“Your Car’s Suspension”Apart from your cars tyres and seats, the suspension is the prime mechanism that separates your body from the road. It also prevents your car from shaking itself to pieces. No matter how smooth you think the road is, its a bad place to propel over several hundreds of kilograms of metal at high speed. So we rely upon suspension. In a car, the rubber in your tyre helps with this little problem, while all the other suspension parts do the rest. In its most basic form, suspension consists of two basic components making up the suspension and these are as follows:- Springs - These come in three types. They are coil springs, torsion bars and leaf springs. Coil springs are what most people are familiar with, and are actually coiled torsion bars. Leaf springs are what you would find on many medium vehicles up to about 1985 and almost all heavy duty vehicles. They look like layers of metal connected to the axle. The layers are called leaves, hence leaf-spring. The torsion bar on its own is a bizarre little contraption which gives coiled-spring-like performance based on the twisting properties of a steel bar. Its used in the suspension of the likes of VW Beetles, air-cooled Porsches (356 and 911 until 1989 when they went to springs), and the rear suspension of Peugeot 205s amongst other cars. Instead of having a coiled spring, the axle is attached to one end of a steel shaft. The other end is slotted into a tube and held there by splines. As the suspension moves, it twists the shaft along its length, which in turn resist. Now image that same shaft but instead of being straight, its coiled up. As you press on the top of the coil, youre actually inducing a twisting in the shaft, all the way down the coil. I know its hard to visualise, but believe me, thats what is happening. Shock absorbers - These dampen the vertical motion induced by driving your car along a rough surface and so should technically be referred to by their proper name – that is dampers. If your car only had springs, it would boat and wallow along the road until you got physically sick and had to get out. It would be a travelling death-trap. Or at least it would be a travelling death-trap until the incessant vibration caused it to fall apart. Shock absorbers (dampers) perform two functions. As mentioned above, they absorb any larger-than-average bumps in the road so that the upward velocity of the wheel over the bump isnt transmitted to the car chassis. But secondly, they keep the suspension at as full a travel as possible for the given road conditions - they keep your wheels planted on the road. Technically they are velocity-sensitive hydraulic damping devices - in other words, the faster they move, the more resistance there is to that movement. They work in conjunction with the springs. The spring allows movement of the wheel to allow the energy in the road shock to be transformed into kinetic energy of the unsprung mass, whereupon it is dissipated by the damper. The damper does this by forcing gas or oil through a constriction valve (a small hole). Adjustable shock absorbers allow you to change the size of this constriction, and thus control the rate of damping. The smaller the constriction, the stiffer the suspension. If you thought they just leaked oil didnt you? Then think twice!
