Currently overseas, but looking at preformace overhauling my 1991 Trans AM GTA when I return home. Looking at replacing the suspension with a coilover kit. Has anyone done this or have any opinions about it. And also how do i determine/figure out the spring rate?

 

From what I've learned from here and my mechanic is that coil overs in front would not be suggested since there is wheel interference with the width of a wheel. So ibwent the shock and weight jack route. Also called Detroit speed today and thatbwas mentioned as well but that coilovers in rear was okay. I have Koni sport yellow shocks with
UMI cc plates, UMI strut bar, UMI wonder bar brace, BMR A-Arms and NApa steering components up to the steering box. As for the rear i have all UMI LCAs, panhard bar, relocation brackets for LCAs, and koni yellows as well. As for the springs i have Ground control weight jacks all around. The spring rates are 850 in front and i think 250 in rear. In line i have that detroit speed steering intermediate shaft and UMI subframe connectors. Now i did call detroit speed about their fbody Speed kit 3 front suspension and rear and if they are for for daily driving and i was recommended to get a speed kit 3 front single adjustable and a speed kit 2 rear coilover. Nice all in one purchase if that is easier.
i wonder if there is anyone that has any comparison or info on these kits. I have a 91 z28 305 so its stock as for what im working with.

 

 

I think it had to do with the room where the shock was and adding the coilover would clutter it up and make an issue with the size of my wheels. I have 18x7.5s . Mechanic mentioned something about weight distribution changing from one spot to another since you wont have springs holding up weight where they once were . i found this thread that has similar things ive been told. Even detroit speed mentioned this to me yesterday. I chose this setuo with the weight jacks and konis due to it kewping everything in place and still being able to adjust height on my lowered camaro.
let me know what you find and hope someone helps give better advice. Im still learning as well . goal is to improve this vehicle for reliabilty and fun

 

Here is one that explained what i was told about the weight distribution between strut/spring vs coilover
https://www.thirdgen.org/forums/suspension-chassis/712449-front-coilovers.html

 

I've always heard that thirdgen front strut towers aren't designed to handle the load that a coilover would place on them. Having repaired one, I am inclined to believe this. Rears work good from what I've heard but, imo I'd go all or nothing not just two. I went with the sold out Tokico ILK208 kit for the base of my suspension overhaul.

 

I would say it really depends how you use the car and what your goals are for the car. Coil overs do limit how wide of wheel/tire combo you can run to about a 275 width tire or 9.5" wheel. This is very satisfactory for many. Also, the strut towers were never designed to hold the weight of the car or take the forces coil overs introduce.

Drag racers use coil overs a lot. I've seen several street cars with them also, but most autoX/Road Racers don't use them because of the tire limiting factor and to prevent the possibility of damage from the variety of extreme loads these types of racing would put on the strut towers with coil overs. Types of loads vary between each form of use as well as the amount of force. Most autoX/RR guys use Weight Jacks.

Best way to determine spring rates is to talk with manufacturers and others using their cars the same way you plan to use yours. UMI, DSE and Ground Control are all great places to shop.

 

Do not get coil overs, especially don't get them for the front. The front strut mounting area was not designed to contain all of the weight. Here is the easiest way to illustrate it (even though it's not exactly accurate): In stock form the springs mount below the inner frame rails and the struts to the strut mount that is between the inner and outer frame rails and is made out of 13 gauge steel. People use strut tower braces because in a OE configuration the strut towers move IE they're flimsy. Knowing that, why would you want to use a front coil-over setup? They also limit the width of wheel that you can run and that width will change with the rim diameter. IE you will fit a wider 18" tire than you could a 16" tire. I question being able to run a 275 tire with a coil over setup. I run a 275 on a 17" rim and have very minimal clearance between the rim and strut and my wheels sit at the edge of the outside of the fenders.

Go with the ground control weight jacks. I have UMI weight jacks and I'm not able to appreciate the difference in price. Ground control is less. Go with an 8" spring if you want to be really low (if that's the case you'll need extended ball joints) but for a more stock height go with a 9.5" spring both in an 850# for the front and 200# for the rear. You will have to use a performance strut/shock and you should also get an extended strut mount. I'm running 3/4" extended ball joints, 9.5" 950# front springs on weight jacks and 200# rear springs. I'm happy though I might move to a 225# spring in the rear. I wouldn't enjoy a front spring >1000# in the front. The 950's are very firm, you know when you go over bumps. If you have a V6 or LS1/2/3/6/7 you should be able to go with a lighter spring up front in an 8" height.