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?

[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

[tim_krueger]

im only on my 2nd beer and you already lost me...lol

[DPpatrol]

Colin's logic is correct.

jason

[FABRICATOR]

Colin's logic is correct.

jason
Then why do dual rate springs have two different winds (pitches) on the same spring? There has to be a ratio between pitch and wire twist. A flater wound spring is always softer than a steeper wound one.

[ntsqd]

In the case of a dual rate/pitch spring you have to consider each pitch section as a separate spring.

If you want to have some fun try calcing the rate for the springs first used on the Porche 917 Can-Am cars. Tapered wire stock, progressively wound (constantly varying pitch). And just for fun they made them from Titainium.

[ChuckH]

I have to agree with the other Chuck, aka FABRICATOR

Lets go to the TelePrompter :D

Same wire size different pitch

Straight Rate.............Dual Rate.............Progressive Rate

http://motorcycleinfo.calsci.com/Images/SHOCKS3.gif

[Ramsey_ElWardani]

A flater wound spring is always softer than a steeper wound one.

To state the obvious, a coil spring is just a torsion bar wound in a coil. The tighter the winds, the longer the torsion bar is. The longer a torsion bar is the softer its spring rate is.

Progressive wound springs become progressive as the tighter wound coils reach coil bind. The same applies to tapered wire coils.

[FABRICATOR]

To state the obvious, a coil spring is just a torsion bar wound in a coil. The tighter the winds, the longer the torsion bar is. The longer a torsion bar is the softer its spring rate is.




Closer coils have the effect of being a longer "bar", but the wire can be the same diameter, length, and wound in the same coil size. The reason for different spring rates has still not been explained.

[AaronDixon]

Closer coils have the effect of being a longer "bar", but the wire can be the same diameter, length, and wound in the same coil size. The reason for different spring rates has still not been explained.

The different rates come from coil bind. Once part of the spring is in coil bind, that cuts the length of the spring and rate goes up. Its like a stop nut on a dual rate coilover, once the slider hits that stop, the upper springs quits working, and the high-rate lower spring is the only one working.

Aaron

[V8Ranger]

Closer coils have the effect of being a longer "bar", but the wire can be the same diameter, length, and wound in the same coil size. The reason for different spring rates has still not been explained.

Wouldn't the spring rate of a dual rate progressive spring (K effective)) just be 1/(1/k1+1/k2) which would end up being less that k1 and k2?

I think each time the spring has a change in pitch you have to analyze that part of the spring as a separate spring (ie k1, k2, k3 etc).

[FABRICATOR]

I think we got the coil bind part of it...


Wouldn't the spring rate of a dual rate progressive spring (K effective)) just be 1/(1/k1+1/k2) which would end up being less that k1 and k2?

I think each time the spring has a change in pitch you have to analyze that part of the spring as a separate spring (ie k1, k2, k3 etc).

Obviously a dual rate spring is comparable to 2 springs of different rates put together. But "both" springs together have the same diameter wire, same diameter coil, same overall length of wire, and the same number of active coils as a comparable straight rate spring. With that in mind, it should be safe to say that the spacing of the active coils, or pitch, can make a significant difference in the spring rate. So, how then can one calculate the spring rate without knowing either the overall length of the spring or the pitch of the coil?

[toddz]

I think we got the coil bind part of it...



Obviously a dual rate spring is comparable to 2 springs of different rates put together. But "both" springs together have the same diameter wire, same diameter coil, same overall length of wire, and the same number of active coils as a comparable straight rate spring. With that in mind, it should be safe to say that the spacing of the active coils, or pitch, can make a significant difference in the spring rate. So, how then can one calculate the spring rate without knowing either the overall length of the spring or the pitch of the coil?

By using the equation that was posted earlier in this thread!!!

Todd Z.

[DPpatrol]

Mr. Aaron Dixon is absolutely correct. A progessive spring only become progressive once the closely spaced coil begin to touch (binding). Once the coils touch, they cant compress anymore, so they are no longer active coils. So the spring rate is adjusted by the number of active coils being reduced. A "progessive" rate spring with a million different pitches on the same spring will have a constant spring rate as long as all the coils remain active.

jason

[FABRICATOR]

Mr. Aaron Dixon is absolutely correct. A progessive spring only become progressive once the closely spaced coil begin to touch (binding). Once the coils touch, they cant compress anymore, so they are no longer active coils. So the spring rate is adjusted by the number of active coils being reduced. A "progessive" rate spring with a million different pitches on the same spring will have a constant spring rate as long as all the coils remain active.

jason

You are both correct, but that was not the point. So what you are saying is that if one spring is wound like the soft side of a dual rate spring and one like the stiff side, the rates would be the same?

[DPpatrol]

Yah, if the only difference were the pitch of the springs (same number of active coils, yada yada yada) they would have the same spring rate. The only difference is the "soft side" one would be longer and the "stiff side" would be shorter, assuming all coils remain active.

jason

[FABRICATOR]

Yah, if the only difference were the pitch of the springs (same number of active coils, yada yada yada) they would have the same spring rate. The only difference is the "soft side" one would be longer and the "stiff side" would be shorter, assuming all coils remain active.

jason

You might have the long/short reversed, but why would the springs be different lengths?

[DPpatrol]

The "soft side" pitch is usually larger so the coils are less likely to bind. A "stiff side" pitch is usually smaller so the coils will bind. If they have the same number of active coils, the "stiff side" spring will be shorter because the coils are closer together (smaller pitch) than the "soft side" spring (larger pitch).

jason

[FABRICATOR]

The "soft side" pitch is usually larger so the coils are less likely to bind. A "stiff side" pitch is usually smaller so the coils will bind. If they have the same number of active coils, the "stiff side" spring will be shorter because the coils are closer together (smaller pitch) than the "soft side" spring (larger pitch).

jason

Hmmm, I thought pitch, distance between the coils, and spring length, had nothing to do with spring rate...

[dislocated1]

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?


Why dont you just run a stock coil in there, I am pretty sure that Braden's 7100 truck runs a stock coil and that should give you the droop you want

[mattrick8888]

that doesnt look like a stock coil. with a stock coil the lower arm would be about flat. that truck looks like it rides about as high as mine is right now. maybe they spaced the coil down in the bucket somehow?