Unsprung mass

This contrasts with the sprung mass (or weight) supported by the suspension, which includes the body and other components within or attached to it.

If the vehicle does not have adequate wheel location in the vertical plane (such as a rear-wheel drive car with Hotchkiss drive, a live axle supported by simple leaf springs), vertical forces exerted by acceleration or hard braking combined with high unsprung mass can lead to severe wheel hop, compromising traction and steering control.

A beneficial effect of unsprung mass is that high frequency road irregularities, such as the gravel in an asphalt or concrete road surface, are isolated from the body more completely because the tires and springs act as separate filter stages, with the unsprung mass tending to uncouple them.

Heavy components such as the differential can be made part of the sprung mass by connecting them directly to the body (as in a de Dion tube rear suspension).

Lightweight materials, such as aluminium, plastic, carbon fiber, and/or hollow components can provide further weight reductions at the expense of greater cost and/or fragility.

The term "unsprung mass" was coined by the mathematician Albert Healey of the Dunlop tyre company.

[2] Inboard brakes can significantly reduce unsprung mass, but put more load on half axles and (constant velocity) universal joints, and require space that may not be easily accommodated.