Coilover Spring Rate Calculator
Calculate the recommended spring rate for your coilovers based on corner weight, desired ride frequency, and motion ratio.
| Application | Front (lbs/in) | Rear (lbs/in) |
|---|---|---|
| Economy sedan | 150–200 | 100–150 |
| Sport sedan | 250–350 | 200–300 |
| Track / autocross | 400–600 | 300–500 |
| Time attack | 600–900+ | 500–800+ |
What Spring Rate Means
Spring rate (k) is the force required to compress a spring by one inch (lbs/in) or one millimeter (N/mm). A higher spring rate means a stiffer suspension — less body roll and better control, but harsher ride. Most factory springs are 150–300 lbs/in on a typical sedan; performance coilovers may run 400–800+ lbs/in for track use.
Motion Ratio Explained
The motion ratio is the ratio of spring (shock) travel to wheel travel. If the wheel moves 1 inch and the shock moves 0.8 inches, the motion ratio is 0.8. A lower motion ratio means the spring must be stiffer to achieve the same wheel rate because mechanical leverage is reduced. Wheel rate = spring rate × motion ratio².
Front-Rear Balance and Handling
Running a higher natural frequency at the rear than the front (rear-biased setup) tends toward understeer — safer for road use. A front-biased setup (stiffer front) tends toward oversteer. For most street builds, keeping front and rear frequencies within 10–15% of each other produces predictable handling. Consult a suspension engineer for dedicated track setups where handling balance is critical.
Wheel Rate vs Spring Rate
Spring rate is what you measure on the spring itself. Wheel rate is what the wheel actually experiences, accounting for the motion ratio and any leverage geometry. Wheel rate = spring rate × (motion ratio)². Always calculate wheel rate when comparing setups or using this calculator — the spring rate alone without knowing the motion ratio is not meaningful for predicting ride quality.