By 
Coil springs and leaf springs are the two most common type of spring within the automotive and motorsport industries. However, other types of spring have been tried and tested in an attempt to get the edge over competitors. Some of the following springs are still used within motorsport today.
Torsion Bars
Torsion bar springs work in an almost identical way to anti-roll bars. They are effectively a length of bar, usually steel, mounted within the chassis length ways. One end is fastened to the chassis and the other to a lever arm connected to the wheel. When the wheel lifts up, the torsion bar is twisted and wants to spring back to its resting centre. This spring force from twisting the metal rod and putting it in torsion acts as the spring against the wheel and the cars mass.
Torsion bars need to be quite long in order to be able to twist to the enough of an angle to be usable. However, even with a lot of leverage, the available space to mount a lever arm and a length of bar is only so large. Therefore, there is never a lot of movement available from the bar and therefore needs to be used in a very stiff application where the wheel isn’t required to move vertically by very much. Due to this it has only really been used within formula 1 and world endurance series where body roll and wheel movement is kept to an absolute minimum on a very smooth track surface.
A benefit to using a torsion bar as a spring is that it is very slender and therefore can be packaged out of airflow within the cars body work, whilst still allowing the body to remain very thin and sleek. The aerodynamic benefits of a torsion bar spring are the main reasons why they were adopted within motorsport.
Furthermore to being sleek and easy to package, the torsion bar is usually very easy to swap out for different sizes and stiffness’s for fast spring rate changes on the car. A wide range of spring rates can be manufactured and stored easily and are all interchangeable in the setup, often by simply loosening a grub screw and sliding the bar out form the body.
Rubber
Rubber has been tried and tested within motorsport a few times as a spring. It has appeared in two main forms as a spring; one as a rubber dohnut and one as a large elastic band.
The rubber dohnut spring uses a large block of rubber with a metal disc mounted to the top and bottom. A lever arm is mounted to the hub and pivoted on the chassis. The other end is then mounted to the top of the rubber block and compresses it when the wheel rises. If the rubber is compressed it will spring back up and if the rubber is stretched in droop then the rubber will pull back to centre position acting as a spring. The rubber dohnut is a light and durable option for a spring but it has more flaws than benefits.
Firstly, the rubber block, even with complex contours and shapes, is difficult to compress and does not have a lot of movement. Therefore, a larger leverage arm is required in order to apply enough force to the rubber block. The increased sized leverage arm requires stronger pivoting points and stronger components which develop into a heavy system in order to be reliable. Secondly, it is more difficult to accurately determine the spring rate of the rubber especially as the lifetime increases and the rubber begins to wear and perforate.
The elastic band system is rarer than the rubber block spring and was a shorter lived experiment. It worked by having a large elastic band mounted to the chassis and the other end mounted to a pull rod. The band was always in tension so that it would work in bump and droop. However, the complexity of the system required to operate the bands took up too much space and was effectively the downfall of the system within motorsport due to the increased weight from extra linkages and the unreliability of the system.
AIR
Air is still a successfully used spring within the automotive industry today. However, it is mainly used within commercial and very specific tuning applications. Due to being all around us and free, air is an obvious choice to try and make work as a spring. Once compressed and contained it is also good as a spring and can be adjusted constantly just by increasing and decreasing the air pressure.
It is used within large commercial applications more than anywhere else. This is due to it being a cheap and highly adjustable spring that can be changed for increased loads and can raise and lower ride height for loading etc. However, air springs require many extra components to make it work. They require an air compressor, plumbing, seals and strong rubber bags to contain the compressed air. All of this requires a lot of space to be mounted and weighs a lot more than alternatives such as coil springs or torsion bars.
Furthermore, air heats up a lot when it is being worked repeatedly by a vehicle over rough surface or travelling at high speed with constant multiple direction changes. As the air heats up, the effective spring rate changes constantly which is not ideal for a competition car as the spring rate needs to be calculated and remain as constant as possible.
Another application where air springs are used is within the low car tuning scene where the only objective of the car is to be as low as possible. The use of air springs allows large height changes to be made to the ride height at the touch of a button. This ease of ride height change has also seen air springs applied to off road vehicles where different off road settings can be altered by the driver within the cabin.
Oil
Oil has been used as the fluid of choice within a damper for years now. As the fluid is already mounted to the car, it makes sense that it should be used as a spring as well. This was tried for the first time in the development years ahead of the 1987 Lotus 99T formula 1 car. In these years not only was the oil used as a spring but it was also part of an elaborate first attempt at an active suspension system. The thought behind it was that along with the use of a sophisticated electronic system, the oil could be used in place of the coil springs and torsion bars to not only constantly adjust the ride heights and damping but also the stiffness of the car. However, the death of Chapman brought an end to the idea of fully replacing the springs with the oil system and led to the final solution utilizing the oil as an active suspension system coupled with more conventional springs on the 1987 Lotus 99T.
The active suspension system was so good that it immediately started winning races and raising eye brows within the world of formula 1. It was not long before this system became banned to level the playing field and it has not been seriously revisited since. This is most likely due to the complexity and extremely high cost of the system making it not worth the while of less wealthy racing categories to trial.
