Coil compression cause spring rate loss / spring damage?

[sled_dog]

A friend and I are discussing coilovers at the moment. He is thinking about his Ranger and doing a SFA swap, told him I hope to have a connection for coilovers by the time he is thinking of doing it so maybe we can help him out. Anyway, he brings up an interesting point in one of his questions. When a spring is fully compressed, does it become damage? Does it lose spring rate? Wear out? I know when a leaf spring is compressed into negative arch it is damaged and loses spring rate. So theoretically if I parked a buggy up on a ramp for a week in front of a shop as a show off piece, could I be damaging its suspension? At the same rate, when the coils on the rear of my S10 are compressed up in the same manner, am I damaging them? I'm talking like, coils touching coils, can't go any farther compressed.

 

[sled_dog]

My friend pointed out that on SAW's site they have what looks like a stopper setup on the threaded body of their coilovers. Looks like it stops the slider so you can't fully compress the upper spring. Wondering if that is in fact its purpose. Emailed SAW about that and their opinion of coil compression.

 

[sled_dog]

can someone else email Sway-A-Way? I tried twice, once on my email and once from a Yahoo account and it bounced back both times.

http://www.swayaway.com/

I'm looking at your 2.5" coilover remote resovoir shocks. I noticed you have what looks like a set of lock nuts on the threaded portion of the shaft below the upper coil retainer. Is this a stop for the dual rate slider? I'm wondering, is it bad to fully compress one of the coils on the coilover? Does it damage the spring? Thank you in advance.

 

[tx_sub]

Its really a function of the material the springs are made of. If you exceed the yield strength of the material, you will have deformation. That's about the best I can explain without getting into the math. That being said, common sense would say not to put your leafs in a negative arch or bottom out your coil. I would hope that SAW or other aftermarket coil spring manufacturer could tell you a maximum compression for a particular spring to prevent failure.

Rereading your post, when it comes to coilovers, the shock is the limiting factor. the shock will max out compression well before the coil is completely compressed.

 

[sled_dog]

Rereading your post, when it comes to coilovers, the shock is the limiting factor. the shock will max out compression well before the coil is completely compressed.

You can't make that statement with the coilovers we have. There is so much threaded body to adjust coil position I can definetally see maximum compressing one of the coils before bottoming the shock.

 

[muddybuddy]

good question, also would the side thats fully extended be perminantly stretch a little and cause it to sit unlevel when not flexed?

 

[sled_dog]

I know my S10, when you flex it out big time, it leans toward the side that was compressed afterwards. However that is soft springs and after you move it around a bit it settles back.

 

[tx_sub]

Ok, I looked at the 2.5" remote res coilover on the web page. Are you worried about the shorter spring? Regardless of position, if you bottom out the spring, you need stiffer springs. It a function of spring rate and compression distance. F=-kx. The force is equal to the spring coefficient (spring rate) and distance it compressed, or extended. I'd have to dig deeper into my brain to remember the formula for dual springs.

 

[tx_sub]

good question, also would the side thats fully extended be perminantly stretch a little and cause it to sit unlevel when not flexed?

I have to disagree here. There is no force pulling the spring beyond its neutral position. It should always be in some compression to stay put, ere it would fall out.

I know my S10, when you flex it out big time, it leans toward the side that was compressed afterwards. However that is soft springs and after you move it around a bit it settles back.

There are a lot of factors that could contribute to that. One that comes to mind is mismatched components like springs, shocks, suspension mount position. If the sets of components are slightly different, you might notice it. Does the lean affect the performance of your rig? Have you finished it yet?

 

[BAJA_BLAZER]

Here are some miscellaneous ramblings that might help:

It helps to think of a coil spring as a Torsion Bar. To state the obvious, a coil spring is just a torsion bar wound in a coil. In fact that is how it works; the “spring” is a result of twisting the spring wire when the coil spring is compressed. A coil spring’s spring rate is primarily a function of the wire diameter and wire length (i.e. how thick and long the torsion bar is). Wire length is a function of the spring’s diameter and number of free coils. If everything else remains the same (OD, Free Length, Free Coils) a thicker wire will result in a greater spring rate; more free coils (longer wire) results in a lower spring rate (the longer a torsion bar is the softer its spring rate is).

Can you over twist a torsion bar? Yes. Can you over twist (compress) a coil wound torsion bar (coil spring)? It depends on the construction of the coil spring; if it is compressed to the point where adjacent coils are touching each other (coil bind) it will stop twisting. If there are enough free coils (length) it will have plenty of twist left. If there is not enough length (free coils) it could get over twisted and fail or fatigue. So, coil bind in and of its self is not going to cause a properly designed coil spring to “fail”.

By the way, these are the principals that make a progressive wound coil spring progressive.

My friend pointed out that on SAW's site they have what looks like a stopper setup on the threaded body of their coilovers. Looks like it stops the slider so you can't fully compress the upper spring. Wondering if that is in fact its purpose. Emailed SAW about that and their opinion of coil compression.

Its purpose is to set the position where the dual rate transition occurs.

Ok, I looked at the 2.5" remote res coilover on the web page. Are you worried about the shorter spring? Regardless of position, if you bottom out the spring, you need stiffer springs.

Coil binding one of the coils in a dual rate setup is another often used but not adjustable method of transitioning from a primary rate to the secondary rate.

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.

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

 

[surpip]

i would think that if you left it bottomed out it would affect it, but just a momentary soft bottoming it would be fine.

 

[sled_dog]

I have to disagree here. There is no force pulling the spring beyond its neutral position. It should always be in some compression to stay put, ere it would fall out.

in a coilover, you are correct, in a coil sprung suspension(not always but in my case and many I know) you are quite wrong. Many people use a positive retainment method. I have clamps at each end of my coils. So the spring can be pulled right passed neutral position.

 

[ntsqd]

Steel is elastic up to a particular point, the "Yield Point", beyond that it is plastic. So stresses that deform it below the yield point don't change it and when released the steel returns to it's original shape. Beyond the yield point the deformation is at least partly permanent.

As Ramsey pointed out, if you can twist the coil far enough (that is what is actually happening) to go above the yield point then the spring will "take a set." It will loose some of it's ride height. It hasn't changed in spring rate, just lost some of it's height.
It is possible to make a spring that has never gone metal to metal and still have caused permanent deformation from overly compressing it. It is equally possible to make a spring that can not even get close to the yeild point and be completely compressed.

The deformation can happen from over extension too. I'm sure more than a few have 'adjusted' a too-tight throttle return spring this way.