Motion ratios are defined as the ratio between the displacement of a specific point of interest in a mechanical system with respect to another point in the same system. More specifically, in automotive engineering, the motion ratio "MR" is defined as the ratio of wheel displacement to shock/coilover travel. Motion ratios are critical in suspension design as it defines the spring force to be roughly the vertical force at the wheel contact patch divided by the motion ratio, i.e.

Additionally, the spring rate (i.e. the force required for one mm of spring compression, also known as the spring constant) is approximately the product of the wheel rate (i.e. the actual rate of the spring acting at the wheel), the angle correction factor, and the motion ratio squared, i.e.

where the angle correction factor is computed as:

Motion Ratios in MSXII

MSXII is using a pushrod inboard suspension design for a handful of reasons, the most important being decoupled shock to wheel travel (i.e. the coilover may travel more/less than the wheel), and easier access to the suspension for servicing and tuning (alongside slightly improved aerodynamics). As such, our motion ratio must compensate for a pushrod as well as a rocker coupling the pushrod to the coilovers.