Spring Rate & Wheel Rate Calculator
Calculate the effective wheel rate from spring rate, motion ratio, and installation angle � essential for suspension tuning and natural frequency calculations.
Results
What is it?
Wheel rate (also called "wheel centre rate") is the effective spring stiffness measured at the wheel contact patch � what the tire actually feels. It differs from spring rate because of the mechanical disadvantage (motion ratio) of the suspension geometry and the cosine effect of the spring installation angle.
How to use
Enter the spring rate (measured or from the spring manufacturer in N/mm), the motion ratio (measured by jacking the wheel and measuring spring travel vs wheel travel), and the spring installation angle from vertical. Wheel rate = Spring Rate x Motion Ratio� x cos�(angle).
Example scenario
A 200 N/mm spring with a motion ratio of 0.85 and 10-degree installation angle: wheel rate = 200 x 0.85� x cos�(10�) = 200 x 0.7225 x 0.9698 = 140.2 N/mm. The suspension geometry and angle together reduce the wheel rate by nearly 30% from the spring label rate.
Pro tip
Use wheel rate (not spring rate) to calculate suspension natural frequency: Fn = (1/2p) � v(wheel rate / corner mass). Target 1.0�1.5 Hz for comfort, 1.5�2.5 Hz for sport, and 2.5�4.0 Hz for track use. Lower natural frequency than the body roll frequency will cause "push" understeer in fast corners.