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Spring Rate Calculator
The ride-frequency method race engineers actually use, in metric, without the forum folklore. Corner weight and motion ratio in — the spring rate your target behaviour demands, out.
Frequency method · v1.0
K = m·(2πf)² / MR²- In lb/in280 lb/in
- In kgf/mm5.0 kgf/mm
- Wheel rate44.2 N/mm
Starting point, not gospel: dampers, sway bars and aero all shift the final choice. Run front and rear separately.
The method engineers start from
A corner of a car is a mass on a spring. Give it a natural frequency and the required stiffness follows: wheel rate equals sprung mass times (2πf)². The motion ratio then converts wheel rate to spring rate — squared, because leverage costs you twice. That's the entire calculation, and it is the same one in professional race dampers catalogs, just usually hidden behind imperial units and lookup tables.
Frequency is the honest way to talk stiffness because it is car-independent: 2.0 Hz feels like 2.0 Hz whether the corner carries 250 or 450 kg. Rules of thumb worth keeping: rear typically runs 10–20% higher frequency than front for flat-ride, and if the calculator sends you far from your coilover maker's range for the car, re-measure the motion ratio before trusting either.
Frequency targets
| Ride frequency | Character | Typical use |
|---|---|---|
| 1.0–1.3 Hz | Plush | Comfort saloons, OEM softness |
| 1.4–1.7 Hz | Tied down | Sporty street, fast OEM |
| 1.8–2.1 Hz | Firm, flat | Fast road, occasional track |
| 2.2–2.5 Hz | Track stiff | Dedicated track cars |
| 2.5+ Hz | Aero territory | Race cars with downforce |
FAQ
The suspension is treated as a spring-mass system with a natural frequency. Pick a target for how the car should behave — 1.3 Hz comfort to 2.5+ Hz race — and the wheel rate follows from K = m(2πf)². It is how race engineers start every setup.
Wheel travel divided by spring travel. Strut coilovers sit near 0.95–1.0; inboard springs on wishbones typically 0.7–0.9. Measure if you can — the ratio is squared in the result.
Curb weight plus driver, split by your car's published front/rear distribution, halved per side. A 1,400 kg car at 60/40 puts ~420 kg on each front corner. Corner scales refine it later.