cutting coils and spring rate

[mattrick8888]

here is the situation. i have a 00 a arm ranger with a camburg 5.5 lift kit. the truck has some 2.0 resavoir shocks as well as some air bumps. the ride hieght right now is to tall. as it sits it only has about 2" of droop. i want to cut the coils but i need to know how much the spring rate will increase by doing this? i plan on cutting a qaurter of a coil off at a time. anyone have any experience with this?

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[FlyHiFlyLo]

The spring rate won't change assuming it isn't a progressive spring. The only thing that will change is the collapsed and extended length. If you cut it, I'd try to do it with as little heat as possible. You might be changing the properties of the material in an unfavorable way.

Your right. but I have always used a die grinder to keep the heat down. One coil is 2" on a stock Ranger.

[ntsqd]

google coil spring rate calculator. You can calc the spring rate if you know the OD, Coil diameter, and number of active coils. By measuring how far the truck compresses the springs now you can guess how far you have to go. If you have to compress the springs now to get them in it will throw things off a bit at first.
As you cut the springs will increase in rate which means each 1/4 coil cut will have less effect than the previous 1/4 coil.

[V8Ranger]

Disregard my previous post about the spring rate remaining constant. I think my brain was still out to lunch. If you haven't found a spring rate calculating program yet here is the equation: Spring Rate=(G*d^4)/(8*n*D^3)

Where:
G=11.5x10^6 for spring steel
d is the wire diameter in inches
n is the number of active coils
D is the mean diameter which is equal to the outer diameter minus the wire diameter

n is equal to the total number of coils for springs that are open and not ground (ie a stock ranger I-beam coil) n is equal to the total number of springs minus two for closed and ground springs (ie a coil-over spring).

Hope that helps. If the equation is confusing post the data on the springs and I'll calculate your spring rate before and after the cut length.

[partybarge_pilot]

http://www.proshocks.com/calcs/coilsprate.htm

For the lazy people.......

[Scott_F]

Thom, I think you said it backwards. Each 1/4 coil cut will have a slightly greater effect, as it will be a higher percentage of the remaining coils.

As you cut the springs will increase in rate which means each 1/4 coil cut will have less effect than the previous 1/4 coil.

[ntsqd]

Thom, I think you said it backwards. Each 1/4 coil cut will have a slightly greater effect, as it will be a higher percentage of the remaining coils.

I was referencing my previous sentence.

[Scott_F]

Oh, OK, you were referring to preload.

[FABRICATOR]

Something is missing from these formulas, including the one from Proshocks. These must all be assuming a certain pitch. The length of the wire in a coil spring affects spring rate just like the length of a torsion bar. Dual rate springs have two separate winds (pitches) to them all the time. Without knowing the pitch of the wind or the length of the spring, how can you calculate the spring rate?

[grantdcol]

Fabricator - I don't think that pitch and length matter, as they are accounted for in the number of active coils. Here is my line of reasoning:

Suppose you have two springs with equal wire thickness, inside diameter, and number of active coils, but with different overall lengths due to different pitch. Wouldn't they be the same spring rate? They both would have the same length of wire.

-Colin