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 was 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 drivers 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 thicker gauge was 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.
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:
