Suspension Spring Rate Calculator
The stiffness of a coil spring is not the same as the stiffness felt at the wheel, because suspension geometry applies leverage between the spring and the contact patch. This calculator takes your spring rate, the motion ratio (spring travel divided by wheel travel) and the sprung mass at that corner, then returns the wheel rate (effective vertical stiffness) and the undamped ride frequency in hertz. Wheel rate uses the motion ratio squared, and ride frequency follows the standard single-degree-of-freedom natural-frequency formula.
Spring rate and frequency formula
Wheel rate (N/mm) = spring rate * motion ratio squared
Wheel rate (N/m) = wheel rate (N/mm) * 1,000
Ride frequency (Hz) = (1 / 2 pi) * sqrt(wheel rate N/m / sprung mass)
Because both the force and the displacement at the wheel scale with the motion ratio, wheel rate equals spring rate times the motion ratio squared. The undamped natural frequency is one over two pi times the square root of stiffness over mass, using stiffness in newtons per metre and mass in kilograms.
Suspension context
- Wheel rate is always lower than spring rate when the motion ratio is below 1.0.
- Comfort road cars often sit near 1.0 to 1.5 Hz; sports and race cars run higher.
- The sprung corner mass excludes the unsprung wheel, tire and hub.
- Ride frequency here is undamped; dampers reduce the effective oscillation.
- Use measured motion ratio and corner mass for your specific vehicle.
Suspension spring rate: frequently asked questions
What is the difference between spring rate and wheel rate?
Spring rate is the stiffness of the coil itself. Wheel rate is the effective vertical stiffness felt at the contact patch, which is lower when the spring is mounted with leverage. Wheel rate equals spring rate times the motion ratio squared.
What is the motion ratio?
The motion ratio is the ratio of spring travel to wheel travel. If the wheel moves 2 inches while the spring compresses 1 inch, the motion ratio is 0.5. Because force and displacement both scale with it, wheel rate uses the motion ratio squared.
How is ride frequency calculated?
Ride frequency is the undamped natural frequency of the corner, equal to one over two pi times the square root of wheel rate divided by sprung corner mass. It is a standard measure of how soft or stiff a suspension feels, expressed in hertz.
What sprung mass should I enter?
Enter the sprung mass carried by that single corner: the portion of the vehicle weight supported by that spring, excluding the unsprung wheel, tire and hub assembly. This is your measurement for your car, so it is a user input.
What ride frequency is typical?
Comfort-oriented road cars often sit around 1.0 to 1.5 hertz, sports cars higher, and race cars can exceed 2 to 3 hertz. The right value depends on the vehicle and use, so the calculator reports the frequency your inputs produce rather than recommending one.
Official sources
- NASA Glenn Research Center: Natural Frequency and Oscillation.
- U.S. National Institute of Standards and Technology: SI Units and Conversions.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.