3 Wheeler Car Build


In 2002 a three person team designed and built this 3 wheeler vehicle in 7 weeks.

The 3 wheeler project all started at Rugby College as part of a General Engineering training course. We had to work in teams of 3 people and come up with a project that included design and manufacture of a product in 7 weeks. Our team consisted of an Electronic Engineering graduate (Myself), an Electrical and Electronics graduate and a Mechanical Engineering with Manufacturing Systems graduate. This represented a broad range of experience and knowledge. One of the team members had an old motorcycle that had suffered crash damaged; however the engine was still in good condition. We decided to design and develop a new working vehicle in 7 weeks, with the overall aim of eventually passing an MOT and getting it road legal.

We looked at the motorcycle to help us consider various vehicle options since our plan was to use as much of the original motorcycle as possible. We identified a potential problem that the motorcycle engine is designed to power a chain and a sprocket to the rear wheel, whereas in general 4 wheeled vehicles use a drive shaft powering a differential. We decided that given time constraints and for simplicity we would limit our ideas to 3 wheeled vehicles, utilising the existing bike engine and swing-arm for the back wheel and 2 wheels at the front. Therefore the design of the drive system consisted of copying the mounting points from the motorbike to the frame design. This not only simplified the drive system but also kept the cost of the project down because existing parts were being used instead of having to purchase new ones.

Given these criteria we researched various three-wheeled vehicle options. The website www.3wheelers.com provided us with inspiration and an interesting A-Z history of three wheeled vehicles. We also researched the legal requirements for self built three-wheeled vehicles, to help us make it road worthy.

3 Wheeler Initial Design

After the initial research, various sketches were produced to help decide on a style of vehicle. It was decided early on that the vehicle would be a single-seater to reduce weight and design complexity. The aim was to keep the weight below 410kg which puts it in the same category as a trike. This is covered by the B1 class on a standard drivers licence. This class of vehicle was exempt until June 2003 from the SVA (Single Vehicle Approval) test that other kit cars require to pass before becoming road legal.

As long as the car was registered with the DVLA before this deadline then it only has to pass a standard MOT test to be road legal. This not only reduces the cost of the test but is less strict than the SVA test. The car was registered with the DVLA and allocated with a chassis number in May 2003.

Several methods were used to start planning the specific details of the vehicle. Firstly MS AutoCad was used to create a block sketch of the various components of the vehicle. Using a CAD package allowed for design changes to be made easily. To check the design, a full size 2D plan of the vehicle was made on the floor using masking tape (see below). This allowed various components to be laid out and for the driver to get a realistic feel of the size of the vehicle.

The following factors determined the size of the single seater vehicle:

  • The first and most obvious factor is the driver size. The dimensions of the three-team members were measured. A comfortable driving position was also recorded.
  • Rear-wheel and swingarm attachment are already determined from the existing frame.
  • Engine positioning. Since the chain from the engine needs to be taught when going over bumps, the chain needs to be kept horizontal, limiting the engine position to in front of the rear wheel.
  • For safety reasons it was decided to keep the driver’s feet just behind the front axle, to allow for a small crumple zone.
  • It was decided to use a rack and pinion and wheel hubs from a ‘donor’ vehicle. These would determine the width of the front of the vehicle.
  • A ground clearance of 15cm was chosen, similar to that of a normal road car, suitable to clear speed bumps. The size of the drivers determined the minimum height of the vehicle, given that role bars were desired.
  • It was desired that the driver’s arms would be contained inside the body of the vehicle; therefore this sets a minimum width.

3 Wheeler Detailed Design

Once the design had been agreed by all the team, a detailed model of the vehicle was created in AutoCAD. This would ensure that the frame was designed accurately and that everything would fit together before manufacture began. The CAD model would also aid manufacture considerably, allowing for accurate dimensioned cutting lists to be created for the space frame. It also allows for changes to be made to the design cheaply, as opposed to during manufacture where costs of design changes increase exponentially.

CAD Space Frame Chassis
CAD View with Driver
CAD Rear View
CAD Full Render

Given the time constraints of the project, it was felt necessary to acquire some of the main vehicle components from a ‘donor’ vehicle. The nature of a three-wheeled vehicle meant that parts would be required from both a motorcycle and a car. The Kawasaki that inspired the project would provide a large number of parts.

3 Wheeler Vehicle Parts

Existing Parts:

  • Rear wheel
  • Swing arm
  • Rear Suspension Unit
  • 500 CC Engine
  • Radiator & Cooling System
  • Vehicles Electrics
  • Rear Lights & Mudguard

Parts to find:

  • Rack and pinion
  • Front wheel hubs and assembly from a rear wheel drive car
  • Front suspension coil and dampers
  • Front Wheels
  • Steering Wheel
  • Steering Column
  • Master brake cylinder
  • Brake Hoses
  • Lower Ball Joints for Suspension
  • Cables for rear brake, clutch and accelerator
  • Piping for cooling system
  • Fluids

Parts to make:

  • Space frame including engine and suspension mounts
  • Panelling for frame
  • Front wishbones and bushes
  • Pedals and mounting brackets
  • Fuel Tank
  • Steering Column
  • Adapters
  • Driving Seat
  • Miscellaneous mounting brackets and fixings

3 Wheeler Chassis

It was decided to use a space frame design for the chassis. This was made out if 25mm 16 gauge box section. The cutting list was taken directly from the AutoCAD drawing. This included cutting angles as well as physical sizes. The box section was cut to size and clamped into a wooden jig to keep it in place for welding.

Welding Jig

Small metal plates were placed under each join to stop the wood catching light during welding. Oxyacetylene welding was chosen to weld the frame together. This was mainly due to the portability of the kit involved and it was the one method of welding that the whole team felt comfortable in using.

Welding of the main Chassis
Grinding and Finishing the welds

Any brackets that required large amounts of heat to be welded were arc welded by our master welder Sid. Sid also did the more difficult and safety critical oxyacetylene welding.

3 Wheeler Suspension

It was decided early on to use the rear wheel, swing arm, suspension and existing drive mechanism from the motorbike to provide the suspension setup for the rear of the vehicle. It was decided to use a double wishbone suspension system for the front of the vehicle. Due to the nature of such a bespoke car design, the front suspension needed to be designed and built from scratch. This proved to be a complicated part of the project and was critical to make sure that the vehicle handled correctly under load. Some help and guidance from a certain Prodrive Suspension Guru proved invaluable.

Several key components played a major part in suspension calculations and design. See the CMDT3 Suspension Guide for more details on calculations and measurements. A rack and pinion were acquired from a scrap yard from a Ford Sierra. The width of this set the width for the wishbones. For safety reasons, we felt it was important to have some of the car frame in front of the driver’s feet position to absorb some of the energy in the event of a crash. The plan of the car was designed in AutoCAD before any manufacture began.

It was desired to make the wishbones out of seamless steel tubing approximately 20mm in diameter. However, the local steel supplier did not have any seamless tubing in stock, therefore seamed steel tubing was used, but a larger diameter (27mm) and a thicker gauge were used to increase the strength. The wishbones were joined to the frames using brackets that were made by bending steel strips. The sides of the vehicle are not parallel and therefore the angle of the brackets needed to be manufactured such that the axis of the right and left wishbones were parallel. To ensure a smooth motion of the wishbones, brass bushes were made, such that the brackets clamp to the bushes leaving the wishbones free to rotate.

I dependant Front Suspension

The ball joints for the top and bottom wishbones were sourced from local scrap yards. Ball joints from a Ford Sierra were used for the bottom wishbones, these have now been replaced with stronger, replacable Ford Cortina ones. Larger track rod end ball joints were used from a Ford Transit for the top wishbones.

The size of the bottom wishbones obviously affects the size of the top wishbones. Once the ball joints were acquired we then had to decide how to mount the ball joints to the hubs. The wheel hubs were from a Ford Sierra, and therefore are designed to hold McPherson strut suspension units. An extension unit was made to fit in the mounting for the McPherson struts and hold the ball joints at the other end. The length of the extension would determine the angle of the top wishbone.

The vehicle needed to be designed such that when the car is fully laden with the driver, the suspension system is in the desired position. The ideal position of the wishbones in the fully laden position is such that the bottom wishbones are level and the top wishbones angle down inline with the mounting point of the ball joint and hub on the bottom wishbone on the opposite side of the car. This was achieved by careful design of the suspension system.

Here is the completed suspension system:

Complete Suspension System

3 Wheeler Engine

The engine for the 3 wheeler is from a 500cc Kawasaki GPZ500 motorbike. The picture below shows the engine mounted in the 3 wheeler frame at the same angle as it was in the motorbike frame. The information below explains how this was achieved.

Engine and Swing Arm

Engine & Swing Arm Mounting

The location of the mounting points for the engine, swing arm and rear suspension were taken directly from the frame of the motor bike. This was achieved by creating a jig due to the complex nature of the bike frame.

The jig was nothing more than two pieces of chipboard with a large block of pine in between. The jig was drilled to create a location or origin hole that all the mounting points would be found from. The jig was then bolted into the frame of the motor bike. This enabled the other mounting points to be located on the jig. The jig was then removed, drilled and refitted to test the accuracy. As predicted all the holes lined up and the jig was then measured to gain the dimensions for the engine mounting points and swing arm.

Creating the rear mounting frame

After studying the bike frame a design was decided on that consisted of two vertical plates mounted on and separated by box section. The plates were drilled using the dimensions from the jig and then joined together with the box section. Once the frame had been produced that had the two rear engine mounts and the swing arm pivot hole drilled the front engine mount was designed. It was clear that to extract the engine from the frame with relative ease would mean that the rear engine mount frame would need to be removable. This was accomplished, produced and works well.

Adding the rear suspension mounting points

To find the positions of the rear suspension mounting points, a jig was created that consisted of bars with holes in that were bolted together. The main bar was drilled with holes that exactly matched the rear engine mounts. The jig was then attached to the existing bike frame by the rear engine mounting points and the top suspension mount. The bolts in the jig were then tightened so that the location of the top suspension mount could be located from the locations of the rear engine mounts. The jig was removed from the bike frame and bolted into the rear mounting frame.

A bracket was created and welded in place whilst connected to the jig. This ensured that the accuracy was high. The bottom suspension mounts position was calculated in the same way but it was decided that to gain some more rear ground clearance the mounting point would be changed.

A problem that later occurred was that one of the engine mounting bolts was in the path of the chain. This was corrected by creating another bracket that was welded into the frame. This ensured a clear path for the chain.

Adding the frame to the main body

Once the entire rear mounting frame had been created it was welded onto the main frame of the car. Other struts were added to give strength that was needed to cope with the forces that would be generated by the drive system.

3 Wheeler Cooling System

For the engine to run correctly, a cooling system needed to be designed. In the original bike the radiator was mounted close to the engine. This could not be achieved in the car due to the position of the engine. It was decided that the radiator should be mounted at the front of the car. This is the natural position and the most efficient for cooling. This raised the issue of whether the internal water pump on the engine could cope with the extended water circuit.

After some discussion it was decided that as long as the radiator was not mounted in a higher position than it was in the bike relative to the engine the pump should be able to cope. Two lengths of copper pipe were purchased and fixed into the car. These along with new flexible rubber piping completed the water cooling circuit. The front mounted radiator and cooling pipes are shown below.

Cooling System

3 Wheeler Pedals

Due to physical size constraints with the height of the bonnet, standard pedals from a donor car could not be used. Most pedals are quite a bit higher than the pivot point which would have stuck out of the bonnet in this vehicle. Also the correct leverage for the motorbike engine was required. This meant it was easier to start from scratch and design the pedal system ourselves.

Measurements were taken from the chassis with the seat in place to get an idea of the pedal position. The mock up shown below was then used to try and calculate the correct height for the pedals and the pivot. A wooden pedal was then made up and tried in the chassis with the seat in place to get the correct pedal position. A mounting bar was welded at the correct height and position for the pedals.

Pedal Mock Up

The correct ratio for the pedals also needed to be calculated. The maximum movement of the clutch was measured from the engine end. The same was done for the accelerator and brake. Then the amount of pedal travel on a standard car was measured. Therefore by calculating a ratio between the two the pedals should feel the same as a standard car.

As it happened all ratios required were 2:1 which made the building of the pedals easier. Pivots for the pedals consisted of a metal bush and Allen key bolt. This pivot was attached to the mounting bar by using 1.5mm angle iron. The 3 pivots were tacked in place. The actual pedals were made out 4mm thick, 40mm wide steel strip. It was welded together in a Z shape. One end accommodates the pedal, the other the cable end.

The pedals were put in place and tested for height and spacing. Legally pedals have to be at least 50mm apart between the pads. These pedals were positioned 70mm apart including room for pads. It was soon clear that the Angle iron brackets for the pedals were not strong enough because they flexed when pressure was applied to a pedal. These brackets were replaced with 4mm angle iron instead. This was much better and reduced lateral movement of the pedals.

One of the main problems with the pedals was actually finding a suitable way of clamping the cable to the pedal without it slipping. Nipples that clamped the cable were made and tried but slipped and frayed the cable under heavy load. This was deemed not suitable. To solve this problem the cable ends were silver soldered to the cable and longer cable adjusters added to take up any slack. Extra slots had to be added to the mounting brackets to make the cables removable.

3 Wheeler Brakes

The braking system on this vehicle is complicated, mainly because the rear brake is a cable driven drum brake and the front are hydraulic disc brakes. Combining the two is not easy and there needs to be room for adjustment to allow for correct biasing of the whole system.

There are certain legal issues which arose during research that come into play. This concerns cable driven brakes such as the rear brake on this vehicle. Whenever using Bowden cable (wire rope) it is not suitable to just clamp the cable at both ends, correctly soldered ends need to secure it. It therefore made sense to use a ready made cable if possible. The obvious choice for this is a handbrake cable. However the length required was between 2.5m-3.0m long. Most cables are a little over 1.5m long. After doing some research the best solution was to use a handbrake cable from a transit van. This was 2.8m when fully stretched out. Using long brackets at either end meant it was just long enough.

The following adjuster was made for the rear cable connection. This adjuster also accommodates the handbrake cable. This is the main source of adjustment for the brake bias. On a vehicle like this the brake bias should be 75% on the front and 25% on the rear. This is very difficult to calculate in a situation like this. So it can be roughly tested by moving the car forward in a straight line and applying the brakes with force. If the rear brake locks up then the brake should be adjusted until it doesn’t lock anymore.

The front calipers were part of the sierra hub assembly along with the disks and pads. The master cylinder was taken from a VW Polo because this is a non servo assisted cylinder which is ample for this project and keeps everything nice and simple. Copper brake tubing was used to connect the master cylinder to the edge of the car then flexible sierra brake hoses to stretch to the brake cylinder. The master cylinder was positioned just behind the brake pedal so a short rod joins the two together, this can just be seen in the picture below. The rear brake cable also connects to the same pedal.

3 Wheeler Fuel System

On the donor motorcycle the fuel tank sits on top of the engine. The design of the chassis meant this would also be a suitable location for our fuel tank to be positioned. There was not space for the bike fuel tank to be used; therefore a new tank had to be manufactured. There was an obvious space for the tank above the engine and behind the seat and in front of the roll bar support. These three determined the limits for the tank size. It was also desired that the tank not protrude outside the lines of the vehicle already set by the chassis. The tank was designed to be as large as possible whilst still limited by the above constraints. The tank capacity was calculated to be 26 litres. The picture below shows the tank mounted in the frame.

Aluminium was chosen to make the tank as it will not corrode and is of lower density than steel. 1.6mm aluminium sheeting was used. The sides were designed to leave an edge to allow the tank to be clamped more easily for welding, as well as providing adequate material for welding, as shown in the righthand side picture above.

The locking mechanism was taken from the fuel tank for the bike, therefore a mounting system needed to be designed for the inside of the tank for the lock to bolt onto and seal against. Once the tank was welded, it was tested for leaks by filling it with water. Several leaks were spotted, and these were then re-welded to ensure a watertight seal. This would prevent the dangerous occurrence of petrol leaking onto the engine.

Air Filters

For the carburetors to function correctly and to protect the engine two air filters were designed. They consisted of a two sheets of aluminium rolled into tubes with a thin layer of foam clamped to one end. The other end fitted over the air inlet of the carb. Different thicknesses of foam were tried to gain the correct resistive pressure and it was found that half the thickness of the normal foam was needed. These filters were a quick simple and very efficient way of filtering the air for the purposes of getting the vehicle going. This solution is shown in the lefthand side picture below.

Early Temporary Air Filter

Subsequetly we found out that when we took the vehicle for it’s first proper test drive the air filters setup shown above restricted the air too much leading to the fuel burining rich. We ended up using the original air filter from the motorbike with flexible pipes which now provides a much more consistent air flow to the engine. This better solution is shown in the picture below.

Final Air Filter with Adapted Motorcycle Air Box

3 Wheeler Steering

The rack and pinion was acquired early on in the project, since it was needed to confirm the design of the frame. The steering column was also removed from the Ford Sierra. A universal joint was purchased to attach to the end of the spline on the rack and pinion. This joint was then connected to the steering column. A steering wheel was acquired from a scrap yard. A new mounting plate was manufactured for the back of the steering wheel. A nylon bush was made to support the steering wheel and act as a bearing, as shown below. All three drivers sat in the seat, in its different position and an optimum steering wheel position and angle was determined. A frame was welded onto the main chassis to support the steering column.

3 Wheeler Seat

It was decided to build the seat for the vehicle rather than buy a second hand one. This was mainly due to size constraints and DP’s eagerness to build it. The frame for the seat was made out of electrical conduit piping donated by the college. This was easy to work with because it could be bent to the required shape by using a pipe bender.

Welded and painted seat frame

The individual tubes were bent and tacked together to provide the frame. Once happy with the shape the whole frame was welded together. A base plate was also welded in place. This needed to be rigid instead of using strapping because the seat may be used to in and out of the vehicle. Once cooled, the frame was painted in silver Hammerite paint.

Straps were added for support

Support strapping was then riveted on to provide sideways support between the metal framing. An aluminum back plate was also riveted on to provide back support. A dense blue foam was sewn to the strapping to provide a good support and soft foam was glued to that to provide comfort. A slightly denser chip foam was used for the base just in case the seat is used to enter and exit the vehicle.

Foam then added for padding

It was decided to use leatherette vinyl for the covering. This would provide a relatively waterproof and durable cover and is far easier to machine than leather. Patterns were firstly made using thick brown paper. This is easily cut smaller or made larger by sticking bits on before it is cut out in the vinyl. When happy with the shape in the paper it was transferred to the vinyl. An extra 10mm was added to the border to allow for the seam. The Cover was made in 2 parts. The headrest, back and sides were made in one piece.

Leatherette Vinyl Cover

The seat base was made as a separate item. The whole seat cover is removable, just in case of damage at a later date. It is secured underneath by shoelace style webbing. Other areas are held in place with industrial Velcro.

The final seat

The seat has been made adjustable by mounting it on rails. This allows 3 different seat positions depending on leg length. The back is not reclining but the seat angle was agreed by all team members.

3 Wheeler Electronics

The wiring loom from the bike was attached into the car and all the control boxes and relays were mounted onto a board. The wiring loom proved not to be quite the right length, so some of the circuits were extended to fit. The battery was purchased and a mounting tray was designed and produced. This held the battery firm and allowed the power leads to be connected to it.

The horn, indicators, lights and starter/stop controls were wired up to a switches on the dash board. This involved further extensions of the existing wiring loom and the buying of new swithes to replace the original handlebar controls. The speedometer on the original motorbike was embedded within the front wheel so we had to come up with a suitable solution for this vehicle. A bicycle electronic speedo has been used because these are easily calibrated. A magnet has been arildited to the wheel to trigger the sensor and the display has been put inplace of the original speedo readout.

3 Wheeler Lights

The rear lights and rear number plate mounting were taken from the motorbike frame. These were connected up to the existing electrical harness using the existing connectors.

The front lights needed a complete redesign because 2 lights were now needed instead of one. We needed lights that were external self contained pods, an obvious donor vehicles for such lights was the Citreon 2CV. We found a suitable set in a local breakers yard for £15. They needed a bit of attention and a good cleaning but were sufficient for what we wanted. They were attached to the frame of the vehicle using a mounting bracket that would allow full adjustability of the lights.

The front indicators were made out of motorbike indicators mounted on a simple aluminium bracket. The switch for the indicators was made form a simple toggle switch mounted on the top of the steering column.

3 Wheeler Body Paneling

Various options were considered for the paneling for the vehicle. The first option was to not use any paneling and leave the frame exposed. This idea was rejected due to the issues of wind on the driver and for aesthetic reasons. Obvious choices for paneling were sheet aluminum or steel. Steel could be welded on, or either could be riveted or stuck on. Before the decision had to be made, we were made aware that the college could acquire large quantities of toughened foam, the type that is normally used for manufacturing signs. We decided to use this, firstly because it was free, and secondly it is lightweight and waterproof. It was decided to have several flat panels as opposed to bending individual panels. Panel frames were welded together for the bonnet and rear for the panels to be mounted to. This way the panels could be removed easily. The pictures below show the bonnet and rear panel mounting frames.

The panels were not produced within the 6 week schedule. The joins will be sealed with a paneling sealant and then smoothed down to leave a good finish. Cellulose paint has been purchased, as this can be used in a compressed air spray gun. It has the added benefit over enamel paint that it dries within 30 minutes and therefore if a mistake is made, it can be rubbed down and reapplied very quickly

Completed Car

The 3 wheeler now has all of the electronics complete and nearly all of the mechanical aspects of the car. The Mudguards are currently being made and the next priority will be the body work. The photo below is how complete the car was after 7 weeks of work.


In 2009 the car was eventually sold as the project was going nowhere and our eldest son was due to be born so we needed the space and I was not going to have time to progress it any further. It was time to say goodbye to the 3 wheeler and it was sold with 100% of the proceeds going to Help for Hero’s charity. Goodbye 3 Wheeler!

2 thoughts on “3 Wheeler Car Build

  1. Stevie Brad Reply

    i now have this car had it some years now still not on the road but hoping to one day soon

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