“Sprung” and “un-sprung” mass: what those are?

The mass that form a vehicle’s total weight can be split in two types:

  • the sprung mass are the one linked to the ground through the shocks, and consequently subjected to variations in the ground clearance: these are usually the chassis, the engine, the body and all those parts rigidly bolted to these.
  • the un-sprung mass are the one wich are not (or shouldn’t be…) subject to any variation in ground clearance since they follows the ground pattern: typically these mass shall consist in the wheels and all the components bound to them, as some shock dampers and braking system parts.

  • Sprung mass;
  • Un-sprung mass.

The sprung mass changes its distance between the ground and the un-sprung masses by the shock dampers that, by compression and extension, absorbs the road’s bumps.

The un-sprung mass consists in wheels and oscillating suspension parts, that are in contact with the ground and then follow the road pattern, keeping a costant ground clearance.

Even with equal total mass, it’s important that the sprung to un-sprung mass ratio will be as high as possible: this determinates in fact to have a lower inertia of wheels and suspensions, that can promptly react to the road’s asperities; and thus a major inertia of the vehicle’s body that suffers to a lesser extent from the stresses transmitted by the shock dampers. In other words, the higher will be the sprung to un-sprung mass ratio, the lower will the frame’s transmitted vibrations be.