| Motion Ratio | Wheel Rate |
|---|
What Motion Ratio Is
Motion ratio describes how wheel movement relates to spring movement. Because springs and shocks are rarely mounted directly above the wheel, the wheel usually moves a different amount than the spring does. That geometric relationship quietly controls how stiff your spring actually feels at the tire, and it is one of the most overlooked numbers in suspension setup.
Why It Squares
The effect on rate is not linear, it is squared. With the wheel-to-spring convention, a motion ratio of 1.25 does not cut effective stiffness to eighty percent, it cuts it to about sixty-four percent, because both the force and the distance are reduced by the ratio. This squared relationship is why a small change in mounting geometry has a big effect on ride.
Measuring Your Motion Ratio
Jack the suspension through its travel and measure how far the wheel moves versus how far the spring or shock moves over the same span. Divide wheel movement by spring movement to get the ratio. Measure near ride height, since the ratio can change through the travel on many suspension designs.
Frequently Asked Questions
Why does my spring feel softer than its rating?
If the wheel moves more than the spring, leverage works against the spring and the wheel rate is lower than the rated spring rate. Motion ratio explains the gap.
Which convention is this?
This tool uses wheel travel divided by spring travel, so the ratio is at or above one for most inboard setups and wheel rate equals spring rate divided by the ratio squared.
Does motion ratio change with travel?
On many suspensions it does, especially toward the ends of travel. Measuring around ride height gives the most representative value for tuning.