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Spring Rate Calculator:

To calculate your target coilover spring rate, enter your vehicle weights and suspension details in the fields below, then click the calculate button.

(A) Useable Wheel Travel: in.
(B) Coilover Angle: deg.
(C) Lower Arm Length: in.
(D) Shock Mount Distance: in.
(E) Sitting Droop Ratio: %
(F) Corner Sprung Weight: lbs.

Spring Rate:

For dual rate and triple rate coilovers, click here.

*If you are looking to correct your existing coilover springs, please see our Coilover Spring Re-Calculation Guide instead.*

(A) Useable Wheel Travel is the total vertical distance that the suspension allows your wheels to move without binding.
If the lower coilover mount is welded to the axle, then this measurement is that same as the shock stroke.

(B) Coilover Angle is the angle at which the coilover is mounted, measured in degrees from absolute vertical in any direction.

(C) Lower Arm Length is the length of the lower A-arm, trailing arm, or 4-link bar measured from the frame pivot to the wheel center.

(D) Shock Mount Distance is the measurement from the frame side pivot of the lower link to the lower coilover mounting point.
If the lower coilover mount is welded to the axle, then this measurement is equal to the lower arm length.

(E) Sitting Droop Ratio is the percentage of the shock shaft positioned inside the shock body at ride height.
(For example, if you want 6" of shaft showing at ride height on a 14" coilover, that's 8" of shaft inside the shock: 8/14 = 57%)

(F) Corner Sprung Weight is the total weight supported by the coilover. Sprung weight does not include axle or wheel weights.

A photo of a traling arm suspension with coilover angle, pivot distance, and trailing arm lengths labeled b, d, and c, respectively A photo of a 4-link suspension with coilover angle, pivot distance, and lower link lengths labeled b, c, and d, respectively A photo of an IFS suspension with coilover angle, pivot distance, and lower control arm lengths labeled b, d, and c, respectively

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Dual Rate Spring Calculation Guide

Performance off-road coilover shocks are designed to have two different springs installed on them such that the vehicle transitions from a softer combined spring rate to the stiffer lower spring at some point during the compression stroke. For 8" and smaller coilovers, there might only be space for a single spring while 16" and 18" coilovers may require a third "tender" spring to prevent the springs from going loose at full extension.

In a dual rate coilover setup, the upper primary spring is placed on top of the secondary spring which is either the same rate or heavier than the primary spring. During the initial stroke, the two springs will compress together to give you a lighter combined rate (see table below) for the initial up stroke until the slider hits the transition nuts (secondary nuts) at which pint the upper spring is taken out of the equation and all remaining up travel is transferred to the lower secondary spring.

For dual rate coilovers you will need to multiply the spring rate calculated above by two to get the required spring rates. While running the same spring top and bottom will still give you a transition, we recommend (if possible) a 50 lb. heavier lower spring in the 100 to 300 lb. range and a 100 lb. heaver spring for spring rates 400 lb. and above for a more significant transition. The lower spring, in general, should never be more than 150 lbs. heavier than the top spring.

Effective Primary Spring Rate In A Dual Rate Configuration

100 50
150 6075
200 6786100
250 7194111125
300 75100120136150
350 78105127146162175
400 80109133154171187200


Combined effective coilover spring rate listed in lbs./in.

Triple Rate / Tender Springs / Helper Springs

Tender springs, also known as helper springs, are used in applications were the primary springs don't allow the coilover to settle down low enough under the weight of the vehicle to reach the desired ride height. This happens most often with long travel coilovers in applications with a relatively low ride height. Tender springs are low rate (50 to 90 lbs./in.), short (3" to 5"), and often made with flat wire. They remain compressed under load until the other springs fully extend at which point the helper spring expands keeping a load on the springs to prevent them from going loose.

Video: Coilover Springs, Spring Rates, and Calculations

This coilover spring calculator is ©Copyright - Please provide a link back to this page when copying.
Data is accurate to the best of our knowledge and is offered as-is with no guarantee.

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Shock Rebuilding Tools - A list of tools needed to service high-performance shocks and coilovers.
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Shock Tuning Guide - A guide to how high-performance shocks are tuned and valved to work well.
Shock Valving Shim Stack Examples - A list of common, basic valving shim stack configurations for high-performance shocks.
4-Link Suspension Guide - A quick overview of the most important elements of 4-link geometry.
Shock Rebuild Parts - A link to Filthy Motorsports' shock parts page.
How To Measure For Coilovers - Order the right size shocks and coilovers by following these detailed instructions.
Coilover Install and Setup Guide - Proper coilover installation, setup, and fine tuning instructions.
Coilover Spring Re-Calculation Guide - How to easily correct coilover spring rates to achieve your desired ride height.
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