Suspension
Apart from your car's tires and seats, the suspension is the prime mechanism that separates you from the road. It also prevents your car from shaking itself to pieces. No matter how smooth you think the road is, it's a bad, bad place to propel over a ton of metal at high speed. So we rely upon suspension.
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 most American cars 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.
It's used in the suspension of VW Beetles and Karmann Ghias, 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 it's
length, which in turn resist. Now image that same shaft but instead of being
straight, it's coiled up. As you press on the top of the coil, you're actually
inducing a twisting in the shaft, all the way down the coil. I know it's hard to
visualize, but believe me, that's what is happening. There's a whole section
further down the page specifically on torsion bars and progressive springs.
Shock absorbers
Strangely enough, absorb shocks. Actually they dampen the vertical motion
induced by driving your car along a rough surface. If your car only had springs,
it would boat and wallow along the road until you got physically sick and had to
get out. Or at least until it fell apart.
Shock absorbers perform two functions. Firstly, they absorb any
larger-than-average bumps in the road so that the shock isn't transmitted to the
car chassis. Secondly, they keep the suspension at as full a travel as possible
for the given road conditions. Shock absorbers keep your wheels planted on the
road. Without them, your car would be a traveling deathtrap.
You want more technical terms? Technically they are called dampers. Even more
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.
Phew!....and you thought they just leaked oil didn't you?
The image above shows a typical modern coil-over-oil unit. This is an all-in-one system that carries both the spring and the shock absorber. The type illustrated here is more likely to be an aftermarket item - it's unlikely you'd get this level of adjustment on your regular passenger car. The adjustable spring plate can be used to make the springs stiffer and looser, whilst the adjustable damping valve can be used to adjust the compression damping of the shock absorber. More sophisticated units have adjustable rebound damping as well as a remote reservoir. Whilst you don't typically get this level of engineering on car suspension, most motorbikes do have preload, rebound and spring tension adjustment. See the section later on in this page about the ins and outs of complex suspension units.