Dr G

Guys,

I'm considering getting some custom length and rate coil springs made up.

Does anyone have any opinion on what strength/rate to get. Do any of you have experience of custom rate springs or opinions on what has worked for you or what has not?

Here are the rates for the various Eibach springs available:- https://www.thirdgen.org/forums/susp...t=eibach+rates

Pro Kit: 714 lb/in linear front 1 inch lower front
109/177 lb/in progressive rear 1 inch lower rear
I've just measured my ProKit front springs and they are 4inch internal diameter, 14.1cm outer diameter, 12.5inch/42cm length.

Sportline: 700 lb/in linear front 1.6 inch lower front
80/137 lb/in progressive rear 1.3 inch lower rear

Drag launch: 337/514 lb/in progressive both front sides
80 lb/in linear driver side rear
80/217 in/lb progressive passenger side rear

This thread https://www.thirdgen.org/forums/susp...t=eibach+rates says the stock IROC springs are 649 lbs/in. I've just measured the stock front spring to 4inch ID, 14cm OD and 14inch length.

Currently I have the Eibach ProKit along with adjustable Koni Yellow Shocks and Struts. I think I'm looking for 1inch lower all round and perhaps 15-25% stiffer?

All opinions are welcome.

BMmonteSS

I go over how to calculate your spring rate in https://www.thirdgen.org/forums/susp...g+rate+formula thread. Using the formula in that thread and assuming that your stock springs are 650 lb/in I did a little math and figured out what your spring rate would be by trimming the stock springs.

1/2 coil cut = 713 lb/in 9% stiffer
3/4 coil cut = 750 lb/in 14% stiffer
1 coil cut = 791 lb/in 18% stiffer
1.5 coil cut = 887 lb/in 27% stiffer
2 coil cut = 1010 lb/in 36% stiffer

For a 1" drop you would need either 1/2 or 3/4 of a coild cut. After that you would need a spring spacer (not rubber) to space the spring up to your desired ride height. I have a set of weight jackers in my car and have several sets of stock moog springs trimmed to various rates. I'm currently running a set with 2 coils cut.....it's not for the feint of heart. It is however whats needed for hard core auto-x and road racing.

Check out www.speedwaymotors.com for spring spacers that will fit your stock spring pocket with no modification or the parts to make your own weight jacks. Lucky for F-body owners hobby stock cars are based on metric (g-body) chassis and use the same type of springs and control arms as F-body's.

Edit: I wanted to add that your post is one of the best I've seen lately, you clearly ask your question and quote threads that you have searched and read that pertained to your question... you should check out www.corner-carvers.com, read the wiki site for newbies, abide by the rules and you can learn a LOT on that site.

JamesC

iTrader: (5)

FYI. Moog says 748, should that make any difference.

JamesC

BMmonteSS

There's been some debate as to whether or not those figures are accurate. My own measurement of the springs shows it's closer to the 650 figure.

Dr G

BMmonteSS:- Thanks for the reply and link. Also, thanks for the compliment about the quality of the question and information set out. I'll let you know how I get on.

matt_p

Thanks for doing that math BMmonteSS. Someone cut 1/2 a coil off their stocks springs and then noted that he had a 1.25" drop a month or so back.