Coilover springs and spring rate (Page 1/3)
sdgdf FEB 20, 06:00 PM
I got the ground control systems coilover kit for my '88 coupe, and it has the wrong springs, and/or I told the shop wrong. I told them to remove the spring perches per Fieroguru's writeup, but it turns out through more research they should've just trimmed them down. So, time for new struts or to replace the springs with something that'll work. They're 7" springs. I'm thinking 10 or 12" springs will fix the issue?

I don't understand spring rate. The springs I got from ground control, are 400 lbs spring rate. That's per inch right? So if I go up to 12" springs what spring rate do I need? Anyone else deal with these kind of issues with the ground control kit?
sdgdf FEB 20, 06:11 PM
Here's a picture of what is happening:



I see springs @ Summit Racing and I could go pick them up tomorrow.
cvxjet FEB 20, 07:24 PM
Spring rate refers to how many pounds it takes to compress the spring one inch. Has nothing to do with spring length.

Also, you may see two different ratings;

A) Actual spring rate, which would be equal to what a Strut-type suspension sees (The Fiero rear suspension)

B) The spring rate through the suspension geometry- The front springs on the Fiero mount at (Approx') 60% of the A-arms length, so the actual spring rate is reduced to what the car sees (at the end of the A-arm)

Fieroguru on here supplies all the components you need for a coil-over conversion- including springs- I would talk to him if I were you.

[This message has been edited by cvxjet (edited 02-20-2023).]

pmbrunelle FEB 20, 07:37 PM
Does the car bottom out right now if you attempt to put its weight on the tires?

You could keep the spring rate where it is... how did you choose the spring rate? Is it a good spring rate for your use?

If (temporarily) you can make some wood blocks as spacers for the springs, and you can get the car to the ride height you like (with the threaded adjuster in a good position, not at the end of the threads), then your new springs (assuming you stay with 400 lb/in) should be longer than your current springs by the amount of the spacer thickness.


quote
Originally posted by cvxjet:
Fieroguru on here supplies all the components you need for a coil-over conversion- including springs- I would talk to him if I were you.



Buy from vendor A, ask for support from vendor B?

Seems like it would be more logical to ask for help from vendor A, rather than bother vendor B who didn't get a cent from the transaction.

[This message has been edited by pmbrunelle (edited 02-20-2023).]

sdgdf FEB 20, 07:50 PM

quote
Originally posted by pmbrunelle:

Does the car bottom out right now if you attempt to put its weight on the tires?

You could keep the spring rate where it is... how did you choose the spring rate? Is it a good spring rate for your use?

If (temporarily) you can make some wood blocks as spacers for the springs, and you can get the car to the ride height you like (with the threaded adjuster in a good position, not at the end of the threads), then your new springs (assuming you stay with 400 lb/in) should be longer than your current springs by the amount of the spacer thickness.


Buy from vendor A, ask for support from vendor B?

Seems like it would be more logical to ask for help from vendor A, rather than bother vendor B who didn't get a cent from the transaction.




Does it bottom out? It bottoms out just sitting there in the shop. There definitely isn't enough spring.

How'd I choose? Forum search. Most people on coilovers here seem to run 300-400 lbs, and on the higher end if you've got an engine swap. Car has a 3800SC. What I read today also indicated I need springs for the front or else the handling will be off, they're only 150-200 up front stock?

Well, fieroguru is an expert on this and made a very good write-up on what he does with his kits for DIY and ships out good kits. I talked to him and he said it'd be 2 weeks until shipping, and it'd probably be another week for it to arrive. To me that's the backup plan right now is to get the stage 3 of his kit, the struts I have are cut to use with his kit. It wasn't until I did more digging with the search today that I found a thread on the ground control kit I got that said not to remove the spring perches but to just cut them down, so I instructed the shop wrong.

Right now the car is at the shop, and I have 2 options:

A. Figure out the springs I need and go get them from Summit tomorrow, get them to the shop and they can complete the coilovers.

B. Buy from fieroguru and wait 2-3 weeks. I'll have to go get the car with the old struts/springs/wheels/tires on it and go back to get things installed later.

I'm looking at 2.5" ID 400-lb 12" springs on the summit racing website. I think that'd do it. I wasn't planning on lowering the car at all and haven't gotten front springs. Forum search says I should get equal springs for front and rear on this car, so 400? I was hoping to find 350 lbs. It has a 3800sc though so 400? I'm pretty sure the eibach springs ground control sent are 2.5" ID but I'm waiting on that measurement from the shop tomorrow.

[This message has been edited by sdgdf (edited 02-20-2023).]

sdgdf FEB 20, 07:54 PM

quote
Originally posted by cvxjet:

Spring rate refers to how many pounds it takes to compress the spring one inch. Has nothing to do with spring length.

Also, you may see two different ratings;

A) Actual spring rate, which would be equal to what a Strut-type suspension sees (The Fiero rear suspension)

B) The spring rate through the suspension geometry- The front springs on the Fiero mount at (Approx') 60% of the A-arms length, so the actual spring rate is reduced to what the car sees (at the end of the A-arm)

Fieroguru on here supplies all the components you need for a coil-over conversion- including springs- I would talk to him if I were you.




Thanks for the explanation, I didn't get much out of google search on it. I thought that's what it is but I haven't dealt with springs/suspension in years and wasn't sure, the summit website just lists the springs as "400 lbs./in.". So go from 7" to 12" I didn't want another 2000 lbs though you know that wouldn't make much sense regardless
pmbrunelle FEB 20, 08:16 PM

quote
Originally posted by sdgdf:
I'm looking at 2.5" ID 400-lb 12" springs on the summit racing website. I think that'd do it. I wasn't planning on lowering the car at all and haven't gotten front springs.



I think that 10" would definitely be too short.

12" sounds like it might work.

Seeing as the threads of the Ground Control sleeve are pretty down low on the strut, I'm not sure if you can have "no lowering at all" with a 12" spring. I'm thinking that maybe you need a 14" spring, if you want stock ride height. But I'm not sure.
Raydar FEB 20, 08:41 PM
I bought "guru's" kit. 12" springs. I told him what I had, and what I was doing, including the 3.4 DOHC swap. He suggested 250# springs.
It can be lowered from stock with that exact kit. Mine is as low as I'd pretty much ever want to go with it. (2-3 fingers between the tire and the wheel well opening.
Here are some pics of the assembly. Before and after.

This was what I removed from the car. These were 88 front springs adapted to the rear.
I decided to do "guru's" coilovers because I have plans for the car, and also needed the shorter springs for my GT. Purely cosmetic.


This is the strut with the perch and all the other stuff removed. Painted with rust converter/primer.


This is the assembled coilover and strut, ready to go back into the car. After I set the car on the ground, and drove it to allow everything to settle, I ended up dropping it about another 3/4". (There are calibrations on the sleeve. Made it very easy.) It's essentially the same height that it was before I started, which is what I wanted.


Ride height. It's maybe actually just a "tick" lower than this, now, but that's okay.

[This message has been edited by Raydar (edited 02-20-2023).]

fieroguru FEB 20, 08:58 PM
At a 400 lb/in spring rate, you will want a 10" spring.


sdgdf FEB 20, 09:11 PM

quote
Originally posted by fieroguru:

At a 400 lb/in spring rate, you will want a 10" spring.




With your kit?