Free tool

Spring rate calculator

Estimate the spring rate your car needs from its weight and how you drive it, then convert between kg/mm, lb/in and N/mm. Most coilover listings, including every SF Racing kit we carry, quote spring rates in kg/mm.

What spring rate do I need?

Weight units

Curb weight

Front weight %

Axle

Unsprung per corner Wheel, tire, brake, hub, half the arms. 70 to 110 lb is typical.

Suspension layout (motion ratio)

How you use the car Ride frequency is how fast the car bounces on its springs. Higher means stiffer.

0.0 kg/mm

Spring rate converter

Rate

Unit

1 kg/mm = 55.997 lb/in = 9.807 N/mm.

Common rates

kg/mm	lb/in	N/mm
4	224	39.2
6	336	58.8
8	448	78.5
10	560	98.1
12	672	117.7
14	784	137.3
16	896	156.9
18	1008	176.5

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