What are sprung and unsprung weight and why do they matter?
First, we will discuss unsprung weight. Unsprung weight, when considering the automobile, is the mass of the vehicle’s suspension system. To make this clear, the unsprung weight has to do with the vehicle’s suspension system, the part of the vehicle that supports the chassis and drives the wheels into contact with the ground. Unsprung weight usually includes the wheels and anything directly connected to them. You may consider a portion of the struts, braking system, axles, wheel bearings, and vehicle control arm assemblies when speaking of unsprung weight.
The mass of these items is not supported by the suspension system and is the unsprung portion of the vehicle’s total mass. When observing a vehicle traveling over a bump, the vehicle’s chassis seems to rock while the wheels and tires remain in contact with the road. The portion of the vehicle that does not rock is unsprung mass, while the moving chassis represents the sprung mass of the vehicle.
Sprung mass represents the portion of the vehicle’s weight that is supported by the suspension system. The sprung mass includes the vehicle’s chassis and anything directly fastened to it that is able to move while the unsprung mass does not. You may consider the seats inside the vehicle, the engine and transmission assembly, and a portion of the drivetrain as sprung weight.
Unsprung and sprung mass are very important when considering ride comfort and vehicle traction control.