# Spring Rate Tech

Our Spring Rate Chart PDF lists spring rates for several popular vehicle applications as well as average street rod weights. Click on the red button to open the pdf file.

What is spring rate?

Spring Rate Correction for Angle Mounting Shock Angle Angle Correction Factor (ACF)
10° .98
15° .96
20° .94
25° .91
30° .87
35° .82
40° .77
45° .71 Example:
Straight Mounted Spring = 200 lbs.
Spring Mounted at 30° = 200/.87 = 230 lbs.

How to select the spring rate for independent suspension

Select your spring rate by using the following calculations: D1 = The distance from the pivot point of the a-arm to the mounting point of the spring/shock.
D2 = The distance from the pivot point of the a-arm to the center of the ball joint.
Divide D1 by D2 to calculate the force ratio (Fr).
Force Ratio (Fr) = D1/D2
Weigh your car to determine the weight on the wheels (W).
Divide the weight on the wheel by Fr to determine the force required at the spring (Sf).
W/Fr=Sf

If your spring is mounted at an angle you will need to consider that in your spring calculations. Measure the angle (A) of your spring from vertical in degrees. Use the table above to determine your Angle Correction Factor (ACF). Now divide the Spring Force (Sf) from the earlier calculation by the Angle Correction Factor (ACF) to get the Adjusted Spring Force (ASf).
Sf/ACF=ASf

Note: This calculation determines spring FORCE not spring RATE.

The required Adjusted Spring Force (ASf) can now be used to select the proper spring rate for your application. The required spring force can be obtained several different ways. A lighter rate spring with more preload or a stiffer rate spring with less preload will generate the same spring force. The softer rate will generate a smoother ride while the stiffer spring will result in a firmer ride. You need to consider these options when you are selecting the proper spring rate for your application.

ASf/(spring free length x 0.25) = Firmer Spring Rate