Sprung And Unspung Weight

A reduction in weight of 1 kg on the unsprung mass is equivalent to a reduction of 8 kg on the car overall.

Another factor affecting how the wheel will behave is the mass of the components in contact with the road. Everything on the wheel side of the spring is known as unsprung weight and includes the wheel, tyre, hub and bearings, the brake disc and caliper and the lower portion of the damper, usually containing the oil. Everything above the spring is considered sprung weight and is basically the rest of the car.

Reducing the unsprung mass helps enormously, since it means the suspension can control the wheels' behaviour much better, think of the bowling ball on the end of the spring; a lighter ball will be much easier to handle. In fact, a reduction in weight of 1 kg on the unsprung mass is equivalent to a reduction of 8 kg on the car overall, in terms of the vehicle's dynamics.

Lightweight wheels can help here, as can replacing cast iron brake discs with two-piece versions, using an aluminium mounting bell, which sits behind the wheel with a cast iron disc bolted to it. Aluminium or even magnesium hubs are typically used in motorsport for the same reason. Remote reservoir or some gas-charged dampers can sometimes be mounted upside down, eliminating the mass of the oil from the unsprung weight.