Spring Rate
Spring rate is the change in spring force divided by the corresponding change in spring deflection.
What the number describes
A linear spring has approximately constant rate over its working range. A progressive spring’s rate increases with deflection, while air springs and shaped or staged components can produce strongly position-dependent behavior.
Spring rate is a property at the spring, not automatically at the wheel. Mounting position and suspension motion ratio convert it into wheel rate. Tire stiffness, bushings, bump stops, anti-roll devices, and multiple springs can further change the effective vertical stiffness felt by the vehicle.
The rate also does not state ride quality by itself. Sprung mass, damping, available travel, seat and body structure, tires, and excitation frequency all affect the response.
For spring types and load support, see Suspension Springs. For motion ratios and wheel response, see Suspension Kinematics and Vehicle Dynamics.