Suspension Motion Ratio
Suspension motion ratio relates wheel movement to the movement of a spring, damper, anti-roll link, or other suspension component.
Why the convention matters
The ratio may be stated as component travel divided by wheel travel or as its inverse. A number is ambiguous unless the convention and measurement direction are given. Installation angle and changing linkage geometry can also make the ratio vary through the suspension travel.
Motion ratio converts component stiffness, damping, and force into their effects at the wheel. For spring rate, a consistent displacement ratio commonly enters the wheel-rate relationship as its square; force and damping conversions must use the same defined geometry and sign convention.
A spring and damper mounted at different points can have different motion ratios, and the ratio in roll or steering motion may differ from the simple vertical value.
For the full wheel-path and force relationship, see Suspension Kinematics and Vehicle Dynamics.