Shortening a coilover coil spring

[breakaway500]

If you shorten a linear wound spring,do you change its rated loading per inch? Case in point....I need a 7" long, 750lb/inch spring,but they only make them 8" or 6" long with a 750lb/inch rating.(7" springs only go to 650lb/inch in 2.5" diameter)
If you cut the 8" spring,do you alter its spring rate? I say no...but I'm really not sure.
I know you will alter a progressive wound spring if you cut them, but am not sure about a linear wound one. The Eibach salesperson just said don't cut any of our springs,period. I'm sure they are instructed to say that.(for a good reason...)
I can't use the 8" because of clearance problems with the adjuster collar and the upper control arm,and the 6" is too short. I suppose I could use a 1.75" keeper spring stacked on the 6" but really did not want to do that...I would like to have 100% of the suspension travel suspended by the 750lb. springs.
Any thoughts?

[jlwhorf]

Hi Mark,

When you cut a spring, you DO increase the load pre square inch. If the springs are not too expensive, get a couple and find a race shop that has a spring tester. Then cut them too size and get them checked. I have played around with cutting springs (I only used large diameter ones) and from what I remember, the spring rate change was not that drastic.

Hope this helps.


Jonathan

[breakaway500]

Excellent suggestion,Jonathan! I have a pair of 180lbs/inch linear springs I am not using,that I could test,cut, and then retest.To test, I could place them on one of my car scales and place them both in the press,and could measure the change in lbs/inch of compression.This would at least give me an idea of how much of a percentage it should be.The new springs are about $12o/pr. If the rate only goes up like 10-20% I could live with that..
Thanks!

[drgrumpus]

Spring rate varies with the inverse of active coil number.

[breakaway500]

Oh,the inverse. I see...

[chaos4NH]

Spring rate varies with the inverse of active coil number.

My girl friend likes that Inverse stuff!

[Grippy]

Hey Mark,

I have a pair of 14kg (784lbs) springs in 7" x 2.5" dia. that I would be willing to part with. Only used for 2 days. No cutting needed.
Give me a call if you want them 774-319-1562

Gordon

[breakaway500]

Hi Gordon.I ordered an 8" set on Friday, as I wanted to get them installed by next weekend.Paid for 3 day delivery too.
If they don't work out,I will give you a call. I checked with H&R,QA-1,Ground Control and Eibach,and none of them made a 7" long,2.5" dia,750lb spring.Where did you find those?

[Grippy]

They are made by Swift Springs, very high quality and VERY light weight. They are a bit more expensive which may be why they are not more popular in the USA. But it is only a bit more and the weight savings are worth it. Let us all know how you make out with the 8" springs.

[jlwhorf]

Mark, when you are cutting the springs, make sure you nibble them a 1/2 coil at a time. Be care full, the compressed height can disappear quickly.

Jonathan

[breakaway500]

Understood. The 8" springs may fit uncut,as I have been experimenting with the height of the lower spring perch in relationship to the opening in the upper control arm,vs. ride height, and it may Juuust work,with a ride height of 12.5"-13". (center of axle to fender lip) That would leave me some room for wider tires/wheels. It does have the same bolt pattern as the Atom...

[breakaway500]

Thanks for the springs Gordon! They are going to do the trick perfectly Much lighter than the Eibachs as well.

[Grippy]

Your welcome, glad they are going to work out for you.

[Stynger]

Understood. The 8" springs may fit uncut,as I have been experimenting with the height of the lower spring perch in relationship to the opening in the upper control arm,vs. ride height, and it may Juuust work,with a ride height of 12.5"-13". (center of axle to fender lip) That would leave me some room for wider tires/wheels. It does have the same bolt pattern as the Atom...

Unless you really need the room for wheels and tires 12.5-13 would be on the high side.
Help the CG and get down to 12-12.5. It will also help get more neg camber if you're not running offset bushings.

[breakaway500]

I have a bunch of 225/50/15" BFG-R1's on TD 38mm offset wheels I need to use up (Atom rejects) and they just clear the front fender lip at 12.5",so I'm shooting for that as my ride height.
I'm running 1.5 neg camber all around,with just the lower control arm cams doing the adjusting.
Any lower than 12.5" and I have to jack the car up to get it on my lift.