The wheel rate is the product of the coil rate, the mounting location of the spring, and its inclination. It is improbable that the mounting of your coil springs will result in a 1 to 1 ratio unless you have inboard suspension. Therefore, it is crucial to determine the leverage and calculate the effective wheel rate to ensure optimal performance.

Basic calculations

Traditional calculations use these three sums to calculate the suspension leverage.

Mounting point moment

Taking the lower wishbone as the lever arm with the chassis being at the pivot point and the center of the wheel being at the outermost point, how far along the arm does the spring attach?

Spring inclination

With the spring ideally being mounted vertically, adjust the leverage based on its inclination. This is cos(angle).

Rocker gearing

The difference between the distance from the pivot to the spring and the pivot to the rod. In most cases, this calculation replaces the spring inclination calculation.

Racing Aspirations Calculations

The basic calculations are okay for quick calculations but do not take into account how the leverage changes over the range of the suspension travel. They are not entirely accurate without delving deeper into the spring mount relative to the rocker position.

The wheel rate is affected by the motion ratio, which is the difference in movement between the wheel and the spring. Suppose the wheel moves 10mm, but the spring only moves 5mm. In that case, the suspension leverage is 0.5:1. If the wheel moves 10mm, and the spring moves 8mm, the suspension leverage is 0.8:1. It doesn’t matter which kinematic mechanisms connect the spring to the wheel; comparing the wheel’s travel with the spring travel is the most accurate method of calculating suspension leverage and wheel rate.

The RA calculators use this method since it’s the most precise way to calculate suspension leverage and wheel rate.