Most of a vehicle’s weight is supported by its suspension system. It suspends the body and associated parts so that they are insulated from road shocks and vibrations that would otherwise be transmitted to the passengers and the vehicle itself.
However, other parts of a vehicle are not supported by the suspension system, such as the wheels, tires, brakes and steering and suspension parts not supported by springs. These parts are all called unsprung weight. Generally, unsprung weight should be kept as low as possible.