Motion ratio

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The motion ratio of a mechanism is the ratio of the displacement of the point of interest to that of another point.

The most common example is in a vehicle's suspension, where it is used to describe the displacement and forces in the springs and shock absorbers. The force in the spring is (roughly) the vertical force at the contact patch divided by the motion ratio, and the wheel rate is the spring rate divided by the motion ratio squared.

This is described as the Installation Ratio in the reference. Motion Ratio is the more common term in the industry, but sometimes is used to mean the inverse of the above definition.