Damping

Damping is the controlled resistance applied to the movement of a vehicle's suspension in order to dissipate energy and prevent the springs from oscillating freely. It exists because a spring on its own, once disturbed by a bump, would continue to bounce up and down for several cycles, storing and releasing energy without ever settling. Damping converts that kinetic energy into heat and bleeds it away, so the wheel returns to the road quickly and the body comes to rest, which is fundamental to both ride comfort and the tyre's grip on the surface.

The resistance is provided by the dampers, almost universally known as shock absorbers, although strictly it is the damper that controls motion rather than absorbing the initial shock, a job the spring does. A typical telescopic damper contains a piston moving through oil within a sealed tube; small orifices and spring-loaded valves in the piston restrict the flow of oil from one side to the other, and the force needed to push the fluid through those restrictions is what resists the suspension's motion. Because that resistance rises with the speed of movement, dampers react gently to slow, gentle inputs and firmly to sharp ones.

The quality of damping is a careful balancing act, and getting it wrong is immediately noticeable. Too little damping leaves the car floating and wallowing, the body continuing to heave after every undulation and the wheels skipping over bumps with a loss of grip. Too much damping makes the suspension harsh and reluctant to move, transmitting every ridge into the cabin and again hurting grip because the tyre is jarred off the road rather than kept in contact with it. The art of chassis tuning lies in finding the resistance that keeps the body composed without sacrificing compliance.

Dampers are tuned separately for the two directions of travel. Compression, or bump, damping controls the wheel rising towards the body as it strikes an obstacle, while rebound damping controls the wheel extending back down as the spring pushes it away again. These are usually set to different values, often with rebound damping stronger than bump, so that the suspension absorbs impacts softly yet recovers in a controlled way without flinging the body upward.

Damping need not be fixed. Adjustable dampers let the rate be altered by hand, while adaptive suspension systems vary it electronically in real time, using valves or magnetorheological fluid whose viscosity changes under a magnetic field to stiffen or soften the response according to road conditions and driving style. This allows a single car to offer both a supple ride and tight body control on demand.

Damping is inseparable from the components and concepts around it. It is delivered by the damper, or shock absorber, works in partnership with the springs it restrains, is split between bump and rebound phases, and reaches its most sophisticated form in adaptive suspension.