as the design will change many, many times.

Engine mounts.
Once the engine is positioned on the garage floor relative to all the other items in the best possible compromise, then it is time to consider where you will start building the frame.
(Engineering is always a compromise in a search of perfection.)
Car engines can, and do leap about in their mountings, so keep the original rubber mounts for the engine as these will reduce the chances of frame fracturing.
If making special engine mounts, they should be 'tuned' to the engine vibrations, to minimise the worse effects and be able to resolve the torque reaction from the engine into the frame. Always use any original engine steady bars in the same way as used in the car, as they are not always obvious in the way they should be mounted.

This Jag efi V12 engine is mounted on just two main rubber blocks the size of a fist, with a simple spring at the rear of the gearbox. Very simple and very effective, but then, V12's are delightfully smooooooth.

This may sound obvious, but make sure that parts can be reached easily and that it is easy to remove the engine. Some poorly designed trikes are atrocious to work on. If it is necessary to remove the engine to set the valve clearances, try again. All maintenance should be simple.
In an ideal world, it should be possible to lift the standard engine, complete with mountings and all ancillaries, out of a standard car, straight into the trike with just a couple of friends, a plank and some ropes.

It is not unusual for car based trikes to get through many engines a year, being thrashed regularly as their owners demand the same acceleration as their motorcycle.
Wherever possible, make the engine easy to replace. For those who wish, the frame can be designed to have removable sections for extremely easy engine replacement. Far too many trikes either need the engine to be stripped for removal, or to be hoisted out from above, or fitted from underneath. Make life easy for yourself. If design problems get bad, at least make it easy to drop the engine and simply lift or roll the trike off. An adequate compromise is to be able to block the rear wheels and lift the front wheel very high, to extract the engine from underneath.
Even a five litre V12 can be designed for easy engine removal and yet such engines are easily designed to flex safely upon their standard engine mounts, albeit with attitude to enhance the experience.
Ordinary engines should be an absolute doddle to maintain and replace. If the popular transverse engine is mounted normally on its rubber blocks, then most engines can be removed easily. The rear of trikes can be simply removed or unbolted for total and easy access and removal. This is particularly useful for changing the clutches of some transversely mounted engines.

If the engine has a turbo, complex fuel injection system and loads of computers and electrical junk to make it work, then consider mounting some complex assemblies in modular form so they are both waterproof and easily removed as discrete units to allow a complex engine to be more easily repaired or replaced.

Once the rear is reasonably well defined, the general layout of the frame must know just where the tubes are to end at the front. The front end tubing is important for trikes, as not only is structural integrity important, but the style is also a critical component of the design.

For many engineering or style reasons, the steering head angle (known as castor or rake), is up to the builder. Cars use about 2 to 3 degrees, bikes about 20 to 25 degrees from vertical, especially if using telescopic forks. The best is to find trikes which handle well, then find out why. There are no real hard and fast rules. You may be surprised what you can get away with.
Some of my road-legal hubcentre steering motorcycles have been ridden quite happily with almost vertical steering angles, while some of my friends severe customs seem to get away with extremely long forks.
If in doubt, don't go stupid, stick to what looks right. That is, the same as bikes, especially if using standard bike forks. Steering head angles are often chosen to reduce stiction in telescopic forks.
Extended forks are weak on bikes and even more so on trikes, especially when braking.
A rake bigger than normal as on extended forks may occasionally lead to an enormous turning circle, so at least make sure reverse gear is easy to find to get out of tight situations. As trikes do not lean, they can get away with less radical front tyre profiles, allowing a greater foot print to take a larger load while maintaining sensible tyre pressures.
Good design will allow even a long raked set of forks to have a sensible amount of trail. Alternative front ends are mentioned later.

Frame designing.
With the above in mind and much of the rest of the text well considered, plus with everything blocked up and in place, start to design the frame. Take at least a week to design a couple of frames, preferably a month or more with a difficult design. The average is about a couple of weeks to a month, but for some, it takes so long that rust gets there first. Do not give up easily, but definitely do not rush the design.
As the design develops, you may soon fall into the trap of following a single, obvious frame design. Use your drawings and trace out at least three different frames. At least one frame design should be radical, - really off the wall, blue sky thinking.
The final frame will probably be a mix of the better aspects of each.
Always work in all three views, side, plan and front views, as what seems good in side view can be awkward or dangerous in front view. It is a process of continual refinement.
When satisfied, you will surely want to make it better a couple of days later, in the light of inspiration when daydreaming at work. Talk it through with friends when they call, make a cuppa and stand around in the garage discussing, with all the bits arranged as intended. It happens all around the world.

Always start frame design with imagination, with a feeling of the weight and position of the components. Then imagine just what is happening to the main components. Get a feel of the whole machine. Write down good ideas immediately so they won't be forgotten later. (All too easily done.) Even experts forget superb insights and possibilities for want of a piece of paper. Backs of cigarette packets and napkins attest to the ambiguous nature of the design process.

From the start, mark in the steering head, engine mounts and suspension positions which are often demanded by the chosen engine and suspension.
Carefully rearrange or compromise anything which gets in the way of a strong frame with good weight distribution.
Play around with the components until they look about right. To get the forks positioned (if used), simply rest them against a chair, or strung from the roof by the handlebars. Use modelling clay or tape to keep the front wheel in position on the floor.

Tubes that are spread wide and well supported to make various triangles will give some of the strongest frames.
Design the main tubing to connect the steering head, engine and suspension first. Then subtlety add any secondary tubes to improve triangulation to prevent these main tubes from flexing or buckling. For simplicity and strength, main frame tubes should be one length from front to rear.
Wherever possible, make the frame design a mirror image each side, as this makes for easier manufacture and alignment. More importantly, this also keeps any frame flexing even, creating less distortion and better handling under heavy loads. Try not to have all welds grouped close together unless well gusseted.

The style of the frame is an open book, there are no all-encompassing constraints other than common sense and safety.
Only 'mass produced' trikes have any similarity in design. The standard trike is often far less than the art form it could be. The exceptional trikes, - and there are quite a few select machines out there, - have an overriding theme to their form, with form being drawn into the function in a positive way.
An exceptional trike will naturally draw people to it. Occasionally a trike does it so well, while making a bold statement. This is art, possibly even aggressive art. A trike should be a statement, be it parked outside a pub or cafe, conveying bridesmaids to the church, on show in an exhibition, or being thrashed around a corner in a power drift past open jawed pedestrians.

Trikes need not be simple front ends with tubing to hold bits together. They can be gracefully swan necked in the Swedish style, perhaps styled as an alien artefact, or a techno or engineering tour de force. As car based trikes are not afraid of a few extra pounds of weight, consider using stronger tubing if a 'swan neck' design is preferred.

Trikes should always be art forms and a little extra strength in the right place will keep them looking great.

A few more weeks drawing radical designs can often change the whole path of the project.

Then sweat blood to keep and enhance this style so it will also stand out from the crowd when built.

Whatever is designed, do not be happy until your sketches stand out from the page.

Occasionally, the concept shouts at you from the page that it must be built. You will know when this happens.

Everyone has at least one exceptional idea hidden inside them. This will surely need to be built for the real world, so engineering is the fundamental stage.
With the sketch pad in one hand and a tape measure in the other, study the components laid out in the garage and consider the following.

Looking down from top.
How much weight is on the front wheel with rider(s). Too much, too little?
Sketch in the radius arms and where they will mount to the frame. (to prevent the rear wheels jumping ahead of the machine when opening the throttle, or flying off behind when you apply the rear brakes.)
What part of the frame actually supports the weight of the trike at the top of the shock springs.
What will keep the top of any McPherson struts from flexing fore or aft when accelerating or braking, it may be a light force, but it exists. Will the bracket support or foul the rear of the passenger seats, or can it be angled back and down slightly with extension brackets.
Where will the gearchange linkage fit relative to the riders seat.
Will the rider be able to reach the handlebars or is a linkage needed.
Will there be enough room for passengers and a trunk. (boot).
Are the riders and passengers feet going to be in the right places.
Exhaust routing.
Fuel storage.

Looking from the side.
How much weight is on the front wheel.
Will the rider be comfortable, and how low can the seats be positioned without compromising strength, or will the rider be hanging onto the handlebars like a flag in the wind when thrashing corners.
Will the steering head bend upon landing after the first wheelie or over a hump back bridge. Steering head extra support tubing and fillets: size and shape.
Are the tubes from the steering head to bottom of the frame securely positioned at their low points and what type of fillets or gussets are needed to maximise strength.
Is the ground clearance adequate.
Are wheelie bars needed because you decide to use an air-cooled Porsche engine hanging out the rear.
Will emergency stops become dangerous.
Are the riders and passengers feet going to be in the right places.
Gearchange routing.
How can an exposed engine be made to look better.
Exhaust routing.
Fuel storage.

Looking from the rear.
What exactly is holding up all the weight. Decide what is actually holding up the top of the rear shock absorbers and the springs. Also decide what is preventing the shock mounts from being pushed up and inwards when landing off a hump back bridge at fifty miles an hour.
Is the ground clearance adequate.
Is the engine easily accessible for replacement.
Where will the gearchange linkage fit. - Is there a suitable gap between gearbox and sump on a transverse engine. Can it run safely under or over the engine in a straight line towards the rider, or need to be routed over the motor or gearbox.
How can an exposed rear engine be made to look better.
Exhaust routing.

Looking from the front.
Can you see the side lights.
Will the passengers be safe when cornering.
How will cooling air flow be captured and directed to the radiators.
How can an exposed front engine be made to look better.
Exhaust routing.

Also consider the general style from all angles.
Will the passengers look good for the camera, or are they stuck like flags in the wind. Will the radiator ducts blend in and around the frame tubes.
When not using safety belts, the passengers should be considered as dumb, unsecured loads, especially when braking or powering around corners. Also give them decent foot rails to take the braking forces. Seat side support or hand rails also offer a chance of survival.

With the above in mind, the main structural areas are now marked on the drawings. These are then gradually refined, especially the steering head, engine mounts, rider load points. This is the important part of frame design, but the engine and frame component mountings will decide and constrain much of this work.
Also mark in the forces of both the static loads and the full acceleration and braking forces, and when landing off a jump. Mark them on the paper as arrows if necessary, to maintain the most effective use of such drawings.
Marking the arrows on the sketch pad proportionally large to the forces involved, helps direct the subjective design of the frames form and structure. A yellow felt tip pen will allow the drawing to be modified over these underlying guides to highlight what will be happening to the overall structure.

Always try to break the design in your mind.
Where are the weakest places, where are the places of greatest load. What happens to the frame when the bike is cornering hard with a full load? What will break first?, What happens if.....? Get to fully understand the designs and ask everyone what they think and how they would design the frame. This gives more options and time to spot any hidden problems in the design at an early stage.

Overall design and bracing will require careful design of the chassis. Computer aided finite element analysis can help. Those without access to such assistance can model the structure and test load until inappropriate distortion occurs.

The main tubes are often four long tubes with engine and suspension fittings often mounted directly.
On a recent V12 the front frame was essentially a massive Norton Featherbed frame. On another, the frame was four almost parallel tubes with the flat four engine slid in between them.

If you can make a real frame, you can make a wire model. It doesn't have to be accurate, just use solder and straightened paperclips or similar materials. With a soldering iron and some wire, build an approximate model of your frame, then load it to see where it breaks. If you have a small soldering iron, then straighten some paperclips. If you have a big soldering iron, then scrape the flux off a few arc welding rods.
Don't just see which wires bend, but also the direction that they bend. Model the engine and suspension at their mounting points to apply the loads at as required. See what the engine and suspension mounts are going to do. Modify and try various designs until feeling confident. Do not confuse poor soldering with poor design. If you make three different wire frames, comparative tests can be used using standard weights such as bags of sugar balancing precariously on the structure for spot loadings. Load and twist it in many ways so it distorts or breaks. An evening spent like this tells you loads (pun intended) about your design.

Consider the frame as a means of holding all together and the forces under acceleration, braking and cornering. The rider and passengers are just loads, whereas the engine and brakes are much more interactive parts of the structure and apply the larger loads and forces.
If you don't like soldering, then get some drinking straws and blue tacky office putty and make a lightweight test rig. If you want to know what type of loads are acting on each weld, then make a model from straws and blue tack, then load gently to see how the structure pulls apart.
If a trike is to take a few months or more to build, just one evening studying and testing the structure is always time well spent. The final frame design will probably be a mixture of the initial frames envisioned. More importantly, you will have much greater understanding as to what is happening to each part of the frame. Design it many times, so you need build it only once.
Which would you prefer - build a model and find out problems on the kitchen table, or after you have welded up the real frame ?
Reading the way the designs finally fail will highlight the probable way the forces are acting and where. Scale models do not always model truthfully at full size, but anything which gives insight will always help understand the forces and their problems. Final testing will be at full size, although the loads are much higher, which can get awkward. See testing later.

Passengers deserve consideration, so always make your machine comfortable and safe. The best trikes are very comfortable for many hours, often employing modified car seat components. The best trikes should have the passengers luxuriating in comfort comparable with the best cars, with plush armrests and well angled foot rests. Your grandmother is usually the best tester for comfort.
Trikes do not lean, so thrashing around corners will have the rider hanging off the handlebars like a flag in a tornado. This is acceptable in cars with side supports on their seats and doors. But trikes with unsupported riders can cause steering problems of rider leaning inwards against the centripetal forces while trying to steer. Therefore ensure the riders legs and butt are positioned to handle excessive twisty lane thrashing. For the rider, the handlebars can be hung on to if the pivot is fairly central between the grips, but if the handlebars are long pull-backs, things can get annoying, so consider the design well.

Monster amplifiers and cup holders although not compulsory, may also be considered, as some superb trikes are sometimes naturally used for posing on boulevards. Not everyone has serious thrashing as the main goal, for others a trike is used for daily transport. If polished walnut trim, connoly hide and champagne is the style required, then go for it. Trikes are designed and built to be enjoyed. See sculpting later.

All frames will differ. The problems with the Alfa 1500 flat four engine meant the lower frame rails will have to run partially under the front of the engine, but with the main support tubes over the engine to allow engine removal. The frame will have four main tubes from the steering head, triangulated with smaller tubes in between, like a space frame. A Ducati trellis is similar. Two tubes run above and two tubes spreading wider and lower to hold the engine mounts. The upper tubes will let the rider sit astride them, then have hidden box section support tubing widening out and up to the upper suspension points at the rear. The suspension is mounted to the frame at the top. As the suspension is pushed upwards, a cross member will prevent them folding. The radius arms are mounted on the lower tubes near the engine in a rubber bush at the front, near the clutch housing via welded brackets. This was later changed to a combined radius arm and anti roll bar to improve strength and reduce complexity. The rear swing arms pivot near the gearbox in the original bushes. The upper arm is also the suspension unit, fitted to the frame using the original rubber block. The biggest problem with the Alfa was that the engine will tend to push out of its rubber mountings when braking or accelerating hard. A rubber mounted rod was chosen to transmit the braking and accelerating forces between the engine and frame. This was later replaced with a small suspension A-frame as it also prevents sideways motion. Engine vibration is not transmitted as the rod is placed neutral to the way the engine vibrates. If needed, a triangular engine brace will allow an engine to move without misalignment. All the parts you need are available, they just have to be discovered and decided how to be used to advantage in differing ways.

For all designs, there are many problems, but their solutions are not always obvious. Spend time to check the various possibilities.

On most trikes, the front end is usually the steering head, although hub centre steering and other options are also available. The distance from the steering head to the nearest upper and lower engine or suspension mounting points will usually decide the general shape of the front of the frame. In plan view, the width should be reasonable, allowing the rider to straddle the frame comfortably. In side view the front may not look quite right with straight tubes, so tubing may need to be bent for giving a better shape to the tubing. Trikes with rear engines often look good with a gently reducing frame taper or swan neck, but this must be strong. If the steering head support tubing makes a triangle when seen from the side and from above, then this is unlikely to flex, with only a few fillets or gussets needed to keep the head stock from distorting under load.
Extreme swan necks may need extra support near the headstock to prevent distortion. For those who want to keep the clean lines on their front tubing, the usual side fillet plates can be replaced with a much stronger central fillet plate between the frame tubes. This may need to be fully welded to the steering head before fitting to the tubing, so that it is welded securely in an area otherwise impossible to reach.
Trikes with engines at the front will often naturally have a well supported head stock as they often employ tubes over and under the engine, which naturally curve up to form a well supported head stock.

Hydraulic pipe benders can be hired. When bending main tubes which are also cosmetic, make sure the hydraulic benders formers do not make scratches or other imperfections. A light polishing of the formers with emery cloth or wet and dry paper or a flap wheel does no harm, and if pampering the tubes, consider a nylon cloth lining. Consider using sheets cut from old plastic oil containers, as the HDPE (high density polyethylene) is a superb material, as used on replacement hip joints and takes high loads with minimal abrasion.
It is not necessary to make just one bend in the frame tube. A series of gentle bends can enhance both the styling lines and riding position. As the rear of the frame widens past the front rider, the tubes can sweep up towards the top of any shock absorber mountings, but these may often compromise passenger seating. Secondary or alternative upper frame tubes, running each side of the engine can usually support separate triangulated suspension tubing which clears the ideal passenger seating areas.
In both plan view and from the side, the main tubes must not be able to spread apart under load, so upper and lower central cross tubes are often used. When designed badly, cross tubes can prevent engine removal and cause other annoying problems. It is better to position two well spaced tubes for an easier life than a single tube to save a little weight. Alternatively one very large frame tube may make servicing easier.
The lower frame tubes will usually support the radius arm loads and must not spread apart under load.
The Rob North Trident frames show what can be done with a tube bender.

Assuming a four tube frame with motorcycle forks : Take careful note how the main tubes from the steering head will flow backwards and downwards to the obvious engine mounting points. There may be a problem with decent seating and so the upper tubes may need to curve low to allow the rider to straddle them comfortably, and then up to the upper engine mounts or rear upper suspension points. If the upper tubes are low, then the lower tubes must be even lower to allow a decent distance between them for structural strength. If the tubes were too close together, as seen from the side, then the front end would want to bend upwards and collapse the frame. If the tubes are close together, then consider a trellis design of intermediate strengthening as seen on mass produced roof frames in sports halls and cheap conference centres. This is a pair of tubes with an intermediate zig zag to give intermediate triangulation to prevent bending and collapse. This applies to both side and plan views.

Like many trike engines, the Alfa engine was front wheel drive, so the original steering linkage is stripped to use just the inner cross shaft which holds the inner steering ball joints. This shaft is welded to a frame bracket to prevent moving left and right, and positioned in the same way as the original, so that up and down suspension movement will not affect wheel alignment.
It is often seen that the rack outer retained for easier mounting, with the steering shaft stub welded to prevent movement. The best method is to retain just the inner rack shaft and weld mounting brackets directly onto it near the ends for greater security and lightness.
Retaining and fixing the steering linkage is very common on trikes and if done properly will allow adjustment toe-in of the rear wheels. This is important during testing so always build it so it can be adjusted, usually at the outer ball ends. The angle of the steering link arm should parallel the drive shaft or lower wishbone link, as seen from the rear.

Toe in, is when the wheels point inwards slightly, usually measured in degrees, or in differences in millimetres between front and rear of the rear wheel rims. Toe out is simply the same, but the wheels point out towards the front of the vehicle. Camber is the amount of lean from the vertical on the wheel, as seen from the front. This is often easily noticed on some formula one front ends. A simple ball park position is to set the wheels straight ahead and straight up when normally loaded. From this the toe in can be adjusted during testing to get the best handling. The camber is best left as vertical for best tyre wear in a straight line. The upper mounting of the suspension could be given adjustable positions to allow the camber to be adjusted, but is rarely applicable for most machines unless building your own suspension.

There are many variables which decide the optimum toe in or out and the camber, such as when cornering, where the outside wheel is the most heavily loaded and can take advantage of a little toe in or toe out to help steer the machine should it exhibit oversteer or understeer. Under power, the driving wheel will want to gain traction in such as way as to cause problems in poor suspension, where toe in or out can counteract problems. Camber could be set-up so the outside wheel in a turn, when it's suspension is more heavily loaded than the inside wheel suspension, then the outside wheel will lie flat on the road for maximum grip. There are many variables which are mentioned earlier and can be studied in many standard books on the subject. If in doubt, set at the standard for the original machine. If it's a front wheel drive donor car components used in a trike, some tyre wear may occur, requiring gradual adjustment for a few weeks until the optimum is attained. Use the worst two wheels of the four until the steering is optimised.

Suspension must be stopped just before maximum travel by a strongly mounted rubber block. These are usually stuck to a plate on the frame and can be carved to size, using any of the many blocks available.
The McPherson strut design uses a rubber block in the upper damper and spring unit to absorb the road shocks. This shock unit also maintains the camber and supports the weight of the vehicle at maximum load. On McPherson struts, alignment can be done by simple positioning of the upper mounting point, which also supports the weight of the machine. A little rearward movement is possible, allowing the top of the rear shocks to be further back by an inch or so, especially if the passengers can sit lower, but may require similar angluation of the lower wishbone or arm and anti roll bar or radius arm, only possible with rubber bushes or spherical pivots.

When accelerating, the power to the wheels will make the wheel hubs want to move forward. For wheel hubs to push the weight of the trike forward, this is done by using the radius arms or wishbones connected from the wheel hubs to the frame or engine. Braking forces are the same, but simply working in the opposite direction. Brake drums or callipers must not turn and the radius arms or wishbones usually handle this problem.

When the suspension is at mid point, the suspension arms and propshafts should be about horizontal. If you use a double wishbone design, keep them the original length, unless you know your geometry. Always make sure the drive shaft splines are correctly positioned.
If making your own double wishbone design, then design the upper and lower wishbones so that the wheel will remain as close to vertical throughout the suspension movement. (In a roll situation) This is usually done by having the upper wishbone about 10 to 20 percent shorter than the lower wishbone, depending upon the position of the pivots from the chassis centreline.
Always build as matched left and right hand side symmetrical pairs wherever possible, using a jig. A simple welding jig will greatly assist the alignment of such suspension components. The distance between the inner and outer axes should normally be the same length as the distance between the centres of the universal joints in the propshaft.
If you have a subframe such as used by mini's, then simply keep the original set-up intact.

Although not recommended, there is nothing from an engineering point that prevents three wheel steering, taking advantage of this ability to steer the rear wheels. Not recommended for road use, but may make very long show trikes easier to manoeuvre and more fun to ride and easier to park. Some 1990's cars offered all wheel steering, but it seemed merely a fad.

Once the basic frame has been decided, refining the frame will make life simpler as you work around, or even remove problems that are discovered while looking at the assembled parts.
Sketch out ideas on paper. With a little extra time, parts can be made simpler while adding reliability, by simply keeping your eyes open and pinching ideas from other designs.
The more you look and think, the better your ideas will be, so take time at this stage to make for an easier life later on. Make loads of drawings no matter how bad they are, they are worth more than gold at this stage. It must be right and if you don't know why, then give up now or decide that you want to learn more, and keep trying before building. The more thought applied, the more possible it is to get the centre of gravity lower, make the frame stronger, lighter and also easier to build.

Whatever the frame design, the steel tubes used will be either tubular, square or rectangular, or a selection of all three. Where parts are hidden, use square tubing, as its easier to fit, stronger and easily shaped. Square section tubes which are open to public view are usually considered a styling failure unless styled really well.
Composites are still difficult for cars and bikes, so don't bother. Likewise for monocoque, as the panel work will give a little more rigidity and lightness at the expense of far too many hours work and inability to repair easily.
If you want to go the composite route, start with studying formula one design and modify from there, choose your engine very carefully and consider at least six cylinders to reduce vibration. Best of luck and feel free to email the author.
There is nothing wrong with tubes, they have a long history of both success and failure.

Always mount engines as the manufacturer intended. Building an engine into a frame so it is part of a rigid structure is OK for bikes with their high revs and low reciprocating masses, but a car engine is often more agricultural. Only six cylinders and over should be contemplated for rigid fixing, as their vibrations are less. If rigid mounting is used, be very wary of fractures in the frame over long periods of time and spread the load into the frame with smooth and well spaced engine mounts. Rubber mounting helps resolve torsional effects around the flywheel axis and for this reason, most engines are rubber mounted and also have an engine head steady.

If you have an engine with dry sump, you may want to use the frame for the oil tank. Use a good MIGor TIG welder which causes far less slag in the tubing. Do not position any connecting pipes where they can encourage fractures to occur. Drill adjoining holes for both oil drain and air venting between the connecting tubes before welding and always have an oil filter after the frame outlet and definitely before the engine. Oil holes in the frame tubes must be large enough for maximum oil flow at top revs, otherwise oil starvation will occur. An average engine will pump well over a litre every ten seconds at LOW speeds, so always ensure the holes in the frame can handle a lot more than this, and never rely upon pump suction to prevent oil pressure loss.
A simple vented cap from a moped two stroke oil tank will suffice for filling and venting, if hidden from sticky fingers. Never take the oil feed from the bottom of the tank / frame, always allow an area for unwanted sediment to settle, with the oil pipe a little higher, preferably with a wire mesh screen. Make sure most of the oil will drain out.
The simplest oil level assessment is via a dip stick. This can be a flexible piece of thin wire strip to access the curved frame tubes, possibly even an old speedo cable. Make sure the oil level area of the dipstick is protected by dimples or bumps, so the position of the oil level is not wiped off when removing the dip stick.
Where oil level cannot be assessed by a dip stick, then the oil level can be seen via small tubes above and below the level, connected by a clear plastic tube. If welding small pipes is difficult, simply push the pipe in a small hole in a safe part of the frame, below the intended oil level. To save bends in the small pipe, place a steel rod in the hole and lever the hole so the pipe is fairly vertical and weld from the inside if possible. Then run a drill though the tube to allow oil access. Then solder around the outside of the tube to seal it. For safety reasons, the oil must not be allowed to drain from a broken pipe, so this should not be too far below the oil level, but low enough to see when filling up. To protect the pipe, the clear plastic tube can be protected along its whole length with strong sleeving, and just the oil level area exposed for inspection. Alternatively a second, larger bore clear pipe can also be employed to protect the smaller oil level pipe. This can then be run along the frame tube to be vented into the oil cap.
Oil in the frame can show up any fractures at an early stage and should be considered a safety feature rather than a problem.

There are various techniques for welding frames.
Arc welding is the most common form of welding and when done properly, can accomplish all needs of construction. Thin sheet is the usually the most difficult, so fuel tanks can be flanged to make welding easier, or tack welded then handed over to a professional mig or bronze welder.
Bronze welding is better for strength and ideal for reducing fracture points of small tubes and fittings.
Very lightly loaded fittings such as oil level pipe can be heavily soldered.
Mig or Tig welding will leave the frame with minimal internal slag which could flake off and clog the oil lines. Always clean the insides of the tubes before final assembly and welding. Where welds are to occur in the frame tubes, clean back to bare metal prior to tig or mig welding to minimise internal slag. Follow up with regular inspection of the outlet pipe to check for any clogging.

The Lamborghini Countach has a tubular chassis which is made up of a large number of small round tubes arranged to make many triangles, called a 'space frame'. The triangle is the most rigid shape around. If you don't want to bend tubes, then try designing a frame from many big and small triangles. The later Lamborghini Diablo used square tubing for it's space frame, was easier to build than the Countach, and was stiffer and lighter.
Do not have long unsupported tubes. Always employ smaller tubes to stop the long main tubes from flexing or bending. The whole frame can be made from large and smaller triangles. A rectangle can distort, so guess what you should do. Some motorcycle trellis frames use an appropriate method.
With all your ideas down on paper you will soon see where you can improve the frame.
Creating a merely adequate design is a weak excuse, while common sense and inspiration are infinitely more applicable for trikes.

Bike frames.
Trikes based on bikes can be comparatively easy. You often keep the frame, modify the rear and add a differential and wheels.
The builder will of course be accepting that there will be a large roll component, caused by the ride height of the rider and this will need reasonably stiff rear suspension to prevent roll if for some reason, an anti roll bar is not used. This tendency to fling the rider sideways in a bend, can be overcome with some clever rear end design and is being researched for reader wanting his trike to lean, but this is presently beyond the scope of this monograph until I have refined my designs and tested them. This is particularly useful for some disabled rider, who cannot always support the torso easily around a fast corner. Email for details.
Bikes and their engines will need accurate chain-drive alignment and a sprocket on the differential.
A modified swing arm is not adequate for the solid type of rear axle unless for slow riding.
Radius arms are needed for decent independent rear suspension. The rest is widely open to interpretation. Whatever you do, keep it light, or at least keep weight down, unless you are using a 'busa or dual engined nitrous big bore Harleys.
Some quad bikes now use independent rear suspension with a differential of a size and weight commensurate with a lighter bike-based trike. Such items can be lighter and more appropriate than heavier car items for a more balanced lightweight machine which does not handle too much power.

It is very important to match the gearing of the shaft drive systems. Work out the revs of the shaft at top speed and calculate if this will match the revs required for the proposed differential unit and wheel size. Most shaft drive bikes use a similar arrangement and the differences may not be far from what is needed.
If you don't like arithmetic, then wheel size can adjust the final overall gearing to allow a decent top speed plus reasonable hill climbing ability without trashing the clutch. Gearing can be raised by fitting larger wheels, which may or may not increase top speed and vice versa. Gearing can reduce any bad design tendencies to wheelie, usually at the expense of the clutch.

If the radius arms of a solid rear axle are positioned so they pivot concentric with the front sprocket, then chain play will be minimal and your chain will have a happy and long life. A motorcycle chain can handle a little amount of sideways play as the axle lifts on one side, but the panhard rod will ensure it keeps in line and does not wear badly.

There must always be allowance for chain adjustment, so the differential must be able to be adjusted on its mountings, or the radius arms lengthened to accommodate for chain wear. If this is not possible, then you may wish to use a roller on the lower chain run and a strongly sprung loaded jockey pulley, or preferably an adjustable pulley wheel which can be secured so that there is minimal slack on the overrun for a well behaved power train.

One-piece rear axle units, consisting of the differential, brakes and wheels will need to be kept central while allowing for suspension movement. Front to rear movement is prevented by a radius arm on each side, as shown in the little animation shown earlier, pivoting at the front in rubber bushes and usually fixed to the axle unit to prevent its rotation. On some designs, the radius arms do not prevent rotation, so the design must prevent the whole lot turning when accelerating and braking, requiring either an upper brace, or other method to prevent the axle from turning.

Component choices: Swing arm and radius arm bearings are either rubber bushes, metal bushes or needle rollers. Balls are not recommended, nor are large rollers, because swing arms only pivot over a few degrees, so the point loading of the bearing is far too localised to ensure long life. Although taper rollers are used on the swing arms of shaft drive machines, it may be easier to use needle rollers, which spread the load wide and roll over larger displacements for even wear. Needle rollers cannot take end loads, so either bushes or some other form of end load resolution should be accommodated as trikes suffer vastly worse from this than standard motorcycles. If the swing arm bearings are well spaced and the swing arm a rigid one piece design, then rubber bushes are acceptable for many reasons including simplicity and reliability.
There is no need to use metal suspension bearings to mount shock absorbers, as the shock absorber is a flexible medium. The use of rubber simply refines the set-up and reduces shocks into the frame.

Front ends.
Forks are always the weak point of trikes from an engineering point of view.
Forks are often the strong point of trikes from a styling point of view.

The forks must have twin discs to stop a trike which is probably twice the weight such forks and brakes were designed for. Standard motorcycle front ends are not up to the job of a big trike.
From a safety aspect, the forces applied by twin brakes will at least be matched to the forks and allow the braking forces to be applied evenly and fairly safely. The forces on standard brakes will be similar to that which the forks can take, ensuring a fair degree of safety. In many cases, standard brakes may not be able to offer the braking forces required of a larger, heavier machine.

Never accept the fact that because someone has already built a two litre trike with 125cc trail bike front end, that it is a good idea. Yes, they do exist, but probably not for very long.
I know of a car engined trike with 1980's 125 trail bike front end. The owner says he 'only gets the front brake working once a year for the MOT'. It oozes rust from the brake drum plate and patently only there for legal rather than safety reasons. Such machines are a statement of design failure far beyond mere ignorance, and are most assuredly an engineering death wish. Everyone has the right to be stupid, but never abuse the privilege.

Standard forks should be used as intended, with their rake angles designed to take the shock loads as sliding tubes. The amount of trail will depend upon how they are mounted, but keep it close to original as this is how they are designed to work.

Long telescopic forks for styling purposes will often act as simple beam springs, absorbing the shock by bending rather than telescoping. This makes it a spring, not a damper, so will resolve the force by flexing back in an uncontrolled manner. Go carefully and make sure your forks act as shock absorbers, not as undamped springs.
Girder forks at least offer the chance for their small bottom swing arms to flex through an arc as intended and thus take some shock out of the legs. Do not expect such designs to handle too well or give any subtle feedback as to what the road is doing with the steering, but properly designed, they can act effectively as steering and suspension devices, and with an easily adjusted amount of trail to refine the steering.
Long forked, custom front ends with a large amount of rake, will allow a motorcycle tyre to be used in preference to other options. This is because the amount of lean of the wheel in the forks when cornering, (not to be confused with roll) will allow the side of the tyre to be applied to the road surface. This also reduces the amount of side force on the tyre, trying to push it off the rim as found on heavier trike front ends. Manoeuvring around tight car parks will demand a reverse gearchange or friends to help push the machine backwards.

Standard telescopic forks may not be up to the heavy side loading as found with trikes, so the front tyre may want to roll off the rim. Therefore any design where this can be limited or designed around should be used. Tyres are more prone to bad effects such as wear on larger machines and will tend to distort when given the unusual side loads of a trike, which does not lean in the same manner as motorcycles. (An engineering advantage of long forks is that the front wheel lean relative to the road is improved, reducing the tendency of the tyre to roll off the rim, but as such forks usually cannot apply any reasonable force, this aspect of trike design is purely academic.)

Use of inner tubes should be considered where extreme side loads are applied to motorcycle tyres. Where inner tubes and tyres are used heavily with side loads, they may distort or lift off the rims and may on rare occasions get hotter, so check during early tests on twisty roads. The tyres should cool down to more sensible levels during straight line running and is rarely a problem, but inner tubes are well worth the safety factor.

Strength is a main area of concern. It must be kept in mind at all times when choosing front end components. Therefore, where style comes before practicality or suitability for the purpose, make sure you do not put yourself in a position of danger.
With large engined machines, the builder must look for alternatives to motorcycle fork legs unless the machine is primarily for posing.
For fast road work in country roads, where braking into fast corners and subsequent powered fast exit cornering, then motorcycle forks and wheel design will compromise the limits to which the design can push. Weight balance and centre of gravity will also be major deciding factors as mentioned earlier. A very low trike with strong, balanced front end working in concert with the rear will handle almost any situation.

The car wheel is designed for, and less prone to the side load problems of trikes. Unfortunately car tyres and wheels are not designed for fork legs, where the steeper rake angle of fork design prefers a more rounded tyre profile. There is also the problem of the car wheel not being compatible with forks, or style.

Car rims usually have an inner lip to reduce the chance of the tyre from peeling off under extreme side loads. Using car rims with this attribute will assist with some extreme problems of thrashing a trike in twisty roads and fast corners. If the wheel size does not have inner lips on both sides, then either build up a similar profile inside the rim by careful welding, or mix split rims or lathe the rim on the trike and weld two halves together. This also allows for custom wheel rim widths, as found useful on some of the authors machines. See also wheels later.

A few pointers.
Most heavyweight trikes use serious front alloy wheels on special axles, but the tyre is the main component, choose it well. The basic car tyre can often be found in almost, or partially round profile, usually on cheaper tyres with narrower cross sections. For ordinary wheels such as the standard car 13" wheel with narrower section, the cheaper tyres are often of a partially rounded profile. So off to the local tyre dealer and look at the tyres, then choose the one with the most rounded profile. It is also usually the cheapest tyre.
If worried about fitting bike tyres on car rims, then check the rim dimensions and profiles with the SAE standard dimensions. SAE= Society of Automotive Engineers. I've been doing this for years.

Look at the options available in tyre dealers, and choose your tyre profile first.

The tyre is the main component, choose it well. Then mount it on a decent front end.

If making new front ends, then making the wheel rim and hub is the best place to start. See making wheels later.

Steering head.
If not using a bike front end, get the steering head made professionally. Invest in a decent item using larger taper roller bearings available from any bearing shop.
As a good alternative, choose the often cheaper yet equally suitable bearings as used in car wheel hubs. These often use excellent large taper bearings at sensible prices and offer excellent spares availability. Where wheel bearing kits are supplied with two sizes, usually a larger outer taper roller and a smaller inner, then buy two sets, as the price is still often much cheaper. Alternatively, use the smaller bearing at the top, where the forces are much lighter and the larger one to take the main load.
Whether with identical top and bottom bearings, or a more suitable, cheaper and lighter form, - always ask around first, before building, as many people will machine a steering head for a small fee during the night shift.

Keeping to standard components from other sources, means keeping it cheap and keeping it reliable.

If making a steering head, get tubing much stronger than the original and take time to get everything perfect. Where possible, reassemble accurately using old bearings, so you can weld to it without damage. Then be prepared to replace with new bearings after welding if they become damaged through excess heat.

The simplest steering head is a large tube with a close fit for taper roller bearing outer race which can be carefully ground or machined away inside to accept the bearings firmly. Alternatively use a split tube slightly smaller and clamp firmly over the bearings with Jubilee clips or exhaust clamps, then weld the gap. Alternatively use a larger tube and grind down the slot, and again clamp tightly then weld the tube to fit the bearings. Tack weld the tube, then remove the bearings and weld fully. Make sure the bearings are a firm fit, if they are not, saw a slot and tighten the gap slightly before re-welding.

The final tube must fully support the taper roller at each end and must be perfectly parallel, and axially concentric. If the bearings are a slightly loose fit, simply hammer the outside of the tube to reduce the diameter by a few thousandths of an inch. Do this evenly while rotating the tube, to ensure the tube remains circular. Gently fitting the bearing in position for checking during the process then removing before further hammering will allow the swaging to be applied with some engineering finesse.

Then make an inner spacer tube to fit snugly inside the main tube to keep the taper roller outer races apart. Carefully lathe the ends of this spacer tube so they are perfectly set at right angle to the tube. Alternatively use a set square, file and a practised eye. This is the work of a genuinely qualified engine fitter. (No GNVQ's here!) The final head stock tube should fully shoulder and support a taper rollers at each end, and they must be perfectly parallel and axially concentric. A variety of large holes and slots are then made in this inner tube so that it can be securely welded inside the main tube. The welding of the inner tube must be strong, as the bottom bearing presses against this to take the whole weight of the front of the trike.
If the bottom fork yokes are close to the steering head, then weld failure will not be catastrophic, as the bottom yoke should be designed to collapse only a few millimetres until resting on the steering head. A very small gap reduces the need for a dust seal, requiring just a lightly fitted O ring or a foam washer to protect the lower bearing from corrosion.
Careful design of all main components should be fail-safe wherever possible.

The central spindle is usually a solid bar or large wall thickness tube, machined to fit firmly into the bearing inner races. As the spindle need only snugly fit the bearings where they are positioned on the spindle, the rest of the spindle can be slightly reduced in diameter, to allow the bearings to slide easily into position. Only where the bearings will fit, will the spindle need to be a snug interference fit, needing the bearings to be lightly pressed into position. If the machining is a little too keen, simply build up with weld and file or machine until perfect.
Securing it all together will need a threaded adjuster to apply just enough pressure to the taper rollers so they will turn freely, yet have no play. This can be done by simply welding a strong, fine threaded bolt, with spacers and lock nuts on the upper part of the inner spindle or to weld a large barrel nut inside the spindle.

Many firms can build steering heads, as it is basic engineering. Take the chosen bearings along, plus details of the length needed between them. Get the spindle made at the same time. Likewise, many engineering firms will make slab yokes. Always ask around first, as someone often knows of someone else who can make a set at work during the night shift.
Always make a strong shoulder on the bottom of the spindle. It is preferable to make the bottom yoke a very firm fit on the spindle, preferably with a small taper section to ensure the spindle fits securely and aligns perfectly in the yoke.

If alloy slab yokes are not suitable, too expensive, or just wanting something for testing purposes, the yokes can be built up from round and rectangular tubing and steel plate. It is possible to build steel yokes, then smoothed and alloy sprayed for styling purposes. (Alloy spraying is also useful for improving the external longevity of one-off steel exhaust systems, when used in conjunction with petrol additive to give a light oily internal film to the otherwise easily corroded exhaust steel.)

Most bike engine trikes use standard bike front ends. This can also apply to average car engine designs, but forks are not suitable for trikes with large engines.
Heavyweight trike steering is either by a variation of fork legs, or hub centre steering. Usually highly modified and often employing some car components. Custom made units will go though a series of refinements with time, so begin with yokes which can take strong, easily available, replaceable fork leg tubing. This will allow various improved versions of fork legs to be slid in easily without other modifications.
By using easily replaced tubing which can slide in the fork yokes, a variety of fork heights and design options can be mounted; leading link, trailing link, Hosack, or a host of others are possible.
The usual set-up for heavy front ends, such as where a V8 is used, is leading link and is often the first attempt, as it is reasonably fail safe, adaptable, strong and comparatively easy to build and can be set up to greatly reduce dive under braking. It also has the advantage that it is much easier to play around with the amount of trail to refine the handling prior to more advanced designs. The down side is lack of style, so careful effort must be made to glean every ounce of style from such designs.
The two main fork tubes should curve down and backwards from the yokes and end in pivots. These pivots are usually either side of the rear of the front tyre and a couple of inches above the front axle height. This is best done once the steering head is on the trike chassis. Use the yokes and a long bar as a guide for the position of the front wheel axle.
Once the front wheel is positioned, a pair of arms will pivot forwards from brackets mounted on the bottoms of the curved fork legs. Standard motorcycle style shock absorbers will maintain the swing arms and axle in position. When testing, the steering may be heavy or light, so be prepared to shorten or lengthen the arms as required to adjust the amount of trail. If in doubt, start with a couple of inches of trail, but prepare to modify as all machines will require their own geometry. The easiest way is to adjust trail is to remove the legs and slightly bend them to suit until perfect. When in the hydraulic bender, pump up until just the slightest movement is noticed, then count the number of pumps. If in doubt, one pump, relax and check against the other leg until the required difference is attained. Then use the first leg as the gauge for the second. Always replace the fork stanchions in the yokes with the spindle to ensure the pivot is perfectly aligned.
Use plastic sleeving in the U groove of hydraulic benders to prevent scratching of the tubing. HDPE high density polyethylene from old plastic oil containers is ideal.

Trail is the distance between the ground position directly under the wheel axle and the position on the ground, as projected through the steering head axis. The normal amount of trail for standard rake angles is the same as that for most motorcycles
It can be difficult to measure the amount of trail, as getting an accurate line through the steering head is difficult. A piece of extruded angle metal bar can lie alongside a steering head if the head stock has parallel sides. This will help project the steering head centre line to the floor, from which the wheel axle can be positioned slightly behind, depending upon the design. Although this way is good for checking, unfortunately, this is not the best way steering heads are fitted to the frame. See later. The rake and trail are best decided on the drawing first, and built into the steering head, forks and yokes accurately prior to fitting. It is common to temporarily weld the steering head in position to check prior to final welding.
If trail needs adjusting, the fork tubes can be bent or straightened slightly or the swing arms shortened or extended. They can also be slid up and down the yokes to level the rear of the machine, so always make the fork stanchions longer than needed, to allow for later adjustments.

The front swing arm pivot bearings on the bottom of leading link fork legs must be strong and the whole arm assembly must be able to take the high side loads. (Trikes don't lean). For good results, machine the pivot tubes with internal shoulders to mount two deep groove ball races or taper rollers each side. Internal spacers are often needed. Needle rollers are even better, but side thrust washers are also needed. For the strongest pivots, use small motorcycle steering head ball races, or taper roller head races and use a very accurately fitting spindle. The spindle must be able to lightly adjust the pressure on the taper rollers and will therefore employ a lock nut or similar adjustment. Bronze or brass metal bushes are possible, tend to last only a year or so and will require regular greasing.

Rubber bush pivots are only acceptable if the whole swing arm assembly is a single, well cross-braced item with the left and right rubber pivots spaced well apart and this is usually a large bore U bend tube.
No matter what bearings are used, the two swing arms should ideally be joined as one piece, similar to a conventional motorcycle swing arm. This is to prevent twisting under side loads, especially when cornering. This usually means bending a single tube to make wrap-around design.
The front wheel and brakes should be able to fit easily into the assembly.

When the fork legs, swing arm links and front wheel are assembled and you are ready to mount the shock absorbers, lift the front end of the machine so the swing arm is at the middle point of travel. Then raise the front of the trike by a further half the vertical shock movement. This is normal rest position of the shocks. The front wheel and it's swing arm are then positioned for the shock absorber units to be in their fully extended, 'at rest' position. Knowing this before building the frame helps to create a little leeway in the frame manufacturing process.

If the engine is at the front and you want a little anti-dive to counteract the heaviness under breaking, then lock the front wheel to the swing arm prevent rolling, lift the rear of the front suspension swing arm on a freely rolling trolley jack, to adjust the height until the front end lifts a little when the trike is pushed forward to simulate braking forces on the front wheel. Do not exaggerate the movement, just have the slightest lift possible to counteract the braking forces. This may need a few friends and a long bar to lever the trike against the wall. This will get you into the ball park but real testing will be needed. When braking for real, this will tend to lift the front end, thus compensating for the dive effect, which causes forward pitching of the trike. In an ideal world, a little dive is recommended, to enable feedback from the braking to enable the rider to get a feel of what the front is doing while braking hard, so back off a little from the ideal position.

Once on the completed frame, the temporary front shock positions can then be further refined so they are compressed slightly under the static load. The shock positions should also be adjusted so their movement is tangential to the arc from the pivot, so they will compress in an even manner. Only use tack welds at first and test lightly. This will give a rough starting point for the suspension.
Do not confuse the difference between the position of the swing arm angle to give anti dive, with the position of the shocks for supple suspension. The swing arm angle is decided first, then the shocks are mounted to allow a slight compression on standard load. So first get the anti dive angle about right on the trolley jack, then make a guess for the shocks, tack weld in position, remove the trolley jack, and test. Then change the shock positions relative to the amount of sack or stiffness in the initial test. do many times until its about right and you should be in the ball park for your first road test.

It will be noticed in the drawing of a front end, above, that the upper and lower shock mounts are plates either side of the main tubes. This will allow for almost any sort of positioning, not only for choosing the ride height of the swing arm, but also for the angle of the shock units to give a suitable spring and damping rate.

Correctly set up, the shocks should compress about five to ten percent when at rest under the load of the complete trike. On a trike with a heavy front end, the suspension should also want to rise slightly when forced against a wall.
When about correct, weld a little more fully and try loading by jumping up and down on the font end. Be prepared to readjust if the full movement is too soft or too hard. If the action is too soft, moving them further from the pivot increases the spring rate at the expense of movement. If the action is too hard, moving the shock units closer to the pivot makes the suspension softer with more wheel movement.

On a recent V12 trike project, the single front shock compressed just a little while at rest, but it took a person jumping on the 2 inch thick, CNC machined alloy front end slab yokes to get a decent amount of compression movement. In this case, the shock was ready to compress further under the weight of the machine and respond well to the road surface in bumps as well as hollows. The main trick is choosing a suitable shock unit and optimising its position. Carefully considered rough guesses are fairly reliable for initial testing. During testing, the machine will show up if the springs and damping are not in the ball park. Most shocks are easily adjustable or replaceable. (For the V12, the front end used a monoshock with adjustable spring rate and damping from the rear of a 1200 cc motorcycle.)

Always ensure that the main fork components, especially the main tubes are not compromised by badly positioned welds which will weaken them. Always make the welds up and down the length of the forks tubes and most definitely never fully around the tubes. Warning: Welding around the tubes will cause a weak area.
The swing arms should be linked for strongest alignment under all suspension settings. A single large bore tube which wraps around the back of the wheel is ideal, but not too bulky. Also consider a strong wrap-over support to add further strength which can be disguised as part of the mudguard support.

Where a car hub is used, the leading link 'fork' could be single sided, but must be very strong. An upright support tube from the axle, over the top of the wheel, curving back down to the rear pivot will help reduce distortion of a single sided axle mounting. This support tube can be disguised by a mudguard. Ensure the wheel can be easily removed, by using the standard car hub items as a starting point. For single sided axles, always make them stronger.

Other forms of front end should be done in the light of experience. The ultimate for some machines is hub centre steering, such as the variants used on the ELF 24hr racers. Also consider three wheeled cars as starting points for alternate front ends of heavier trikes, then gradually replacing parts to keep strength while enhancing style.

Design Summary.
You have chosen the best engine and transmission.
You have checked it runs, then carefully deconstructed the donor vehicle.
The basic components of forks, engine, wheels and suspension are laid out on blocks in their intended position.
you have now spent at least a week just looking at he layout and considered how it will handle.
Some modifications and final juggling have led to the best possible layout.
The frame has now been designed to fit the layout and three designs developed and the final frame is probably a mixture of the best aspects of these.
You have checked the ergonomics and seating are as you desire.
You have checked the gearchange will be reasonable and reliable.
You have checked all components are accurately aligned and blocked to prevent any inaccuracies.

Building the frame.
It may seem a long time to get to this stage.
But the frame holds all the rest together, and must do so with the many demands as mentioned which are placed upon it. This is now the final chance to refine the frame design, ready to commit the design to metal.
Understanding all these other requirements first, will always help make a better frame.
New stock steel tubing is surprisingly cheap. So are simple hand-held angle-grinders, so make life easy for yourself.
Goggles, a dust filter mask and ear protectors are even cheaper and will pay the highest dividends in the long run, while also reducing hospital visits now and in later life.
There is no point building a trike if you cannot ride it.
Get safety equipment the same time as the tubing and welding rods, plus the grinding and cutting discs for the angle grinder. Make sure the discs are for metal.

When building a frame, alignment is everything. Accept nothing less than perfection.
When problems raise their ugly heads, use your head, not a hammer. There are many subtle ways to ensure good alignment.

Important notice: Never be afraid to discard a poor first try of building a frame, as the cost of tubing is minimal compared to the time and effort involved. Getting it right from the start ensures a much better machine. The first tubes to be built are the most important, so go for gold from the outset. If the first attempt at a main frame tube is less than perfect, then remove and refine, or simply make another and use it's remains for smaller cross tubes and other secondary items.

Decide how the frame will handle the loads and forces, then choose your tubing accordingly. Look at tubing used on bikes, trikes and cars to get a feel of the sizes needed. Find out the wall thickness of the tubing used, for this is just as important as the outside dimensions. If in doubt, always use stronger tubing. You may be able to afford a lighter seat lug to break, but not a structural part of the frame. A few extra pounds or kilos on the main frame tubes are always good insurance.

If in doubt about tube diameter and style, always make a cardboard tube to see what diameter tubing will look best when set beside the parts laid out on the garage floor. - Use those old kitchen towel roll centres as a starting point and reduce or enlarge as needed for good looks with strength.

If you dislike metal work, use square tubing, it's easier to fit. Round tubing needs a lot of profiling work to join properly.

Make sure you use ordinary steel and use seamless tubing if you can. Iron is never used and stay clear of fancy steels unless fully competent. Don't try saving money by buying cheap tubing for the main structural parts of the fame, and stay clear of wrought iron.
An cheap 4.5 inch angle grinder with cutting and grinding discs is a must.


Types of steel. - For most frame purposes, just use mild steel.


DEAD MILD or low Carbon. 0.07 to 0.15 percent carbon.
Available as Black and bright bars. tubes, wire.
Pipes, chains, rivets, screws, nails, wire. boiler plates.
Easily worked when hot, but difficult to machine owing to tendency to tear.

MILD. 0.15 to 0.25 percent carbon.
Available as Black bar sections and sheet Bright bar strip and tubing Forgings.
Ship plates and forgings, gears, shafts, nuts, bolts, washers, rivets, chains.
Easily machined and welded, and is cheapest steel.
Ideal for bike frames. Welds easily. Available in many sizes shapes and wall thicknesses. Preferably non seam welded tubing, but seam welded tubing is perfectly good too.

MEDIUM CARBON. 0.25 to 0.5percent carbon.
Available as Black bar, sheet, sections and plate Bright bar. rods, flats and strip Forgings.
Machine parts and forgings. castings. springs, drop hammer dies.
Responds to heat treatment and can be machined satisfactorily.

HIGH CARBON. 0.5 to 0.7 percent carbon.
Available as Black bar and stripSilver steel rod.
Hammers, sledges. stamping and pressing dies. drop-forging dies, screwdrivers hammers, set-screws

HIGH CARBON. 0.7 to 0.8 percent carbon.
Punches, cold chisels, hammers, shear blades, drop-forging dies, lathe centres. spanners, band saws, rivet sets (not rivets). vice jaws.

HIGH CARBON. 0.8 to 1.0 percent carbon.
Punches, rivets, sets, screwing dies, screwing laps, shear blades. drop-forging dies, saws, hammers, cold chisels, springs, axes, rock drills, milling cutlers, lathe centres, reamers. See also my knife monograph.

HIGH CARBON. 1 to 1.5 percent carbon.
Drills, milling cutters, lathe tools, files, wire drawing dies, hacksaw blades, ball bearings, screwing dies and taps.


CHROMIUM Up to 1.5 percent. Used with nickel and / or molybdenum increases hardness and allows high UTS with considerable ductility

COBALT. 5 to 10 percent. Retention of hardness at elevated temperatures.
COBALT. 12 to 18 percent. Increased corrosion resistance in stainless steel.
COBALT. up to 40 percent. Improves coercive force in magnet steels.

NICKEL. 1.5 to percent. Increases tensile strength and toughness.
NICKEL. Over 20 percent. Used in corrosion- and heat-resisting steels.

TUNGSTEN varies. Strengthens steels at normal and high temperatures.

MOLYBDENUM varies. Used in stainless steels to provide resistance to sulphuric and other acids.

VANADIUM varies. Increases hardensbility.

NIOMUM. TANTALUM. TITANIUM. All three prevent weld decay in chromium steels and in nickel stainless steels.

BORON 0.003 percent. Great increase in hardenability.

COPPER 0.2 to 1.0 percent. Increases corrosion resistance.


When built, you will be loading the frame to see where it flexes, so expect to add some more tubing, fillet plates and/or gussets as required later.
Make a rough guess of the sizes of tubing you will need, but prepare to change them slightly when confronted with the metal stockist's options.

A good looking trike is a subjective analysis of a machine which needs not only strength, but also style and proportion of the frame tubes in relation to the other components. To get a good idea of what looks good next to the engine and wheels, make that cardboard tube as long as possible, so it can lie along the arranged components to help gauge the general look of the frame tubes. Then find the nearest match in the steel tube available.
Always measure the length of the main tubes, so they can be cut a little overlength as a single length for strength and reliability.

Grab your drawings, metal tape measure, a pencil, then find the local metal merchant and see what they have to offer, and ask their advice.
There are many metal stockists around the world, and you can buy anything from single tube and a pack of welding rods, to enough to build a battleship.
The best way of deciding is often simply looking and deciding what seems best. - 'I'll have two lengths of that heavy tubing, four of that smaller square tubing and a sheet of that'.
This is not at all scientific, there are no calculations and no structural analysis. If in doubt, use the scaffold tube as a reference point. Do not put yourself down, even a poor mechanic has a working knowledge of what has been used in similar circumstances. Your main assessments are comparative to similar structures plus a safety margin. The ability to use the eyes in conjunction with common sense is a very powerful tool.

The good engineer and designer would consult engineers tubing data, to check the actual working loads, then choose from suitable tubing and give a safety margin. Later versions of the design would then be refined according to bending tests and real world loading feedback data, as mentioned later.
As trike builders do not like arithmetic, then use common sense and a sense of proportion and comparison with other machines. I have seen lightweight trikes safely using three scaffold tubes, and car engined trikes with four scaffold tubes.
If in doubt, look for similar successful engineering equivalents. If in doubt, ask friends. If in doubt, build stronger than expected. If in doubt, be cautious and try it anyway, you will often be pleasantly surprised during early testing. Doubt is a positive attribute, it can also be a safe one.
If in the worst case, the frame fails during initial testing, then you will need to strengthen, or even rebuild parts with stronger tubing, simply returning to the start in the light of experience before too much expensive work is done. Initial testing is always done on the basic rolling chassis, so that in the worst case, the whole basic frame can be affordably discarded and a better frame made, before all the fiddly, time consuming work is done to turn it into a work of art.

You may be surprised by the vast selection of tubing available and it is always in a variety of wall thicknesses. Always measure the tubing on equivalent machines for comparison.
Circular, square and rectangular tubing, strip and rod. Make yourself a shopping list and be prepared to have it cut for a small fee, as it usually comes in twenty foot lengths which the supplier can cut to what ever length you need. Measure three times, cut once, or do they deliver? I take along a hacksaw and a few spare blades in a friends van, to keep costs down.
There will also be alloy sheet, wire mesh and a host of other stuff. Don't forget to buy the welding rods and grinding and cutting discs at the same time.
And to repeat; goggles, ear defenders and breathing mask too.
A decent set of leather welding gloves is useful when handling hot metal.
If in doubt, ask for a photocopy of their materials list, and retire to a local cafe to think, or return next week.

When carrying long tubes in a car, always take newspaper or rags to cover the seats as the tubes are covered in preserving oil which stains easily. Take plenty of cloth to wipe off excess preservative. Most trike frame tubes can be cut overlength and still fit in a car if stuck into the passenger foot well, and the tail gate open with a warning red flag attached. The passenger seat may need to be removed, so take a few spanners. Take bungees to keep the tail gate from bouncing around.

When the tubing meets the trike bits, it may be decided that it is not the right size. At this stage, a rethink will be a lot better and the original tubing will become stock for other work, such as to align the wheels to the floor lines, or gateposts and drains, or perhaps an engine hoist.
Therefore just get the main tubing first, and if in doubt or on a tight budget, simply get one length, then return for more as needed. Practice bending and welding on the first choice of tubes, and when competent, get the perfect tubing later.

To repeat, if worried about wall thickness, go safe. A few extra pounds in the main frame is weight well spent. You can be less cautious for non structural parts such as seat bases, battery box mounting brackets etc.

Check out the local hire firm for tube benders if needed. Get the hydraulic type and check the tubing diameters that the bender can handle the tubing you have chosen.

Before making the main frame tubes, it is better to make the suspension and engine mounting items first and position them correctly. Then the frame can then be made to fit the set of perfectly aligned suspension components.

Understand the hierarchy of the structure you are building.
The engine powers the tyres. The tyres transfer forces to the machine and the steering controls the direction. Therefore the wheels are the prime concern, with the suspension used to keep them in an ideal state under all conditions. The frame is there to keep the suspension in the right place, so it can do it's work properly. The engine and riders, although not structurally important, also sit on the frame, as this is a very convenient way to accommodate them. Therefore if suspension is to be custom made, it should be made first, to fit the perfectly aligned wheels, but with the frame mounts left until later. The frame then made to fit the perfectly aligned suspension. In reality, the chassis is always made first, so the engine is well supported, and then the suspension is built and probably lightly adapted to ensure good wheel alignment to a possibly unsymetrical chassis. The mounting of the steering head is left for much later.

If you have to modify or make new suspension components, always build them as mirror pairs before making the frame. A simple wooden dimensional welding jig will help enormously. This applies not only to front fork parts, but to all symmetrical pairs of components, right through to the symmetrical rear radius arms. Fit them to the components such as hubs etc and ensure they work as required.
When making the suspension arms, fit the spindles and bearings in their housings, supported level and straight on Vee blocks, then carefully make the A frames or whatever to fit. Then tack weld in position, with three tacks per join, remove bearings and fully weld. When cooled in air, return to the jig and tweak if distortion has occurred during welding. Where shock units are to be mounted, leave these only tack welded, as they may need to be repositioned once the rolling chassis is refined for overall balance and suspension rates.
Never cool metal components by plunging in water, as it can cause uneven hardening and fractures. Allowing the metal to cool in air is much safer.

Tweak, adjust and modify the frame tubes before assembling to fit these pre- aligned components. If the suspension units are symmetrical and built in a simple jig, the frame mounting lugs are fitted easy to be tack welded to the frame, and the wheels lined up accurately, then the frame will naturally be positioned accurately.
Working from accurately positioned wheels to the frame will allow the whole machine to be accurate and handle well.

The frame can now be built.
Building the frame should be surprisingly straightforward as by now you will know what it is that you are intending to create, and should have thought it though many times. The main clues to the overall frame design are the components which have been sitting in place ready to be joined with a competent structure to take the forces which have to be resolved.

Clean all parts and tubing, then practice with, and set up the welder. Have safety equipment at hand and ensure plenty of room. Check the fire extinguisher, preferably carbon dioxide, or at least a bucket of water.
Always make welding a positive experience. When everything is prepared, frame building can, and should be fun - serious, but enjoyable. Very creative.

Warning: If you have never welded before, expect to spend a month of an hour a day or more getting to learn to weld to an acceptably high standard. Some people are born welders, but most people are not. It takes skill and it takes time to make a neat, fully penetrated, and clean weld with no distortion. So if you have never welded before, get the welder six months before you intend to start building the frame and practice, practice, practice. If you are really bad at welding, go to a night school on the subject, or learn to tack weld and hand over the assembled frame to a professional welder.
A section on welding is in the appendix to this monograph.

Clean a flat and level floor.
If you don't have a level floor, then three concrete paving slabs in the garden will suffice, but they must be level. You may be able to get away with building on a less than perfect floor, but it is imperative to keep the spirit level correctly aligned. Therefore mark one end of the spirit level so it will always be aligned pointing to the right and the front of the machine. If this is not done, a less than accurate bubble will soon be followed by a less than accurate machine.
If you have not done so yet, mark a thin and perfectly straight centreline on the most even part of the floor, and another centre line at ninety degrees to it for the alignment of the rear wheels.
Straight lines can be made using a chalk string, pulled tight and flicked vertically to leave a straight chalk line. Standard building site practice. Then use tape either side to allow a painted line to be made. This line is a guide, the final accuracy will be done with a metal rule directly on the machine. To get the perfect line at ninety degrees for the rear axle, divide the main line in half, draw an arc from each end, and where these intersect at each side, can be joined to give a line at exactly ninety degrees to the centre line. Alternatively use the sides of a good, big square machine-made cardboard box, or fridge door or similar as a large set square. Double check this alignment.

The original engine mounts should be ground out of the donor machine if required, reprofiled to fit the new frame tubes and lightly bolted on the engine to hold them in place. The transmission is double checked, aligned and centred. All the suspension will be blocked in place and accurately aligned, with frame mounting lugs in position ready to accept the frame tubes. Double check that all mounting bushes, brackets, spindles and relevant components are in place.
Where the engine mount and suspension cannot both easy fit onto the line of a frame tube, the suspension takes priority if they cannot be easily modified or shifted slightly to clear the engine mounts. The engine mounts can be extended or modified later to fit the frame in a slightly better way. This may also be a good opportunity to tease the centre of gravity a little lower without upsetting the layout.
The gearchange should by now be well considered for future reference, and decide where it can and more importantly, cannot fit. If in doubt about the gearchange path, use temporary dummy set-up using broom handles or whatever is suitable so it is not obstructed by frame tubes. See Gearchange later.

Use blocks to accurately position the engine, transmission and rear wheels in position above the centreline with the right ground clearance. Use a spirit level, straight edge, plumbline and your eyes to make sure everything is aligned and level. If there is a propshaft between engine and differential, do not cut it yet, but make sure there is adequate room so the splines will be positioned to take all movements into account.
On independent suspension rear ends, it is important to have all drive splines from the differential to the rear wheels in the correct position for the movement they permit.
It is assumed the tyres are pumped up and the rear tyres are of identical size and type. If you have four wheels to choose from, always use identical wheels and tyres, with similar amounts of wear, pumped to the same pressure.
Set up and check the rear wheel camber and toe in, ground clearance and any other aspects of the design. If the steering rack is retained, make sure it is set in it's mid position and prevented from moving. Leave the toe-in as per original machine until after the first few test rides. Refer to car manual.
Make sure any drum brakes are on the correct sides of the machine.

Block securely and mark it all so you know when it's disturbed; do not line up perfectly to wrong positions.

Measure diagonally from points on the wheel mountings to front and rear of the centreline using a metal tape measure. Do not use string or a cloth tape measure which can stretch too much.
Accuracy should be less than 5mm across the widest parts, preferably zero and don't take just one measurement, double check, and triple check for all the main parts.
Position the front end with steering head just ahead of its intended position, to allow a little room for excess front frame tubing. Align with spirit level and plumbline, then block in position. If this is difficult, fit the handlebars upside down then rest them between two chairs. It's not ideal, but as long as it's approximately in the right place when you start welding the main tubes in position, this will do for now. Front end will be accurately aligned later. Block or tape the front wheel on the centreline.
The trike has the advantage of being a triangle in plan view, so overall accuracy is easier than most other vehicles.

If simply building a trike rear end to fit a bike frame, then it is often easier to build the rear frame to align the differential to the chain run, then build the suspension afterwards.

There are two ways to build a frame from scratch for a car engine design: Front to back, or back to front.

Front to back means building the front end complete with steering head and mounting it to the engine mounts first, then aligning and then building the rest. This can lead to gradual misalignment. Used only for bike based trikes, which use a ready built standard bike frame.

Back to front is safer, because all the heavy work of building the engine and suspension is done first. This then allows a solid assembly for mounting the steering head and front end. This allows the builder to tweak the bare front tubing after the major rear alignment and welding are done.
When mounting the main tubes to fit the temporarily positioned steering head, leave a little excess length at the front which can be finally aligned and trimmed to size.
With the rear assembly tack welded in position, the front tubes can then be teased and coerced into line for a perfectly accurate steering head relative to the rear wheels. When perfectly aligned, the steering head mounting tubes can be ground back and fitted until a perfect rake angle is achieved, then aligned and tack welded.

Test pieces:
Preparation is the key to good welding. Clean the tubing first and also weld some test pieces and break them until you get it absolutely right. For deep welds, cut through the welds to see that the penetration is of good quality, with minimal slag inclusion or holes. Unfortunately the first few welds are the main frame welds. If in doubt, tack weld and hand over to an expert.
If you know of a professional welder, then they will often do extra work in their spare time and may come to the trike, so all remains accurate. They can also offer advice prior to final welding. Do not be surprised if the welder asks for many areas to be dressed or chamfered and other requirements, as they know their job, and are always worth the cost of a second visit. See also welding later.

Always try to employ full length tubes from the rear suspension mountings through to the steering head for the strongest frames.

The bottom frame tubes should be able to have the radius arm mountings or pivots welded to them. Likewise the bottom wishbones and similar items. Where structural components are welded, try to position the fittings to be fail safe. Check the direction of the forces and position appropriately, so that if a weld or tube fails, it will fail as safely as possible. Remember the wire and solder model frame.
A strong frame will hold everything together.
A rigid frame will ensure the bits hold together without flexing.
For best results, go for both.

Start making the frame by aligning one main tube, bending if and where needed. Never exert any force while offering it up to the machine for checking the fit. Always remove the tube and modify until perfect. Then gently mount in position and check, or remove and tweak further if needed. This reduces chance of upsetting the alignment of the whole machine. It is much quicker in the long run than causing unseen distortion in the aligned components.
The more common designs use dual upper and lower main tubes. Such a main frame tube will be running from the rear suspension, past the engine and curve up to the steering head.

Where possible, always try to make frame tube as mirror images. When the first tube is made, it is easier to make a mirror of it when it's off the machine, allowing ease of comparison. (It also helps the frame to flex evenly under extreme handling conditions :)

Chalk or a felt tip permanent marker pen is also priceless at this stage. It allows accurate marking of the centres of the curves for the bender, where to clean the metal for fitting the brackets and where to modify the engine mounts etc. A felt tip pen can also stir the tea, as this is a slow, steady process with plenty of looking and refining as the main components gradually take shape. It is not a rush.
Align the main tubing on the engine and suspension mounts with excess metal sticking forward for the steering head. Then mark their position on the tube and carefully remove the original engine mounts to allow final trimming to fit the frame tubes. Replace and tack weld the tubes just enough to hold in position. See welding appendix.

You may be very keen to get the main tubes in place and fitted, but this is the time when a very slow approach is needed. You can afford to rush the seats and battery box, but not the main frame tubes.
Take your time and always take some time out to just sit and look at the main frame tubes which are lightly tack welded in position. your initial sketches will surely be modified at this stage as you work through in 3D reality and this is what makes a much better machine.

Now recheck the alignment of the wheels, engine, forks and adjust as needed.
By making the tubes as mirror pairs, inaccuracies in alignment will show up more easily, such as misalignments of suspension or tubing etc.
Tweak and adjust as needed. When accurately aligned, add some more evenly spaced tack welds on each join to prevent it all moving about.
Then the other main frame tubes can also be added, again as mirror pairs wherever possible.

Build the whole structure to make the smooth, clean lines so exemplified of better trikes. Making the tubes to fit the assembled components helps the builder refine the whole machine as it grows. There will be unseen problems, so take time to work out at least two different ways to solve any problems, as this is a crucial time in the machines creation and extra time spent now is well repaid.

Now check that the engine can be removed and replaced fairly easily.

There may be other main tubes, which may suspend the top of McPherson struts or similar items and these secondary frame tubes can now be positioned to support the main tubes.
To keep the main tubes aligned during side loads of cornering and jumping hump back bridges, secondary tubes are required. Unlike main tubes which should maximise the most natural and strongest forces, secondary tubes can be fitted in a variety of positions to help minimise distortion in the main frame tubes. Triangulation between the tubes is will always make for stronger and more rigid frame.

Once the basic frame is built without the steering head, the tack welds can be built up to be structurally competent enough to allow removal of the blocks. Some of my machines are road tested with fifty percent welds, but at this stage, just enough weld to hold all together will suffice.

First test:
At this stage the basic frame tubes are in position, with the suspension and engine lightly tacked in place.
Tack weld a piece of tubing to roughly replace the forks for basic testing purposes. This should keep the front of the trike in the correct position off the floor as the frame is allowed to relax when you remove all the blocks.
If you have tightened any mountings, then lightly loosen all engine and suspension mountings, as this will allow the whole structure to relax naturally.
Lift one rear wheel and slide a piece of plywood underneath and a few ball bearings or marbles under the plywood. Now you can gently load the structure, to see how the suspension units behave and the rest of the structure distorts when gently loaded with a rider.
Make another check of the alignment and look for any signs of untoward distortion in the frame structure. If a rider can sit gently on the structure, the differences when being on and off can be viewed from various angles to see how the structure behaves, especially the suspension units and also general frame flexing.

Gently push on the upper suspension mounts to check the suspension settings are reasonable and to see how the frame flexes. If you have a digital camera or cam corder, you can make a little animation of the frame flexing from front and side and the rear, then run the animation sequence to check where the main frame tubes flex.
Check if anything has bowed badly, curved inwards or other unexpected problems. Likely areas are between the lower suspension wishbones, where the frame wants to pull apart and the upper shock mountings, when may not yet be finished, so use this opportunity to assess the best possible way to keep these highly loaded structural areas well designed and built. - Well deigned and built does not mean lots of heavy metal.

Where the upper suspension mounting points can be adjusted to fit the frame tubing, it can be advantageous to lightly test the rear suspension mountings, adjusting them so the frame sinks just perceptibly on the springs indicating a reasonable amount of suspension in the rest state for a finally loaded frame. If a light machine is intended, then the springs should compress about ten percent with a single rider. If a heavy shell or three or more riders, then just a slight amount of spring compression with one rider may suffice at this stage. Reposition the suspension units until a balanced rear end is attained. This does not apply to McPherson struts, which may need the strut to be modified.

NOTE: It is very important to test the frame with one rear wheel which can be allowed to slide sideways. This will show up any sideways spreading of the frame. Place one rear wheel on a piece of plywood so that it can slide on small balls or marbles and then watch the way the rear of the chassis spreads apart under careful loading. This will show if the rear frame is spreading. This cannot be tested with both wheels on the ground, as they prevent such spreading, but must be able to spread. Where any spreading occurs, cure at this stage with suitably strong tubing, as this is the main structure of the machine. Do not fully compress the suspension, but a moderate load will show if any unwanted distortion is happening at an early stage and that the shocks are reasonably well positioned for their purpose.
Also carefully check the top shock mountings, the bottom frame cross pieces and radius arms or wishbone suspension components.

With the shocks removed to allow the suspension to move fully, check the wheel alignment as it compresses and that the wheels do not change inappropriately from their vertical alignment. The rear wheels should lean in slightly at full compression, so they will stay fairly flat on the road, with just the outside of the tyre being slightly more compressed. If the trike can be removed from the blocks, then by using a plank to lever the sump, the frame can be raised and lowered as if cornering, to see how the wheels align to the road. The plywood on marbles now shows its worth.

If all is well, add a few more tack welds to strengthen the frame and test further.
If all is not well, it is easy to replace the blocks and wedges, grind out the tack welds and replace or modify any components as needed and this may even include the main frame tubes.
Perhaps you may wish to shorten the upper wishbones and make new mounting points on the frame.
Perhaps you may wish to make a deep sump brace, so the engine can be removed, but still have a strong lower frame. Perhaps the upper shock mountings need a re-think.

This first test is a good time for reflection on the overall design, so use it to good advantage. It's called sitting in the garage with a cuppa tea or a can of beer.

If all tack welds are fairly equal, and wishing to know what part of the frame will break first, then this is an unique opportunity to do so in the simplest way possible. Loosely replace the blocks so that any component drop is less than an inch.

Once satisfied, a few welds to strengthen the frame are added, you may now tweak, kick and/or adjust the whole assembly as needed. This is a good time to begin to understand the way the frame performs / distorts. Remember the wire frame model. If a weld breaks, then little is lost at this stage and knowledge is improved. Then re weld and try again until the frame is behaving well.
If necessary, the whole chassis can be disassembled and re-shaped by grinding off the tack welds with only a loss of time and effort.

If all holds together well with minimal distortion, then confidence is improved.
Re-tighten components and check for distortion when tightening them to resolve such problems early. It is often possible for a 'relaxed' frame to distort slightly, causing engine or suspension bolts to become misaligned. Check for this by partially removing each bolt to check they slide easily in a well aligned frame and it's mountings.
Further distortion will occur with full welding, so getting it close beforehand will minimise any further misalignment and make heavy maintenance much easier.

For mid or rear engined trikes, the non structural, minor seat tubing at the rear of the frame can be removable, leaving just the basic frame, engine and suspension in position. It can be a good alternative for particularly awkward engine removal or for maintenance on a fuel injected transverse Vee six with turbo etc. This is similar to some motorcycles, where the rear is bolted in place. It also allows for a rear shell to be fully opened for showing the engine at custom shows.
Do not mount passengers on removable sub frames unless the design is fail safe.

Fitting the steering head last will allow all the main parts of the frame to be sorted first. The wheels accurately aligned, the engine correctly aligned to the differential, and engine mountings correctly positioned and tested under load.

Once the rear end is sorted, the main part, the steering head can now be done at leisure.
Double check the rear end and add more tack welds to keep it all in position. If deciding to fully weld the rear at this stage, it should only be done after the gearchange linkage is made and fitted and any prop shaft modified, as many problems may yet be unseen, especially on transverse engines. See gearchange later. There is no need to fully weld at this stage, but all frame joins must have at least four evenly spaced, strong welds (three plus a safety) to prevent any movement or breakage of the temporary joins.

Check list for the engine:
Ability to flex on the original rubber mountings.
Alignment of the differential to the rear wheels.
Restraining of engineering using original engine struts.
Ability to remove engine easily and to change the clutch plate.
Clearance for the carbs and exhausts.
Gearchange routing clearance.

Check list for solid axles:
Radius arms which pivot at the front either side of the engine output shaft or sprocket.
Upper suspension mounts.
Panhard rod.

Check list for independent rear suspension:
Shorter upper and longer lower wishbone sets, the lower ones including radius arms, or have other support for fore and aft force resolution into the frame under acceleration and braking.
Shock mounts.
Differential mounting and any chain adjustment.

Fitting the front end demands good accuracy.
The two rear wheels do not worry if the engine is slightly off centre, or a host of other minor inaccuracies. The front end alignment requires real accuracy.

Assemble the steering head, forks and yokes and front wheel.
Pump al three tyres to correct pressure, ensuring all is secure and perfectly aligned on the floor once again. Use a plumb line to get the wheels centres aligned on the floor.
Measure the position of the steering head from the two main alignment points, these are usually the centres of the rear wheels or their bearing housings. With the wheels perfectly aligned and set, (double check) tyres pumped up, and blocked underneath to prevent any movement, mark in the centre line of the wheels.
Check the rear wheels are horizontal with a plank on them and a spirit level.

Assuming the wheels and tyres are identical, then the most accurate point is the outside edge, directly above the axle centre line. Each rear wheel should be on the accurately positioned floor line, securely blocked and identically aligned with the other rear wheel and their axles at ninety degrees to the centre line. Mark the top of the tyre above the central spindle, using a plumb line to check. Block securely and do not disturb anything. Marking a tyre is difficult, so use masking tape on the rubber and the alignment mark should be easily made to within a millimetre.
It is not possible to make a mark exactly at the edge of the tyre, so an accurate point must be made on the masking tape, close to the outside of the tyre, which is evenly positioned from the centreline of the machine.
For real accuracy, usually the wheel mounting flange faces are used for this purpose, by measuring in the distance from the outer rim to the flange face and marking this on the masking tape. Formula one rigs have dummy solid wheels for alignment checks.
NOTE: It is imperative not to disturb these points, so block the wheels securely by making four wooden wedges. If in doubt, then use the upper pivot points of the outer rear suspension, which cannot be disturbed. If in doubt, such as the kids playing around without you knowing, always use a symmetrical part of the wheel bearing housings.

To position the steering head central with the whole machine, measure the identical distances from the alignment points on each wheel.
If the front wheel is perfectly on the centreline, the rear wheels are perfectly spaced on the cross line, and all else is well, then the front end tubes can be tweaked into position to match the steering head. Use a plumb line (string and weight) to get these tubes accurately over the centreline while the rear wheels are at perfect right angles to the centreline on the floor.

The front tubes may need a little persuasion, by hammering with a length of similar tubing, (most hammers are too feeble) with a block of wood to protect the tubes. If larger adjustments are needed, then bracing a length of tubing through the frame using blocks of wood and ropes, such that the tubes can be bent with minimal stress on the welds.
Once the front tubes are perfectly central, AND the frame alignment checked yet again, the ends of the front tubes can be ground to take the steering head. The front wheel is fixed on the ground and the steering head and forks rotated on the fixed front wheel until it kisses the frame tubes perfectly. If the frame tubes are a little low or high, then just jack up the front of the trike frame. The steering head should now rest on the frame tubes, equidistant from both rear wheels. The frame tubes can now be ground and dressed to fit the steering head perfectly and at the correct rake angle.

As the steering head begins to sit snugly in the tubing, gradually roll the front wheel along the floor centre line until the desired rake angle is achieved. Careful grinding with the angle grinder will then help to create a perfect fit.
If the frame tubes are a little low or high to fit the steering head, then simply raise or lower the front of the frame with wedges or a jack, as this does not appreciably change the overall alignment of the machine.

When welding the steering head in position, the heat will damage the steering head bearings. Just tack weld the steering head in place, then check carefully. New bearings can be fitted after initial testing. If special pullers are available, which will NOT upset the steering head alignment, then this is acceptable to remove the races after the steering head has been tack welded. Do not hammer them out, as a misaligned steering head is infinitely more expensive in the long run than a new set of head races. It is better to leave them in place to reduce chances of misalignment. Yet another advantage of using affordable, easily available components.

Getting the steering head tubes equally positioned relative to the rear wheels is simple, just two equal measurements. Making the forks vertically takes a little more work prior to tack welding the steering head in position.

To get the front end accurate when seen from the front, use a straight plank across the top of the identical rear wheels and check with a plumb line and a spirit level. If the tyres are not identical, probably with a slight more wear on one side, then measure the difference in overall diameters then place a shim of card on the smaller wheel to make the plank level with the axles. Now mount the spirit level in a similar manner beside the front wheel and note the bubble position. Then a set square can be positioned on the spirit level to give the accurate alignment needed. A plumb line will confirm.

Measure many times, then tack weld the steering head in three places for each frame tube, plus a couple of strong welds on the bottom of the lower tubes.
The rear wheels will be perfectly horizontal with the spirit level, so the front forks can be aligned with the spirit level, as seen from the front. On well raked machines, this is often done by suspending the plumb line from the centre of the top yoke, over the centre of the bottom yoke and dangling close to the ground, to be perfectly in line with the centre line on the floor. It is called being accurate.

When the steering head is fitted, gently allow the whole machine to relax, free of any supports.
Unblock the wheels and always roll the machine backwards and forwards to allow the chassis to fully relax.
Now check ALL alignments again.

Check the front end accuracy from two independent methods, to help confirm accurate frame alignment. Also checking the distances between front axle and left and right rear axle bottom pivots. Checking the alignment of the top of the steering head from the top of the wheels, and also checking the alignment of the bottom of the front wheel from two lower wheel hub mounting components will give a confirmed check of the accuracy. If a third check is needed, mark the centreline on the rear of the machine and view from this point, to confirm the front wheel is accurately aligned relative to a plumbline hanging off the centre of the steering head.
If anything seems wrong, take your time to find out why. Also use your eyes and common sense for anything obvious or dubious.
A classic trick for most of us humans with mismatched eyes, is to look down the length of the machine using a pocket mirror as well as normally, as any non symmetrical aspects will show up more easily.

You now have a basic rolling chassis, which is tack welded so that it can be easily modified or even replaced.

Place each of the three wheels in turn on a bathroom scale and note the load. Do the same with the rider and make a note, so that you can adjust the load on each wheel according to its size and profile, by moving the rider and later, the fuel and battery etc.
If you have a mid - mounted car engine, then your three wheel loadings should be close to a very nicely balanced machine.
If you have a VW with a moped front end, then you may wish to consider your wheel loadings very, very carefully.

Take your time at this point and give yourself a good long breather.
Allow a day or two, to remove doubts or reconsider any suspect or marginal design areas.
You can still break the tack welds if needed. Be prepared to do so, as you will find it increasingly more difficult to overcome inaccuracy as the work progresses.
Checking costs nothing but is extremely important. Keep in mind what happened to the Hubble space telescope.

Now carefully assess the forces ruing though the frame, and decide where the bracing is to go. For long lengths of unsupported tubes, then triangulation is needed, unless you are using very strong tubes. Flex the frame and see where any secondary strengthening us needed.
Where fillet plates are to be used, such as either side of the steering head, these should be done after the main welds are finished.

When the basic frame is complete, carefully remove the engine and all components.

Fully welding a chassis while it is off the machine will allow easier and thus better welding.
It also encourages the builder to add any little fillets and refinements, and also to add any late changes, flourishes and to dress the welds for a smoother shape and reduces chance of fracturing from any sharp stress points. A clean profiled chassis makes checking for fractures much easier during initial testing. A bare frame can also be measured for assessing general accuracy from it's basic alignment points.
Where any last minute changes are to be made, usually in awkward areas, such as a better fitting tube, always brace the area with tack welded tubes before removing the item, then fit new and finally remove the temporary bracing.

NEVER weld on one side of the chassis and then the other side, as this will cause distortion. Weld both sides of the chassis as pairs in the same manner. For example, weld the left, then the right upper suspension mounts, then the left then the right rear engine mounts etc.

A fully welded chassis will allow the chassis to be fully loaded at rest position, and the steering head to be checked accurately for distortion prior to final welding of any head stock fillets. You still have the chance to twist the steering head into perfect alignment if the welding causes distortion.

Replace the fully welded chassis, note the problems and then tweak, or grind out and reweld parts if distortion occurs.
Use the tape measure and spirit level with a vengeance.

When fully satisfied, check and double check the steering head and then add any steering head and other fillets when confident.

A bare, fully welded chassis will often show up imperfections when the components are replaced. This may require minor grinding or tweaking for an easy fit of the engine, suspension etc. Occasionally the steering head may need a little tweaking back into line with a scaffold pole, which is best done before the side fillets are welded in place, and old bearings are still in place.

No chassis is perfect.

Having made all the effort, the chassis may well be a great deal more accurate than most. Accuracy does not ensure good handling, but it does eliminate many handling incongruities.

When fitting the engine again, there will probably be a few holes to file to get a clean engine fitting, but if the holes need a lot of filing, then just make another check that all is well, as this is sometimes a way to tell if something is amiss.

Removing big engines.
Where a big engine is fitted, perhaps a V8 in front, then it may be necessary to extract the engine by having a lower frame rail removable.
If particularly heavy, such as Detroit lump or a V12, both bottom frame rails could be removed as part of the engine, and supported on a rolling dolly, allowing a more rigid upper frame which can be lifted off the engine.
When building a removable tube, first get the main frame strongly tack welded in position to keep it all together. Do not use full welds at this stage, as distortion may be incurred, causing springing when the tubes are cut, thus helping to misalign the frame.
Support the engine just enough to take the load off the frame, but still keeping it in place on the trike. Then cut the tubes where needed to remove the engine. A hacksaw is ideal as the resultant gap is small. Undo any engine mounts and remove the section of tube.
The removable tube can be secured in place in many ways. The simplest is a slightly larger diameter tube which is split lengthwise, to act a split sleeves, so the inner part of the split tube is welded to the bottom of the fixed frame rail, and the other half welded to the removable tube, so that both halves will support the engine and ensures that failure of any bolts will still keep the engine from dropping.
Slash cutting the main frame tube will allow the engine to rest on the lower cut of the frame, and if done with a little sophistication, will be self aligning and allow easier removal and replacement. It can also be a little more fail safe.
Only tack weld the split tube components, to check the tube can actually be removed and will not distort under load. When satisfied, fully weld, fit bolts and release the engine weight to check for frame distortion. Adjust as needed. This is an advantage of building rear first without the main frame fully welded, as any deformations are accounted for before final front end alignment and final welding of the steering head.
If through bolts are used, the inside of the frame tubes will need spacers to prevent the frame tubes from squashing when the bolts are tightened.
Solid split bar ends are also possible, but heavier, requiring an engineering firm to make matched pairs to fit the tubing. Also study motorcycle split frame tubes for alternative mountings for lighter engines. Reassemble and fully weld the removable parts and refit to the engine, suspension, forks and wheels. Allow the frame to relax fully and check before further welding. Always build up and fully weld split frame tubes before fully welding the chassis.

A build sequence.
As all the differing parts need conflicting requirements, there is always room for confusion or pitfalls. To sum up the many sequences, the following is a generalised build sequence for a trike based on a generically common transverse donor car engine and transmission.
Find the most level part of the floor, make a paint line with a second line at right angles to align the rear wheels. If in the garden, place three concrete paving slabs so they are level when checked with a spirit level and a straight plank. A central line is scratched accurately on the slabs.

Block up and align the engine and wheels, the anti roll bars, radius arms and prop shaft splines.
Make any special suspension items such as wishbones and radius arms, preferably on simple wooden welding jigs to improve accuracy, and fit them in position on the hubs etc.
(For front engined trike with a shortened prop shaft and a one-piece, solid rear axle, reposition the front mounting of the radius arms to be either side of the front end of the prop shaft.)
Align McPherson strut suspension units, which may need tying a plank over the engine to keep them in position.
Position the front wheel, forks and steering head, to give a guide position of where the front of the frame tubes should reach.
Start the frame by bending and fitting the two bottom tubes of the frame using two long, symmetrically shaped tubes. Such tubes are often similar to scaffold pipes in diameter and wall thickness. These often run from engine mounts and suspension mountings, to a little beyond the steering head area. Check alignment and tack weld in position to align engine and suspension. Front of tubes may need a simple offcut of sheet steel support to keep them in position while tack welding.
Fit a dummy gearchange linkage using an old broom to check the clearances of subsequent tubing.
Add upper main frame tubes as needed. Check accuracy.
Add cross braces and any suspension mounting lugs for the rear springs which take the main load of the trike.
Add all other main tubes, such as for cross bracing and to reduce flexing.
Strongly tack weld all parts with four tack welds per joint. Three to maintain alignment, and one for luck.
Loosen all engine and suspension bolts to allow frame to relax. Remove all blocks. Allow one wheel to slide sideways on a plank and rollers, then lightly load the structure to check for any obvious deformations and suspension movement. Decide on any strengthening requirements.
Check alignment and tweak as needed. Tighten components and check. Expect a few welds to break. If all welds are equal, then any breaking will highlight the areas of most concern, as this may be the weakest part of the design.
Replace the machine accurately on the centre lines.
Fully align front end and steering head, yokes and forks etc. Check trail at proposed steering head rake angle. Adjust position of the front of the frame tubes as needed.
Grind out shape on front of frame tubes to accept the steering head. Align the whole machine on a perfect centre line and roll the front wheel on this line to align to the front fame tubes. Adjust height of front of frame for perfect fit. Align rear wheels to be level to ensure a plumb line will give accurate front fork alignment.
Use metal tape measure, spirit level and plumb line to check front end alignment relative to the rear wheels. Tack weld the steering head in position and check. Tweak as needed. Add more substantial tack welds. Add support or localised strengthening where needed. Gently test until acceptable.
Place each wheel in turn on bathroom scales and note the load. Do the same with the rider and make a note, so that you can adjust the load on each wheel according to its size and profile, by moving the rider and later, the fuel and battery etc. If you have a VW with a moped front end, then you may wish to consider your wheel loading very, very carefully.
If you have a mid -mounted car engine, then your three wheel loadings should be close to very nicely balanced.

When it is as good as possible, remove all items and weld the frame fully and evenly.
Reassemble, check alignment and tweak if needed, then add any steering head side plates. At this stage a structurally complete, if very basic trike is created.

Now check you can easily remove the engine, and also gain access to service the engine completely.
Ensure easy access to replace the clutch plate may be particularly useful for thrashers, or those with unusual gearing or excessively large rear wheels.
Check the exhaust and gearchange routing and any other potential problem area is acceptable.

Once the basic frame is built and fully welded, now try to break it !

Trying to break the design is necessary to ensure the basics are right. There is no point doing anything else until the basics are right. It is better to find out at this stage if there are any dangerous aspects as yet unknown.
NOTE: If anything may break, it should be allowed to break at this stage, as it is much easier to remedy.

Remove the blocks to allow one wheel to slide sideways again, as mentioned above using a plank and dowels or marbles. Now, with at least three people on it, jump up and down on the basic trike frame, complete with engine, forks and wheels. Give it a really hard time.
Simulate hard front braking by rolling it gently into a wall, so the front telescopic forks will just bottom out, many times.
The steering head bearings may need to be adjusted as they settle. Jump up and down on the inner rear suspension mounts to get the suspension to move fully, right up to the rubber bump stops and preferably beyond.
As a group, kick the wheels really hard from the front, back and sides to simulate rocks and kerbs. If this is your first trike, you may well misjudge the kerbs, so do this testing with real dedication.
Do not omit this initial testing, you know why, so don't delude yourself.
Continue until confident.

After this disgusting act of gross abuse, inspect everything carefully, especially where the wire model frame broke. If the frame fractures or breaks, you have everything on hand to repair and modify the design.
Check to see if the frame has twisted or become distorted, then straighten it and design a cure for the problem, possibly a little more triangulation or a fillet plate, cross bracing etc. It is better to do this now, rather than after the paint and expensive work has been added. Load to max, see how it flexes, then think, then modify as needed.

If not at all happy with the design, then simply design and build a new frame in the light of experience. You may simply wish to grind out the upper or lower main tubes and replace with a different design, or reduce the wheelbase, or make a better riding position, or any of many aspects of the design.
Now is the time to get the basics as good as possible. Small changes may make minor differences to handling, but may make a stronger, or less flexing chassis.

You now have just the three wheels, suspension and engine
in what is hoped is perfect harmony.
The most important part is now completed, give yourself a pat on the back, you deserve it. Now a real breather is possible and to take time to truly appreciate your work.

Will it handle well ?
If a first rolling chassis, the builder simply cannot know if it will handle or not. This is very common, as although a lot of work has gone into the machine by this stage, it is purely hypothetical and not really very scientific. (I've tried to steer clear of the arithmetic.)
It is rare for a reasonably well thought out machine to handle badly enough not to be of little use, but for some, it is worth while at this stage to get a closer check of your machine.
Now that the basic design is available for assessment, (as much of the work from now on will be fiddly and cosmetic), but the fundamental must always be as good as possible.
Even if not up to expectations, it often needs just a little modification to the basics to make a good machine. The toe in, tyre pressures, even the rake and trail can be modified.
From now on, it is the rider, battery and fuel weight distribution which will help refine the last few percent of its potential.
If in doubt about handling, then make a temporary lash up to see how the machine handles.
A simple moped fuel tank, a bungeed plywood seat and a lots of nylon tie-wraps or luggage straps around a small battery or use jumper leads, and minimal wiring will often get most machines up and running.
A quick thrash around a few quiet bends or carpark, once the brakes are working, will usually instil confidence in a reasonable machine.
It is possible to bump start the machine in second gear with a little help from friends, and pull the wire off the battery to stop the engine.
This is also a good opportunity to refine the riding position and suspension.

If a bracket is made, so the front wheel is replaced with a towing hitch, then the trike can be towed behind a car like a trailer, using it's own rear wheels, so it can be towed to a testing area. A simpler design would have a special spindle or special bracket to replace the front wheel, so the trike can be attached to the towing hook. A simple Y frame bolted to the frame, possibly with a couple of bars to make a rigid structure and to take the towing hitch. Or you can make a ball cup to replace the front wheel axle. (Make sure the trike cannot jump into gear while being towed, or remove the chain.) Don't forget to fit trailer lights and a copy of the towing vehicles number plate.

Centre of gravity: Part II.
With a complete rolling chassis, but not a finished trike, it is a good time to check the basic weight balance, especially if you cannot test ride the machine at this stage. This will give a good view as to where the weight is acting and allow you to modify the seats and secondary components to refine the weight balance. As mentioned earlier under the section on the centre of gravity, it is also possible to predict if the trike has a predisposition to roll or slide. This requires knowing the centre of gravity of the basic machine, so it can be further refined.

On a trike, the weight probably precludes the option of hanging a complete trike from different positions from the roof and probably not a good idea unless you have a chain block or other tackle. Luckily, the centre of gravity is usually along the centre line of the trike. The centre of gravity when seen in plan view will depend mainly upon the position of the heavy bits.
If you decide to hang the trike from the ceiling, make sure it is as complete as possible, or at least with all the heavy bits and wheels etc. Then take a photo, with the chain or rope in view, plus a plumb bob, so you can draw a drop line. It will probably be best to put a strop or the hook through the rear suspension or around the diff or gearbox area, or somewhere near the middle of the trike, so that it hangs at an angle which will highlight the centreline below the pivot, usually the top of the chain or rope. Where the vertical crosses the trikes centreline will be the centre of gravity, although for most accuracy, check from two different points.

A safer way:
If your roof is weak, but you still want to know where your centre of gravity is, then pump up the tyres, grab a few strong friends and balance the trike on the ground on one wheel. You will have to block the wheel or apply the hand brake. Now lift the trike up so it balances with no effort on a single point on the ground. Use a plumb line to see where the centre of gravity is directly above this point on the ground. In this example, it goes through the gearbox and assumed to be on the centreline of the trike.

As shown in the second piccie, when hanging or balancing the trike, also look for the vertical line from the side of the trike, with all three wheels level in your sight, so you can see how far above the ground the centre of gravity is. The riders weight will raise this, but it is not recommended to have a rider sitting on the trike in the search to get perfect data.

Now that you have a couple of chalk lines on the trike, one to show where the centre of gravity is along the centre line, and another to show the height of the centre of gravity as seen from the side, then you will truly know where the centre of gravity is for the basic trike.
The centre of gravity will be somewhere near the mid point of all three wheels, and should not depend too much upon where the engine is.
If you have a flimsy front end, then you may wish to move the weight back a bit. If you have a special front and want serious stonking ability, then you will be looking for almost even balance on all three wheels, dependant mainly upon the relative sizes of front tyre and rear tyre choices.

The centre of gravity when looking down from above the trike in plan view, will give you a good approximation of the overall balance on the three wheels.
Although you will have known the weight on each wheel from the bathroom scales, until now, you did not know just exactly where this weight acts. This can now be improved with sensible rider placement fore or aft of this point to get the axle loading just the way you want.

Now you can re-read the section on heave, yaw, and slide or skid etc - to assess what you have in front of you.

Heave up and down. The amount of stiffness in the springs and the damping rates. These are best sorted out with test rides, but the shocks should be such that you can push them down to make them move with a reasonable force. If they are really stiff, then you have to modify.
Pitch fore and aft. You can asses the chassis under braking by using the bike front brakes to see how the trike pitches.
Yaw side to side. This cannot be easily assessed, but if the engine hangs out the back like a VW then expect a dumb bell effect. The best machines have their mass centrally, like a fighter aircraft.
Roll. This can be assessed by pushing the trike sideways, to see if it is too supple or too harsh. The real test is on the road, but a rough approximation can be made at this stage, and a hard push sideways from the tallest part of the trike will show up any tendencies which may need to be restrained later, perhaps with an anti roll bar.

Camber angle. At this stage, the wheels should ideally be pointing straight ahead, and any adjustments should be made for this, although a slight toe in may help with cornering. If the engine is from a front drive car engine, then you will probably be using the steering linkage to make easier adjustments to the wheel alignment.
The Camber will also be set up to allow the tyre profile to remain as ideal as possible with the suspension at 1/3 rd compressed, where most cornering forces will be applied. So remove one rear shock and see how the tyre lies relative to the ground as one side of the trike is lowered across its full movement, to simulate a side roll or over a big bump in the road. Also check the toe in while under this extreme movement. See also camber, above.

Will it want to Roll or Skid ? See above, especially now that you have the actual centre of gravity measurements. Don't expect big fat tyres to give more grip, as they will be applying lighter pressures, so the overall effect will not depend solely upon size. (excuse the pun).
When seen from the side, this check will indicate the height of the centre of gravity above the road surface and will depend upon the height of the heavy bits. The lower the centre of gravity, the less roll. See earlier concerning whether the trike will roll or slide. Height will often be limited by sump clearance and how the riders are seated. Have a look at a Porsche V8 and consider why it's sump is wide and flat, allowing the whole engine to be so low.

You now have a general idea of the overall balance of the machine and can further refine it by carefully placing all the other bits and pieces, including the riders.

Poor integration of the rider and styling can now spoil all this good work, so don't let standards slip.
Even an excellent rolling chassis and engine can be turned into a pile of poo if not finished decently.
Do not worry too much, as a good frame can have many and various generations of superstructure and brackets ground off and replaced until a perfect trike is achieved.

The above offers much towards spending a lot of time and effort for a decent frame. Unfortunately it can also cause the reader to decide against bothering with the effort entailed.
It is better to make an adequate frame than to be frightened off by too many expectations of having to make a perfect frame.
If deciding to try a rough frame rather than take the effort of a more involved approach to design, manufacture and testing, then do so. You may possibly be on a tight budget and using scaffold bar, off-cuts and recycled bits to keep costs down, then do so. I do.
It is preferable to make a second rate machine than to make none at all.
(One of my finest ever handling chassis was just thrown together to check a design concept. The whole bike cost 35 quid to build and handles far better than my Ducati.)

Now that the main frame is in place, the next stage is to fit the parts which take priority over all minor items. Start with the just the riders seat and gearchange as first priority.
The steering, brake, clutch and passengers should then be positioned ergonomically. You may have to juggle these with the overall style, gearchange, fuel tank, the airflow for the radiators and all their associated mountings.

Before building the rest of the trike, an appraisal of the various parts which must be considered more closely now that the rolling chassis is ready for the seat, the controls and the many other aspects. Building these onto the rolling chassis are discussed, so they can integrate better, once they are more fully understood.

Riders seat.
This should be simple as there is often only one ideal position for the rider, which was decided when all the parts were laid out on the garage floor, but the actual rolling chassis is no more easily considered in a pragmatic way.
As there is often a wide range of positions, then use the opportunity to help get the axle loadings as well balanced as possible.
I always build my machines without the seat, then place the machine on bathroom scales, to position my weight for an ideal front to rear axle loading. Do the same for the trike, but taking into allowance the type of front wheel and whether it is a lightweight custom front end, a standard bike forks, or a special heavy sort of front end. If the front end is too heavy loaded, then always try to get the rider and passengers as far back as possible.
Use a foam base from an old car seat and check all possible positions for comfort. Check that controls including handlebars and foot controls can be positioned effectively and safely. Remember what it is like when thrashing around tight corners, so ensure the riders control is as perfect as possible.
Use this opportunity to give the trike the best axle loading.

A trike need not be an example of discomfort over style. It should always be an enjoyable experience and this is the time to get it right. Trike riding positions range from a racing bike forward lean, to fully recumbent as in a reclining chair. Whatever is decided, do it well.
If wanting a comfy seat, but not the style of a car, but needing spinal support, then get a car seat and cut the frame down to be narrower at the top. This is simple cut and weld, so that you can retain the adjustment of the squab (backrest), which may make a trike usable for many hundreds of high speed miles, especially if disabled.

If very disabled, then you can retain the electric adjustments of a second hand car seat, allowing you to power yourself into position and perhaps even allow the seat to power sideways to slide into a wheelchair. - The technology is there for pennies, so don't be afraid to use it. See disabled options in the appendices.

In some cases with front engines, exhaust routing will be a problem for the legs, so either work around the standard exhaust for convenience of replacement, or be prepared to modify or build new items. Seriously consider the heat flow from the engine mounted between or around the legs, and how it will be shielded, or have fresh air flowing around.
Exhausts are incredibly light, so they can be fitted anywhere without upsetting the balance.
This is the time when remote or direct steering must also be finalised. Foot controls should be positioned for best control in conjunction with the seating. See later.
Only when the ideal position is decided should any extra support tubing be added for the seats. On some seats, a removable base will allow access to the electrics, plumbing or an air filter under the rider.

This is often a can of worms.
Gearchanges can also be a superb piece of engineering, if done well.
Like all development constructs, all gearchange parts should be built with tack welds until everything works fine.
Fit the riders seat in place to decide the most natural position of the gear stick. You will surely have problems with some areas of design, so start with what seems worst to sort out. This is usually deciding on the best path for the gearchange linkage, as nothing should get in the way of smooth gearchanges.
Left or right hand gearchange will depend on personal preference, often by the country in which you normally drive.
There is nothing stopping the designer from having the gear lever sticking up from below, or pointing forward out of the engine bay, or whatever works best. Car-based trike gearchanges are a riot of up-down, left-right, fore-aft, and pivoting from all points of the compass. Whatever suits your fancy, it's usually possible, and probably been done before. If using a hand clutch, you may have problems.

The mid engined transverse engine is often the worst gearchange offender. If lucky, the gear linkage may be above the gearbox. Always bear in mind such annoying problems when choosing a donor vehicle.
The biggest problem is when transverse engines have the gearchange entering the sump. On many engine / gearbox combinations, the gear linkage is often a stub-shaft mounted low down and to the rear of the engine, the worst possible position. The paths of such linkages are particularly difficult.
It is this offender which will be used as an example of how to solve such problems.

The linkage must obviously pass over or under the engine. On low gearboxes the higher route may be preferable, especially if the gearchange is modern, very slick and easy to use. This allows a small, slick gearstick, and occasionally a gate similar to Ferrari's. It may be necessary to allow room for an intermediate linkage. Where the sides of the sump have a gap, usually between sump and clutch housing, study this as a possible path for the linkage.
It is not recommended to pass any linkages under the sump where ground clearance will be a problem. A gearchange over the gearbox may conflict with the passengers seating area. Also consider the fact that engines move about on their rubber mounts, where a low linkage, positioned close to the area of minimal engine movement will tend to be easier to control.

Think it through very carefully.

Automatic gearboxes also need a change mechanism, which usually employs a cable. Always use the standard components wherever possible. This must be set up carefully, so begin by mounting on the gearbox to see where the standard controls can fit for the riders benefit. If required, use a longer cable from a similar design. If no suitable cables available, then consider small aircraft throttle cables, or carefully modify a thick car clutch cable, such as from a Ford Escort Mk4. A rigid link or rod, if used, must allow the gearbox to move without upsetting the settings.
As modern gearchanges are appearing with increasing regularity, then for those with the luxury of paddle or button shifts, similar to formula one gearchanges, then these can be integrated into motorcycle handlebars, but will need to be on adjustable mountings until the ideal ergonomics are sorted. This is especially important while hanging onto the handlebars when cornering. Paddles allow a strong grip on the handlebars and interferes less with the brakes. If using a handlebar mounted front brake lever, then consider changing down from third to second etc, with the free left hand. (80's BMW bike indicator switches are rather good for this.)

Manual gearchanges.
The design mentioned below is not the only way to make a manual gearchange linkage, but it is one of the narrowest and more reliable. The other main methods include using two separate link rods which in many situations may be preferable and can utilise parts from a similar dual bar linkage such as from a box van.

If the gear connection is a small stub shaft exiting the rear of the sump or gearbox, it is usually rotated and also moved in and out. There are usually three positions for rotation, plus two for the in and out action.
Always insist on being able to use reverse gear.

On most well designed engines using an awkward stub shaft gearchange, there will also be a fixed mounting point on the gearbox casting. This mounting is for the original gearchange linkage which must be securely connected at the gearbox end. This is an important part of any design, by ensuring the linkage will not misalign as the engine leaps about in it's mountings. Use this mounting appropriately for mounting the gear linkage on the engine, and expect the riders end of the gearchange linkage to move relative with the engine.

The gearchange 'in and out' is normally indented. This is so that each gear is mechanically aligned inside the casing.

In some cases, the rotation of the sub shaft may not be indented, as the external part of the original gear lever may be sprung loaded externally so that the driver of the standard machine will know the levers default position when in the middle. (Sit in a car and note that the gear lever is normally sprung to sit in the middle of the left - right movement.)
Often the low gear means having to push the lever to the left, and higher gears pushed to the right, with a couple of fun gears self aligning in the sprung loaded middle position. This means that this (slight rotational) alignment may be controlled with an external spring or pair of springs. In such cases, the rotation of the shaft will need to be centrally sprung loaded by the new mechanism. This is not difficult and can be left until later, with a spring each side of any new linkage, or a single centring spring and simple arm often doing the job perfectly well.

Two control rods are needed. One rod is to rotate the gear shaft, and the other to move the shaft in and out. A narrow tube with internal push rod is often ideal for both the rotating and sliding linkage between rider and the rear of engine.

The rotation tube is considered first.
The rotation of the gearbox stub-shaft is often about thirty degrees. This is easily managed by fitting a simple lever on it.
The rotation control tube that will lead forward to the rider, can lie over or under the engine, and the engine end of this tube can employ a similar lever to match the lever on the gearbox stub shaft. The engine end of the rotation tube should rotate on a bracket mounted securely on the engine or gearbox.
A simple link arm connects both these arms, so that rotating one, rotates the other in a similar manner. If the gearchange action is back to front, then simply rearrange the levers to give the action in the other direction.
The front of the rotation tube will contain the gear lever so it can rotate about the angle required. Because of the rotation forces and the distance involved, the rotation tube should be of a reasonable diameter or wall thickness to prevent buckling. This rotation rod need only be fixed on a simple pivot mounted on the engine, but the front of the tube must be mounted flexibly to allow it to move as the engine moves.

Push pull shaft.
The push-pull part of the gear linkage will need to slide the engine stub shaft in and out.
This can be accomplished by moving the stub shaft in and out by using a forked end on a lever which fits either side of the rotating lever already connected on the sub shaft. A simple forked end around the stub shaft which rubs against the rotating lever, to pull it out. A single finger pressing on the end of the stub shaft can push the stub shaft inwards.
By ensuring the forked end of the arm acts directly on the stub shaft lever, good alignment and feedback is improved.
This forked lever is part of a longer arm which is pivoted half way between the stub shaft and the rotation tube. The pivot for this arm may not be easy to mount on the gearbox, and may require a large plate or bracket to position the ideal pivot mounting which must be attached to the engine or gearbox. See drawings.
A simple bracket welded onto the tube so the gear lever pivots above central axis of the tube will move the inner rod and also rotate the outer. If the fore aft movement is the wrong way around, then simply mount the front gear lever pivot below the rotation shaft, rather than above it.

Pulling and pushing the top of the arm should be able to easily move the sub shaft in and out.
Rotating the tube should easily rotate the stub shaft.
If an external centring spring is required to centre the rotation arms, one or a pair of springs can be fitted in one of many places along the linkage.
It is very sensible to run the push-pull rod through the centre of the rotation tube.
This layout makes it easy to swap gearchange movement at the riders end for standard gearchanging positions. If the in out movement is the wrong way around, then simply change the arm pivot at the front of the tube.

Large scale engine movement.
As engines flex on their rubber mounts, especially under acceleration, then they can cause the gears to be missed or even jump out of gear when the engine rocks about. Therefore the rear of both gearchange parts of the linkage must be mounted on the engine, not on the chassis. Because the rear of the linkage is mounted directly on the engine, the riders end of the linkage must therefore be rubber mounted to take into account the engine movement.
If you have a lively engine and a long or heavy gear lever, then always add a mass balance on the other side of the gear lever pivot, so the lever does not jump out of gear - or far worse, jump into gear when revving the engine in neutral !!

Because of engine movement, some pivot links should be slack, so they can flex with the engine.
Therefore some of the pivots are allowed some play, in the Kalashnikov tradition, and some foam or rubber padding added to stop them rattling around noisily. Expensive spherical rod ends will also do very nicely, but can be added to exhibition trikes, once the initial design has proven effective.

Because the front of the tube is rubber mounted, and the engine often rocks fore and aft in the chassis, the rear mounting of the control linkage will tend to fracture. Therefore it is very important that the engine mountings at the rear of the linkage must be secure, but also rubber mounted to account for any bending forces caused by the engine movement. A basic engine steady is very important to prevent the engine rocking too much.

As the rotation shaft is ideally a straight tube, the push pull rod can run inside it. The outer tube works the rotation, while the inner works the fore and aft movement.
A few simple plastic bushes slid inside the tube will prevent the inner push-pull bar from bending and a little extra rubber foam will reduce rattling. The advantage of a single tube is that it will pass through a fairly narrow gap in the engine or frame and just as importantly, will not catch or snag any other components.

There is a large amount of design freedom to allow such linkages to clear obstacles. The only real concern is to ensure both ends of each rod will slide and rotate freely under full control of the riders gearshift lever, and to take into account the effects of a flexible engine mounting.
The front of the rotation tube must mount the gear lever such that it can move the push-pull rod along the tube and also rotate the tube.

The riders end of this gear linkage must be flexibly mounted to allow engine movement. For simple rubber mounting bushes, use old motorcycle swing arm bushes or rubber blocks compressed between bolts and washers. For simple alignment bushes and pivots, such as for the rear push pull arm pivot, also for the front upright gear pivot arm bush, simply use Honda C90 stepthru front fork bush kit and push fit the plastic sleeves into old handlebar tubing.
It will be seen from the little animation, that if the rear end of the tube is not connected to the engine, but allowed to float and slide freely on a sufficiently strong inner bar, then the upper linkage can be loose. This allows the rear linkage to have adequate movement as the engine moves on its rubber mounts, yet the linkage will still work effectively. Therefore only the middle point of the in/out lever need be mounted on the engine casing.

Do not use rubber bushes in the actual linkage, only for their mountings. Rubber bushes in the links will want to return to a mid point, causing the gears to jump back to the neutral position.
A slick gearchange linkage requires a smooth, slop free linkage. This will take time to refine, but well worth the effort.

As some modern gear changes are extremely slick and very smooth, there may be no need to use a traditional large gear linkage. The use of modern, small stub gear levers makes for a neat layout, especially if ergonomically positioned. This also helps the trike riding experience to be faster and more responsive.

The front ends of gearchange should be positioned for the best ergonomics and will depend upon rider preferences. Because the described linkage is nicely concentric, the orientation of the riders gear lever can be at almost any angle. If the tube ends level with the rider, the gear lever can be straight up in the traditional manner. If the tube ends a little way behind the rider, the gear lever could be bent upwards and forward, to give an angled action. If the gear linkage can be made to end in front of the rider, the gear lever can be angled back to face the rider. A simple, solid bar front gear lever arm can be easily bent to clear obstacles such as frames and knees.
To repeat: If you have a lively engine and a long or heavy gear lever, then always add a mass balance on the other side of the gear lever pivot, so the lever does not jump out of gear - or far worse, jump into gear when revving the engine in neutral !!

This is the system I prefer for most trikes, but the Alfa gearchange finally used two bars, adapted using the gearchange from a small Japanese box van, extended with a little extra tubing. After a few attempts, the front gearchange eventually exited close to the handlebars for minimal hand movement and for fast gearchanges. A small lever allowed reverse to be locked out or engaged.
A reversing light plunger switch was fitted on the rear gearbox mounting via a bendable bracket and adjusted to work when in reverse by shorting the live reverse light to earth. As this was a live connection near the fuel tank, this was soon changed to a sealed switch for safety reasons.

If in doubt, check out the arrangement and how to design the linkage before buying the donor vehicle. The scrapyard can often supply the automatic variant, but this may only be considered as a final option, or as a temporary measure until gear linkage design skills improve.
Use whatever is available from other machines, as there is often very little need to reinvent the remote gearchange.
Gear changes can pass over the top of the engine or underneath, but the underneath is occasionally difficult if there is lack of room between sump and clutch housing. No one would want to pass the gearchange under the sump if trying to keep the centre of gravity as low as possible for better handling.
Yes, I have seen trikes where the gearchange passes under the sump and often smashes up a gear when rubbing over a speed bump in the road. - Just don't go there !
Where there is a gap, then underneath is common as it allows the front lever to be long, allowing easier control, especially on older, clunkier gearboxes while it also clears the passenger area. As the engine mounts are usually on the bottom of the engine, a lower gear linkage will not move much.

Make sure that all gears - including reverse - can be EASILY distinguished from each other and do so smoothly. This may take some fettling and tweaking of the assembly, often a little redesign work too. Then remove any sloppiness at this stage by removing and refining the linkage until slick rather than slack.

When building a linkage, some play is quite acceptable. In the Kalashnikov tradition, a little play prevents the links from getting locked or stuck, which can be ameliorated by light springs or foam rubber to prevent the assembly from rattling.

Work the linkage hundreds of times until it beds down well. Take time to get the gear change right, as it is often the biggest disgrace on trikes and can destroy the enjoyment of the driving experience.
Gearchanges are difficult, but after about three attempts, it should be working as required. If the gearbox is well designed, it may only need a small amount of effort to transmit the movement, allowing a light, slick gear linkage with a small control arm.

To see a really classy piece of engineering design, check out the original Porsche Boxter front gear change linkage as shown at it's Geneva launch, it's a work of art. (Unfortunately the production Boxter gear levers are a very lame design and nowhere near as good.)

Make all other trike owners jealous by making the gearshift a work of art, not just a suspect metal bar with a brass skull screwed on top. A couple of weeks of intriguing work is not unknown to get awkward gearchanges working well. The effort is always well repaid over the following years of use.

Actuating the reverse gear usually requires a simple lock out mechanism, often by pulling the standard car gear knob up, or pushing down to release before being allowed to move into the reverse position. This is usually done in the linkage. Reverse can be a problem for trike riders, especially if forgotten while riding.
When building a simple mechanical reverse interlock, place the gearlinkage in reverse and then decide a basic mechanical lock-out. This is often fiddly and annoying rather than difficult, so keep trying. On a particularly sloppy gearchange, this should ideally be close to the gearbox stub shaft or arm.
A simple movable block, lug or arm and corresponding obstruction plate often works well. Fit a small spring loaded lever under the gear stick operating via a pedal cycle brake cable so the block can be lifted away to allow reverse to be engaged.
If the riders gear stick is tubular, then a plunger or pull action could be used by making the top lever slide on the shaft, with a stiff spring to move the block.
If like some brave or foolish trike builders, it is decided that a reverse lock out is a little too complex, then leave it out, but remember the consequences that can ensue.

Such gearchanges are the sorts of problem I've developed carefully for my production trike designs so the customer always gets a well behaved, reliable machine. I've spent a lot of time over trike gear changes, and so should you.

In many cases simple motorcycle handlebars will do. On long, front engined trikes, long pull back handlebars which act more like a tiller may suffice. As most riding above ten miles an hour does not need much steering movement, most designs will do the job adequately well. But with long pull back bars, high speed cornering can be a problem, and inner city manoeuvring will cause unusual arm actions which may impede handlebar controls such as throttle with some awkward wrist angles.
On particularly big trikes with a front engine, such as V8's, the remote steering will need a second fork yoke to mount the handlebars nearer to the rider. Steering engineering takes precedence over steering style, so get the steering sorted before fitting instruments and such like which may mount in the steering area. Remote handlebars allow almost perfect handlebar position, so use the opportunity to advantage. This occasion should also be used to maximise the available space for easy interaction with the steering and engine. With such a big engine requiring remote handlebars the cornering forces may well be large, requiring larger effort and control.
Always try to make the pivot point centrally between the grips, so the rider can hang onto, even wrestle with the bars around fast, bumpy, off camber corners, without upsetting the steering.

Wherever possible on distant front ends, use parallel push-pull rods for a remote fork yoke. Two link rods offers higher reliability in this area which must not fail. Keep the linkage parallel and equispaced on both front and rear yokes. If the front pivots are X mm apart, and Y mm forward of the steering axis, then make the rear pivot points X mm apart, and Y mm forward of the steering axis. Geometrically similar.
Keep the rods widely spaced apart for best control. This eliminates any compound geometry misalignment which could lock up the steering at high angles. Use spherical 'Rose' joints and their rubber covers for reliability. The threads on rose joints will enable slack to be removed. Keep a minuscule amount of tension in the rods, to reduce buckling.

Low speed cornering.
If the machine is large and long, then a front end with a large angle of steering lock may cause damage. Most front ends are ideal when pointing straight ahead, but at full lock, the angles of the forks can get desperate. Find out which is the maximum safe steering lock, then weld stops to prevent the front end turning too far.
Trying to get around tight car parks in one go, may cause a poorly designed front-end to tuck in, or even collapse in on itself. This is particularly important where the front brake is suddenly applied at full lock such as in car parks, where other drivers have sudden, dangerous or simply ignorant habits.
During testing in a clear car park, always check the steering close to full lock with a blip of throttle power, because the steering may pull out of your hands. Steering dampers will not cure low speed problems.
Fettle the rake and trail if needed, then finally weld strong steering stops to prevent extreme steering angles from causing problems. Always fit the steering stops between bottom yoke and frame. If needing maximum steering lock left to right, but worried about the forks tucking under, then use heavy bolts as the steering stops. Weld them to the frame using barrel nuts, which are long nuts. Then bolts can be fitted and adjusted to give the largest amount of safe steering lock. Always use locking nuts or machinery adhesive, or a strip of nylon in the threads to prevent the bolts loosening.

If the machine is a monster, you may wish to retain the power assisted steering and use a car set-up using the original steering wheel at first, purely for testing purposes, then modify this to assist normal handlebars later. The control valve on the donor vehicle steering will need to be carefully modified. For both style and lifestyle reasons, use of a steering wheel is often frowned upon. For disabled bikers, variations on this theme can be a godsend.
Even granny should be able to safely ride a V12 trike.

Wherever possible, use either motorcycle OR car control layouts, so your reactions will be natural and instinctive in an emergency.
Do not mix your drinks, and do not mix your controls.
When properly designed, even an extreme invalid can ride a V12 trike.

Controls are personal, but don't expect to design a foot gearchange for a car gearbox with reverse overnight, unless you cheat with an automatic.
Car clutches working off the handlebars are no fun, try if you must, but practice by squeezing tennis balls first.
A realistic approach for car engines is to use a hand gearchange with foot clutch and foot rear brake. Using automatic transmission is a perfectly legitimate cop out.

Throttle can be a handlebar device similar to a bike, or foot similar to a car. The foot design will also need a foot rear brake close by, being ideal for posing / cruising hands off, such as looking cool while rolling a cigarette in a traffic jam, on a hot bank holiday. This may also be preferred for custom shows, where waving to crowds is expected while under power. Choosing car style foot controls will help clean up the handlebar clutter to just a couple of switches for horn and dip, or even less.
The classic bike throttle is often considered as part of the biker image and should be decided according to lifestyle. See also cables later.

Warning: Contrary to popular belief, designer shades are not the most important part of a trike, especially if the rider ends up stuffed into the side of a bus.
Stop looking in the mirror, put the sunglasses down and prepare for a little truth.
There is no point in making a trike if it's going to be dangerous. Brakes are very important, they save lives - but only if they work properly.

There used to be an awful trike in my neighbourhood, VW engine with small trail bike forks and rust coming from the front drum brake. He said he "only got the front brake working for MOT's".
I have not seen him recently.

There is little to worry about when balancing the pressures in a dual system, as both outlets of the master cylinder are pressurised identically.
Where you have to worry, is where this pressure is applied.
The main reason for dividing the outlets is to allow the design to fail with at least one front and one rear brake. (When two independent front callipers are used.) It is the relative diameters of the pistons and the disc rotor diameters which will decide the overall braking balance.
On some cars, there is a pressure limiter in the rear of the system, so that a lightly loaded rear axle does have too much pressure applied relative to the front to help prevent skidding in cars. This is often operated via a lever sensing the load on the rear wheels but can be adapted to a manual control.
If great differences in luggage and passengers are expected, arrange a pressure limiter as on the original vehicle. It may also be used with a manual adjuster to allow the builder to simply modify the front to rear brake balance during testing and should be considered a useful option if excessive rear braking problems occur.

If keeping any of the original car plumbing, then blank off any redundant splitters with blanking bolts and copper washers, or steel ball bearings under the old threaded pipe fittings to seal the internal holes. Do not use small ball bearings, as these may get trapped, so always use large balls so they can be easily removed.

If using a jet engine, then seriously consider using two sets of 320mm diameter bike disks on each rear axle, separated by the width of the callipers and well ventilated. If you can fit inboard and outboard disks then do so.

Like any vehicle, the front brakes should be the strongest.
As some trike front ends leave much to be desired, it may be preferable to have the rear brakes with a slightly heavy feel, to prevent the rear brakes doing all the work. Some people prefer rear braking, but is not conducive to ultimate twisty road thrashing.
Rear brake effort can be increased by removing the servo from the brake master cylinder which was designed for a four brake system on cars. This will also make mounting the basic master cylinder easier. The pressure needed can be easily accomplished and the pressure modified to suit rider preferences by using a longer lever or suitable ratios in the linkage.

A servo will be needed if using a fully linked car system to operate both font and rear brakes from one foot lever, or if disabled. There is no need to fit the servo where it may be seen.

Both the brake and clutch levers should be adjustable for leverage to sort out any problems when testing on the road. Use temporary adjustable actuating arms, with various connecting rod mounting holes to allow adjustment of the lever pressures applied to the master cylinders.

The brake and clutch master cylinders can be positioned under the seat to prevent little fingers from messing about with filler caps and because these cylinders are often ugly items. Motorcycle items are less ugly, but may not always manage the volumes of fluid displacement required, unless used in the standard manner with bike components. Check first and try to match with the original components.
On a recent project, the trike had forward controls using stainless steel link rods to the brake and clutch master cylinders hidden beside the hidden rear car engine.
Always prefer a tension rod to actuate brakes. If going for a push rod, make it a reasonable diameter tube so it will not buckle. Also make sure it cannot be stepped on by the passengers to prevent it being used, or buckled. If they are running near the passengers foot well, then decide if you need to run them inside safety tubes.
Make sure the brake and clutch systems work exactly as required, modifying the pedals until they work smoothly and efficiently. Make sure it is easy to check and fill the brake and clutch fluid levels. Wherever possible, use the original donor machine clutch master and slave cylinders in conjunction with the original donor brakes and clutch actuator.

The designer may want to use a right foot brake lever to couple both the front and rear brakes off the master cylinder. When using a single master cylinder for all the brakes, the vacuum servo assembly should be retained, but hidden under the rear. It can be activated using a remote linkage and a longer length of special vacuum hose, available from many car shops. Vacuum hose is specially designed, thick wall tubing that will not collapse under the effects of high vacuum, especially when on the overrun.

Do not attempt to fit fiddle brakes as per trials cars and Formula one, as setting them up is a nightmare.

The brake master cylinders of most cars operate two diagonal circuits separately.
If connecting to just the rear brakes, then use both pipe outlets, one to each rear brake. This arrangement gives an even and balanced pressure across both, due to the nature of most single barrel master cylinder designs. The two separate pipes also give a degree of redundancy for extra safety. For rear brakes only, a servo may not be needed.

If connecting the car brake master cylinder to dual front discs and car rear brakes, then connect one master cylinder outlet to one rear and one front brake and the other outlet to the other front and rear brakes. This ensures that should a brake line fail, the other will still allow reasonable braking.
If you only have one front disc, then fit one master cylinder outlet pipe to the front brake and the other to split to the rear brakes. This way, if one fails, you will either have the front brake or both rear brakes for even stopping. If you had it linked to the one front brake and a rear, and the other outlet to just one rear brake and one failed, it may well leave you with just one rear brake - not a nice thought.

The single foot brake car set-up is open to interpretation, even though this is how a car works and would leave the handlebars free of clutter.

Linked braking is often less than well appreciated, being either a fixed design by the manufacturer, or a cobbled together design without adjustment. It is not difficult to see why such brakes are often ridiculed, even when expertly made by large manufacturers.
Simple braking application from a single lever is an ideal, but only if it can be set up for personal preference and the road conditions.
Ideally a braking system should be able to sense and adapt to the axle loading, such as passenger or not and if the weather is wet or not.
Anti lock braking is for the oft common real world scenarios where inaccurate braking skills, unknown road variables or poor feedback are to be expected.

The following is a simple yet effective design to see if the builder wishes to reconsider linked braking for a particular design.
Never try to link braking with other components such as electronic gearchanges until all other parts of the primary design have been fettled and proven reliable and safe.
For the simplest, yet effective linked braking with cables, a linked cable dual braking from one lever is possible using a swingle tree. A swingle tree is a cross piece for an equal pull on two horses when ploughing a field. (See appropriate text books. - Any farming text from the Middle Ages onwards should suffice.)
The basic principle is equally valid for linked braking on modern vehicles and systems. More so, as it can be adjusted for a proportional load on front and rear brakes. Yet even more so, as by using cables, one of the brakes can be also independently incorporated into this design without an extra brake being needed. This is applicable for any cable brake or a hydraulic system with the master cylinder force applied by cable.
For cable and hydraulic brakes, the swingle tree is best employed by a direct action on front and rear master cylinders when positioned close together. This allows easy adjustment of front to rear braking bias, even while riding, so that even this simple system can be adaptive.
The basic set-up uses a linked bar between the front and rear master cylinders, acting on the pistons. The pull on this lever is offset, with a bias for the front brake and should be adjustable. The rear brake should also have a secondary, independent action on the rear master cylinder end of the lever. Do not use linked hydraulic braking unless a second, separate brake system is also employed.
As shown opposite, Formula One now use a similar system which is adjustable from the cockpit. The system has the brake pedal pushing against the front and rear master cylinders, with a central link which can be offset. The F1 design is poor, and uses a primitive adjustable pivot, rather than a proportionally adjustable movements which would be far more subtle.

Another fault of the F1 design is that it is not fail safe should one system fail, whereas fitting a back stop to allow one side to work if the other fails, will be far more relibale.

There are many variations on this theme which can be used to assess this concept.

Brake imbalance.
If separate front and rear brakes, then the leverage of each is easily modified to give good braking.

Warning; Because the pressure in the car and bike lines are probably not designed to be the same, the braking effort of the rear and front brakes on a linked system may be out of balance.
There are ways around this.
To get more braking effect on the front brakes, use larger diameter piston cross section at the front than at the rear, or use larger discs and callipers on the front than those used on the rear brakes. A mixture of both usually helps balance out the braking to match the handling characteristics.

If using a linked system acting off a single car master cylinder, where all the brakes receive the same pressure, then the brakes themselves will have to be modified. -

You cannot add extra force into the system unless using a servo. Therefore, if the main brakes are good and just wanting to decrease the offending brakes, then these can be ameliorated to behave properly.

Light Laden Valve. If you suffer serious problems with fore to aft imbalance, then the offending braking circuit could employ a light laden valve. This usually operates via a lever which can be adjusted to balance out the rear brakes relative to the front brakes. These are often found near the rear underside of cars and vans, where the rear load makes a great difference to the braking and enables the rear to be less effective if the van is unloaded. To decrease the firmness of rear braking, a car load limiter as fitted on vans (e.g. Ford Escort, connected to the underside via a lever to the rear axle) is a way to be able to adjust the system to the rear braking forces. By adjusting the lever, you have the ability to modify the pressure applied to the front and rear brakes, as used on dual braking line systems.

Alternatively, the brake pads could be cut down to offer less braking material to the disc or drum.

Another option is to change the callipers for smaller units. Reducing the disc diameters is not recommended, as they are usually proportional to the wheel diameter and will ensure the forced needed to be applied will be of the correct magnitude and within safe limits.

Where the front brakes need to be stronger, then the trike with a bike front end can have the latest large diameter discs and multi piston callipers. DO NOT apply servo assisted braking to motorcycle discs, as they may possibly warp under the excessive pressures. Only apply hand pressure, to stay within working limits of these flimsier types of brakes.

Where the front end uses a car disk brake, then TWO callipers can be fitted onto a single chunky car disc, preferably working off separate mater cylinder outlets for balanced braking under partial failure. This doubles the braking force with no other modifications. Where possible use the ventilated disc from the sports version of the donor car, especially if using dual callipers on it. But do not put excessive pressure on the disk, as the tyre will be limited in its ability to transmit the force to the road.
Dual callipers should be used as part of a dual linked system, such as used from just one foot brake in a car style, linked system.
When fitting dual callipers to a front car disc, the symmetrical donor callipers will be handed pairs, so the bleed nipples of both can be mounted to allow easy bleeding.

On a trike, the braking will be compromised by the amount of weight on each axle and the tyre profile. A lightweight front end with a skinny tyre is not going to be able to handle too much of the braking. Therefore a truly reliable rear braking system, well balanced and effective will be necessary, even though it is not ideal for best control or handling. Conversely, a trike with a heavy front end should not have too heavy a rear brake set-up, neither should it apply all the braking to the front, even if of a soundly built design.

In small trike set-up, the front brake is usually a motorcycle handlebar set-up, simple and easy, with a car rear brake without the servo, just acting on the car master cylinder, without the vacuum pipe attached. If the rear is then too soft, the servo can be connected, and the vacuum pipe partially strangled and the foot brake linkage modified to get a good balance with the front brake.

On a recent V12 trike project, the whole machine kept the Jag braking system, acting off a foot brake lever, but the front axle was replaced with a much stronger axle machined from EN steel allowing heavier single axle loads and braking. The original Jag front disc and wheel was retained but a second calliper was added, so the whole system was balanced fore and aft, although the front tyre had to do more work. Because it's a trike, and the prop shaft was shortened to get the engine rearwards, there was a little less front axle loading, to help ameliorate the overall braking balance on the wheels.

Parking brake.
When using a front wheel drive set-up as from a transverse engined car, with the front brakes now on the rear, and the original handbrake no longer used, then another form of parking brake will be needed.
The options are fairly wide if occasionally awkward. The early 2CV's used to be supplied with wooden wheel blocks but don't try this in modern Europe.
The parking brake is often a problem for trikes. The transverse engine front wheel drive being the worst offender, as most parking brakes are on the rear wheels. Mounting a second calliper on the rear discs can work well, or alternative callipers from a car with discs all round. Using the car's REAR wheel callipers on the trike (front, now) rear discs often works well, if the disc rotor diameters are not too dissimilar.
Because most cars have the same wheel studs front and rear, and the cast iron brakes are often mounted on these, then it is often very easy to fit standard rear disks to the front wheel assembly of car wheel hubs for the use at the rear of trikes.

Mount the callipers on the disc, then look for the easiest way to retain them. Sometimes just cutting off the original mounting lugs, fixing them on the calliper, then rewelding into their new positions. Sometimes a simple extension plate will suffice, but make sure it tends to straighten when braking in the forward direction, as this is how the heaviest braking forces will act.
When mounting callipers, use new pads and always slip a strip of thick cardboard on the edge rim of the disc, to give suitable clearance and maintain even radial alignment while fitting.

Where no room for extra calliper or suchlike is possible, then a special parking brake cylinder which works in-line with the standard hydraulics and acts on the original callipers is available from some racing suppliers. This often fits between the master cylinder and the rear brake callipers, allowing the brake line to be locked hydraulically, usually by a hand lever. It closes off the rear hydraulic line and then applies pressure on a standard handbrake ratchet.

Some front engined modern cars with rear discs have the parking brake integrated into the design, needing little or no modification. Occasionally a modified calliper mount or cable mount is needed to employ this particular set-up on the discs.

For many of the lighter show trikes which need a much better disc than the lump of iron normally supplied with cars, then motorcycle discs and callipers can be used, especially if seen through three spoke wheels. These lighter trikes will also require motorcycle callipers and if rear engined, will probably also need the intermediate hydraulic hand brake unit.

Some Honda callipers use dual systems on single callipers, allowing the main braking to be on the outer two of the pistons, with the builder adapting the parking brake to act on the centre cylinder. Similar alternatives are also found with car systems.

For front engined trikes with central prop shaft, use the following to eliminate complexities and to have completely independent parking brake for emergencies. This also allows for a cleaner inner wheel look with a single calliper of choice.
On many cars with a prop shaft leading from the gearbox to the rear differential, then a single motorcycle or car brake disc can be fitted on the prop shaft flange on the differential. A brake calliper can then be fitted to lock the whole drive assembly. This is excellent yet common practice on 4WD's such as Land Rover, allowing them to lock all wheels with just one brake. This is simply done by welding on a mounting flange, or inserting a thin flange between the prop shaft and the differential, then running the engine and prop shaft while truing the disc mounting flange in situ.
If machining without a lathe, mount the blank metal disc carrier on the end of the gearbox , as the diff and gearbox flanges should normally be the same dimensions. Then fire up the engine as a lathe. Carefully apply the angle grinder or file until a perfect fit is made to mount the brake disc. Ensure a shoulder is included to align the disc before drilling its mounting holes.
If there is no room in the differential area, then the parking brake disc may possibly be mounted on the gearbox output flange of many car engines.
As the differential has a large gearing ratio, the effort required on such a disc is low compared to a wheel mounted brake. Because of this gearing, small discs are possible. A second calliper on this disc can act as the rear brake if wanting to have a clean rear axle for show use.

If a cable is preferred but a cable operated calliper is not found, then simply use a standard car drum brake on the prop shaft, which can also fit on the rear wheels or around the propshaft, although the brake shoe backing plate will need modifying to fit the appropriate mounting. There are a few cable operated car disc brake callipers and these should be considered, although they are rare and will need hunting down in scrap yards.
Please note that drum brakes with a leading and trailing shoe are usually better in one direction, so choose the donors vehicles left or right drum brake appropriately so that pulling away uphill will be easier, requiring less force on the handbrake lever.

If the gearbox is integral with the engine with no prop shaft, there may be room for a small disc in the inboard coupling of the drive shaft. The inboard discs of the Alfa and later 2CV's and 4CV's make parking brakes an absolute doddle. They also allow a totally open and clean inner rear wheel area, ideal for wire spokes and skinny three spoke alloys.

When mounting disc or drum brakes, always mount and true the disc or drum first, then fit new pads or brake shoes, and apply pressure to the calliper or shoes, to align the supporting assembly in position. Then the backing plate can be welded in position with perfect accuracy.

When mounting parking brake callipers, remember that they must work in both directions, - when parking both uphill and when pointing downhill. Ensure the calliper mounting is secure in both directions. If using a car control layout, always ensure the parking brake will work easily and safely, especially when pulling away uphill.

Some trikes have problems with a basic parking brake which works on single piston callipers. In some cases, a simple valve in the rear hydraulic brake line can suffice, as shown in the picture. Push the brake pedal down, then lock the hydraulic line. I personally don't like it, but evidently this has passed the MOT. In such a system, I would prefer cheap rubber pipes, which allow a degree of flexible 'pressure reservoir' for any minor leakage, as the high spec. hydraulic lines would not give this slight margin of safety.

I have ridden a trike where the clutch was a hair trigger with no chance to reference the foot to enable some subtlety. Do not go there, get the controllability of all systems correct from the outset.
On the clutch, (and rear brake) the foot should have complete control, so design the foot rest and it's lever to pivot as one, usually near the heel or instep. Often known as an 'organ stop' pedal. This will allow the rotation of the foot to work the action for accurate control. This is particularly important for a sensitive foot clutch.
If the movement is large, then use running boards with a heel support to act as a reference point for the foot on the lever. This way you will have much better control over the clutch 'bite' point.
Car clutches working off the handlebars are no fun, try if you must, but practice squeezing tennis balls first. See also cables later.
Only if the trike is a light weight design, and not intended to carry extra loads, then a car clutch can be operated by a hand lever, especially if the fingers of a clutch diaphragm spring are reduced. This can be modified by removing opposite fingers of the clutch spring until acceptable. Always note that if too many fingers are removed, the clutch will no longer be able to transfer the same amount of power, so clutch slip may occur at top speed. (where aerodynamic drag is high).
For an easy life in town use with a 2CV engine, always consider fitting the superb automatic clutch option, which releases at low revs, not dissimilar to a Honda C90.

Fuel system.
Trikes don't have to use conventional bike tanks, possibly employing one, two, or even more fuel tanks to make use of otherwise unused areas on the trike, especially if using a massive and thirsty engine such as a V8, V12 or Wankel rotary.
Always consider two large sheet steel fuel tanks hidden under the shell, with a stylised motorcycle tank containing just emergency fuel and used to fill up the fuel system.
Side loads when cornering will cause sloshing in long across-frame tanks, so ensure they have baffles, or use a standard tank such as some cars mounted in their normal alignment.
The fuel capacity is normally similar to that of the donor car, so that the range is sensible. If touring abroad, a second long range or emergency tank can also be of use.
All tanks should be rubber mounted to prevent fracturing. All tanks should be away from damage by other vehicles to minimise fire hazard during crashes.

It is very popular to have a small motorcycle tank for styling purposes. This need not be a limitation, but an advantage if a secondary, hidden main tank is also employed.
If filling a main tank from a primary tank, always make the interconnecting pipe large enough to allow petrol to flow reasonably fast when filling. This will mean modifying with a large bore stepped pipe in the bottom of the 'bike' fuel tank.

Please note that there is a very good reason to have the large filler interconnecting pipe high on the primary, filling tank. When filling, the primary tank will fill and then overflow into the secondary or main tank.

If one tank is the reserve, make it the smaller of the two and always fill it first. Don't let the emergency tap leak so that both tanks empty without knowing, leaving the trike stranded without a reserve.
If the primary tank is a small capacity, traditional bike tank with the main filler cap, and it is used as the reserve, then the filling connecting pipe should be positioned high inside the tank. In this way the first tank will always be filled first, ensuring the tank is always full of fresh emergency fuel. The bottom of the upper tank can be tapped for reserve only.

Ensure a breather pipe is fitted on each tank. If the tanks are at different heights, use long breathers to a high point above the highest tank, or into the highest tank for a neater look. A small plastic fuel filter makes an excellent vent filter on the end of such a pipe.
Where a large bore intermediate pipe is used, then it is very easy to fit the lower vent pipe inside the larger pipe, up to the upper tank, so the plumbing is neater, with less chance of fuel leaks and only the upper tank needs a vent hole. Make sure that each end of the vent pipe is in the top of both tanks.

If no emergency tank is used and dual tanks are fitted, then only one fuel gauge sender is needed if the tanks empty evenly. If they do not empty evenly, put the gauge in the last tank to empty, to get a genuine reading of when fuel is low.
Most fuel gauges work in the same manner, allowing the float arm to be reshaped to give sensible readings. Always keep the same matched fuel sender and fuel gauge. Always test and check by moving the arm when wired up, but before fitting into the tank, then adjusting it's arm as needed.
If using bike or car fuel senders, simply cut out the sender and its mounting for welding into the new tank. A C90 sender and gauge will do just as well as any other fuel sender. Simply modify the arm to sweep through the full displacement of height of the fuel tank.

On some trikes with high fuel tanks and low mounted carbs, a fuel pump may not be needed. But high, heavily loaded fuel tanks will make cornering a little more difficult by accentuating roll. Wherever possible, keep all heavy items as low as possible, this includes fuel and passengers.

For better handling, the fuel tanks should be mounted low, so their mass does not cause the trike to roll sideways excessively when cornering. Low fuel tanks require a fuel pump.
There are two types of electric fuel pumps for ordinary car engines. One about three psi, the other about six psi. The low pressure type is for a pump mounted near the carb. The high pressure pump is used when mounted near the rear fuel tank of a front engined car. Use the low pressure type as the first choice unless the trike is long and the fuel pump is far from the carbs.
Connect the fuel pump on the ignition circuit so it won't pump when parked. Use a separate fuse, because pump contacts occasionally weld themselves together. Spare contacts are normally available for decent electric fuel pumps.

In rare, exceptional circumstances it may not be possible to connect the fuel pump directly to the carburettor, whereupon a header tank is required. Possibly a set of carbs fed from a motorcycle tank, with a secondary, main tank elsewhere. This should maintain a reasonable height (head) above the carburettors and maintain the level with an overflow back to the fuel tank. With such header tanks, the fuel pump will want to over-pump constantly, so a restrictor can be used, capable of being adjusted to supply fuel at just a little more than constant full throttle requirements. This can be easily calculated at max miles per gallon, then the time for this distance, then time and measure the fuel flow from the pump into a measuring jug, then restricting the flow as required.
For simple, adjustable restrictors, the use of the very old technique of fitting a larger restrictor, then adding more or fewer fine wires though the restrictor to attain the required flow. It also has the advantage of being partially self cleaning, as the loosely held wires will help to unblock any small particles. Wire brush strands are ideal. This is also fail safe, as an escaped wire will increase the flow, but be trapped by the fuel filter. This is an old technique from the steam age, but still applied on modified or development engines to vary their oil flows.
An alternative is to fit a simple level gauge in the tank to operate a relay to the pump. On a small plastic tank, a simple float with a magnet on its base can operate a reed switch on the base of the tank and thus a relay for the pump. For micro header tanks, there is a vast choice of discarded two stroke oil tanks with level sensors, which are ideal for operating fuel pump relays of engines with moderate fuel needs.

Never fit a fuel tank where it can be damaged in a crash. This is especially important at the bottom rear of the trike, where a shunt will spill the contents and lead to serious burns. On a trike you are less likely to be trapped in the flames, but never take chances.

Most fuel tanks are mounted in rubber and held in place with steel straps. Use donor vehicle components if they are appropriate.
For those who build their own fuel tanks, then either make the shell mould first, so the fuel tank(s) can be built to fit within the shell without upsetting the overall shape of the trike. Or make a special fuel tank, making sure the shell can be well styled. This may also require juggling the shell mounting points to clear the fuel tank. Hidden fuel tanks can be built in any shape and should be considered as adaptable items which can utilise wasted space.

When making sheet steel fuel tanks, arc welding can be tricky, so the edges should be flanged outwards and clamped, tack welded and then finally fully welded. Tack welded outer flanges allow a neat seam with a little extra flange strength to prevent fracturing. There is nothing worse than poor welding on a fuel tank. Unlike a frame weld, a fuel tank weld can rarely be ground out and neatly repaired.
Always fit baffles if in doubt, which can be soldered into place using plumbers solder before the tank is sealed.
It is often easier to weld the filler pipes and fuel level sensor mounting flange prior to assembly of the fuel tank outer surfaces.

If not at all happy about making small pipe outlets at the base of a fuel tank which can leak, simply because welding such thin metal is too difficult, then use a punch to pierce the top of the tank with a hole. Into this hole can pushed a long tube which will touch the bottom of the tank. Always make sure the bottom of the tube is a little way off the base of the tank to prevent clogging and to allow good fuel flow. The top of the metal fuel pipe can be soldered in place using plumbers solder, which is stronger than electricians solder. The shape of the punch hole will give a little extra strength as it helps create a longer pool of solder. Always clean back to bare metal before soldering. The shorter filler and vent pipes can also be done in a similar manner. Where the bottom of the fuel pipe is located, make a small sump in the fuel tank base to allow all the fuel to be used. If you can get hold of brass wire mesh, then this makes a neat sediment filter around the base of the fuel pipe, and the larger it is the better. As the fuel sloshes around, it may even be self cleaning if designed well.
Always fit a cleaning hole, probably the fuel sensor plate, and if this is not used, then make a small bolt which will allow the fuel to be drained out, especially if the fuel tank is not easily removable for servicing.

If worried about sludge or sediment, then leave a small sump in the fuel tank and also a small magnet to catch any rust. The fuel filter should preferably be transparent and with a paper element. A good engineer will always align the filter so the sediment can be easily seen.

The connection between the fuel tank and the filler cap is done with a simple length of fuel resistant rubber pipe and if needed, an intermediary length of standard car steel pipe, all secured with hose clamps.

On cars, the carbs are hidden under the bonnet (hood) and rarely suffer from rain. Some are even heated with ducted air. If open to the elements as on some trikes, the carbs may be prone to water ingress and severe winter cooling. Also little, and sticky fingers. Therefore some form of protection may be required after testing and setting up.
Heating ducts are possible from the exhaust headers, use them if the trike is needed to be ridden in cold climes. Alternatively isolate the carbs from excess cold with shielding and some insulation.
Little, or sticky fingers may also find carburettors irresistible, so some stylised form of shielding or security may be suitable.
Alloy sheet can be easily shaped by using a ball pein hammer and a bag of sand. Panel beating is an art, but even minor attempts can make a sheet look like it naturally belongs there, rather than just another nondescript bracket. When shaping aluminium, it will work harden, so regular softening is needed. Rub some ordinary soap on the alloy and heat until the soap begins to turn brown, then quench the alloy in water to anneal it to make it malleable.
There are alternative ways to secure expensive carbs to engines, including special nuts, or simply making the removal components very difficult to reach.
If out in the open, the carbs may get cool in winter so the covers should try to duct some warm air over them in the winter, to keep from icing at high speeds and in bad weather. Shielding should also prevent any linkages from sticking from road salt and general road dirt. If this is not possible, liberal amount of rubber boots and thicker silicone maintenance spray may suffice.

To make custom plastic boots, cover the linkages with plaster of paris, then covering in silicone rubber. This will allow the plaster moulding to be picked out, leaving a perfect silicone rubber boot. Using white foam is much easier, as petrol will dissolve it after the silicone has set. Carving with a concertina shape and some styling will offer a degree of style to the proceedings. Using silicon bathroom sealant which is colour matched to the trike, creates a little more perfection. If not for show, but used in harder climes, preferably look for harder rubbers, such as shoe base material which can be applied from a tube.
Fibreglass suppliers also supply a plastic dipping moulding material similar to that used on the handles of pliers and similar tools.

The authors simplest and shortest throttle cable was on a fuel injected V12 trike. (14 inches).
Unfortunately, few cables are this easy.
As many engines are rear mounted, the cables will be often need to be modified and lengthened. It is increasingly difficult to find anyone who will make a custom cable, causing the builder to improvise or make their own.

Improvise: Using a standard bike twist grip and cable, position the cable in the best route towards the carb. Then fit the standard engine throttle cable and route it towards the front cable. They will either reach or not reach. Then make up an intermediate connection to fit the standard cable ends of both. This intermediate linkage can often be a third standard cable or a light rod mounted along a frame tube. Make suitable clamps to securely position each outer cable in a suitable position along the frame.

By employing standard cables and components, many hassles will be negated and spares will be much easier to buy and fit.

Make your own: Some motorcycle aftermarket suppliers still sell reels of Bowden cable and a selection of cable ends. Find a cable supplier and buy plenty of inner and outer cable. With many trike friends, cable skills will soon be in demand. Choose the more flexible inner type of cable, as all throttles should be a light action. Outer cable should ideally be nylon lined. Also buy a good selection of nipples and ferrules at the same time.

In Britain finding cable may be a pain, but it does exist. Go to a friendly dealer, the sort who is a small motorcycle shop and ask when the parts supplier representative turns up, they invariably arrive within the same hour every week.
"Hi, when does the pattern spares rep turn up? Tuesday afternoons? - great. Is it OK to be here to see if he can supply some rolls of control cable and bits, as it's a bugger to hunt down. - Cheers, - I'll pop in early on Tuesday afternoon."

The problem behind making a direct approach is that most big dealers want to sell full price cable, and smaller shops simply don't want to have the hassle of ordering bits you may or may not want. If you turn up in person, then you can ask the rep yourself and the shop owner will have no hassle over what is available and what you think you may need, nor end up with unwanted stock.
Be polite and ask it its possible to be there when they arrive, Then ask the rep what cable they have and then order it though the shop, leaving full price as it's not really expensive. It should arrive within a couple of days. My friends shop's rep can supply four sizes of wire and outers, plus a host of cable ends, nipples and ferrules. But I can only get the stuff if I am there to quiz the rep.

Use light cable for throttle, and strong cable for clutch. If a cable operated car clutch, preferably keep to the original components. Again, if too short, use two standard car clutch cables and make a simple cable joining linkage.

Scavenge the ends off old cables to make a good fit for the twistgrip, then clean up to fit the outer cable.
Where the cable outer will not fit the standard mountings and will tend to misalign, it is often possible to slide a short length of rubber fuel pipe over the outer cable join to prevent misalignment of the cable run.
When cut to length, fit the outer and check the run. If suitable nipples are not available, then make them from steel or brass bar. Brass is better as it solders easier and wears better. Old brass screws can supply the twist grip nipple, by drilling a small hole first, then countersinking the hole slightly and then cutting to length evenly either side of the hole. Larger nipples may need to be made from old steel bolts. Always countersink the nipple holes.
The inner cable should be soldered around the new ends before cutting, so the strands will not distort. When the strands are in the nipple, file a small nail to a tapered point and gently hammer into the centre of the strands to swage the strands open and spread in the countersink. This is particularly important for clutches with their heavy loads. Then solder fully and file flush when solid. Make sure the nipple will rotate freely in the twistgrip to prevent undue wear. Always lubricate fully before use with a light grease around the nipple and light oil in the cable, allowing the oil to drain all the way through the cable. Always use a light oil in the throttle, not a thick engine oil, as this causes drag. Always make the cable route as smooth as possible with minimal bends.
The carburettor end may require an unusual fitting, possibly the use a push bike brake type of clamp to secure to the carburettor linkage.
If the car carburettor return spring is too heavy, try modifying, or use a different spring. Double check it will not stick open and always use an ignition kill switch if in doubt. (See my 'Builders Guide to Motorcycle and Trike Wiring'.)

Choke. Where a choke lever is needed, it can be mounted almost anywhere, possibly even with a simple high tech variant of a piece of string and a return spring. (Please don't use string.)
Some automatic chokes work on engine or water temperature acting on a bimetalic strip or similar device. As a trike carb is mounted in the open, some adjustment may be possible, such as adjusting the setting for winter use. See the appropriate car manual.
Some vehicles can use aftermarket manual choke conversions for carburettors for those who prefer this option. As the engine may be front mounted, the choke lever on the carburettor may even be operated directly or by using a simple extended lever.

Fuel injection.
Always fit and use as the manufacturer intended. Use standard chips in any engine management computer until everything else is fettled.
A fuel filter must always be used and must be the recommended type for a pressurised system.
As fuel injection is expensive, use a new fuel filter and strip the old filter to assess the state of the fuel supply. If doubtful, consider adding fuel injector cleaner for a little while to reduce nozzle pintles from sticking. With multi point injectors and engines with many injectors such as V12's and with the engine running, a cheap kiddies stethoscope or sounding tube will help diagnose sticking pintles, as will separate exhaust headers dabbed with a wet paint brush. Engineers stethoscopes are also available for about a fiver from the big red shops which sell lots of welders and tools. Have a good listen and compare each injector.
As the fuel lines forward of the fuel pump are at high pressure, make sure all pipes are protected and rubber mounted to prevent rubbing or wearing on the frame. Always keep fuel lines away from exhausts.
Electronic fuel injection invariably imposes a control box or similar, so keep this dry and mounted in soft foam which will not absorb water or oil. Usually placed under the rear shell, or make a safe box for it with the other electrics. If a finned case, or the case gets warm, allow cooling air flow. Ensure all wiring is protected well and further protected with rust preventing maintenance spray on the connectors.
Some of the controls or commands can be overridden, but rarely worth the effort.
On trikes, where bonnets (hoods) are not used, the fuel injectors are open to the weather, so protect the injectors with the genuine rubber boots with a little extra clear silicone sealant, and prior to this, fully spray with maintenance spray which dispels moisture, to prevent corrosion of the wiring and connections.
As most fuel injection systems employ pressure and volume sensors in the air inlet plumbing, air and engine temp sensors, plus a host of other sensors, always start by using the wiring and plumbing exactly as the manufacturer intended. Nothing removed, nothing replaced and nothing added. Keep the airflow sensor and the whole air filter system etc. These parts may be able to be repositioned later after initial testing, but must retain their original purpose and general orientations.
If problems occur, then have the engine set-up and fettled by the certified specialist. They usually know what they are doing and have the tools to do it. They may often offer priceless advice to improve the system. (Ask the mechanics quietly if the motor will take the 'sports programmes'. This is because some computers can have their programmes wiped and the faster upgrades written into the EPROM's for an extra 10 percent horsepower over the standard model. Usually a 'test drive' to somewhere quiet with a laptop and a few minutes reprogramming with the updated software and a few quid changing hands for an easy extra 50 horse power.)

Do not expect people to get excited over radiators. For many, there is nothing worse to destroy the looks of a trike than a huge, ugly car radiator stuck in font of the engine. Hopefully the car engine is all alloy, with dual rocker covers and some degree of style. So don't spoil the plot.
In most cases, only oil coolers look good at the front of an engine, more so if using racing stainless steel braided plumbing.

If the engine has an engine driven cooling fan, simply remove it and place the radiator anywhere suitable by employing electric cooling fans instead.
The pulley part of the fan mounting may need to be retained, as it is often part of the V belt drive for the alternator and water pump, or a mass damper to prevent unwanted vibrations building up in the longer crankshafts such as straight sixes.

When choosing different radiators, keep the radiator cooling area at least the same as the original or a little larger. See what the scrapyards have to offer. Radiators are a design opportunity, so don't be afraid to experiment with them.

Radiators are essentially simple technology with only a few booby traps. They are fairly cheap and are easily made to measure from most local radiator suppliers at prices less then original components. You can specify the positions of the inlet and exit pipes, choose from a variety of widths and have the matrix any height you want. You can also specify single or double thickness matrix. So get the tape measure out and study the possibilities. Make a cardboard cut-out as a pattern to check fitment and for the local radiator maker to copy if you can't find anything suitable in the scrap yards.

Radiators are prone to stones, road kill and general clogging, so keep the airflow away from wheel tracks or similar impact problem areas. Wheels can also cause air turbulence and upset an otherwise superb air flow. A wire shield or F1 style 'barge board' deflector may be needed in some cases.

Keep the engine areas looking sleek, so consider placing the radiator(s) out of sight. Hide radiators unless they are stylish such as the styles so enamoured of formula one and some supercars. Even then, some stylised ducting to control airflow should be considered. See also shell later.
Study the Lamborghini Countach and formula one cars, they seem to have more than just a little style in the radiator area. Always consider if two smaller radiators will be preferable for aerodynamic and aesthetic reasons. Or maybe different shapes and mountings can be used to enhance the looks.
Styling of the rear shell will open up many possibilities with air ducts and such like. The Ferrari Testarossa, (Red head) for all it's faults, had world famous side mounted air scoops.

Modern cooling systems use a header tank to allow for expansion of the coolant when hot, which must be placed at a virtual 'high' point in the system. Make sure all air in the system can bubble its merry way up towards this tank or can be bled from the system at a high point. Many modern cars use little plastic air vent taps for this purpose. Recycling the cheaper screw-in schrader cycle and motorcycle inner tube valves can also be employed for awkward plumbing, but good design is better.

Rubber mount the radiators as they can be fragile. Make all connections with rubber tubing. The plumbing can be a mix of radiator hose and steel pipes that can be easily shaped to fit awkward bends. Ask the radiator builders what types of inlet and exit pipe positions are available to make plumbing much easier.

The thermostat, temp sensor and the cooling fan control will do their jobs whether in a car or trike, it doesn't matter which. As the temp sensor and thermostat are built into the engine, they all work at the temperature that the engine designer requires. If a remote thermostat, it must be kept very close to the engine.
If the radiator is large and mounted horizontally or at an angle, then the matrix should be supported at various points to prevent collapse when jumping hump back bridges. Use light steel bars and heavy duty foam which will not collapse, with a hard rubber pressure spreader sheet between matrix and foam, to prevent the matrix cutting through the supporting foam.

On front engined trikes where the water pump is positioned at the front of the engine, use large bore coolant pipes hidden under the frame rails. If they cannot be hidden, use stylish tubes and routing, possibly stainless.

As the radiators may be much further away, the use of larger bore coolant pipes will reduce problems of restriction from the longer coolant flow. Never use smaller pipes as the water pump may not be up to the effort of a restricted flow. If things get really desperate, such as for big motors, an electric water pump or even two can be used, one for each radiator.
Connect the engine with steel or stainless cooling pipes to match the shape and style of the engine, so they won't look out of place. Alloy or copper pipes can fracture with time, so only use if building for show or custom. Steel pipe will rust unless using antifreeze, so always use antifreeze except when on racing circuits. If in doubt, clean the steel pipe fully, then coat the inside with epoxy resin. Paint may flake off and impede the water pump or radiator matrix.
For many trikes, the coolant can flow through the frame tubes. As coolant rarely exceeds boiling point, most paints will be unaffected. Another reason for having long, uninterrupted frame tubes.

It may be advisable to place the small coolant header tank under the steering head, so it can be seen when it overheats, especially during testing or if wiring up a temperature sensor and gauge is too much hassle. Ensure the header tank can accommodate the difference in volume between cold and hot as the system reaches operating temperature. The cap will normally maintain pressure in the system and allow excess coolant to be vented if overfilled.

On the Alfa, two smaller radiators are used, partly to keep the height down and partly for posing in style. They are wide and short, rubber mounted an angle either side and just in front of the suspension, angled to catch the updraft of the hidden air dams under the passengers feet.
The coolant split to flow into both radiators to prevent causing too much drag on the water pump. If the water pump had to pump through one radiator then the other, the increased pressure drag may cause the flow rate to drop, and overheating could occur. By using two radiators in parallel, if one radiator becomes damaged, it can be clamped off and allow the other to be used to get home. If one radiator becomes clogged, the other will still work.
Two vent pipes allow trapped air from the top of the radiators to go to the header tank via a Y piece from a windscreen washer system. Wire mesh protects the radiators from damage.
With passengers either side of the rider, make sure the footrest position is chosen with heavy braking in mind, or you will be scraping friends off the wheels. On the Alfa, two seats are fitted between the wheels and driver, slightly higher, to clear the radiators, the back of the seats resting against the suspension cross member. The front of the passenger floor panels could then be angled up to channel the air into the radiators, acting horizontal air scoops with side dams while maintaining styling. It also helps to keep road spray from the front wheel off the passengers.

On most car cooling systems, cooling fans are used and controlled by the standard car temperature sensor via a relay. The water temperature sensor often shorts a fan wire to earth when the max temp is reached. This can be used to control one radiator fan, or control a pair of fans via a simple relay. Some temp switches work directly on the fan without need for a relay, but check the manual first.
The radiators may not get enough air at low speeds, so make sure the thermostat, cooling fans and temperature gauge work properly. The temperature gauge should be the standard donor vehicle item, as the engine designer prefers it this way, although just about any thermostat will do. The temperature and fuel gauges may need a voltage stabiliser from the dashboard to keep them reading properly, as most gauges are voltage sensitive. Check the wiring diagram, or check by noting the cold and then the hot position on the gauge at running temperature.
Make sure the cooling air can flow easily between the engine and passenger seats so no-one gets too warm. For trikes used in more Arctic climes, switchable positive heat ducting louvres should also be considered.

Radiators and aerodynamics.
The biggest problem with cooling is not the radiator size, nor bad design causing the coolant flow to be restricted, but the inability to get sufficient cooling air though the radiator to begin with.
If the cooling fans are often on, or if the engine keeps overheating, check the thermostat, carburetion and ignition timing first. Then check the water pump and at the same time flush out the engine block and all waterways with a hose pipe.
If the engine still overheats and all else fails, then check airflow. Cut some three inch long strips of bright wool, grab a friend, a bamboo stick, some blue tack and find a quiet road. If you can see the radiators while riding, stick some wool strands in and near the radiator matrix to highlight the airflow. Blue tack some tufts of wool around the air flow areas, wool strips around the radiator areas, with the passenger using a piece of wool on a stick to check other areas.
Ride the trike through different speeds and wind directions to find out just where the air actually flows. Problems may involve the action of the wheels, a 'dead spot' of air flow, or turbulence which can break up or destroy a clean airflow through the radiators. Not only must the air reach the radiators in a clean flow, the heated air from the radiator must then exit cleanly away to ensure a totally balanced and effective air flow.
The passenger may also be able to use a flat piece of card while driving to deflect the air to effect possible solutions, followed up with Duct (gaffer) tape and cardboard ducting modifications. See also aerodynamics.
Too many trikes suffer poor cooling, especially when thrashed. Poor cooling will destroy an engine especially on a long run. It should be sorted at an early stage.
If you have a laptop with a remote USB web cam, then this may also suffice while riding, if its secured to the seat with bungees and the camera to the radiator area with lots of blue tacky office putty. (More fun with laptops later.)

If suspension fails, a rider will slide to a halt, but if a wheel fails, the consequences can be far worse. Where possible, buy commercially available wheels.
On rear wheels, ridiculous oversized rear wheel spacers will soon trash axle bearings, so are only applicable for show use. Rear wheel spacers are not a good idea.
Front wheel.
On light trikes, a motorcycle front end will often suffice.
On heavier machines, some work is involved to get the best from the design.
The tyre is the most important item, so choose it well. The front wheel profile is mentioned earlier and will help get the best from a trike front end.
Buy a steel wheel to fit the tyre. Sensibly compromise rim width, to retain the little rounded profile on the front tyre, but not that it looses its lateral stability. Check by moving the mounted tyre in the manner expected by the trikes front end, taking into account the rake angle, to see how the profile matches the road surface. As the trike does not lean like a motorcycle, a partially curved profile tyre is ideal.
By using a steel rim, a special wheel and hub can be more easily modified to fit a set of forks.
A steel motorcycle hub with dual discs can be built up to take a car rim, but make sure it is as strong as possible and with strong bearings. As such hubs are rare, simply make new items using similar techniques to the steering head to give a strong, twin taper roller or ball race hub and axle. Motorcycle wheels rarely take side loads, except for sidecars, whereas a trike will be pushing standard motorcycle wheel bearings to their limits, so always build a better, stronger hub. Harleys and some BM bikes use taper roller wheel bearings and are recommended for medium heavier trikes.

There are two basic front hub designs. Either to build a simple axle unit similar to a steering head or to modify or re-engineer a bike or car hub. Re-engineering a car hub or a bike hub such as a Harley rear hub with taper roller bearings is often easiest, but it must be steel to allow easy welding. Those who can afford to commission special billet wheels should have few problems.
For those who need to, or prefer to engineer and build their own wheels, then there are many ways, and careful consideration always repays the effort.

The standard car dished wheel centre will only easily accommodate a single disc. If a standard car wheel is used, choose one piece car disc. Shy clear of a lightweight motorcycle floating bike disc except for show use. Trikes need all the help they can for front end braking, so get strong tyres, a good footprint and strong brakes. With a very strong solo disc such as used for a car, it is possible to use dual callipers, usually spaced 180 degrees apart on the disc, to double the stopping power. The tyre will often handle this, although severe braking on cheaper tyres may lead to more regular disc and tyre replacements for purposes of safety. Don't go stupid, so never put more braking than the tyre can handle. If desperate, consider using rim bolts as used on motocrossers and trials bikes which can prevent the tyre from slipping on the rim, but these are only available for bike rim profiles.
Car disc and pads are very cheap, even the ventilated types, costing less than a set of bike brake pads and they last much longer.

The only limits to building a decent front end are the strength of the hub, brake components, a decent tyre and a strong fork design.

For wheels which look more like bike wheels, it is easy to demount the steel car rim by grinding away the inner spider. Drill or grind out the six or more heavy spot welds keeping the rim on the spider.
If you don't want to remove the centre, a lighter, 'motorcycle style' inner design can then be built up by carving the original centre to maintain some motorcycle styling. Alternatively, use tubing to build three or five spokes or whatever wheel design is appropriate. Most custom catalogues offer some ideas on the wide variety possible.
I often rebuild car rims to make narrower or wider rims on standard spiders for rear wheels, or my own specialist centres for front wheels for my hub centre steering bikes.

When suitably strong, the shape can then be built up with filler or fibreglass to match the style of the rear wheels. Sometimes it is possible to wax the rear wheel and take a cosmetic moulding using cloth and plaster, then apply this to the front wheel and lay up the identical shape for cosmetic reasons.
If required, a car rim can be drilled and recessed for heavy wire spokes, but must be mounted on a strong hub. Always spend plenty of time getting the spokes accurately positioned. Indent the nipple recesses using a simple jig and nipple profile socket BEFORE drilling the holes at the correct angles. Some earlier sports cars had spoked wheels - seek and enjoy.

Alloy car wheel rims can be deconstructed and rebuilt onto motorcycle alloy wheels. Both will need careful machining and welding. If using alloy sheet, the new wheel may also need heat treatment prior to final machining. It may be preferable to use a rear motorcycle alloy wheel at the front if needing a wider rim and tyre profile. Many car tyres will fit bike rims and vice versa. Check S.A.E. rim specifications.

Building stronger front ends does not mean that style flies out the window, even though many trike alternative front ends leave much to be desired. Most front wheels for car tyres can be built up from a wide variety of parts. When forks are not acceptable, especially where the engine is large and intended for serious thrashing, then strength and suspension control are major design concerns.
For alloy wheels, choose the tyre first, then find a suitable wheel, probably styled to match the rear wheels. Many custom wheels can be matched in a variety of rim sizes.
Buying two very fat versions of an alloy wheel and one skinny version may cause the retailer to give you a weird look, but you are the customer, so get what you want. If they get worried, say the small wheel is for an emergency backup wheel to fit in a small boot (trunk) storage space.
Some top of the range car alloy wheels are built from split rims, where the rim is in two or even three parts. If lucky, the manufacturer may be able to mix these parts to give wide rims at the rear and a narrow version for the front wheel.

Where designer alloy wheels are used at the rear, possibly low profile racing tyres, then the front should consider machining back a similar wheel rim area and adding an alloy rim machined from a much narrower, larger diameter car rim. This rim can be machined to a narrower version by careful deconstruction followed by welding. Cross breeding the two will maintain compatible styling. This is often the case where an excellent rear tyre is not available in a suitable front rim size.

For those on a budget or who prefer to try this themselves, then off to the scrap yard and buy a set of four wheels. Two for the rear, one to deconstruct for the front wheel centre and one for a rear spare. Then either cut the sides to fit a narrower tyre or cut to fit a different alloy rim.

Alloy can be machined comparatively easily. Mount the wheel with the new front rim in the trike and run the engine. With a differential, it is necessary to lock or brake the other wheel, which puts a strain on the diff, so do not go stupid. A high tick over is usually sufficient. Using a strongly mounted lathe tool, carefully trim back the inner part(s) of the alloy spokes until the rim is left with a sensible amount of metal so it can be welded the reprofiled inner rim.
If brave or stupid, you may be able to get away with a coarse hacksaw or old woodsaw mounted incredibly strongly to a broom handle to cut away the wheel rim as the wheel turns. Always wear strong gloves, jacket and goggles and be ready to jump out of harms way.
You must ensure the rim sides of the wide car wheel can be remounted to the new, narrower inner section, therefore make the cut stepped to allow easy alignment for welding.
Once the side of the rim is off, leaving a bare wheel centre, then a chamfer cut, so it parts off cleanly. Do likewise to machine back the inner wheel section of the wheel with the worst rim, so it matches the chamfer of the new outer rim for perfect alignment. As the new front wheel is often of a larger diameter, just the sides of the rim may need to be removed. If there remains a gap between the rim and the wheel, then a spacer strip of alloy can be shaped to fit the gap.
A slight interference fit keeps it all together prior to welding.
Do not use magnesium alloy wheels.
Always take great care when using power tools and similar set-ups. If a cutting tool is not available, it is possible to use an angle grinder with the wheel spinning to ensure concentricity of the cutting process.

The wheel must then be tested. If possible, use as much water in the tyre when pressure testing, as this reduces the explosive effect should it fail. Place the wheel and tyre on the trike, then load it fully and then a bit more, to about 30 percent more than normal load, to simulate heavy braking forces. With the tyre pressure gauge at the top to prevent water damaging the pressure gauge, check the tyre pressure as the reference. Then remove the wheel and pressure test fully. Always pump up the tyre behind a brick wall, so nothing flies your way. An alternative is to have a tyre pump with a pressure gauge, with the connecting pipe running under the garage door to the test tyre on the ether side for enclosed safety.
The tyre is then pumped up to 25 percent more than the maximum reference load pressure and left for at least an hour. If all is well, the water can be drained out and the wheel inspected.

If a wanting a different rim, perhaps from a motorcycle to fit a car centre, then trim the inner item to fit the new rim, then get it welded by an expert. For best results, leave a full circle of the original rim area around the outside of the machined down centre section, so the rim can be welded fully around the rim.
If the two parts are machined such that they are a concentric, firm press fit, then this is ideal for checking and adjusting the centre line alignment to the rest of the trike prior to welding. Alternatively a corresponding alignment ridge, step or flange could be accurately measured and machined on each item to ensure perfect alignment prior to welding. Three self tapping screws will prevent misalignment before welding, but always remove them and fill their holes after. If thrashing, this is a good time to get the rim welded on both sides with an inner ridge, similar to a car rim, to reduce the chances of the bead parting from the rim during side loads. The welds can then be dressed to shape on the axle used as a lathe. If you take the axle along, it can be mounted in a vice so the welder can more easily make a truly concentric, neater internal bead lip.

Once the wheel and discs are mounted, it is possible to weld on brackets to fit better brake callipers to position them where they will not foul the steering. Clamp the callipers in position on the disc prior to welding by connecting the plumbing and pressurising the system, as normally used. With new brake pads and a clearance spacing strip of thick cardboard on the edge of the disc, adjust the callipers as required. Then the mounting brackets can be accurately made and welded onto the hub carrier, torque plate or other brake calliper mounting device.

The use of dual callipers may be considered for both front and rear. Dual front for extra braking or linked or biased braking. Dual rear for separate main braking, with the other calliper for the parking brake. See also brakes.
When fitting dual callipers to a front car disc, the symmetrical donor callipers will be handed pairs, so the bleed nipples of both can be mounted to allow easy bleeding.

For rear custom steel wheels using donor components, the standard axle mountings may not fit the larger wheels required, either for gearing or style. Begin with larger wheels using the same studs, or redrill the hub to take a new stud pattern or have adapter plates made. Adapter plates are similar to wheel spacers, but without excessive overhang which destroys the wheel bearings.
If redrilling the flange, always make sure the central aligning shoulder is accurately machined first, so the new wheel will align concentrically. This can be done by simple welding of three alignment lugs followed by machining in place, using the engine to power the wheel flange. When concentric, the wheel is then mounted accurately on the flange to align the new stud holes. This must be done extremely accurately.
For greatest accuracy, drilling the stud holes is best done on CNC or a milling machine with an indexing head. Alternatively spin the hub in the axle and carefully cut a fine groove to the 'pitch circle diameter' of the new wheel studs. Then weld up spot welds then spin the hub and dress the alignment welds to accurately become a minimal mounting flange so the inner hole of the new wheel will align. Then the four or more stud holes can be positioned accurately around the PCD. Not all hub flanges will be able to take slightly larger wheel stud patterns, but some can. If the stud holes are close to the edge of the flange, add a safety band and weld it fully.

Rear wheels can use similar techniques as for the front wheel.
There are many basic front and rear wheel hub to rim support designs, including carved from a single sheet, modified or re-engineered car parts and a set of new identical spokes built onto a hub with central mounting flange.
The simplest is using a standard bike or car steel rim and modifying a standard car centre. A car rim can be removed by drilling out the large spot welds then cutting and reprofiling the centre to run true to the new rim position. By slitting the outer bell of the standard car centre, it can be opened up and reprofiled to accept larger diameter rims for lighter use.

Alignment of rim to hub. If jigs are not available, the hub can be built up and assembled in position. Jigs are second best to building on the actual bearings and spindle which allows absolutely perfect alignment and balance.
For first attempts, consider re engineering car or other steel wheel centres, trimming them down to suit any lighter loads and new profile.

Rear wheel and single sided front new wheels centres which bolt onto the hub can be built from steel and fitted accurately to the hub flange and studs. Fixing is usually via conical faced nuts on studs. Always dish the areas where the nuts will fit onto the new wheel centre. Then spin to mark in the various alignment and other features, which can then be perfectly concentric. Double check by repositioning on the other studs to check concentricity. Then add the spokes and spin to run true, spinning the wheel and gently grind down the rim mounting points for a accurate fit to the rim.
If the studs do not allow perfect alignment on all holes, make a detent and corresponding hole in the wheel, so only that particular wheel can be used, and it can only be fitted the correct way.
Push fit the rim firmly on the spokes until running true, then tack weld and double check.

Spokes can be built up in many designs, from simple square bar mounted in a triangle pattern, to the many complex designs seen in catalogues. Heavy gauge sheet can be shaped and flanged for a variety of styles to make three or more identical spokes which should align perfectly. Round bar can be gently squashed to create basic aero style spokes.

When building spokes from new, balance is especially important. Always mark out the degrees of equal spacing to ensure accurate centre lines, to which a cardboard profile can be applied and drawn around to ensure even weight and thus better balance. Clamp the bare spokes together and trim them as a matched set before fitting.
If the rim is slightly heavier on one side when the valve fitted, then the rim should be rotated on the spokes until the whole balances as well as possible. Then the spokes dressed to balance perfectly.

If large alloy or steel spokes need some depth in cross section for more rigidity, such as for extreme offset for hubcentre steering, then they will need flanges. These can be made by panel beating grooves along the edges and centres of flat plate spokes. Use a leather covered sand bag, or profiles in the end grain of a wood block and use a ball pein hammer. Edges can also be flanged inwards to create ribs, similar to early Honda Comstar wheels. Cutting lightening holes in wide spokes will allow the edges of any holes to also be flanged for more rigidity. If making from separate sheets, usually as a set of spokes, always grind them to shape as a set, clamped together. On heavy machines, consider using a butted, stepped or overlapping design of spoke to improve both strength and alignment. Align the steps to improve braking load resolution and the central angles to assist accurate radial alignment.

It is possible to use a single sheet of metal for a one piece inner wheel. Start with the mounting either a set of studs on the hub flange or the hub itself. Then a series of concentric lines marked into the sheet for alignment by spinning on the hub and the spokes cut then bent to shape. Rest is as above.
If heating very thick aluminium to assist bending, a rough temperature guide is to rub some soap on the surface and heat the sheet until the soap turns brown, to give a safety margin. Then use a modified pipe bender to give a series of gentle bends so that all the forces are not directed at one place.
Do not plunge hot alloy into water to cool, as this makes it softer. For wheels, always allow to air cool evenly. Then test the design by subjecting the wheels to twice the maximum forces expected under the worst circumstances. See also testing later.

If a hub centre design is employed, always build the hub unit and steering pivot first. This allows the steering axis to be used to align the rim perfectly onto the steering centreline. The swing arm(s) and whole front assembly can then be aligned to the frame.

Most motorcycle engines have the exhaust sorted from the outset, as their exhaust systems are polished and stylish.
Unfortunately car exhausts are notorious for being rusty tubes.
Fortunately car engines are more tolerant of inexact exhaust systems.
Try to get the airflow matched by cylinder capacity, a 500cc car cylinder pumps almost as much as a 500cc motorcycle cylinder. (The difference is the revs involved, numbers of valves and inlet tract design and carb sizes.)
When making car exhausts, routing will be the biggest problem. This splits into two main problem areas, the visible engine mounting area, and the hidden exhaust routing.

The engine vibrates, and so must the exhaust. The exhaust is therefore held in flexible mountings form the original donor machine design, and will thus prevent the more common fracture problems.
If securing the exhaust to the chassis, then a flexible section will be needed. This can be a special flexible exhaust tubing, or a spring loaded ball and socket join, made by panel beating the exhaust pipe ends to a cup and socket which is retained as a sealed flexible joint by strong springs.

Keep to standard donor car exhaust components at first, until the design has proven reliable, then consider any fancy exhausts at a later date, as this is simple customising work.

If making the rear of the trike to look like a formula one car, please note that the vertical exhaust system may need to be a dummy in some countries or may need to be quiet. The public may never know that the 2005 style F1 exhaust has a pair of silencers, or even catalytic converters hidden just under the rear shell.

In lands of excessive bureaucracy, some specified exhaust markings may be needed, requiring specific aftermarket exhausts to be employed, so start here and work backwards from this soulless burEUocracy.

For trikes with open car engines, it is most unlikely that the trike will look exciting with a cast iron exhaust header. If possible, use the exhaust header but cut it down to give the best exhaust mounting flange or brackets. This ensures the standard gaskets can be used. Fit stub pipes into this header flange and bell out the ends to a tight internal fit, weld them to fit internally, then file flush to fit the gasket face. Alternatively, spring mounted exhaust pipes can be used, similar to racing exhausts. This is particularly useful for rubber mounted engines which will need a degree of flexibility between chassis, exhaust and engine.
Where a standard exhaust is used, study how the fixing between engine and chassis is achieved, copying the original manufacturers set-up to prevent fracturing of the exhaust. The standard exhaust may be rigid on the engine but flexibly mounted to the chassis along its whole length to prevent fracturing. Always try to keep to the original exhaust rubber mountings as they are designed to ensure minimal fracturing.
Anything up to twelve separate exhaust pipes may need to join into a silencer. The easiest way is to make each pipe enter a box separately, which can be easily welded from the inside for greater neatness. This can then be joined more easily to an approved aftermarket silencer.
Alternatively, separate exhausts for each cylinder can be employed, using aftermarket, pattern VW Beetle exhaust flutes inside the end pipes to keep the noise reasonable.

Unfortunately some rear exhaust systems may need to be bolted in place to route through some tight or awkward area. This may require a flexible joint. Flexible exhaust joints can be built from special flexible exhaust tubing, available from some retailers. Another method is use of spherically swaged ends to pipes with the other pipe 'belled' or rounded to fit, and the two parts held together with flanges and springs. There are many variations of this on cars, such as the font lower join on Ford Escorts Mk 5, which can be salvaged according to use and adapted to spring loaded use. Keep your eyes open - you don't have to reinvent the wheel.

Trying to make a heavily convoluted formula one exhaust requires many skills and such exhausts may preferably be bought. For those with real-world budgets, get as much new tightly bent exhaust tubing as possible and prefer using oxyacetylene when making tricky snake-nest exhausts. If keeping the trike, use stainless steel and tack weld, then hand over to an expert. If testing, use second hand pipe from scrapyards or exhaust fitters, where a great deal of good piping is thrown away.
By law, exhausts should normally exit to the rear of the vehicle, although some side exiting exhausts are possible. Local regulations may even allow the incredible vertical exhausting slashed systems as per formula one machines - no one need know there is a bog-standard silencer just under the fibreglass shell.

All exhausts get hot and must therefore have good airflow between themselves and other parts. On lumpy engines, heat shields are prone to rattling and falling off, so mount securely. Where exhausts are close to other components, use heat insulating sheets available from most car parts retailers or some caravan / camping shops.

NEVER allow any fuel related tap, pipe, connection or other fitting to be near or above an exhaust.

When mounting turbochargers always keep to the manufactured set-up and waste gate settings until the machine is sorted and fettled. Use standard chips in any engine management computer until fettled. Where the engine is open to public view, cover the turbo with a metal guard and always try to shape the guard to ensure good airflow around the turbo. Panel beating softened aluminium is excellent. Always use an oil cooler with turbo engines.

Catalytic converters are now often mandatory and should be hidden wherever possible. They work best when they get hot quickly, so keep them close to the engine and nice and cosy under their own little heat shield. Likewise any lambda sensors which check for unburnt oxygen.

A V8 or V12 exhaust should be a work of art, not only for looks, but in the music available.
An American V8 throaty burble is never forgotten.
A V12 'on song' is a wondrous song.
Try not to stifle them too much.

Rotary Wankel engines should use the original exhaust, as they have many unusual needs. They get much hotter than others and may have unusual over-run requirements. Done properly, they should howl nicely.

Engine adaptations.
Racing or power enhancements are best left to the individual experts for each particular machine. This is often simple, if expensive catalogue engineering.
I hate catalogue 'customs'.
If building on a budget, the best engine modification for more power is more cubes.
Fit the 1600cc car engine in place of the 1300cc. Fit the turbo version instead of the 1600cc.
Simple, reliable, effective.

If building on a reasonable budget, consider buying a complete, running old Porsche 5litre V8 for a grand or so (2002 prices). It instantly makes engine customising a total waste of time and money - in one simple stroke. It ensures real reliability when thrashed and imbues an instant and serious street presence that few other trikes could ever hope to achieve, but check the insurance first.

If using low, expensive engines such as the Porsche, always consider a sump guard. A steel cage under the engine will take the force without deforming enough to damage the engine. For very low engines, where room is at a premium, this is usually a thick sheet of aluminium restrained firmly at the front, to resolve any drag, and loosely held at the rear, to allow for deformation. There should be a stout piece of rubber between the sump guard and sump.

Do not change too much until primary testing has proven the trike handles and brakes to a high standard. When the design is deemed acceptable, then a programme of engine and chassis refinement can take place over the lifetime of the machine.

When a front engined trike is designed, a lot of junk can be removed from the engine to clean up its looks.
When removing the front radiator for styling purposes, the plumbing and some fan pulleys can be removed or dressed down. Some engines also use the front pulley as a vibration damper, so check first and if so, always leave it in place.
Only the alternator drive may not be negotiable, but if it is a V6, 8 or 12, the alternator can nestle between the rocker banks, out of sight under the steering head gussets. If a belt adjusting bracket is difficult, a spring loaded jockey pulley may suffice to keep tension on the V belt on its slack side. V belts come in many sizes and can turn various corners if needed. Always make sure the drive to the water pump is correct.

A mechanical fuel pump sticking out the side of an engine may look awful, so blank off the hole with a plate and use an electric fuel pump. Alternatively for show use, the hole may be opened up and windowed with polycarbonate, using an internal light to show up the polished crank and con rods for petrolheads. The starter motor must be left on the engine, but it can be colour co-ordinated, plated, covered or disguised with a beer label, such as Old Speckled Hen.

An alloy engine crankcase may often be first target for polishing. The mounting points for alternator, air-conditioning and power steering may look ideal subjects for grinding down for better looks. Do not succumb unless the trike has been fully tested, or if spare crankcases are easy to find. It is better to keep any mountings, simply making them look like they should be there - by employing them as brackets for holding any coolant pipes, cable brackets and such like. Where unused, simply fit short dummy bolts in any threaded holes or use flush fitting plugs or button head Allen screws.

If the engine is long, such as a straight six, the standard head steady may want to fit part-way along the top frame rail. This may not be good practice, as it may cause fracturing of any long unsupported top frame tubes. Therefore consider the use of two lighter head steadies, one at each end of the engine. Use softer rubbers to allow the engine to move as intended. If two head steadies are not desired, then use the standard head steady, but repositioned closer to a strong frame point where it will mount with less flexing of the frame and spread the load into both top frame tubes with a secondary cross brace. A wide Y-shaped head steady may suffice. Then check by blipping the engine, to see if it twists too far out of line, then tune or adjust the bushes as required.

Other bits.
The positioning of 'other bits' is often arbitrary.
I position my battery only after the machine has been checked out on bathroom scales.
Battery box out of the way of rain and dirt, fuses where they can be reached easily. Likewise the air filter, fuel pump, hi-fi amp, beer cooler etc. Easy access for all maintenance work is a must. A tool box with wheel wrench, jack and foot pump should be carried. If the front wheel is a car wheel, carry a spare front wheel if it will also fit the rear axle in emergency (if you did your homework).
If a bike front tyre is used, carry a spare rear wheel and a spare front inner tube and levers.
If the trike is poorly balanced, then consider positioning the battery such that it helps balance the trike. In most cases, the battery is positioned after the fuel tanks, then the axles checked on scales and the battery positioned to even up the axle loads. If you have a VW engine, then the battery is probably best positioned near or under the steering head or any frontal small or dummy fuel tank, to reduce the tendency to lift the front end.
Tool kit. Always carry a tool kit when testing. Carrying it on the person is dangerous. Always carry the tool kit in a secure container on the frame. During testing, the tool kit is always larger than for normal use, so make container accordingly, or use an extra strap on tool bag. Always include a first aid kit and carry a cellphone when testing.

If the donor vehicle is a common machine and spares are cheap, and you intend to tour many countries, then consider adding a backup fuel pump, electronic ignition unit, coil and other parts. They could be mounted beside the original and protected in sealed plastic bags ready for use, ISDE style. Likewise cables.

This and lots of other stuff is available on my website, including 'A Builders Guide to Motorcycle and Trike Wiring'. A couple of generic trike wiring diagrams are included. There is a lot of other useful stuff here as well.
My home website resides quietly at
The first and best check is to check it all works properly before the donor machine is stripped. Removal of the loom from the car can be difficult, so be very careful. An extra half an hour teasing a loom out of a car is still faster in the long run than having to fault-find, then repair or rebuild a damaged wiring loom.

As mentioned earlier, the modern car alternator is a self contained item, supplying perfect 13.8 volts and even a warning light connection. It can be positioned almost anywhere a V belt will fit. Make sure it rotates the same way as originally fitted, remount, or use a different alternator. Alternators are very easy to mount and adjust for V belt tensioning.

To get started, simply use the standard wiring loom and carefully blank off what is not needed. If preferred, lay the donor wiring loom in position, then connect up all relevant parts, even if they are not in the right places. Then cut away the loom binding and rearrange. Do not remove, but tidy up any redundant wiring, as it may be needed later. Connect the battery and check all works as intended. Modify as required.

Main beam, indicators and horn switches can be made to fit by reading the manual or opening up the car stalks, then deciding which wires are which and paring them back to connect to bike switches. It is preferable not to use car switches, which are only designed for a dry environment. They can be waterproofed, but rarely integrate with trike styles.
Check that the battery charges at about 13.8 volts with the engine running and all works well. Then make a special loom later if needed, or simply, but carefully reduce unwanted wiring from the original car loom.

The way the loom is routed on the trike will depend upon the complexity of the design. If a fuel injected design, then the electrics will often encourage the units to be fitted in just one place, which may require a special housing. If making a front engined trike for show, then consider making a modified custom copy of the wiring loom to position all components out of sight. This includes the loom itself, which can often be well hidden.

As trikes are wide, 5 Watt side lights will be needed which must show a white light to the front and a red light to the rear. As most trikes use dual car rear light units, the rearward pointing red side lights are often unnecessary. Side repeater indicators are also recommended, especially on very long trikes.

If a fuel pump is used, it should be wired in the ignition circuit, preferably with a separate fuse and if a big engine, with a relay. See fuel system above. As the fuel pump is important during testing, make sure you are able to wire it directly in an emergency to get home. Also include an emergency direct connection to the ignition coil for the same reason.
Where complex electronics such as computers and engine management systems are used, keep them on their own cosseted little circuit, well protected with the correct fuse rating and bagged in foam. If they are finned or may get warm, then always allow cool air to circulate.

As many custom builders have a reputation for poor design and manufacture of wiring looms, consider self resetting thermal fuses, which will reduce the number of blown fuses from poor wiring until the fault is found. On a good day, they may even allow you to travel ten miles before the fault re-occurs.

If in doubt, get wiring done by an expert, or keep it very simple and use separate ignition circuits for sparks and for the fuel pump.
Email the author for a re-wire quote. Prices from a hundred quid, even if there is nothing there to start with.

Also consider a separate circuit for lights, with a separate circuit for the rest such as horn, brake lights etc. Protect each circuit with its own fuse.
Always put the fuel injection and such like on a separate circuit.

A basic wiring guide.
The output from the alternator goes to the battery, then to the main fuse.
The main fuse then supplies the ignition switch and any relays.

The ignition switch will also supply power to three other fuses.
These three fuses normally supply 12 (13.8V) volts to:
1. The ignition circuit / electronic ignition.
2. The head and tail lights circuit.
3.The auxiliary circuit which contains the indicators, horn and brake lights.

Three or more separate, fused circuits from the ignition switch output are easier to design, build and repair than one big circuit.

On sophisticated (expensive) engines, the ignition (sparks) circuit should also split into fused circuits for any fuel injection and the fuel pump. Each should be protected by its own fuse. When you switch off the ignition or kill switch, all must switch off.
See also fuel injection.

If required, separate switches can be used to supply power from the main ignition switch (or independently) to each circuit, aircraft style. E.g. sparks on/off, fuel injection on/off, fuel pump on/off. (Mainly for show use or if building with aircraft engines.)

For styling purposes, starter switches can also use an identical looking switch but with a momentary action.
A small light above each switch can be used to check if its on line, or to tell if the fuse has blown and the circuit is out. Safety flip covers or preferably protection bars between each switch are also useful. Do not put a safety flip cover on the spark / ignition switch if there is no dedicated kill switch or if the ignition key is hard to reach. Preferably have a safety cover over the starter button unless an electrical lock-out circuit is employed.

If using this style, always have the switches in a sequenced row, so you can easily switch each in turn, - fuel pump first, to build up pressure, then fuel injection computer to begin reading the temp sensors etc and settle down, then the sparks (ignition circuit) and finally the starter button. - Flick, flick, flick, press.

Load carrying.
The passengers are also a load. When not using safety belts, they should be considered as dumb, unsecured loads, especially when braking and powering around corners.
Give passengers decent foot rails to take the braking forces. Mounting the passengers in a luxurious reclining manner will also help during cornering and especially braking, with a rise to the front of the seat, as shown opposite.
Side loads when cornering will have passengers complaining after fifty miles of country roads, so consider seats with side padding or armrests as shown opposite.
If not offering any form of security for the passengers, at least include hand rails or strong straps to hang on to.
Position the standard car seat belts with consideration for left and right. This way, the passengers get maximum safety and will not slide out from under a right handed seat belt when a left handed belt would save them getting squashed under a bus.
Even if not making an art form, preferably get an expert to make the seats in water resistant leather or vinyl. Also consider a cloth based waterproof lining between seat foam and covering. Fit closed cell foam on most components, but open cell foam or similar between seat base and backrest, so that rain will not accumulate in the seat.

Where required, there is no excuse for not having a trunk (boot) on a machine. My friends first trike shown opposite has a boot (trunk), is incredibly comfortable and can take four people. It also handles extremely well.

Good details not need to be sophisticated. A flush fitting cover in a fibreglass shell, carefully cut from the moulding can be cleanly secured with internal bungees and opened with a simple finger recess. Hinges may also help. The luggage compartment can be built onto the frame to take the loads without actually touching the shell or boot lid.
See shells later.

The bare rolling chassis can now be built up to become a fully functioning trike.
If in doubt about handling, then a simple lash up can be made before fitting the seats and controls in a finalised form, as mentioned earlier.
If the testing shows the trike is reasonable, then start with the riders seat. This should be positioned with reference to frontal axle loading.
If a lightweight front end or a VW, then weight the trike, then place the bathroom scales under the font wheel and sit well forward without upsetting the styling and ergonomics.
If the engine is mounted forward and heavy, then sit to the rear as much as possible to ameliorate the poor effects of a heavily loaded front end.
The passengers can also be positioned to maximise the best handling. Passenger side seat supports are always recommended on trikes.

The fuel tanks should ideally be positioned close to the centre of gravity, so that changes in mass do not upset the overall balance, but in reality, the fuel tanks are mounted low and in a convenient place. See fuel tanks, above.
The battery can now be positioned to help refine the balance.

Once the heavy parts are positioned, the superstructure can be made to support them. This should be such that the riders and passengers are kept low, where the gearchange and suspension permitting.

Most superstructure can be built from three-quarter or inch section square tubing for ease of manufacture and lightness.
Where the engine needs to be replaced often, then the superstructure can be pivoted or lifted off, with a few bolts to hold it in position. Always use nylon locking nuts or other safety retainment to prevent serious failure.

Where a boot (trunk) or rear engine cover is used, then make a suitable superstructure to support the hinges, and support the lower load carrying floor, either from steel or heat resistant or coated plywood on a steel frame.
If using countach style radiators, then make up suitably shaped superstructure to support the radiators in rubber supports, and without airflow obstructions.

If supporting exhaust systems, then the superstructure tubing should have strongly supported exhaust brackets which can take the rubber or flexible mounting lugs.

Onto the superstructure may be mounted any electric fuel pump, electronics, fuse box, etc. It is often preferable not to mount too much directly onto the chassis, as there is often a major rebuild just a few months or a year away. This ensures the main chassis is kept clean for inspection for faults and reduces the need to respray the trike, other than to build an new, or rebuild the old superstructure. I prefer to mount ancillaries to the superstructure, as this is often changed as the seating and styling are changed, without upsetting or damaging the main chassis components. Unfortunately, the radiators) and exhausts often need secure chassis mounting points so some additional modifications to the chassis will be necessary.

The battery is ideally kept low in the frame unless you encounter a lot of river crossings.
Seats with folding bases make excellent access points for the battery / fuse box and for small luggage areas. Keeping the access areas secure should be done well, with standard locks as used for motorcycle top boxes, or using hidden, spring loaded cable pulls, often hidden under the seat, engine or mudguard area, where only the builder knows how to easily reach the toggles or opening levers.

If very heavy loads are to be carried, consider pulling a trailer.
Trailers are straight forward attachment and often considered boring. But for trikes. . . .
If a four wheel drive engine is used, then a powered trailer is possible. Army Land Rovers do it, then so can trikes. A classic example is the Subaru engined trike, using the excellent flat four engine with four wheel drive.
Build a trailer using the standard Subaru rear axle. The trailer prop shaft should be able to slide onto the spline drive on the rear of the engine and be restrained by the standard towing ball joint or a more sophisticated pivot.
Make sure the ball is just above or below the universal coupling on the prop shaft, as this greatly reduces wear and reduces handling problems. For this reason, the ball joint may be recessed under the back of the trike to get it all properly aligned. Using such a set up makes a good starting point for the ultimate field churner when exiting muddy fields in winter or to roost gravel.
It may be better to be able to disconnect the drive for general purpose use, or even have a differential lock on each axle for happy triking in swamps.

See also the German Kettenrad, a 'half track trike' - thing.

Keeping it tidy.
Either you want to, or you don't. No coercing in print will help.
The rear end of the last trikes I worked on was often mistaken for a Lotus or 'something Italian'.
This should be a basic goal.
Lamborghini Countachs and Diablos look nice too, as do many other vehicles.
For those who want to try, a few words of advice: Take your time and use sketches. 3D computing will greatly help, as will a simple lump of modelling clay or plaster.
If the donor vehicle is a Porsche, an XJS or something of note with a well recognised rear end, and the tail lights are available, then consider making a mould of the original.
Trying for a Ferrari or Lamborginini style is always worth the effort, but the downfall will often be in the details. See later.
Always invite others to offer advice, as the designers ideas are not always what the rest of the world will see.

But despite all best intentions from others to the contrary, always follow your dream.

The first test should be before the trike is begun, when the donor vehicle is still intact. Run the engine, check the clutch, all the gears, tacho, electrics etc. Settle it down with a decent service, then drain the fuel and cooling system and preserve the rest carefully. If the build is to take many years, squirt some two stroke or engine oil down each spark plug hole and turn the engine a few times, add more oil and lightly replace the spark plugs. Gently rotate the crank every three months or so. Spin the gearbox output shaft regularly to get the oil covering the internals. Cover the clutch holes with polythene or duct tape to prevent moisture from corroding the internals.
Secondary testing has been mentioned above, where it is important to test the flexing of the frame with tack welds, allowing modifications to resolve any deformation and fundamental structural problems at an early stage. Then tests after fully welded and the basic rolling chassis loaded with a few friends aggressively testing the structure, plus any front end distortion to be sorted prior to steering head side plates.

The next stage is to get the whole machine ready for basic road use.
This may be riding to the testing station to become legal, or preferably on a trailer to a local disused airfield or other site for gradually increased thrashing and fettling. Fitting the trike front wheel to a car's towing hitch can make it a trailer. If so, use the appropriate number or licence plate. Will need a special bracket to clamp the front assembly.

At this stage the machine will need fettling.
The first few hours of running will be in the garage to adjust the carburetion, wiring, fuel gauge settings, radiator cooling assessment in still air and to get the gearchange and brakes working reasonably well.

Testing is done with the following problems in mind.

If the engine has lain idle for a year or more, test the clutch carefully. The front end may jump up if the clutch is fierce, so use second gear when testing for the first time. - Choose the wall you want to crash into. Use second gear with the front wheel of the trike against a wall and a brave friend standing on the front wheel. Second gear is more likely to stall the engine rather than lift the front end too far. Be ready to jump off if the clutch is too fierce or stuck, causing the front end to lift or plummet you down the road. An anti-wheelie block jammed under the rear of the frame is a must, so place blocks tight under the rear to lift the wheels off the ground if a wheelie should happen. Do not rev the engine as the gear is engaged, but allow the engine to stall, as this may be enough to release the clutch after a few attempts. In some cases, it may be possible to start the engine and pull away in first gear along the road, frantically working the clutch while pumping the brakes and blipping the engine until the clutch releases. It is preferable to strip the clutch if in doubt, if only to save blood or embarrassment.

The engine will need anything from a tune up to a total rebuild. Leave full rebuilds for later. Just get the engine reasonably reliable.
New steering head bearings are probably needed if they were welded with them in place, but old ones can be used for initial testing and if you suspect you may want to rearrange the rake angle.
The radiators may not get enough air at low speeds, so make sure the thermostat, cooling fans and temperature gauge work properly.
The carburetion and exhaust may need fettling.
If a fuel gauge is not fitted, carry a spare can of fuel until the range of the fuel tank is known.
The gearchange may take some getting used to and adjusted.

The brakes will probably be exciting too, so make sure there is some adjustment.
Ensure the brakes are bled properly and all brake items are in good condition and not binding. No serious rust on the drums or discs, with drum brakes on the correct sides and no squeals or rattles. If necessary, lift one wheel at a time in the garage and run the engine gently, to check each brake works as intended and to bed in the pads or shoes.

To check REAR brake balance, allow the FRONT wheel to roll sideways on a plank on dowels, then very lightly apply the rear brakes and ease out the clutch a tad, to see if the rear brakes are balanced, or if the front of the trike tends to swerve sideways while stationary.
Be prepared to find that the rear brakes may be too severe or too weak.

During the first few hours of use, the rear wheel alignment and the tyre pressures may affect the way it handles. Be prepared to experiment with both. Signs include poor wear of the tyres, such as scuffing or uneven wear patterns. Carry tools to adjust the toe in or toe out as they are compared and refined over a good test road.

Stamp your own frame number or that of the donor vehicle on the steering head or as required by local laws. Use proper stamps and take your time to get it tidy. Your own frame number could be your initials, date of birth and other numbers to show its your fifth frame, or whatever.
When stamping, temporarily glue a cardboard guide plate to help make a neat line as the frame number is stamped.
The SAE, (Society of Automotive Engineers) have a special frame number coding, showing the country of origin, manufacturer etc. If it is necessary to have the new machine tested by the authorities, they may stamp their own frame number on it too, according to SAE rules.
There is nothing to say it cannot have your own frame number too, but just one frame number makes for an easier life.

Always keep the receipts for the parts and try to get any documentation such as log book etc. It may even have a 'valid' MOT or tax disc. The ministry will often demand proof of ownership of each and every important part such as engine, frame, differential, etc. In the UK, it may well need to be put through the SVA 'single vehicle approval' for one off designs. This is less than 200 pounds and checks it complies with legal requirements such as mirrors, assembly standards etc. A Retake is twenty pounds. The SVA manual /guide is about twenty five pounds, or visit your library. 1998 prices.

Never assume that because you can ride it, that it is safe. Others trikers may test your machine and offer an endless list of improvements. Therefore it is always advisable get many second opinions before finally deciding the final settings for brakes, handling and a host of other variables.

Spare a thought for the official tester, who may have to test three cars, a campervan, a restored 1920 tractor - and your machine. This poor soul does not always like to have to test a machine which is so far out from the norm that he has to frighten himself before deciding if it's safe or not. At least attach a note as to where the gears are, plus any 'interesting' points of note, definitely including the kill switch. Tape this information where it can be seen. The tester has probably seen it all, so use his knowledge to make a better trike.

Destructive testing should not be necessary if a sensible and cautious approach is taken. If the very rough, early attempts to trash the basic frame were unsuccessful then the reader should be feeling cautiously optimistic.
If a cautious approach is not taken, the test rider may unwittingly be undergoing a destructive test regime, with one of two possible outcomes. - One involves a long wooden box.

If deciding to test on the road, always wear protective clothing until confident. Always test first on quiet roads until confident and the machine is fettled as much as possible. Suspect all possible frame, steering, suspension and brake problems until confident. Never be too confident.

There are two main types of testing. Basic testing using the whole machine. The second form is a more involved structural tests using just the bare chassis so that its flexing can be measured and predicted on a graph. The latter is for techno heads who wish to develop ultra light weight chassis, or simply to understand the structure more fully.
The usual method is to load and test the while machine to about twice what the worst case is likely to be. As leaping off a hump back bridge at seventy miles an hour is difficult to replicate in the workshop, some assumptions must be made. Most other tests are a little easier to do. A variety of tests are mentioned so the reader can get a reasonable feel for the limits of the chassis.

Non destructive testing.
Before loading further, the basic, unpainted trike should be settled down and bedded in during intial tests.
The frame must be checked regularly for fractures caused by engine vibration and road conditions. Check every 20 miles for the first few hundred miles, never easing off the observations completely as the miles build up.
Use easily cracked lacquer over any suspect welds or tubes etc. This will help highlight any problems before they get too serious. Thin, white hard varnish is useful to highlight cracks, or use clear varnish and good eyes.
In some cases, cover large areas which my distort with lightly lacquered fine tissue stretched over suspect areas. This will highlight potential fracture areas and general distortion on long term tests and also during static tests.
If in a country where corrosion is a problem, use a light coating of clear lacquer to stop the frame from rusting for the first few months, allowing regular checks for problems such as fractures.
Plastic coating the frame from the outset is never recommended for obvious reasons.
Before applying the finishing touches of paint and trim, grab a few friends, take the machine somewhere quiet and literally thrash the nuts off it. Jump over ramps, slide into walls, and generally commit positive vandalism. You know it makes sense. You will also get to understand the handling much more intimately.

If you have fuel or oil in the frame, pressurise it for a couple of hours after testing. Use the valve of an old inner tube clamped or tied over the filler hole and a cycle pump to pressurise. If any leaks, lightly grind back and reweld. Preferable not to fill with fuel or oil prior to initial pressure testing, as further welding can cause explosions. Initially pressurise with air and then 'paint' the empty frame with soapy water to check for leaks.

Once the machine is deemed physically safe and seems to work well, then full testing can begin.

The first test ride must concern safety; mainly structural strength and brakes. All cables, bearings and brakes settle during extended testing and will require adjustment.
ALWAYS try pulling away up a steep hill, a short bank, or wheel ramps in a garage to balance the clutch and brakes.
There is nothing more annoying than taking a machine out to test, only to find some simple, annoying problem has halted the test.

Once the machine holds together and the brakes work, the handling can be studied. If using differing or unusual tyre dimensions and profiles, pressures may be even more important. This can only be fully assessed by riding, but start by noticing tyre deformation on standard load. Then experiment with pressures to get suitable deformation patterns. Try to steer clear of maximum rated tyre pressures and be prepared to aim for a sensible and balanced set of pressures. Larger rear tyres may need less pressure for a sensible footprint.

Load the trike to normal conditions. Then roll the tyre over a flat piece of road or a wood sheet. While carefully noticing the contact patch, lower the tyre pressures until the tyre contact profile begins to sag. Note the pressure. Now pump up the tyre until it starts to get too rounded. Note the pressure. Now set your starting test pressure midway between the two.
If you can do this on a wet sheet of glass, then you can easily see the actual contact patch as seen from below. If you have a similar tyre, perhaps on a well set-up Porsche or Jag, then use this too, to check the contact patch as a reference. If no glass floor, then jack up the wheel, rub on a little dark grease, then lower carefully onto a sheet of paper. Then carefully jack up to remove, without rotating the wheel. Use this as a standard starting reference profile for the tyre in question. The tyre pressure will probably change after various testing sessions, but gives a good starting point which should be in the 'ball park'.

Basic tests includes riding in a straight line, applying the rear brake and checking for veering to one side while very lightly holding the handlebars.
Test the fastest constant speed into a sharp turn such as a right angle street junction. The use of real or imaginary road cones, chalk to mark the ground and a big, quiet car park is ideal.

Although this should have been done a long time ago, when setting up the suspension on the bare frame, once again push the wing of a car down, to see how the shocks behave, then do the same on the trike to see if it is in the same ball park.

Important tests include the minimum turning circle, both slow and under power. Both in first and second gear, plus reverse. Check the steering does not want to dive under on full lock.
With smaller front wheels with light loads, the limits of the front wheel may need to be pushed, especially if worried about safety, such as sudden breaking away without notice.
In a safe area, try to get it to break free in faster tight corners, with and without braking. Find out how the front or rear breaks away first and under what conditions. This puts a reasonable load on the suspension and helps show up problems such as sloppiness as the suspension and other components bed down. A little tightening of parts between tests goes a long way.
Always aim to refine the overall handling from the outset, which is always more important than finding the top speed.

Don't loose vital information: The first test gives you a major opportunity which will soon disappear. The first ride will have no reference points and you will be assessing the way the trike behaves in a raw, untainted manner.
As more tests are done, you will naturally adapt to the trikes peculiarities and thus loose totally subjective assessment.
You will get used to the machine and its foibles, so from the very outset, set high standards and always be critical, so that your assessment does not become devalued with familiarity.

A minimum cornering radius at a natural speed will soon be found and could be recorded for comparison with other rakes and trails. As the subtleties of handling are gradually refined, there may often be a trade off between tighter cornering vs straight line stability. The final decision will depend upon use. A comfortable touring machine often turns less well, but with better stability, whereas an animal machine will usually be set up for urban motocross. A comparison is where transport planes are usually stable, whereas modern fighter aircraft are intentionally designed to be partially unstable.

If the machine wants to pull to one side when trying to brake or when driving hands-off in a straight line, then the brake imbalance, steering, frame or rear wheel mis-alignment may be the cause of problems. All machines must brake in a straight line with hands off. Start by checking chassis and wheel alignment, tyre pressures and then the brake components, ensuring they are properly bedded in. Therefore the brake imbalance tests should be done near the end of the test, when the brakes are probably better bedded in.

The front and rear suspension may need to be stiffened or softened. The normal amount of adjustment on standard shocks may suffice, but proper positioning may need a little refinement.
If antidive is integrated into the forks, test to see how well it performs. Tony Foales excellent website contains all the theory. A section for trikes can be added here if requested.

Learning the handling and braking characteristics in a quiet area will be advantageous for knowing the limits. This will help the adjustment of the braking system by modifying and refining brake lever ratios and pressures for best use. It is very easy to build a machine with misbalanced front and rear brakes, yet fairly easy to cure. Choice of pads, reduction of braking material, lever ratios and many other methods can lead to matched brakes which can be a pleasure to use and brakes save lives.

Play around with the toe in to see how this changes the handling, straight ahead and especially in the bends. Adjust the camber and toe in, just to see what happens, If it gets worse, then try adjusting the other way to see what happens. If al beings the overall package closer to the best possible.
Unfortunately, adjusting for tight turns in urban terrain may make the machine handle worse at high speeds. Always make sure the machine handles best at high speeds, then adjust to get the reasonable handling at low speeds too, if possible. While riding in normal use, you may be able to correct an unexpected handling problem at 20 mph, but not at 80 mph.
When it is as good as possible, measure everything, shock settings, tyre pressures, toe in, camber, (rake and trail, if adjustable,) and anything else you have changed.

Mark it all down on paper for the first minor rebuild.

There is no excuse for inadequate or poor braking.

With reasonable brakes, the handling envelope can be pushed.
First practice riding close to walls on each side of the machine, so you learn that bikes are narrow and trikes are not.

Pushing the limits:
Use of a water patch and a gravel patch will help understand the machine, so carry some water for any depressions in the car park, and a small bag of sand to make some impromptu testing areas. An area of sand about four times as long as the trike is excellent for getting a feel of the way the machine breaks away in loose conditions. If it handles well, it may be preferable to choose less efficient tyres if a little power drifting is required.
If no kerbs, a rounded edged wooden strip or preferably an old door, held to the ground with blue tack (after brushing clean) will make adequate bump strip for straight and side angle kerb testing. Kerb tests are not suitable for delicate wheels, unless replacements are available for general road use. (The scrap yards have plenty of cheap wheels.) Kerbs will be an annoying part of learning to ride a trike, especially when used to motorcycles. Be prepared to build up a set of reactions for the times when judgements into corners are not always accurate.

During testing, the more specialist suspensions with custom suspension arms, shock units and front end must be carefully assessed in accordance with what the designer and test rider require. This may require gradually bringing the machine up to roll or slide, and will require a good, accurate speedo and plenty of run off area. Getting the turning circle tighter may require many hours playing around with rake and trail, tyre pressures and profiles. Do not be put off by science or expertise, as most moderately well designed trikes will usually handle quite well first time out. If it handles quite well from the outset, just think how good it can be with a little tweaking and fettling.

Testing must be built up to put a reasonable load on the suspension and help show up problems such as sloppiness as the suspension and other components bed down. A little tightening of parts between tests goes a long way. Always remember what gets loose, so that simple tightening can be done, while also looking for problems such as fracturing, misalignment and distortion.

There are many other tests, such as engine reliability, cooling airflow, comfort, but these are comparatively all fairly straight forward.

After as many problems as can be found are written up, and the builder has decided whether the machine handles poorly and is unacceptable, then it may be preferred to modify or even to rebuild the frame until it handles well, from which a final design can be created.
In less extreme cases where just the steering is not ideal, the builder may wish to modify the front end trail or rake angle until ideal. Do not assume the rake angle is the main culprit of a poor handling machine, as a surprising amount of rakes can be applied on otherwise similar handling machines.
Always test with all other variables where possible, such as adjusting the fork leg offset angle to adjust the trail, by variations on the upper fork yoke or front suspension pivots if using leading link forks. It is highly recommended to have extra pivot points either side of the intended fork pivots, to allow back to back testing of various amounts of trail.

Suspension settings will need careful assessment, especially the front. In easy cases, simply adding fork spring spacers and a little heavier damping oil may suffice for standard bike forks. On special front ends, the spring rates can be too soft or too stiff, which can often be solved by repositioning the shocks slightly.
Never test with a steering damper, as this merely hides bad handling, and you will never get a truly better machine. If you must use a steering damper after final testing, then do so, but it is hoped the machine should never need this level of compromise.

Mark it all down on paper for the first minor rebuild.

Rear suspension should be fairly acceptable, possibly a little soft for three up riding of a transverse rear engined design. If too soft, simply use components from the sports version of the donor machine or fit spring spacers to add a little extra spring preload, or use slightly heavier shock oil for increased damping firmness.
In some cases, you may prefer to angle the rear shock to make a better ride, but this is often about right from the outset when doing initial testing.
Although not officially a good idea, most of the cheaper standard shocks can be drilled near the top of the body and the fluid drained out. Beware of pressurised systems. Then a nut soldered over the hole, ensuring the heat does not damage the seals. Then new, heavier or lighter oil can be pumped in and the shock compressed fully a few times to allow excess oil to drain to prevent any hydraulic lock. Seal with a screw in the soldered nut, preferably sealed with PTFE thread tape.

Mark it all down on paper for the first minor rebuild.

Once a good handling machine is achieved, very accurately measure the rake, trail, toe in or out, axle offset and axle loadings, rider position, steering ratios and whatever else can be measured. Mark them permanently on the main drawing. This is priceless information and will form the basis of the next machine. During any refining process always measure and record all other rakes and trails used for future reference, with descriptions of the effects at slow, medium and high speeds. Also mark this information permanently on the main drawing for future reference.

Yes the next, even better trike is not far away.

Destructive testing.
If the machine is terrible and a new frame is to be built, consider use of the machine for test riding to destruction.
Grab your kids skateboard knee and elbow pads, thickest leather jacket, a helmet and a friend with a cell phone.
Begin by riding over bumps, jumps and anything else it may encounter.
Test, Test, Test. This is positive vandalism. If the machine remains complete, even after many modifications or bodges to improve the problems, then confidence is the first survivor and a lighter machine may be it's progeny. All testing will depend upon the purpose of the machine and its unacceptable problem areas.

If deemed unsuitable, it can be heavily modified to improve it's handling. - Refitting the steering head, rear shock mounts or whatever is needed can be done in light of feedback.

It is such situations that allow the best research to be done. You will soon understand if your ideas make the trike better or worse, and from that you can try modifications in the other direction, or to find that your original idea was pretty close to the ball park.

Do not be afraid to experiment.
The hacksaw, grinder and welder are your best friends.

Saw part way though the frame tubes near the headstock, reposition the steering head angle and weld up fully. Play around with various rear shock mountings. Reposition the anti roll bar or radius arms. Adjust the toe in or out, and finally lower a tall machine, just to see how this makes handling better.

Remember - a lot more can be learnt from a poor machine than from a perfect one.

There may still be a complete machine to test. Where breaks occur, reweld and prepare to test further. So use the opportunity to keep modifying until it is as good as it is likely to get.

The last test, if the machine is not acceptable for general use, is by loading to destruction. Chassis deflections against load could be taken for future reference.

Like JPseries crash testing, if one can't get help from the experts, then study their work and do it anyway. (Always be painstakingly careful when crash testing with real riders.) It is hoped that computer crash analysis will be made available to all vehicle builders as soon as possible. Please contact the author, as the safety of many testers, including the author are directly affected.

Structural testing can be studied from books then applied, but for most purposes, it is just a case of seeing how far a design and it's quality of manufacturing can be pushed.
The headstock, handlebars and linkages are unlikely to be damaged, so can be salvaged later. Remove all expensive non structural components such as lights, carbs, disc brakes etc. Leave the structural parts in position to prevent the machine from distorting unnecessarily, including the engine and suspension.
Unless extremely expensive, the forks should be considered sacrificial and part of the dynamic testing procedure, although fork legs can be replaced with simple tubes for static tests.

Choosing somewhere quiet and safe with good lighting, will allow the builder to see and hear cracks as they form. Always wear eye protection goggles. This is important, as this will help to discover the weakest points earlier than in less refined environments.
Final testing is accomplished by copying the basic loads as found in use, but more so.

First clamp the rear wheels to the floor or a solid wall, or use a plank over the wheels and block with heavy weights or concrete blocks etc. If this is not possible, then weld up a vertical brace and jam it in a door frame.
Lift the front of the machine lightly off the ground with a jack, or simply place the wheel on a plank which is allowed to roll sideways on dowels. Apply a bar across the front fork yokes and measure deflections, by gradually loading to twist the frame. If clamps are difficult, place a bar over the front wheel spindle nut and suspend using a rope from the handlebars to give a crane jib effect. Although unlikely, do not distort the frame too close to permanent failure of the structure.

If you have a digital camera which captures video sequences, then these can be run in a loop to see which part of the frame flexes the most. Try to get visual deflections in plan and looking from the front and rear and from the side, so a tripod is particularly useful. If you cannot run video sequences, then mount the camera on pre-set points, so that it can take individual photos of the deflections which can be built up into sequences using programmes such as Gifcon.

It is important to assess torsion on the front end, as traditional motorcycle forks are not set up for heavy side loads, although symmetrical tubular types are capable of the same forces from braking and gravity. All front ends will suffer from the side loads found when cornering, but also the frame, so checking the way the steering head support tubes behave will highlight any areas of concern. Problems can often be ameliorated with plates or cross brace tubes.

To help recognise fractures early on ultra light machines, do the tests somewhere quiet, so cracks can be heard easily. Also cover the frame in fine strips of tissue paper, tightly glued across suspect surfaces or similar sections, possibly using little strips or larger sheets which will easily tear or distort, or larger sheets which will buckle or ripple. If the machine does not fail where expected, this helps refine the design process by real experience. Listen for creaks and worse noises.

Not all distortion may be in the frame. As the rear suspension is the first part which deflects, block this with wood blocks or temporary welded struts, so that it is the frame which flexes.
Record the torsion deformation at various forces and at various positions along the frame, to see where the torsion is most pronounced. Record for comparison with other machines. Using a video camera looking along the frame to record the deflection will allow the sequence to be rerun back and forth faster on a computer to closely study the chassis deformation. Where possible, viewing from above also helps.
Single sided front suspension systems may need mounting bars to fit. Always test from the front and rear axles, otherwise the exercise is not highlighting all possible weak points along the structure.

This involves adding increasing load onto the trike until a load which is higher than the worst case load is applied. This may be the forces applied to each part of the trike which are needed to survive leaping a humpback bridge at seventy miles an hour, or whatever your approved riding style may be.
To know what sort and ratios of loads are to be applied over the chassis, check the final wheel loading using bathroom scales or something bigger if needed. On a heavy axle load, use two bathroom scales and a plank to spread the load, then add these loads together. As weight balance should have been decided at an early stage, be prepared to adjust the position of the passengers, fuel tank and battery if needed to improve the overall weight balance.
Once about right, measure the wheel loads with a full complement of heavy passengers and luggage. Mark the load for each wheel in pounds or kilograms on the chassis in felt tip pen. This gives the static load on each axle of the structure which can then be used to calculate the maximum 'safe' load. This is NOT a guaranteed safe load, merely an approximation.

As maths is not everyone's favourite subject, consider the front wheel resting on the ground, which is not suffering a heavy load while static. In reality, it is supporting the mass of the trike under the effects of gravity.
At top speed over a bumpy road, this force into the trike can be four times the static force, into the tyre and suspension, and will do so many times a minute, creating lots of stress as well as the general load.
This force and load must not distort the trike suspension or chassis in a dangerous manner. All structures will distort, but they should not impair handling to a dangerous manner. Knowing how much the structure will distort and in what way, is the aim of testing and checking. Some tests must be done while riding, some can be done while stationary.

If you ride gently, then the front end may only need to take three times the static load. If a thrasher, then this can rise to six times or more. Luckily, if suspension is fitted, then the actual force into the structure is gentler, due to shock absorbers which spread the force from an instant shock, to a gentler force over a short time, possibly as long as a second, or as short as a tenth of a second. The tyres usually absorb minor road irregularities. This reduces the shock load onto the frame, but the forces must still be absorbed. As the analysis of the way a structure is loaded dynamically and everyone rides differently, then making the trike to handle three or four times the fully loaded static load will usually suffice for normal safety. If during testing, this load is easily accommodated, then perhaps the trike is overbuilt, or you can thrash the beast a lot more.

Mount one rear wheel on rolling blocks so the frame can spread sideways. The wheels will normally allow the frame to stretch lengthways. If the wheels are not fitted, perhaps just testing the bare frame, then use planks and rollers. This is to ensure no constraint as the machine spreads under the load. To check gradual deformation under the machine, use an extended matchbox mounted on blocks under the frame mid point, so the inner of the matchbox touches the bottom of the frame when extended, and can be marked or measured at each stage. During flexing, the inner will be slid inside the matchbox, and can be read off at each stage, to help generate a graph. Use a matchbox with a stiff sliding action, improved with extra paper in the slit. Anything taller than a matchbox will allow a failed machine to drop too far. Mark with pencil line and the load applied. For basic tests, measure with one rider, then one jumping, then with two riders, and finally measure with two or more jumping up and down. Be ready to support yourself if the frame suddenly breaks.
The crumpled matchbox can be straightened and assessed later.

To see how the machine behaves, a graph can be plotted of load against deflection. Start by gradually applying twice the expected maximum load, as most general purpose machines should be capable of this with minimal flexing. If many plots are made, then the graph may even be able to predict the failure point.

When preferring a subtle approach when loading, it is possible to use two or three dustbins or garden water butts placed on the machine, mounted more securely on a sand bag or a welded support and gradually filled as deflection is measured. If mass measurement is needed, measure the water by pouring in one gallon at a time.
It is important to mount the water butt so that its load will be applied in a similar manner to the ratio of the static load of the trike. If a heavy front end, then place the waterbutt nearer the front. If a light front end, then place the water but closer to the rear. The ideal position would be over the centre of gravity when fully loaded. A reasonable position will often have to be the best guess.
As most vehicles rarely go beyond 2G, in any plane, other than the suspension, then twice its weight is fairly safe, but three times its weight is getting close to a reasonably safe structure.

When filling a water butt, a reasonable load can be applied. Water has a density of 1000 kg/m3. A cubic metre is quite large, but equates to the weight of more than ten average riders.
One litre of water weights one kilo.
If wanting to find out how much load is being applied,
One cubic metre of water weighs one metric tonne. ( 0.98 real UK tons.)
One gallon of water weighs 10 lbs. 2240 lbs per ton. 1 ton = 224 gallons.

Static testing could take all afternoon and best done in the garden.
As big buckets are not too stable, consider using a long plank or small ladder balanced on the seat, its other end on a suitably level item, but free to move. This will keep the water butt level should the frame break.
Always have the water pipe under the water, so that creaks can be heard as the load increases. As the load gets towards the limits, it is worthwhile checking the distortion once the suspension has reached its limits and can move no more, where it is the frame (and tyres) which must absorb further extreme loads. Now the real frame distortion tests can begin, but should not be taken too far, just enough to ensure the frame can take twice the expected load after the suspension has reached its maximum compression.

If forks are removed and not replaced with steel bars, then the genuine bending force on the steering head will also be lost.
At first, the suspension and tyres will compress, then the rubber blocks, and finally the frame will begin to deform. Suspension curve will be a gentle curve, followed by a steeper curve, then as the frame begins to distort, the load will increase for little deformation.

For simplicity, it may be better to remove the wheels and block at the upper suspension points, (upper shock mounts) so that just a frame curve is measured, but this does not allow the tester to see how the suspension load deflection curve builds up to the fully compressed suspension point, then extended into the purely frame distortion curve.
The frame distortion should be fairly straight for a while, then begin to curve. Note the load as the curve starts. This is the maximum load. Relax the load at this point, or if wishing to test to destruction, the curve will get worse, until failure occurs. Failure may be a broken weld, a bent tube or one or more of many other failures.

When the suspension units bottom out, take the process very slowly, and always be aware of any creaks or other untoward noises. Always wear eye protection. At a very basic level, deflection should be proportional to load, to give a straight line. This will gradually deflect more as the maximum safe load is exceeded, so the graph is no longer a straight line. When the graph starts to deviate from the initial line, you know something's getting desperately unfit. Hopefully it's just a weld ripping out, or a tube bending, so take note and stop when you can see the fault. Do not get too close, unless the load is removed, or considerably lightened, otherwise you may get a face full of steel.

A maximum working load (which is not the maximum load, when it can break), but the maximum working load can be calculated from the maximum load to compress the suspension to the rubber blocks, then reduce this figure to take into account high speed heave and roll. About half to two thirds is often acceptable. If the load is too light, the suspension will feel stiff.
For a reasonable safety factor, it is assumed the maximum overall load when testing with the water butt will be at least twice that used to compress both the suspension also the rubber bump stops. These are only rough approximations, so always study your own machines and play safe.

If getting keen, and with at least six points on the graph of load against deflection, (two of the suspension compression and four closer ones for frame distortion), a graph can be plotted of load against deflection. If many plots are made on the graph, then it may even be able to predict the failure point as the curve begins to deviate from the early profile. At a very basic level, deflection should be proportional to load, to give a straight line. This will gradually deflect more per unit load, as the suspension bottoms out and the frame begins to bend seriously. After this point, when the graph is no longer a straight line, then you must go slower, making more accurate plots.
As the maximum safe load is reached the graph will have begun to change from a straight line and stop, and check as the frame may be close to collapse. Therefore draw the graph as it is measured, so any danger signs can be recognised. You may be very happy with a high load and decide not to push the frame any further. It may well take a lot more than you expected, and is not unusual with home made frames, where a cautious approach to choosing frame tubing leads to overly strong metal for the main frame.

Making three different measurements along the bottom of the structure, evenly spaced between rear axle and head stock, will highlight localised deformation and possibly predict the point of highest flexing, which may or may not be the failure point, depending upon the design.
If you feel confident with the graph, you may wish to push further.

If the structure fails, and you are happy with the max load, it may be better to rebuild the frame, as it should not have been allowed to fail more than an inch, onto the safety blocks. It may well be returned to its original state. If this is difficult, then turn the trike frame upside down and do the same again, but to return the frame to its original shape prior to stronger welding at the failure point.

After testing, look carefully for everything from general distortions across the whole machine, to small fractures.
The frame breakage may not be the only failure point.

Soaking the suspect chassis areas in thin fluid such as dyed alcohol, or ink, then lightly wiping dry, so the ink remains in any cracks. Then spray or covering in an absorbent film which will absorb the fluid and highlight cracks and imperfections. Dusting with chalk, or talcum powder from your bathroom, or a thin spray water based undercoat paint often works adequately. This is a cheap variation of the 'zyglo' method used for checking gas turbines etc. Repair if suspect, carve back any damage and repair as necessary. Do not be tempted to simply fill a crack by welding over it until after perfect grooving and cleanliness is done to check the extent of the problem.

If the frame does not break, then seriously consider making the next machine a lighter design, with thinner metal and / or other design considerations. Wherever possible, try until an unwanted frame breaks, as this will highlight the weakest points and offer excellent feedback of the design, its manufacturing and welding abilities and a host of other clues which can only be read directly from the 'failure.'

If needed, return to making a better machine in the light of experience.
Many components can be salvaged, such as the steering head if they survive acceptably. Re-use only after extreme checking for cracks.
The components which did not break should all be carefully studied. The remaining components will probably include the bearing housings, seats and steering linkages which all take time and effort, to leave the next step with 'just' the main frame to build.

Do not get despondent in having spent so many hours building a machine to the highest skills, as this is never lost. Yes, heartbreak may follow such preparation, but the next machine will be even better. A good apprenticeship is never easy. The builder invariably learns a great deal more by mistakes than making a perfect machine first time.

Most trikes are poor, but a few are superb. The poor ones are usually plenty good enough for most purposes, but a few of us aim for perfection in style and handling.
If the second machine is also poor, then consider making a more adaptable design, until the handling is correct. Use the second poor machine as a continuing test rig until a satisfactory design is created. Then use the vital info you have gleaned to build a refined machine from this. Salvaging whole sections from the old machine is often possible by reintegrating engine mount sections, and such like, even if using a very different design, or possibly most of the original.
When just a few problems of flexibility occur, a few gussets or fillets, or cross bracing may cure minor handling problems.

On the occasionally complex or precision machine, testing may take on another level of intensity.
If making a lightweight, or very refined trike, then it would be nice to just use the trike on the road to see what the day to day forces are. Then it is possible to see just how much the trike can take in the workshop, and from this work out the safety factor.
If you have a frame you suspect as being less then strong as you intended, then this will also help you to decide the working safety factor of your machine.

There are many tests to assess the normal forces exerted, so you can statically test the trike later, as you already know the normal working forces.

At a basic level, a digital thermometer can be augmented with temperature sensitive memory strips, - such as where exhaust cooling airflow or cooling from the radiators may be a problem.

It is the frame strength which may worry most people. While testing on the road, the normal levels of stress (load over area) or strain (elongation over original length), can be measured by simple devices. See also Young's modulus in any engineering text book.
Strain gauges need not be electrical, as mechanical deflection devices such as amplified arms can be welded at an appropriate point on the frame, to accentuate movement and to rub on a matt white painted surface somewhere else on the frame to give feedback of the distortion in both directions. A light, flat bar which will not flex in the plane of measurement, by using a wide strip of metal, will often suffice. Similar to the basic, 'bendy bar' torque wrenches, but where it is the frame which bends, not the arm. Make sure it is the frame deflection which is measured, not that of the measuring device. Weld the long, wide plate across the length of the frame, and house the end in soft foam to prevent vibration, and allow a point to rub in a small marker area. This can then be carefully recorded by marking the extents of the flexing during use, by very carefully scratching a fine upper and lower line with a sharp knife. Then the frame can be loaded well beyond this working load to see just how much safety margin is available.

Static load testing, probably with a water butt to the maximum road use, will show how much the machine flexes under road conditions, allowing you to se just how much the suspension has moved and how the wheels align to the road. This can then be loaded further to compare during this non destructive testing to research the true safety margins.

The non-bendy bar in use, when compared to the deflection during static testing is probably your best bet to know just how strong the overall trike actually is. The initial deflection from thrash testing, then compared to static testing until failure will give the best insight to the true safety margin.

For those wanting to know the shock forces on the frame are, then a simple spring loaded pendulum pivoting on a ceramic potentiometer can be calibrated for acceleration and deceleration of the bike or swing arms and other components.
For one G, (acceleration due to Earth's gravity) calibrate with the spring against the effect of gravity. (Turn it ninety degrees).
By using a rubbing mark, then the builder can later read off the maximum acceleration that was acting on the device.
A potentiometer as the pivot of the spring loaded weight, will make a simple electronic G meter. Connecting it to a good battery (not the trike battery which will fluctuate between 12 and 14 volts) and across a volt meter will give a G meter. I would prefer to use mechanical devices as they rarely give false readings if designed well.

Another means of testing is to use electronics such as strain gauges, (although the bendy bar is also a form of strain gauge) but lots of electronics is not only expensive, it does not offer much extra insight, unless running an experimental machine. For most people, a bendy bar will be enough to measure the general parameters.
Real engineering is a craftsman doing for pennies what any commercial company usually does for a fortune. Never be put off by the 'sophisticated' talk and equipment of 'experts'. You can spend a fortune on expensive equipment, but it is rarely necessary. Know the data to gather it and how to assess it. It's not black magic.

If keen, an old laptop or hand-held has analogue, usually joystick game inputs and these are reasonably capable of differentiating between minor changes, then an interface can be built to read resistance's for strain gauges, pressure, temperature and other sensors. Even if the hard drive and batteries have failed, a basic computer can run on 12 volts for simple check routines stored into memory from floppy and stored and down loaded to floppy, powered from the trikes battery.
The BBC micro was a particularly excellent machine in it's day for the purpose of static testing and I soldered up small interfaces and wrote programmes for testing a wide range of things. In 2005, any of the old laptop PCs are usable data gatherers despite their age and can become a part of a test rig. Always mount in foam rubber. Always mount away from moisture or in a poly bag when testing in the rain.
If an old laptop with no hard drive or screen, then make a boot floppy on a desktop PC, so that when the laptop boots, it starts measuring. Then remove the floppy an fit a new floppy ready for the next boot run. Easy-peasy and for pennies. I have three old 'useless' 386 laptops for this purpose; all modified to run from 12 volts supplies because their batteries are defunct. Minimal DOS 5 with a few simple utilities, or with Q Basic will usually suffice. (See my monograph on aerodynamics and wind tunnels for more info.)

If new to this game and just needing a simple counter, use a pocket calculator and connect a wire to operate a switch connected between the + plus sign contacts, then input 1+1= and the switch will count on the calculator for ever. Using the rolling circumference will give an odometer. For rotating or non-contact parts, a magnet and a reed switch are ideal and held in place with glue.
Most PCs can accommodate a variety of simple or complex home made input boards, often using analysis software and virtual oscilloscopes. Basic second - hand laptops with simple home made interfaces are ideal for road testing. Hand help digital oscilloscopes are also useful, especially those with large memories. Cheap temperature sensors are available using a variety of car and other devices.
See my website for windtunnel computer interfacing for pennies to get some idea of the possibilities.

The basics of a good machine still come from optimising the rake or trail of the designs, the wheelbase, centre of gravity etc.
Handling or specific ergonomics must come from experience, so begin by measuring angles and dimensions on the next club run or catalogues and deciding if they have the right answer, or at least the ball park measurements.

Once the frame is good, the rest can now be assessed.

Not all machines will be ideal.
Even the worlds best manufacturers make the occasional blooper. The vehicle industry is littered with vehicles best forgotten, not only by reputation, but also by serious basic design flaws. After an atrocious machine is built, a vastly better machine often appears next time around, in the light of the excellent understanding from the many design hurdles and pitfalls encountered, which focus the mind very effectively.
View a bad machine as an opportunity, not a problem.

Occasionally, an impeccable machine is created. In the JP programme a couple of machines have been created which are sheer bliss to ride. Such machines occasionally exhibit excellent handling, ergonomics or control harmony and occasionally all three.
Never destroy an impeccable machine, but allow others to test it to understand why it's so good. Just knowing it's good is not enough, you must always take this opportunity to understand the fundamentals and subtleties. Always get other riders points of view, ensuring as little as possible is missed from such opportunities.

Some machines 'thrown together' to quickly test an aspect of a design have turned out to be outstandingly good machines.

If not completely happy with the first attempt, possibly because manufacture is not superb, or the ergonomics are unsuitable, it simply does not handle well enough, or a host of other reasons, do not despair. Test ride it anyway to fully understand where the problems are, as bad machines can often highlight what to steer clear of second time around. Only then should destructive testing be considered, possibly with the intention of a partial or total rebuild afterwards.
Much more can be learnt from an imperfect machine than from a perfect machine.

Final testing.
Once a good trike is built:
Very accurately measure the rake, trail, toe in or out, suspension settings and tyre pressures.
Only then can you fully strip, check for fractures and for misalignment between engine and frame etc. Some springing of the frame will occur from normal welding, and possibly after the first few road tests, but not too much if reasonably well designed.
Check the overall alignment of the frame, wheels and engine fitting. If subsequent misalignment is large, then this may be because the engine may intentionally or unintentionally be part of the structure. Modify if needed, possibly a few more fillet plates or an extra cross tube or two.
Sort out the annoying problem that has occurred from the beginning, and add the little flourishing touches that should have been there from the start.
Sort out the nasty little rattle and redesign the constantly fracturing exhaust system. Fit the splash guards under the wheel arches and tidy up the wiring loom. Tweak the gearchange to perfection.
If wiring is not a strong point, learn more and in the meantime buy plenty of fuse wire. (Note for traditional bikers who hate wiring: never waste money buying lots of fuses, simply straddle the fuse holder with correct rated fuse wire and hold in place using a blown fuse. If desperate, use ordinary copper wire from ordinary wiring, and guess a similar cross section of the wire because copper is the same everywhere.)

Decent paint and leather may now be considered.

Perfection is in the detail, - don't spoil it at this stage. Public image may not be the same as the builders image, so consider a variety of form, styles and paint for maximum public effect for all.
Paint and finishing has been covered by many specialist books and magazines and need not be covered here. See also shell later.
Always check for disastrous ideas with friends first, such as colours or floral pattern seats.

The advantage of building the machine oneself is that money, time and skills are the only limitations. Never be put off by all the hype about the expense of racing or development teams. The costs need not be high. Being able to spend money like water is a luxury, whereas being poor is not a limitation, merely a chance to truly understand just what exactly is needed.

Building your own machines and test gear makes the whole process much better understood and develops a natural curiosity with a genuinely innovative approach to design. Having a brain is the best gift of all, use it.

Practical design and manufacturing skills are not that difficult, although often takes time to become refined. Test riding is often a safety based extension of daily riding skills. The refining of designing, building and testing skills as they are developed should not be limitations, but seen as distinct advantages. Designing is often a state of mind with occasionally wonderful insights.

There is no point in building trikes if the builder does not enjoy riding them. Always take every opportunity to enjoy the ride, as this is the ultimate goal of such processes. Always carry a notebook, because further improvement is often just another ride away.

If the machine is so radical that it gets strange looks from others, always smile when parking up, and engage in polite conversation, for the perception of others is always welcome.
A radical machine is often a conversation starter, so use the occasion to advantage. The stranger may well be an old biker to whom you can enlighten to the advantages of new ideas. They will probably want to have their photo taken sitting in it. You may well be invited to the next local bash.
The JP5 when ridden to a show had a massive crowd around it before I could alight. Sometimes I prefer to walk away with helmet on and then quietly rejoin the crowd as another spectator, passively asking questions of others for a true reaction.

You may be followed by police vehicles for a few miles, so get the paperwork sorted, but usually they just want to look and chat, so ride politely and don't bullshit when they enquire.
On one occasion, a radical JP machine was chased for miles across Bordeaux roads to end up in an impromptu photo session by many excited French strangers.

Life is for living.

Nailing an alloy beer barrel on the back for a fuel tank may be saying something, but what do others read into it?
Even ugly sheet steel fuel tanks can be hidden.
The rear of a well engineered trike does not need a bodyshell, but many builders prefer it. Shells are wipe-clean and visually acceptable to the public and keep little fingers out of places they should not be.
An open trike is difficult to get looking perfect, as the many small items must be co-ordinated into a single style, which can be horrendous engineering exercise to get just right.

Shells cover the whole and make the many uglier unseen parts much easier to live with. Shells are ideal for hiding home made tanks, square tubing and to direct radiator airflow.
Shells widen the possibilities for luggage, passenger comfort and aerodynamics. When styling, the shell moulding must take into account the servicing, shape of the fittings such as lighting, cooling and passengers.

The styling ideas are totally personal, so just one tip. Make it look good from all angles and do not be afraid to beat the Italians and British at their own game.

A cheap method of developing a basic sculpted shape.
Decent shells can be made later if required. What you are building is a first attempt, to ensure the aerodynamics are in the ball park, that the radiators get enough airflow and don't overheat the engine, that the passengers do not fall out at every corner, and that the boot (trunk) opens as intended etc.

If in doubt about any aspect such as cooling airflow, then begin with gaffer tape and large cardboard sheets grabbed from behind shops or from recent large purchases.
Use the cardboard to build up an initial airflow test shell for the first few test rides, until the basic shape is decided. All too often the shape is built first, and then modified the hard way when the airflow is inadequate.
The best start is cardboard and gaffer tape lots of it, plus wool strands held by blue tacky office putty in the radiators and run a quiet, open test area. See also testing.
It is not always possible to find a test area for a cardboard test shell to be built up to check airflow. Therefore a first guess is often used, so always ensure the first attempt is as minimal as possible, allowing for hidden air ducts to be rearranged or modified until satisfactory. This usually means a minimal covering for styling purposes, with temporary plastic sheets for under shell adaptations.
If you don't live next to a disused airfield, or even a municipal football car park, then make up big cardboard sheets to fan the air over the rig in the back lane to see how the cotton tufts behave when making the biggest draught possible.

Once the basic chassis, airflow, passenger seating and other problems are sorted, the shell can be built. There are many ways, but a simple and effective way is as follows.

First get the passengers seats, fuel tanks and other parts built and tested. Cover the basic trike with thin polythene sheet to keep it all clean. Food cling film is ideal.
Then build up the trike with large white wall insulating foam blocks. They are available from most building merchants. Restraining the blocks is a problem, but some non solvent glues or double sided tape will suffice. The blocks can be taped or glued together with cheap silicone roof sealer and possibly sewn firmly with string. Anything which will prevent the blocks from moving.
The blocks can now be carved with hot wire cutter, or the very messy sanding disc on an angle grinder technique. (If brave or stupid enough to power sand, do so either in a garage, on a day without wind and have plenty of vacuum cleaner bags and a face mask, or do so in a hurricane.) White foam is cheap and easily cut.

The cheapest method is to scrunch up lots of newspaper and then lay over sheets of paper with cheap wall paper paste, and gradually build up to the shape you want. The make it stronger with more paper or old wallpaper and then with plaster of Paris and unwanted cotton cloth to acheive the final shape. Do one side first.

On smaller trikes, consider using aerosol rigid foam as used by building trade for sealing holes. It sets rigid and can be carved. Another alternative is a two part rigid setting foam as supplied by fibreglass suppliers for filling buoyancy chambers in boats. These are very sticky and the trike must be completely protected with heavier gauge plastic sheeting and this can be held in position with string or tape. Lay the bike on one side, then apply the foam, expecting to smooth the foam around the bike as it sets using cardboard spatulas. This is very messy.

With faom, now perform the art of the sculptor.
The sander, serrated bread knife, wood saw or hot wire cutter will allow the general shape to be developed.

A hot wire cutter.
If using some foams, especially white or blue foam, a hot wire cutter can enable long slices. These slices need not be in a single plane as demanded by a conventional saw.
To build a hot wire cutter, carefully unwind the element of a 1kW domestic electric fire, or heater from an old washing machine or similar item. Stretch this firmly between the ends of a one metre bow, weak bamboo pole or similar, so it is tensioned enough not to distort under the pressure of cutting. A broom handle with end arms tensioned by a Spanish windlass or a spring will also suffice. There is no need to straighten the wire fully, as it will straighten itself wonderfully when heated. It need not get red hot. (Mine stays the same dark metal colour when cutting.)
Connect each end of the wire to a 12v transformer output such as a domestic car battery charger and test. If it does not heat up enough to cut cleanly, use a larger amperage transformer, or tap off prior to rectification, or position one of the connectors to heat a shorter length of the wire.
Although accuracy at this stage is not important, a length of hot wire longer than is needed is not a good idea, as excessive bowing of the cut can ensue. Likewise, if the wire is too short, the ends will cool too fast and will not give an even cut.
Speed of hot wire cutting is important and must be decided by the pressure felt by the builder, as bowing of the wire will cause a variation of cut. Greater wire tension is a solution, but hot wires can only be tensioned so far, whereupon a shorter bow, hotter wire or variation thereof must be contemplated. As this is only to crop the outer layers of foam, there is no need to get too sophisticated.

The use of pinning profiled thick card or wooden side plates on the foam will allow the wire to be cut along an intended path. Reversed, they will allow perfect symmetry on the other side. This has been the stock in trade of most model aircraft builders for many decades. Before doing so, mark out the centreline, using a piece of string from steering head to rear mid point.

Further shaping.
When the basic shape is carved and is slightly undersize, apply plaster then smooth to get the shape perfect. Where the foam blocks leave gaps next to the seats and other areas, simply use a mixture of plaster, cloth and foam bits to fill the gaps.

At first, get one side sculpted as needed, then mark in the centre line and use cardboard or wire templates to copy this profile to the other side.
Thick wire templates allow you to modify the template on an ad hoc basis.
If one side of the foam is cut and shaped, these wire template can be bent to fit. When heated they can mark the identical profile of the other side in the foam for easier sanding or cutting to shape, or simply to melt the rough profile.

If the shape is not what you want, simply add more plaster, or sand away and continue until one side is perfect. If not too sure about how it will look, splash on some cheap poster paint or some pigmented plaster to see how it will approximately look. If you have shaped only one half, use a long, dress mirror on the centreline to get a double sided view.
When the shape is finalised, smooth the whole and make a symmetrical profile on the other side. Take time to get it perfect.

Where needed, carve out the gaps to fit the tail and side lights.
Go berserk, pop down to the scrap yard and get those tail lights and fog lights you always wanted to use. Mask up the lights with tape or thin polythene film then fit in position using a little plaster to hold in place. Then smooth to blend into the profile. The light mounting brackets can be moulded internally after the shell is built. Likewise fit other items which need a carefully profiled interface with the shell.
When the lights are removed and the fibreglass laid up, the lights can be covered in polythene, then pushed into the fibreglass just before it begins to set, to make a perfect fit.

If air scoops are to be used, (always recommended, even if only for dummy styling purposes), then carve the smooth radiuses just enough to allow internal ducts to be added inside the recesses later, to make sure that the moulding can be removed.

The seats should fit neatly and be covered in bin bags for protection.
Do not forget the moulding around the side lights. Always allow the lights and other items to stand off the shape by a few millimetres, as this is to account for the layers of glass fibre and resin which will be laid on the profile. Ensure the various items will lie flush when the shell thickness is built up. This is not too important, as the various items such as tail lights can be adjusted to lie flush later, before final brackets are moulded in place.

The above use of plaster allows the shape to be refined, easily shaped and built up over and over again with more plaster until perfect. Take full advantage of this opportunity to search out the best shape of side and other light units from the many cars available, to integrate into the plaster shape to best effect.

Extreme customs can take just as long to create the styling as it is to make the rest of the machine.

The act of integrating the tail lights and number (licence) plate can become a work of art in it's own right. Sculpting the recessed hi-fi mounting should keep it clear of most rain while remaining stylish. Even the access hatches to the electrics can be sculpted to stylised panels to blend in with the overall form of the machine - simple square openings are rarely necessary. For some, the styling just will not appear easily, taking weeks until the subtlety becomes refined enough for public presentation.
For many, this is the best part of trike building, where the imagination runs riot.

If you find yourself just standing and looking for an hour or so, with a cuppa or beer, do not worry, this is quite normal.

Use a pencil to highlight and develop the styling lines in the plaster work as it develops.

When all parts are fitted into the foam and plaster shell, the lay-up is almost ready to begin. Do not forget items such as the radio slot, any top, bottom and side vents and air scoops, also the badge and fuel filler recesses. Keep all access hatch screws flush and never fit any accessory or item which will impale or damage the rider or passengers.
The simplest theft proof panels are flush fitting and bungeed from behind, requiring blue tack or a sucker from a kiddies arrow or bathroom sucker hook to remove them enough to unhook the bungee from behind. Dummy screw heads will also help. Dummy screw heads can be mounded by using a genuine item as a mould. Prefer the unusual, torx or safety screw head, so vandals are deterred further.
One of my favourite openings is to cut the hole neatly in the shell, then put a small shoulder step on the rear, so the cover lies flush. Then simply put a bungee on the rear of the pannel to keep it in place. To open the panel, simply leave one corner of the support shoulders on the rear missing, so that pushing that particular corner allows the panel to lever open enough to get the fingers behind it. Ideal for engine and battery access, hiding hi-fi, or glove compartment etc. Fitting dummy screws further reduces the chance of theft.

You can always cut the shell later but if you have the mould in place, then take advantage of it for greater styling and accuracy.

Where major openings or slits (cut lines) in the shell are to be made, then it may be useful to make a shallow accurately aligned groove then inset a piece of thick vinyl covered wire or waxed string. This should stand proud of the underlying shell mould, to create a thin recess on the inside of the main moulding, allowing an easier cut very accurately after the shell moulding has set to accurately segment the one piece shell.
To accurately mark any grooves or cut lines, use a chalked piece of string pulled taught over the shell profile. Then draw the string back and forth for a neater line in the plaster.
Where the cut lines are made with string cut into the foam and plaster, a thick plastic strip can be slotted into the groove, to make a plastic wall, allowing the shell to be built in separate sections.
Where the shell is to be later sliced into separate sheets and is of a structural nature, then also carve two strengthening ridges into the mould an inch or so either side of the proposed cut. Do not make the strengthening ridge on the cut line unless they are to be bolted together at the cut line, as the slicing may not align perfectly. It may be better to align and make mounting brackets later.
If the shell is to be separate pieces, then the string can cut a deeper cut, a thin sheet of waxed metal, firm cardboard or plastic inserted and the groove deepened to create flanges.

If the shell is to be a single piece, then take this opportunity to carve strengthening ribs into the foam and plaster profile, to ensure it will retain it's shape as intended. It is very common to fully remove a one piece shell, especially ultra light shells. Therefore it is important to ensure it can support it's own weight when off the machine. Such shells may be hinged for easy access, so will need suitable internal bracing, applied now and refined later.

When all is ready, wax the shape using anything suitable which will allow fibreglass to be removed. Simple candle wax will often do, but do not crack the plaster, so warm the wax and apply with a gentle touch and a hot air gun or old iron or similar. Margarine, grease or the kids old crayons will also do, but may get messy. A couple layers of cling film separated by a thin layer of water may suffice.

Begin by building up the various strengthening ridges in fibreglass and sand them smooth until flush with the profile. Then cover with layers of fibreglass so it is sufficiently strong. Always try to mould it smoothly, followed by sand papering to remove surface imperfections. Pulling on the fibreglass cloth before it sets can give a smoother shape. Build up until sufficiently strong, then smooth again.
While laying up the shell, cover the tail lights in masking tape and offer them up into place to make sure the tail light sockets are perfectly accurate. This is best done just before the green stage, just before the resin is beginning to set.

Remove the lights and seats, then carefully peel off the shell.
Clean and trim to thoroughly to remove any imperfections. The shell may still be a light, flexible structure, so handle very carefully. If very light and flexible, place it upside down on a partially inflated beach air bed.
Thoroughly scrub clean the inside to remove any wax, then build up the inside of the fibreglass shell with more ribs and gussets to create any strengthening and mounting points needed. Simple ribs can be built up over rolled paper, folded card etc.
Cover the lights in polythene. Tape the lights in position making sure they are neatly positioned, then use them to accurately mould their inner mounting brackets in fibreglass.

Loosely mount the metal shell mounting brackets onto the frame, so they will align and support without distorting the shell. Adjust the shell in position on the frame. When aligned, tack weld the final positions of the brackets to the frame. This will allow the shell to fit perfectly, without any undue stresses or distortions. Now the shell mounting lugs can be fibreglassed into the shell. When set, they can be unbolted and the shell removed for more strengthening in these areas. Always make sure all the items can be easily removed.
Remove the shell, then use the internal grooves or ridges to cut any slots or into sections, or hatches to service the engine, access the trunk (boot), fuel cap, or replace air filter, fuses and such like.

The waxed string lines will now make themselves very useful.
When cutting the shell into separate sheets after it has been made, such as a centre section and two side sheets, then fit the basic shell on the frame before any gel coat or finishing, Then mark the proposed cut line with a stretched string, so the line will lie as neat as possible, then carefully use a ruler to make the initial cut using a sharp knife. Hopefully, the internal cut grooves from the plaster profile will have been made beforehand to ease the process. This can then be cut deeper until it can be used to guide a hacksaw blade. Use the blade at a shallow angle to keep the cut line straight or gently curved. When refitted on the machine, use waxed cardboard or thin plastic sheet between the gaps to ensure the gaps remain neat and even when building up further layers and ridges. These gaps can then be sanded smooth with sand paper wrapped over a piece of thin metal to ensure a straight, or gently curving, neat, even gap. Always integrate cut lines into the styling profile.

It is extremely bad practice to have a cut line down the centre of a shape. Bugattis excepted.

When applying a pigmented resin or gel coat for many components, mix just the resin and pigment fully, but do not add the catalyst. Then decant to smaller containers, for use with greater convenience when required and to later allow a perfect match should accidents occur at a later date. Then use the pigment coat with catalyst only when needed.

Once the shell is removed, leave the foam or scrunched newspaper in place on the trike, then carve the luggage spaces, hi-fi boxes and air ducting from any airscoops towards the radiators. It is now possible to lay up these in fibreglass for very integrated components which could also fit and perhaps support the shell perfectly. This is the time to include ducting for heated components such as exhausts, where heat shielding can be formed in metal or in fibreglass with alloy foil coating.

A difficult case may be a transverse V6 with turbo, where some fresh air ducting may be needed, possibly from underneath, or an upper airscoop in the shell, plus a heat shielded area and rear hot air flow vent.
As making smaller ducts is difficult to carve, simply use a small powered sander or a powered wire brush, or perhaps a heated piece of metal which will allow the foam to be sculpted into perfect ducting. None of these will damage the chassis components if cutting a little too keenly into the foam. In some cases, such as luggage containers, then the base should be carved until flush with the chassis or superstructure for support of heavy luggage.
If preferring to make the ducts to shape first, then simply carve and sandpaper the required duct in white foam, cover in cling film and fibreglass to shape. The white foam can then be picked out or dissolved in petrol.

When making ducts for external components, it is best to position them for aesthetic and aerodynamic reasons on the shell, then cut out the holes in the shell using the ducts as perfect guides. External scoops should be made in cardboard until final testing on the road.

For those with low mounted radiators, it may be necessary to copy the foam sculpting process after turning the machine on its side, to allow the lower half to be an efficient airflow design. Aim for a low pressure zone at the rear to help extract the air at the rear of the machine, in the same way as formula one cars.

After the shell is built, it may be necessary to fit extra strengthening ribs underneath, often where the shell is sliced.
Where the panels are to bolt together, a thin, stiff, waxed plastic sheet can be slid in the gap and two internal flanges can be built up either side from the inside. The flanges can be built up form sheet fibreglass or plywood. When set, these flanges will align accurately and can be drilled for bolting together. A thin rubber sheet between panels and rubber washers will prevent water ingress and reduce rattling and fracturing.

Now is a good time to mould in the tubing to carry the wires to the side and tail lights if the lights are moulded into the shell. It is often preferable to be able to lift the shell section off as one, needing to only disconnect a single multipin electrical connector for convenience.

Where the shell section is also part of the radiator ducting, do not route the cooling fan wiring into the shell, but keep them routed on the frame with the radiators. If the shell gets trashed, you can still get home.

Where people are going to be sitting, it is preferable to build the seat base and possibly the backrest as part of the frame. If the seats are to be part of the shell, then reinforce locally to ensure this area will be supported on the chassis by moulding directly over the frame support tubing. Position the tubing for the seat support, cover the frame tubes in polythene to allow for easy removal and build up the seat base along with the rest of the shell.

Under the shell will be problems requiring further panels or ducts. Check whether there is a need to build up the undersides of the shell to deflect rain coming off the wheels, to stop it going on the passengers, engine or electrics. Such items may be best mounted onto the frame, separate of the shell.

For those who have an engine with expensive components, a full bottom pan can be moulded using similar methods as the shell. Preferably in such a way as to improve airflow using techniques similar to formula one to improve airflow or for cooling the exhaust and engine parts. It is unlikely that a general purpose trike will be able to have the bottom pan low enough for low pressure ground effects, but it looks good for shows and can improve radiator and exhaust cooling.

Some parts of the shell will want to vibrate, either in harmony with the engine, poorly balanced wheels or quite often from wind effects. These can be reduced by extra internal ribbing or brackets, or selective use of tarred felt to act as a mass damper, as used in cars. A little extra strengthening fibreglass moulded over a piece of folded cardboard or rolled paper is much lighter and stronger than tarred felt.

For both safety and for styling, it may be necessary to fit mesh or slats in the air intakes. Wire mesh comes in many sizes, so choose to match the styling. Never use variations on chicken wire unless it cannot be seen. For light weight machines, some suitable nylon coated netting is available from camping and caravaning shops.
For slats, an old venetian blind makes a good set of formers upon which to build up a set of identical slats. These may be temporarily mounted in the shell with blue tack, waxed and built up with fibreglass. Removal will reveal perfect shapes, preferably on the upper surfaces, where the public can view. Or simply leave them in place and just build up the undersides. Slats also make excellent and stylistic rear air vents, where the rear of trike styling often leaves much to be desired. (Ferraris excepted).

Remove all fittings and apply a final layer of pigmented gel coat or various layers of paint over the smoothed fibreglass body, then cut back and polish out imperfections. If painting, spend many hours to cut back and smooth any imperfections prior to spraying.

If making seats is daunting or are building on the cheap, then use car seats as a starting point. Make sure the seat padding can allow rain to drain away in the gap between squab (backrest) and base. Use porous, non absorbent foam or many small drinking straw sized pieces of nylon tubing glued in position between base and squab to allow water to drain away. This is another advantage of having the passengers reclining backwards at a gentle angle.
Ask at any motorcycle or car workshop, they often know someone who will cover custom seats. Always retain the original seat covering, as the seat maker may need them as patterns for covering standard seat foam profiles.
For leather seats in the rain, seriously consider using waterproofing leather preparation. Always add discrete drain pipes in the join between the base and the backrest. A gap tends to lose loose items, such as trike keys.

Keep all access hatch screws flush and never fit any accessory or item which will impale or damage the rider or passengers.
For those aiming for the posh end of triking when using carpets, then use removable, washable polypropylene, nylon or similar. Snap studs make removal easy for cleaning. For those who may prefer a traditional form of styling, there is no reason why a trike cannot use connoly hide and have polished walnut trim. Again, keep the original seat covering for the leather worker to use as patterns to match any standard seat foam. For walnut trim, it is best to recess the wood area and use chrome trim from coachbuild suppliers. You will be surprised what is available.

If a hydraulic jack is used to raise the shell for custom use, simply tap off the engine oil pressure side, though a small hole into a small bore pipe as used for oil pressure gauges, and pumped into a modified car rear hatch stay, as this reduces the need for a separate hydraulic pump and any expensive componentry. Alternatively, the guts of an electric / hydraulic car convertible roof mechanism or electric car seat mechanism can be used.

Aerodynamics is not directly part of trike construction, but for those who spend the effort, it can make the design better in many possible ways.
If your trike behaves badly at high speeds, then some aerodynamics may be needed.
The following is far beyond that normally used on trikes, but occasionally, someone will make a machine which may need some of the following, possibly for studying high speed stability. If Merc can get it wrong at LeMans 24hrs, then all builders should treat high speeds seriously and with care.
If making a shell, then aerodynamics is always a good way to maximise the top speed from the power available. Good aerodynamics also improves comfort for the rider and especially for the passengers. It can also help solve some handling problems and improve radiator airflow for engine cooling at maximum power and even the cooling in heavy city traffic in high summer.

Lighter machines are more prone to aerodynamic variations than the mass of a heavier machine. If a very light machine is built with a rear shell, and uncommon problems occur, especially at high speeds, then always consider the airflow along with the many other common causes. Front spoilers, airfoil or variations on such themes, such as an angled screen may be needed if the front gets too light and skittery with speed.

As speed increases, the centre of pressure should be close to the centre of gravity. This is unlikely for trikes, but gives a general direction of what to aim for.

A great deal can be written, but until fully developed, here are a few pointers to help get some ideas up and running. -
The conventional trike is an aerodynamic disaster area. Enclosing the trike has been done on rare occasions, but rarely for aerodynamic reasons, usually for show use only. Aerodynamics may not be generally acceptable or always applicable.

Never confuse aerodynamics as simply the use of a wind tunnel. Aerodynamics is the general approach to airflow over a body. Even simple improvements can be considered aerodynamics, although some simple aftermarket 'improvements' may not always turn out to have such positive attributes as expected.
The wind tunnel and it's associated testing systems are often applicable and many of these practices are available without expense.
The subject of aerodynamics can be read in a vast number of books on the subject. This area takes much development time, and unlike most aerodynamic work, this should be done mostly in full scale, in real environments. Cars with four wheels do not suffer the handling demands of the trikes with it's single front wheel which needs greater rider feedback for control in difficult areas.

Testing a trike at full scale in real conditions may seem less than ideal in an age dominated by high tech wind tunnels, but such luxuries are rare and trikes do not live in an ideal world as assumed by wind tunnels. Wind tunnels are great for formula one, but they do not have to live in, or even simulate the real world of traffic. Formula one often dislike the high side winds at bleak circuits such as Silverstone, upsetting their highly refined settings for the ideal world of sheltered circuits. Wind tunnels are good for some things, but simply cannot afford other machines with the serious and varying situations they encounter in the real world.

The main aerodynamic areas of concern are not overall speed effects from the traditional analysis of frontal airflow, but general cleaning up what is there, to ensure the cooling is safe and the passengers a get minimal buffeting. Trikes are aerodynamically messy and fairly difficult to get close to an ideal, where aerodynamics can only be of limited help. A trike with it's open front wheel and sculpted rear half has only one, narrow front wheel, so can be good for airflow with a mudguard and other ways to clean up and attempt to control the airflow. The bow wave is a major concern for cooling.

Side winds can only be tested in the real world, as a wind tunnel is usually incapable of simulating bow waves such as when passing lorries, buffeting or intermittent and side winds near high interrupted buildings.

The type of forces which may be encouraged are such as downwards at higher speeds, perhaps because of the need for a lighter front end to assist low speed handling and manoeuvrability, or because of poor engine choice, causing a light front end. Some designs could induce a possible lightness at higher speeds but can be counteracted at speed by a belly fairing, airdam or windscreen. These could act downwards against oncoming air and some downforce panels can be disguised as headlight screen covers. Also consider sensible airflows around the lower sections and through a wide belly pan to control any pressure build-up in various areas. At high speeds, there is a lot of power being applied at the back wheels, so ensure the front is also capable of maintaining it's control on the road.
Never let a trike front end get light at high speeds, as there are many influences which may try to upset the steering, from imbalanced brakes to unusual airflow and dangerous road surfaces. It is for this reason that powerful trikes should get the weight balance sorted at an early stage of design.
Side ridges and other top, frontal and rear end refinements may be applied later to offset some effects, as seen in back window edging of the MK2 Sierra.

The trike is not an aircraft generating positive lift, more like a formula one car generating increasingly negative lift with speed. - A clean block moving forward, generating the minimal resistive forces. Because some trikes and rider are quite tall and therefore susceptible to front wind, then whatever can be done to reduce rider drag is useful. Whatever the drag forces that must inevitably be generated, they should be as neutral as possible.

Tail vortices can cause snaking on some aircraft, and as the whole machine could be compared with other dubious machines, especially with a light front end. To use an old phrase, 'the tail wagging the dog'. Much attention may need to be applied to ensure the tail airflow is as clean as possible. Large, dirty airflow over a large tail section may upset the stability of the trike, from frontal airlfow and also from side winds.
Tail airflow should also help to extract air from the rear of the belly pan to assist engine cooling. The tail of many exotic and custom machines can have interesting aspects.

Without a wind tunnel, airflow studies need not be compromised.
If the real world cannot work in the wind tunnel, then turn the problem upon its head. Use the world as the wind tunnel. Like JP crash testing, if one can't get help from the experts, then study their work and do it anyway. (Always be careful when crash testing with real riders, although this can also lead to radical new ideas in crash design and more intensive, first hand appreciation by the designers. First hand crash testing always gives deeper insight to the design needs and possibilities.)

Wind tunnel testing equipment can be taken to the real world. Real assessments can be done in real time on real machines on real roads. Pressure gauges, airflow sensors, smoke probes, pattern assessors and a few of the authors new methods awaiting patents, can be backed up with various data collection and video. These allow most appropriate wind tunnel practices to be applied and more importantly, can do so in real time and at full size.

Most machines are steel framed mechanical devices, with airflow control devices added later. Therefore the adaptation according to feedback can be done easily without upsetting the underlying structure. (Unlike most modern cars.)
Some trikes can be designed from the outset to be aerodynamic as possible, from the minimal frontal area to the overall initial chassis and rider layout. Such high specification trikes are often designed for long distance touring or for top speed with minimum drag.

Choice of landscapes must be chosen to maximise the worst conditions available by airflow over the countryside and in cities.
Using local test sessions and scenarios gives regular, fast and interactive changes to refine the aerodynamics, and of course, there is no need to book expensive wind tunnel time. The testing schedule should be based on the highest, bleakest moorlands during winter and in the windiest towns. This can also give a fine selection of both fast roads with the highest winds normally encountered, with a choice of both clean air and maximum turbulence plus a wide variety of buffeting scenarios. It also has fewer vehicles in the way to allow much better testing.
You may occasionally find the author on Dartmoor in winter with a radical machine, adhesive tape, cotton wool, home made smoke probe and pipes and a video camera.
In such environments, get out the cardboard scissors and gaffer tape, the wool strands and smoke probe. If nothing else, you will get much better radiator airflow.

Once fettled and road legal, the trike can begin to explore bleak sections of motorways in winter with high sided lorries to assess intermittent buffeting, bow waves and whatever else could be thrown at the design.
Wind tunnels may give 'tight' data, but the excellent scenarios of poor, twisty roads in high, buffeting winds probably give better feedback than any wind tunnel could ever hope to achieve. This also allows the rider to feel the true effects needed for improving the handling of trikes. Trikes are unlikely to improve their aerodynamics greatly, but untoward effects such as airflow causing the rear to behave badly (tail wagging the dog) can often be recognised and corrected or ameliorated.

The ability to apply many techniques to real life scenarios does not limit the study, as videoing of airborne particles gives the direction, speed and orientation of the whole airflow which can be measured in single and sequential stop frames. Park the machine on a windy ridge and throw evenly chopped straw into the airflow. Do not use polystyrene chips as these damage the countryside. Straw is available from pet shops, so buy some sharp scissors and start cutting.
Always transfer the video to digital for storage on a computer, as there will be much time spent analysing a selection of single or sequential frames, which would otherwise damage a tape. The length of each strand of straw will be streaked, allowing the distance to be measured and thus the speed, as calculated by the exposure time of each frame. Usually, just comparative speeds will suffice, as it is easy to plot the different speeds across the machine, to see what is happening. Only when maths is involved will the actual speed become relevant.
Conducting the tests in various windy areas at various speeds with video, allows the various changes of airflow with speed to be studied at leisure and videoed from all angles with airflow not only from the front, but also from various side angles.

Use cotton tufts stuck on the machine then ride at various speeds to video external and internal flows just above the surface layer. This can be done in any weather. For radiator exit airflow, use longer lengths of wool knotted and pulled though the radiator fins. On conventional machines for road use, the cotton tufts will highlight a great deal of airflow as well as highlighting positive and negative pressure zones and are easily attached and removed using adhesive tape or blue tack.

For those who wish to use the classic smoke boom, this can be done statically in high winds, or on the trike at high speeds. (Should be done on old airfields or quiet roads.) When testing on the road, smoke generators should be fitted on the machine and vented in various positions to assess overall, general airflow. Most plumbing suppliers stock smoke generators for testing gas flues, or consider fireworks or using a small hand held, static, pyrotechnic flare as used for emergencies at sea. Do not use the rocket/parachute type of flare. Use in a safe, lightly pressurised metal container and duct via a selection of pipes. If of a pyrotechnic nature, use a large metal container and position a downwind vent pipe to prevent excess pressure generation and never use on normal roads.
If too much smoke is supplied, carefully deconstruct pyrotechnics outdoors using safety clothing and a bucket of water nearby. As emergency flares are available in various colours, choose a colour to contrast with the machine to highlight the airflow.
To ignite a soft firework at the appropriate time, simply wire a thin piece of steel in the touch paper and short it via two thicker wires and a switch via a battery. Simply choose a piece of wire so it glows when shorted across a large enough battery, most torches (flashlights) will suffice for ignition supply. Also consider using wire wool and the ignitors from model rocket motors and also a few match heads. Done properly, a smoke generator can be triggered from a simple handlebar switch. Allow a little time for generation, so trigger well before the test run area. If triggering is problematic, the fuse section of bangers and the heads off waterproof matches will help.

Smoke generators using a heating element and special oil are also possible, as used in discos and adaptable for the hot exhaust system as a generator. This will require an exhaust box clamped over a hot area, plus a fast oil drip feed and such like, plus an upwind pressurising system to ensure reasonable smoke flow, but is preferable for stationary testing. It is now possible to buy party smoke in an aerosol.

Although predominantly for dynamic airflows, smoke can be used in a quiet garage while testing for overheating in a simulated summer traffic jam. This is particularly useful for air cooled machines. Place smoke candles under the motorcycle while it is running hot, to simulate traffic jams on hot days in still air. Remember where the most overheated vehicles are seen, usually part way up a long hill on a bank holiday on the way to the seaside. Always check your machine for all forms of aerodynamic problems.

It will take a little time to get a good smoke probe, as it must be designed to minimise any disturbance upstream. Old brake pipe or similar tubing may often suffice for the boom and nozzle. Make sure the tip is a smooth aerodynamic transition to the airstream. Use the bow wave to pressurise your smoke system.
A passenger on an accompanying motorcycle or car can do the videoing from sides and rear, or the video camera on a broom pole.

If wishing to understand the airflow over the rider or shell, use of a surface layer 'slime' across the shell should be water based, so the machine can be hosed clean afterwards with a pressure washer in a trials bike manner. When an emulsion is painted on the machine, study of surface flow is possible, but is very messy, so use after the chopped straw and cotton tufts. Different coloured streaks can be painted into the slime tangentially to expected airflow, to highlight airflow direction and strength. Almost anything will do, from emulsified olive oil, or water based lubricants and many adaptable foams, gels and such like at the discount beauty counter of most chemists. Streaks are easily made with simple poster paints. Then test on the motorway. Some slimes will be affected by the cooling effects of high airflow on cooler days, so choose the materials according to the weather. If expecting rain, oil bases are better. Rain should not be seen as a problem, as it will help the process with its greater mass of the drops to deform the heavier oil based slimes, but only for a short time. Always take videos or photos immediately after a slimy test run. Then look for dead spots, especially where cooling airflow is important. Look for dead spots or where the airflow is reversed to that needed.

In rare cases, it may be necessary to see where pressure build ups or low pressure zones occur. Where a handful of pressure probes are needed, to see where pressures build up or extraction is effective, cheap and simple water manometers can be mounted on the side panels with blue tack and makes life very easy by using simple tubes and coloured water against a contrasting background.
Use car windscreen washer tubing which is clear and flexible. Lightly cover the atmospheric ends with cotton and tape to prevent spurious readings, or route the pipes to a known 'dead' area of pressure. The position of the static water line is not important, just the relative differences between atmospheric and the point of study. If a specific area of concern, simply have the sensor end of the pipe on a stick and have the passenger move it to see where the pressures vary. Carburettor vacuum gauges are rarely sensitive enough. An old barometer can be modified to read various changes in pressure, with an extension tube for remote readings. A digital barometer is often a good option.

There are other methods mentioned in companion monographs, but are rarely applicable to trikes unless a wind tunnel is employed. It is not easy to make a full size wind tunnel to take a trike, although details for cycles are described.

More stuff on aerodynamics from 'A builders guide to wind Tunnel Design' on my website.

Aerodynamics also includes engine cooling which used to be a problem before water-cooling and radiators, but today there should be no excuse for the many strange airflows causing cooling problems. Modern radiators can usually be positioned in cleaner airflows, often with minimal drag.
If belly pan or ground effect airflow is problematic or suspect, simply position a set of smoke risers on the road in still air and drive the machine through the smoke risers while videoing the effects.

Do not be afraid to simply let the machine get hot in still air in the garage and place a smoke candle under it to see if airflow is adequate, when imitating a traffic jam on a hot day. Remember where one sees the most numbers of overheated vehicles parked by the side of the road, so always design the machine to be reliable.

When videoing any of the methods, always hold the video in each position for a few seconds to get a decent sequence.
A vast amount of aerodynamics can be studied without recourse to wind tunnels or electronics. Airflow is a fundamentally basic physical phenomena, which can be measured by equipment developed a couple of centuries ago.
No formula one machine leaves the computer labs and wind tunnel ready to run perfectly. It will leave in a 'ball park' condition, with most of the refining work done by road testing. This applies to all machines used 'near the limits'. Even for trikes, the final adjustments are done over years of pragmatic, hands on testing.

Full scale road testing not only gives objective data, but also the very important subjective assessments only assessable by road testers. A variety of testers will always give better assessment of handling.

Welding is the ability to fuse two pieces of steel together by applying sufficient heat to melt them in a localised spot and if necessary, to add some extra filler metal.
The main welding is electric arc, with either a stick welder, (Manual Metal Arc) or a Mig (Metal Inert Gas) or oxy acetylene. (Gas.)
The picture shows the authors stick arc welder at the top, with the electrode partially worn down. This is useful mainly for steel fabrication and little else, although specialist cast-iron grooving and welding sticks are also available. This uses a simple stand-alone transformer which can work off domestic mains electricity.
In the middle a Mig welder handle with trigger, and the thin welding wire exiting the nozzle which also creates the gas shield. Suitable for most welding of steels, including stainless and aluminium with the appropriate gas and wire. This again uses a stand-alone transformer, but also needs a gas cylinder to create the shield and a motor to feed the wire, which are usually included.
Below this, a standard oxyacetylene mixing handle with a copper nozzle tip. Useful for most metals and also for tempering and hardening processes and many other heat related processes. You will need to rent oxygen and acetylene bottles from a commercial supplier, usually for ten years, then purchase the gas and return the bottles for replenishing. There are small cylinders available which are no bigger then camping gas cylinders for those who do jewellery and small work, right up tot he large industrial cylinders. Always take complete safety procedures with handling of the cylinders, storage and preparation. (See supplier for full safety information - then follow it.) It is possible to flame weld aluminium and the author has done so, but it is very difficult, a bit like trying to solder cheese.

Safety. Welding causes sparks to fly, so no combustible material must be near the welding area. The welding arc is very bright and everyone must be shielded. Welding eye is very dangerous and may last for months, in bad cases it can lead to loss of sight. Always use an approved welding glass. Always throw away a cracked lens. The electrics will need a carbon dioxide fire extinguisher.
Do not cool welded metal in water, as this will cause hardening and cracks. Always ensure a good earth for the welding metal, as a poor earth is accompanied with a poor weld. Always set up the weld to give a comfortable handhold. Always make a couple of practice runs to check and adjust the settings.

Head protection is done with a face mask with a heavily tinted lens. Over the lens is a piece of clear glass, to be easily removable as weld spatter will eventually build up. The face masks may be either hand-held or on a head strap. The head strap must have hinges, to allow the welder to see where the work is, then get into position before a nod of the head allows the mask to fall into position. Rubber washers in the adjustable hinges make life easier. The easiest mask has a light sensitive LCD screen which is transparent when no welding arc, but turns dark upon seeing the weld arc and these are expensive.
Always wear a full length leather apron or similar clothing when welding, as the spatter will burn many holes in clothes. An old (thick) leather coat can be recycled for this purpose. Not-too-thin pure leather gloves are also useful, especially when handling hot metal parts. More spatter is likely to fall on the welders feet than the hands, so never have the boot openings such that they will allow weld to enter the boot, it is not fun.

The two metals can be joined in various ways, such as end to end, or a T or other join. The weld must penetrate sufficiently to be secure, and this means full depth. On thin plates, this may only need a single run of weld to sufficiently penetrate to the other side, ensuring full penetration. On thick plates, then the weld may be done from both sides.

The simplest and still the most effective welder is the manual arc welder. This consists of a transformer to step-up the mains current sufficiently to be capable of welding steel and is quite adequate for bike and small vehicle frames. The currents are usually from 30 to 1000 amps at about 20 to 40 volts.

The heat is generated by the arc. This is the jumping of electricity between electrode and the metal to be welded, creating a localised hot spot which creates a pool of molten metal.
If the metal had no gap, then little or no filler rod would be necessary. But due to the nature of the manual arc welder, the filler rod will still deposit some extra metal so a small bead will form above the join. It is for this reason that a small gap is sometimes left, which also helps the arc to penetrate fully. Full penetration is best seen by a small bead of excess metal on the other side of the weld.

The gaps and welding current will depend upon the materials and conditions and this is where the welders skill becomes apparent. This involves the choice of welding current, the rod size, gap and speed of weld. To this can be added subtle skills and the teasing of the welding rod over the welding area, and being able to read the way the weld progresses, to give superb welds which can be an art form when done properly.
Beginners will not always make superb welds and getting to know the art and preparation will take time. For this reason, it is recommended to get professional help and to practice, as much as an hour a day or a week may be needed to become basically proficient, but years of welding are needed to match the professionals who make it look easy and who create excellent welds.
Practice, practice practice, there is no other way. If you know a professional or good welder, get them to help you to practice. Welding is an art, but do yourself a favour, read the basics and practice adjustments for different scenarios until you are fully conversant with most conditions.

The hardest part when learning is the striking the arc. This is not unlike striking a match, where the rod and metal are struck against anther just enough to create the initial arc, and this is then kept just above the metal to ensure the arc is maintained at an optimum for the weld pool of molten metal. A steady hand is needed. Eventually the strike is not needed, just a dab on the parent metal and away you go.

Practice striking the arc with the power off, by striking the tip for a few millimetres along the metal and then keeping the tip about five millimetres off the metal. For your first time with a stick welder, practice twenty times before switching on as this will save damaging the tip when power is on. If problems still occur, try practising with a short welding rod and a heavy gauge rod and parent metal test piece. Beginners will find using a short welding rod will make handling and striking the arc a lot easier, but this should only be a temporary aid to learning.
If a hole is burnt in the metal, reduce the current. If the weld sticks on the surface with little penetration, increase the current or change the speed and height above the workpiece.
Use a long pencil and try writing a comma on a piece of paper, then lift the pencil off the paper by five to ten millimetres, to write a line of V's or O's in the air towards the angle of lean of the pencil. Keep the pencil at about 75 degrees towards the vertical. Now do this while not being able to see the strike point due to the welding lens and with a 450mm long metal pencil. You get the idea.
When starting, it is easier to cut the welding rods in half and to bend the welding rod in the handle for an easier position. (See blue handle above, with welding electrode bent downwards slightly.
Setting up the welder on a test piece before attempting important welds is a must and well worth a few runs and the cost of a welding rod to get the perfect weld.

Once the arc is struck, the metal will melt and if exposed to the atmosphere the pool of molten metal will absorb oxygen and other gasses, making the weld porous and therefore weaker. For this reason a welder has a shield of flux or neutral gas around the welding area. On manual arc welders, this is generated by the outer flux coating of the rod. The weld makes the molten pool and the flux forms a protective layer over this.

Once the arc is struck and the pool is correct, the welder moves the rod along the route of the weld, ensuring the pool is maintained and the flow of the molten metal is such that it makes a good weld. It is the pool of weld that is important, and maintaining it just the way you want is the whole object of the excersize. If the pool is good, the rest of the weld will follow naturally and the only thing to worry about is loosing the direction in the dark, so make sure the run of your hand is easy to make.
Get in a comfortable position before welding, so your arm won't shake. Again, a dummy run with the power off, as preparation is everything.
Speed will depend upon the parent metal, the rods and current used. Usually the set-up is such that a slow gentle pace will ensure good heating around the weld area, and time to melt the area fully for good penetration. Emphasis on slow, as penetration of the pool of weld into both sides of the metals will dictate the speed, not the welder. Too slow and it will burn a hole in the metal. But too fast and the weld will be shallow and a pretty, but dangerous weld. Always try to go a little on the slow side as is safe for the best pool of weld, as this ensures best penetration without excessive heat.

You are NOT sticking two parts together, but creating a melt between them.
The weld is begun and a pool of molten metal created first. This pool is created to the correct depth before movement. Then move towards where you want to weld. It is usually necessary to tease the rod between the two metals to be joined. This pool is then encouraged to flow at it's own rate, so the rod melts and travels along the gap. Never rush a weld, it must proceed at its natural pace, dictated by the size and shape of the molten pool of metal, which must be allowed to flow in the manner necessary to fully join the two metals. Get to know this pool well. The rod is moved slightly between the two plates to allow pool to flow fully and a good weld to be created.
A good weld will leave a smooth crust of slag which is removed easily. In good welds, this will reveal a smooth weld with a slight raised bulge just above the level of the metal. The penetration should be fully through to the other side. On heavier metals, the penetration may only be half way, then the rear surface can then also be cleaned and similarly welded.

The ideal angle for the rod relative to the weld for stick welding is 70 to 75 degrees vertical, leaning towards the moving direction of weld. (75 to 80 for mig.)

The height above the parent metal will define the nature of the arc and the form of the weld. too high and porosity and a wide weld will ensue. Too close and poor penetration is possible, but a more closely controlled weld especially for thinner metal.
This picture shows a typical heavy penetration weld on structural steel, in this case the front swing arm of a JP8 hub centre single sided swing arm, where poor welds are not acceptable.

If you see a professional welder in action using a stick welder, grab a welding mask and look carefully at the movement of the tip. The rod will not be held to run smoothly in a line, but the arc is played in a minutely circular or side to side action to ensure the heat is directed evenly for the best penetration, but without overheating.

On heavy metal, getting the area hot before the weld arrives is beneficial. For most purposes, starting the weld as a bead just before the start of the actual area to be welded can help get the weld started and settled by the time it reaches the required area.

As the welding rod melts down, the weld rod will need to be changed regularly on long welds, so the slag should be removed and the weld continued such that it makes a seamless fillet.

When welding vertically or part of the join is vertical, then the weld will naturally want to pool under the effect of gravity. Therefore is sometimes better to make a smaller central run, then return to make a large fillet over the original, which will support the overall weld more evenly. Start from the bottom and work up.
On thicker metal, penetration is made easier by chamfering the edges, to give a Vee groove for the rod to access and fill. About 60 to seventy degrees will suffice and reaching down to about three quarters depth. If the welder cannot fill this in one run, then three runs are possible to full the gap, plus another on the rear, or perhaps three on both sides.
On most welds of thick metal as uses on frames, the arc is played gently between the edges of the two parent metals in a V or small circular motion so the weld flows evenly and deposits with full penetration into both the parent metals.

Tack welds with small welds along long gaps, especially on sheet metalwork such as fuel tanks, otherwise distortion will occur and the run may buckle and distort.
The fuel tank in the picture had over twenty tack welds before final teasing into shape before committing to the final long weld runs.

Preparation is paramount for a good weld.
Welding areas on the metal must be clean, with no paint or rust.
Wherever possible, a weld should be a single, neat run.

If a hole is burnt in the metal, reduce the current. If the weld sticks on the surface with little penetration, increase the current, or make a number of passes along a deeply grooved join. A good weld will leave a smooth crust of slag which is removed easily. In good welds, this will reveal a smooth weld with a slight raised bulge just above the level of the metal. Leave it as is if the machine is to be inspected, as this tells the inspector that the build quality is good. The penetration should be fully through to the other side. On heavier metals, the penetration may only be half way, then the rear surface can then also be cleaned and similarly welded. Quite often the weld area is not ideal, so a number of welds may be needed, possibly from one side or end, then the other, In each case always make the weld from the best end, then remove the slag and leave room for the weld to be made from the other end also. This allows the welds to join in a safe area which can be cosmetically dressed more easily.

An angle grinder, leather apron and gloves and face mask are integral parts of a welders kit.

Distortion occurs during welding and is quite normal. This can be evened out by equalised welding of the frame to minimise the effects of distortion. When checking frames is common to saw through some tubes to see how much internal stress is created and the amount of distortion that can occur. Specialist frames can he heat treated to remove internal stresses, but this is rare.

To help make a gap in main frame tubes, use a sliver of steel to lift the component off, or simply make an 'adequate fit' by grinding the ends of the tubes with suitable gaps or pips to allow better penetration.

Test by breaking, hacksawing or grinding through test welds to see just how good they are. Carefully examine the depth of penetration and for any air holes or slag inclusion which can weaken the weld. Keep practising until certain the welding is good enough, or find an expert.

The problem may simply be a welder that is not powerful enough. A basic 140 amp arc welder is adequate for a simple bike or trike, but for tubing larger than bike frames, use it for tack welding. For heavy welding, hire a better welder for the final welding and check that your domestic wiring is in good condition. On a recent V12 trike project, the steering head was glowing red before the welding had finished.

Flame welding, such as oxy - acetylene is ideal for building fuel tanks and to braze delicate fuel tank fittings and more delicate items. The heat spread will cause distortion of large thin plates such as used in fuel tanks, so tack weld all round before fully welding.
When bronze welding, keep all gaps small and check if any preheating is required. Always demand absolute cleanliness of the materials.

Common mild steel tubing and plate should supply all your needs, as it needs no special welding techniques. Welding rods must be chosen to match the metal and the diameter of the rod relative to the thickness of the metal to be welded. Store welding rods in a dry place. I use the airing cupboard.

A basic, affordable arc welder is quite capable of building most bikes, if the builder takes time to become proficient and follows sensible safety rules.
Gasless mig welders are not recommended. Gas migs (metal inert gas) are often better than rod welders, especially for thinner metals such as fuel tanks. Expensive welders are not necessary, but always practice is.
There are often evening classes on welding for beginners at many technical colleges and are priceless. After all the theory is read and understood, there is only one way to learn how to weld, practice, practice, practice.

The picture shows a couple of welders, a second hand 130 amp MIG on the left, with the swan neck and nozzle which takes the gas and feeds the welding wire under control of the trigger. I got this one cheap and simply repaired the wire feed drive.
On the right is the basic 140 amp arc welder with its welding rod covered in flux stick into the holder.
Welding costs are not expensive, as a box of a hundred welding rods is affordable and a length of steel tube for practice is well worth the low cost involved.

When buying a second hand welder, check the condition of the bits and see it in action if possible. When purchased, repair the earth lead and check all the connections to ensure a good weld. Some welders seem to be useless because of simple faults, so a full check and a clean, internally as well as externally.

Most MIG welders have a bracket or strap at the back for the CO2/argon cylinder. If using the small cylinders, then these can be awkward to have standing up loosely at the back. As shown in the picture above, there is usually plenty of room inside the welder, under the wire spool reel. Even with the large spools, these is enough room. A couple of slots in the base will allow the cylinder to be neatly strapped in position. To access the cylinder valve, the front panel can have a hole made in it, so all can be accessed from the front. (Bottom left of the picture.) Likewise, the rear mains cable can also be moved to the front, so the welder can be slotted neatly away beside, or under the bench, without having to lug such a heavy weight about each time it is needed. The author prefers to have the welders on the top of a head-high shelf, so the welding cables and swan neck lie vertically downwards, tucked to one side, neatly and away from damage or kinking. Being positioned high or out of the way, they are more out of the way of grinding dust and thus tend to run a little cooler. Once again, preparation can make the workshop easier to use.

Unless you are a natural born welder, expect to get frustrated for a few weeks until the skills are gradually acquired and you eventually get the feel of welding.

Basic tool kit.
To create a trike is not expensive. You need:
A dream and plenty of time to get it right.
Somewhere to build. Anything from a nice, big, warm garage, to just three level concrete slabs in a garden.
A3 notepad, pencil and eraser for envisioning the dream.
Lining paper for full size drawing and to work out the shape and size of the frame and main components.
Chalk to mark it on the floor.
Basic angle grinder with grinding and cutting discs for metal. Also linishing discs for cleaning and smoothing the metal and to carve the foam.

Face mask for dust, eye protection goggles and ear defenders. These are not negotiable and must be used, especially if you want to be triking in later life.

An arc welder, mask, chipping hammer and various sizes of welding rods.
Electric hand drill, set of drill bits, grinding and other items as needed.
Files, hacksaw, chisels and hammer.
Set of spanners (wrenches) and socket set.
Screw drivers and pliers etc.
Steel tape measure.
Permanent felt tip marker, chalk, spirit level, set square, plumb line, wood blocks and wedges, blue tack, masking tape, small pot of paint and a flat floor space.
First aid kit and fire extinguisher.

Preferable options:
Hydraulic pipe bender for frame tubes. (From hire shop.)
Multimeter for electrics.
Decent vice mounted on a strong work bench.
A decent engineers vice may be expensive, but will last a lifetime, so look around for a good second hand example. Then secure a few good, strong decent planks, such as scaffolding planks onto cemented concrete blocks for a bench. The bench should be big enough to hold a standard car engine. When mounting an engineers vice, make sure the inner jaw is just forward of the front of the bench, so it will hold a long bar vertically without obstructing the bench.
Details of workshop design and practice are in the companion text 'A Beginners Guide to Motorcycle Mechanics' in basic, intermediate and advanced flavours. Available on my website.

You do not need loads of money, just time, unfailing motivation and some room.

Basic materials check list.
Donor vehicle including documentation, receipts, engine, transmission, wheels, brakes, wiring and electrics, ignition, cooling system, fuel system / pump, speedo, air filter.
Workshop manual.
Front end steering and suspension - either decent forks, or parts to make own front end.
Good selection of tubing for building the frame, from local supplier.
Steel sheeting for gussets and fillets.
Steering head, spindle and yokes, made to measure where applicable.
Alternate fuel tanks or steel sheet for fuel tanks.
Old fuel tanks for their fittings, either from bikes or cars.
Fuel tank mounting rubbers.
Selection of tubes and rubber hoses from scrapyards for radiator plumbing.
Tail, side and headlights.
Exhaust system and a selection of extra exhaust parts to modify.
Special radiators. Cooling fans. Fuel pump.
Shell building materials.

There is nothing exotic needed to build a good trike. The only really important thing is knowledge. Knowledge is best learnt by doing it yourself. If the first trike is not good enough, then the next will be a lot better.
Unless the engine is a poor choice, then the only thing lost is a few lengths of inexpensive tubing plus the time and effort. You will have gained, however, something far beyond price, - the knowledge and feedback from the old machine, so the next machine will be much better.
A good artist always says his best work of art is the next one.
Cheap working donor cars are commonly available and can be easily replaced by a better donor vehicle at a later stage. Trike building is not that difficult and many people build for fun.

To make the trike legal, don't forget to check out Tony Alsops excellent website. See details at end.

Disabled riders.
Trikes are often used by disabled bikers.
Typical disabilities are damaged legs or spines, caused through awful bike accidents. This of course does not discourage a true biker, merely changes the rules a little.
The main design problems arise from access and control. The main solution of control is solved by three wheels. This just leaves the minor problems of having no foot controls.
Access will depend upon the level of mobility and arm strength of the rider. Access to a central position of a reasonably wide machine is problematic, but possible with a few interesting ideas.
Getting the rider into position from a wheelchair is the worst case, and involves making the transition as easy as possible.
For front engined trikes, then the wheel chair may be able to roll into the back of the trike, but this will need a strong, well designed rear end. The rider can then secure the wheelchair and slide forward to the riding position, as a wheelchair, unless specifically designed, is not ideal for riding a trike.

For rear mounted engines, start by making the trike seat the same height as the wheelchair seat, then with the removable wheelchair sides, the trike must be designed to allow the wheelchair to be sidled up and allow the rider to slide easily across with minimum hassle and effort. The problem with this of course, is getting one leg on the other side of the trike.

As the rider will slide onto the side of the trike, it may be possible to lean back into the wide seat, probably capable of three people side by side, and thus give plenty of room for access if the leg can be lifted. If the leg cannot be lifted, then the frame will have to be compromised and this will demand a rear engined trike, with a lower set of main frame rails or large box section tubing.

Transferring from a wheel chair has a major problem. The wheel chair is left behind or preferably need to be carried. While the rider is beside the wheelchair, it should be reasonably easy to fold up and fit into a cradle. Such a cradle will not be stylish, but making it close to the seat, will allow relatively easy entry and exit from the trike without help. Where the traditional passenger foot well is positioned, a cradle for the wheelchair is easily mounted. A simple clamp or bungee retainer should also be employed.

If you have limited use of the legs, then it is possible to make the seat such that it is mounted on a parallel linkage, similar to a luxor lamp, allowing the seat to be raised from the riding position, then swung sideways and hydraulically lowered down to the wheelchair position. This is fairly easy engineering using simple hydraulics from a running engine or a remote, electrically powered hydraulic pump.
If you can build a trike you can easily build a wheelchair whose seat is also the trike seat, to minimise the hassle of using a trike. email me at for details.

Once the rider is in position, remaining there may be a problem, especially if thigh strength is minimal, so sliding sideways during cornering will require a seat not dissimilar to a car bucket seat, with its side supports. For easier access purposes, these can be lifted or folded up from below or slotted in by hand, to ensure easy access.

If wanting a comfy seat, but not the style of a car, but needing spinal support, then get a car seat and cut the frame down to be narrower at the top. This is simple cut and weld, so that you can retain the adjustment of the squab (backrest), which may make a trike usable for many hundreds of high speed miles, especially if disabled.
If very disabled, then the seat can be placed on a locking pivot, so that access is far easier, and you can retain and also adapt the electric adjustments of a second hand car seat, allowing you to power yourself into position and perhaps even allow the seat to power sideways to slide close to a wheelchair.- The technology is there for pennies, so don't be afraid to use it.
A well designed trike with one of a vast number of car engines, can have a very low frontal frame and this is ideal for riding a wheelchair very close to the riders seat for solo use, and still have room for retaining the folded wheelchair and a couple of passengers.

Once in position, the controls will need to be adaptable.
An automatic transmission is worth its weight in gold. Manual transmission using a foot clutch will not be so easy for a car, and if a manual transmission is preferred, then consider a bike engine, as a car clutch is extremely heavy. If using a car engine, but the clutch is too heavy, then strip the clutch and remove a few evenly spaced spring fingers. As the trike may not be pulling so much weight, this is a reasonable, if not guaranteed bodge to lighten the clutch pressure.
Both brake and the clutch can be adapted to the vacuum servo of petrol engines, so only the gearchange and throttle need be made smooth and easy.
Motorcycle gears can be controlled in the same way as some Italian scooters, using the twist grip control, but this is not very nice, nor recommended. The latest fingertip gearchange controls of semi automatic cars is a better choice.
Car gearchanges involve a selection of moves, so the clutch if used will need to be mounted as part of the gear lever, allowing one hand to pull in the clutch and also change gears. A simple design for push and pull of sequential gears as used for motorcycle engines which also applies the clutch, is available from the author.
When pulling in the clutch on a hill, the handbrake may need to be used and therefore this should be on the other hand, but the throttle cannot then be used, to pull away. Therefore the handbrake cannot be used, but the front brake is a good alternative and must be designed to be easily used with the throttle. The handbrake can still be used on the level or downhill.
The brakes will also need to be controlled by hand. Unfortunately a hand cannot always apply enough pressure to stop a trike. Worse still, a handbrake will need to apply the force to both front discs and also the rear brakes. Therefore a servo system will be needed.
A servo assisted brake takes the vacuum from the inlet manifold then uses it to amplify the force of the brake pedal. For hand operation, the front brake lever can be used to apply the same braking system as a car uses. Because the brake is operated from a single control, then the front brake should be operated from a cable to push in the servo the same as a car brake. Because the servo can be fitted anywhere, it is best fitted for a reliable brake cable. In a big bike, then the servo and brake can be mounted near the steering head, possibly under the steering head. In a smaller trike then it will have to fit wherever possible. The servo can then supply brake pressure to dual circuits. As one hydraulic circuit may fail, then one rear brake and one front disc is common on one circuit and the same for the other, so that redundancy is available for safer braking. The handbrake is the emergency backup. Using a disc brake on the prop shaft between engine and differential, can offer a very sensitive hand brake, as it applies three times the effort of a similar item on a road wheel axle.
If a handbrake is to be used on the prop shaft, locking this in place can be done using a cam and lever on the hand lever, as on many quad bikes, or with a releasable ratchet or many other devices. Ergonomics for disabled people are important to allow the best control and force. The handbrake is often a lever which allows lots of force though a large arc. Alternatively, the handbrake can be similar to older cars, with a hand control pulling out of the dashboard area to operate via a cable.

Power steering may also be possible, but as a rear engined trike is rather easy on steering forces, then power assisted steering is often not needed and just a light steering damper may be needed for higher speeds. If power steering is needed, then the donor car engine should also have the power steering pump and this is used to control the steering via a carefully modified control valve attached to the fork yoke.

Disabled people may have serious problems looking after legs which may not be under direct muscle and nerve control. Therefore some means of securing the legs in position but not to the extent that the rider is dangerously retained in an accident. Simple shallow foot wells just deep enough to retain the boots from sliding around is often all that's needed unless expecting to travel over bumpy ground. Should the foot come out of the intended position, it must never be allowed to rub against an exhaust or other dangerous feature of the trike, but have subtle guides to ensure the leg return to the desired position.
The legs must not be allowed to become cold, so some form of heating or shielding from wind is often needed. Such considerations will always make each trike design specific to the owner.

In an ideal world, the rider should be able to reach the trike in the wheelchair, slide into position with little hassle, lift the wheelchair into a stowage slot, to remain secure in the trike. Then the trike controls should be easy and natural to use.
If an electric wheelchair is used, then perhaps the steering forces on the trike will be too difficult for the user. With automatic transmission, Citroen type braking system and power steering, then very little effort will be needed to control a trike, but manufacture will be complex.
Feel free to email me at for details.

By now you will have thought of many ways to improve the trike, but by now it's too late. Don't worry, as all great designers, craftsmen and artists have this problem.
The secret is to continue thinking until ready for a better machine. If the basic frame is good, a simple winter rebuild may ensue. If not at all happy, sell the beast to finance the next, better machine.
If the legal paperwork was not fun, (Excessive Brit and Euro crap!) and you decide to stick with this machine, then go back to start, and enjoy the amazing power of hindsight and experience, then be prepared to change everything except the frame number. Normally most of the machine will be retained, with just the front end, the subframe and shell modified or rebuilt.
You may eventually enjoy building so much that a new frame is already in the pipeline, and possibly a better engine.

'Yes, I've had this broom for twenty years,
and it has only had three handles and five heads.'
Do not build your first trike with a Porsche or a V12. Always start with a decent, honest donor machine, which will create a good, reliable trike. Everyone needs an apprenticeship. If this works well, then you can move up to the big boys toys, or loony machines, depending upon one's point of view, and sell the first trike to pay for the ultimate dream trike.

Keeping weight down needs using special tubing, a good grasp of structures such as bending moments and shear loads plus special welding or brazing techniques. These are all in standard text books for those who wish. Some people think that life is too short for total engineering perfection, as understood by white coated engineers. Always choose a suitable balance between mechanical perfection and a life.

Designer shades will not prevent flies getting stuck in the teeth from a big grin. Expect local kids to keep asking for rides. A strong waterproof cover will help keep sticky little fingers at bay when parked outside. Start sewing up a ground sheet or tarpaulin to make a neat fit.
Do not build anything which would bring trikes into disrepute.

Whatever design is created, make trikes something Mr average would like, but would not dare to try and justify. - power with intimidating yet refined aggression, overwhelming style and an outrageous art form.

Blend well for best results.

Copying others is no way to radically improve trike design.
By making full size drawings from scratch, the design of the machine should evolve naturally with guidance and feedback from testing. The few drawings in this monograph will hopefully not confine the overall shape or form, as innovation should be the motivation.

It is the designers own drawings which can only mark out the path to follow. This monograph is merely a guide. By now the reader has probably generated many ideas and drawings, with more yet ideas to follow to create a path into the future.

"The only place you never know is the future,
so that's the place you need to go if you want to make a statement."
John Partridge. B.Ed. B.Sc. Gizzajob.


Copyright (c) J.Partridge. 2000. 2005. 2006.

Sales pitch.
I'm an indentured engine fitter, licensed engineer and designer by trade and enjoy designing and building trikes, have a teaching degree in technology and a science degree in design, innovation and physics. I have worked as a motorcycle mechanic, engineer and draughtsman. I build radical customs for myself, help build more prosaic machines and help out in some motorcycle shops for free.
I prefer to help local people in thier own garages, as I have little room left in mine.
To assist those who want a trike, but not very good at engineering, I've designed a series of clean, neat and lightweight, optimised design of independent rear suspension trike rear ends compete with differential and easily adjustable chain, ready for bolting straight into a standard motorcycle frame using the swing arm pivot and the upper shock mounts. The easy fit design does not damage any of the standard motorcycle parts and can be fitted in four hours with the tools included. I presently price them at 2,000 pounds, made to measure.
If you want to lower the back of your bike frame, then I build a trike conversion with bare tubing for welding to your standard machine, complete with easy follow, comprehensive instructions, although you will need a welder, or tack weld it and hand it over to a competent welder.
All designs include a manual for maintenance and repair, are fitted with linked dual rear brakes with hydraulics and a small choice of standard car alloy wheels. Includes brackets for fitting various seat options should you wish to modify or add items later.
For chain drive machines, the transmission components use lightly modified Ford Escort Mk 4 differential, with a standard motorcycle sprocket to match the gearing of your bike. Spares available within 48 hrs. Available in standard or narrow versions for most bikes from 125cc to 1200cc.
Email your bike and rider needs. - Whether you want sport or a touring version, each can be optimised for rider weight so the suspension can be to your needs. If you want the bike lowered at the rear, have dual rear seats, luggage units, extra fuel or other design considerations, then just ask, as this does not cost much extra.

Custom trike frames for car and bike engines can be designed and built on request. I charge 300 pounds a week for my design and manufacturing skills. A customised trike rear end takes about three days to research and design and about two weeks to manufacture and fit. Material costs are about 300 pounds for the diff, tubing, standard brakes and two alloy wheels. Prices start from about 2,000 pounds per conversion. Shaft drive machines are slightly cheaper.
Full trikes with engines can be designed and built from scratch from 4,000 pounds.
Email me at with details of your machine and needs, for a free quote.

Please supply the following details.
Preferred bike / car and engine size or your donor machine.
If you don't specify a bike or engine, I can recommend a selection of donor vehicles, so please state your working budget for a complete machine and if any engine preferences, eg, Suzuki, Harley, Dnepier, Honda, Ford, Skoda, 2CV, Ferrari or others. - ALL is possible.
Type of riding, general use, shopping, touring, thrashing, custom shows etc.
Seating needs, tandem, R+2, R+3, or three side by side etc,
Special needs, such as lack of legs or weak arms.
Overall dimensions e.g. your garage or parking area.

If you want to start building trikes commercially, you don't have to be a good engineer, but if willing to learn and prepared to work part time to develop a mutually beneficial business.
If there is anyone in the Plymouth England area (or anywhere in the world) who wants to build trikes for profit and has simple garage space with electricity and light, then please, please email. I
've developed four generic trike designs including Suzuki Bandit, Gold Wing, Escort Mk4, and Subaru donor vehicle designs should there be someone who wants to start sensible custom trike manufacture. These can lead to a very profitable business with zero start up funding, to custom build the very highest quality design and built trikes and trike kits for sale to a world desperate for some decent trikes of all styles and with all sorts of engines.
Example, a generic 1400/1600 cc car-engine, three seat trike with independent rear suspension and alloy wheels, and a standard bike front end with dual disks can be built in Plymouth, SVA approved, ready for the customer to drive away for about 800 pounds ! (excluding labour) This can be sold at a sensible market price for a really well designed and nicely built trike from about 3,000 pounds, with 24hr back up support and a decent owners manual, a workshop manual and parts list. This gives a profit of over 2,000 pounds to cover skills and labour costs and can be done every month, as a decent custom trike can be built in just over three weeks. If many similar trikes are needed, then the times are almost halved. Complete DIY trike kits needing just a standard donor vehicle, can be built in six days, with cables, seats, fuel tank, step by step builders manual and wiring loom can be built from 300 pounds and sold from 1200 pounds to cover labour. To this can be added extra profits for turbo versions, fancy paint and special ergonomics, although I never charge for any wheelchair mods.

The world needs superior handling trikes at reasonable cost for discerning trikers. I'm happy to help develop such a trike shop, with just three trike designs at first. Then build up to the worlds premier trike shop, but need someone with the space and funding. Eventually I would like to be able to sell really good range of trikes from 600cc to 2 litres, at sensible prices and also a few Porsche V8 and Jag V12 trikes to keep the profits healthier.
If you need help in building your one-off trike, or considering production, please email. I'm sure there's a market for good trikes. If you have some garage space with electricity and a little elbow room, then I can make a trike within three weeks for a few hundred pounds.
If in India, then I can design the components and jigs to build the shells and frames in India. The fully working trikes and home build trike kits are assembled in the USA and UK to get around vehicle import bureaucracy. Start off with a generic Ford transverse engine, common to the USA and Europe, to allow a range of engines from 1,000cc up to 2,000cc, in various specifications.

John Partridge. B.Ed. B.Sc.


When developing machines, few will have the funds to develop finely finished machines, nor should it be needed to build superb machines.
Brains is always more important than money. Discovering acceptable methods of building should be considered part of the innovation process.
The poor have most to gain, needing to understand problems first hand. Compare the history of innovation of 'professionals' with those of 'amateurs', to understand the social implications. Throughout history, the best experts are often amateurs, as well documented in many excellent articles on the subject.
In the modern world, most high tech items are discarded despite being perfectly serviceable, due to the decreasing ability to educate hands on engineers, where ability to pass exams erodes the ability to do real work. The official engineer is evolving into a creature who plugs in the diagnostics box and replacing the component. This often seems efficient on paper, but has one advantage, as it gives the resourceful innovator an excellent source of componentry if the discard point is targeted. Always aim to be a much better engineer than this.
The world is awash with excellent surplus equipment. Always become friendly with the suitable sources and local recycling centres and carry suitable cash or negotiable goods. When strolling though industrial units, a lightly worn disposable boiler suit makes the scavenger invisible. (See Father Brown book, Postman.) Always carry a large foldable bag, big enough for a small welder. Carry a rechargeable screwdriver with the usual tools to reduce loitering.
Scavenging makes a vastly better engineer and improves confidence, realising just how easy many expensive components are to repair. The most expensive tool of all, a wind tunnel and its test gear, can also be surprisingly affordable. See companion monographs.
Real engineering is a craftsman doing for pennies, what any commercial company usually does for a fortune. Never be put off by the 'sophisticated' talk and equipment of 'experts'. Know the data to gather, and how to assess it. It's not black magic.
A classic example was an expensive piece of modern hardware in the trash of the engineering department of an esteemed university. It needed less than five minutes work to get working perfectly and has been used by the author for many years. Thank you taxpayer. (The author did not get an interview for the universities vacancy for a part time lab technician, so a sense of humour helps in modern Britain.)
Never be too proud to stick your nose in the back of factories, offices and other likely places. Be polite and always ready to lend a hand. With time, you will build up a surprising array of useful resources.

Lateral thinking is a powerful tool. By not having many drawings in this monograph, the mind will hopefully have improved, in a natural, unforced manner. It is the ability to build a mental library of seemingly unconnected knowledge which will eventually express itself with flourish onto paper from the start, and throughout the subsequent evolution of a project.

The ideas touched on in the text are deemed suitable for beginners, but are just the tip of the programme. The basis of the publications was written as research notes between 1990 and 2000 to ensure the final study of the twenty year single track vehicle programme will be comprehensive. The intermediate availability of this information was condensed and offered to help fund research. Trikes are not part of the core programme, as the main work hopes to develop the various future, truly radical machines and advanced systems needed to integrate man and machine.

As mentioned earlier, learning does not mean following others like a sheep. This monograph is not the answer to all, as no text can offer a personal path to perfection, so always glean what is useful, then move forward. For safety reasons, always improve skills as seen fit though careful, well paced steps. The rest of the process usually follows naturally. There will be upsets along the way, but careful thought should ameliorate most and make the process a rewarding one. Enthusiasm will wane occasionally, but is quite normal. It is the open minded approach to making a dream machine that is important.

Keeping eyes and mind open will allow the designer to glean all possible advantages towards the ideal machine, and occasionally a totally radical design may be created for a great leap, hopefully forwards.

Present projects (2001) include JP8a single seat KTM powered recumbent, aimed to be an ultra-light slalom development machine to refine the most important area of research, first developed and ridden on the JP4 and JP5. This requires much higher funding, hence these monographs. JP9 will be a more advanced JP7. JP10a/b will hopefully be the two definitive forms of the JP-FCM which the programme is working towards.

The bigger picture.
Look around you, it was innovators like Babbage and Ada Lovelace, Tomy Flowers and Alan Turin for the computer. Edison with sound and light. From the cup holding your coffee, to the glass window, seat covers, paper, pen, they all needed ordinary people with a dream of inspiration, who created just about everything you now use.
Too few people innovate and build customs, their effects on the environment is minimal, while their effects on human nature is liberating.
Things won't get better unless those who can advance research and design have the chance to do so.
If we all blindly follow the 'experts', then, heaven forbid, we may even end up in a world where all cars begin to look alike, and the only options will be the exciting variations of cup holders or other such facile crap. If (when) this happens we will know we are dumbed down ready to become consumer sheep, fit only to graze in malls. No one has a monopoly on true, radical innovation. History is littered with all types of innovators in philosophy, sociology, religion, economics, science, and of course, applied technology.

There is no point writing monographs like this if they cannot be used. Always use your vote, even if only to keep politicians and bureaucrats from making our lives constrained and boring against our will. Always vote for home built machines, not the Euro crap 'type approval'. Human nature must always ensure its creativity from a world dominated by (m)asses of corporate 'logo based life forms' and parasitic lawyers. Never vote for anyone who wants 'type approval', excessive paperwork or restrictions of custom machines for road use.

The price of freedom is eternal vigilance.
Cherish your aspirations and abilities, and always protect them.

Begging is the bottom line of this work.
Vast numbers of excellent designers and engineers are laid off from the declining British manufacturing industry who then study at university level and beyond, leaving with a piece of paper and a massive debt. The author has managed two full degrees without debt, no mean feat, and presently trying for a post grad, but no capable universities in Britain. In the authors case, the Open University (God bless it) was the nearest equivalent.
Most of the vast numbers of 'begging bowl innovators' have ideas, so please help. British venture capital is unfortunately an oxymoron, a joke comparable with our railways and education system.
Working on a begging level is an eye opener, requiring innovation to make things happen. Each JP research machine needs funding just to build. The two JP7 chassis cost almost too much. Each carefully considered machine has to develop many innovative ideas.
Funding is fundamental to a research programme, hence this monograph. So please order a copy, or offer a donation. Send what you think it's worth, as this also gives feedback. All profits directly support research and honest donations welcome.

If you are embarrassingly rich, please be so kind as to sponsor the research. Just three thousand pounds a year will eliminate delay, allowing the final forms to be developed quicker, and thus be more refined and subtle. Ten thousand pounds a year donations or simply materials supply underwriting will allow headlong path to a truly innovative form of two wheel transport. For those wishing the author to design and build a dream machine, a technology demonstrator or even a two wheeled exhibition piece, or something from the above text, any design can be considered. Full sponsorship will receive an exclusive JP10/FCM.
If nothing happens and the Longbow or JP7 have no public support, they will be allowed to die by simple Darwinian processes.
Being just one of the many long term unemployed English science graduates with a strong engineering background in nuclear, marine and other spheres, the author would like a job. A job teaching motorcycle engineering or creating composite machines would be most tempting.
Please consider this monograph a rather blatant CV.

Thanks and best wishes,
John. Partridge. B.Ed..B.Sc. etc.


Useful sources.
The excellent guide to trike law in the UK by Tony Alsop at

Recommended Reading.
Motorcycle Engineering. By Phil Irving. ISBN. 0-85113-075-5
Build your own sports car. By Ron Champion. ISBN1-85960-636-9. Nice one Ron !

Frame Geometry.
Tony Faoles website. at
Converter prog. via

Useful sources.
These are the suppliers the author uses.
McArthur Group Limited. Plymouth. All the metal you could possibly need, at excellent prices.
Examples: Rectangular tubing, 20mm x 20mm x 1.6mm, to 150mm x 100mm x 10mm. Solid strip. 12 x3 to 400 x 25. Sheet. 2m x 1m x 3mm, to 4m x 2m x25mm.
Woolies. Whitley Way, Northfields Industrial Estate. Market Deeping. Peterborough. England. PE6 8LD. All the fittings for the traditional design. Rubber window strip, carpets, headlining, fittings for vintage and classic motor trim and a host more.
Vehicle Wiring Products. Buxton court, Manners Industrial Estate, Ilkeston Derbyshire DE7 8EF. Excellent catalogue available. Tools wiring, accessories etc.

If interested further: Companion monographs by the author.

A Builders Guide to Motorcycle Design.
A Builders Guide to Composite HPV Cycle Design.
A Builders Guide to Trike Design.
A Builders Guide to Composite Motorcycle Design.
A Builders Guide to Motorcycle and Trike Wiring.
A Builders Guide to Campervan Design.
A Builders Guide to Basic Wind Tunnel Design.
A Beginners Guide to Motorcycle Mechanics Basics.
A Beginners Guide to Motorcycle Mechanics Intermediate.
A Beginners Guide to Motorcycle Mechanics Advanced.

Stonehenge and spanners.
Simple alternative electronic ignition. No spark in your MX, trials or moped ?
Make your own glasses. (spectacles.) 150 quid glasses rip-off? You deserve better.
A Beginners Guide to Building a Computer. Build your own computer, system and desk.
Domestic repair and maintenance.
Save money on plumbing, electrics, cars.
How to walk. A beginners guide to the outdoors, from strolling to evasion.
A Builders Guide to Survival Knife Design.
A Builders Guide to Survival Kit Design.

For those interested, other books which could be published include:
A lateral look at innovation. From Polynesian monkey traps to BV141.
An approach to preventing design stagnation in small businesses. Early draft.
Ergonomics and control possibilities for single track vehicles. Early draft.
Building the Future: Development possibilities for single track vehicles. Compilation.
Stagnation of innovation and the development of the car cup holder.

If you found this monograph useful and build a machine, please feel free to Email. Any requests for a dedicated trike web page or site?, complete with drawings and assembly details. Perhaps the public may be interested in a set of trike chassis kits, with fitted gearchange, fuel tank, steering head and such like. Ready for a variety of donor vehicles and standard bike forks and yokes.
Any other donor vehicles out there that are popular? I'm thinking of three sensible choices.
1. A cheap and cheerful rolling chassis kit for about 2000 quid, using any choice of up to 1600c transverse engine, with unpainted chassis, a set of good second hand Japanese front forks and front wheel with dual discs, full electrics, seats covered in vinyl, but needs paint and finishing.
1a. SVA approved, styled shell and/or ready to run optional for about 3,000 quid.
2. The other option is a ready to run, serious but sensible trike, a Subaru engine (with PTO) or Alfa Sud engine, low stonking chassis made to measure, special front end using a car rim and antidive suspension and low, comfy seats for three across behind the driver, plus a boot (trunk) plus paint and finishes to customer spec, plus whatever else is needed. Rear end styled in choice of fibreglass Lamborghini or formula one styles (upward dummy stub exhausts optional). Probable cost about six thousand quid on the road, ready to run, or four thousand quid for the rolling chassis with engine seats and wiring. Wheelchair aids and other options included.
3. A simple daily trike, using a 600cc 2CV engine, lightweight chassis, with rider plus two or three comfy passengers and a boot (trunk) for shopping.
All would use generic, easily replaced components for longevity, with minimal specialist items other than chassis, suspension and gearchange, wiring and shell.

You don't have to be called racist to love your country.

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Always try to improve society rather than just take from it. Until then, lawyer stuff. Copying or duplication of this material is prohibited without written permission of the author. The content is for information only. No responsibility is accepted for any damage or any injury caused by the above information. Errors and omissions excepted. No-one should try building machines without reasonable abilities and know that injuries can ensue from the materials, tools and from test riding of machines. Have a nice (lawyer free) day.

Copyright (C) J.Partridge. 1999. 2003. 2005.




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