Unsprung weight

Unsprung weight (unsprung mass) is the part of the motorcycle that is not supported by the suspension springs and moves up and down with the road surface. It includes the wheels, tyres, brake discs and calipers, axles, the lower fork sections and part of the swingarm, chain and shock.

The lighter these parts are, the more easily the suspension can keep the tyres pressed onto a bumpy surface. That improves grip, braking stability and ride comfort. Lighter wheels also reduce the gyroscopic and rotating mass, so the bike steers and accelerates more readily.

That is why racers use forged or carbon wheels and lighter brake parts, and why upside-down forks, with their light stanchions at the bottom, reduce unsprung weight compared with conventional forks.