Unsprung Weight
The mass of vehicle components not supported by the suspension springs, such as wheels, tires, and brakes.
Unsprung weight (or unsprung mass) refers to the weight of all vehicle components that are not supported by the suspension springs. This includes wheels, tires, brake rotors, calipers, wheel hubs, steering knuckles, and a portion of the control arms and drive axles.
Minimizing unsprung weight is a key objective in vehicle design and suspension engineering. When a wheel hits a bump, a lighter wheel/tire assembly has less inertia, allowing the shock absorber and spring to control its vertical movement more quickly. This keeps the tire contact patch pressed firmly against the road, improving handling grip and ride comfort. Heavy unsprung weight slows suspension response, leading to a harsh ride and wheel hop.
Upgrading to lightweight alloy wheels, aluminum calipers, or carbon-ceramic brake rotors is a common way to reduce unsprung weight in performance vehicles. If suspension components are replaced with heavy steel aftermarket parts, it can degrade ride quality. Technicians check shock absorbers for wear, as worn dampers cannot control even normal unsprung weight, leading to tire bouncing and cupping.