Coilover Spring rates

[OESMAN]

What spring rate should I use for 72 short step? Running a big caddy with a C4 rear.

[PHATTIRE67]

I am wondering the same thing. I just picked up a set with no springs. Ill be keeping an eye on this one

[Custom 68]

Front? Rear? or Both?
I think there are several variables that will change the required spring rate. First is the angle it is mounted at, this will change the rate. Second is placement. The lever arm of this placement will change the rate. This placement will also change the length of spring and shock you will need.
I have a set of coil overs on the front of my truck. I bought them used from a newer truck and they are 12 inch long springs with 825 lbs per inch rate. They may be too stiff and I might eventually change them but like you I don't know exactly what they should be. I too will watch this thread for some other input. I might change mine to a lower value but I don't want to over shoot and be too soft.
good luck
Dave

[dirtyjim]

on the rear of my 67 I'm running 225# springs and it rides very good,but its a longbed. I've heard start at 200# on the rear & work up or down from there

[OESMAN]

this site may help. I'm still working on figuring out rate for rear IRS.
http://www.hypercoils.com/spring-rate-calculator/
this one for weight
http://67-72chevytrucks.com/vboard/s...ame+dimensions

[OESMAN]

even better site
http://www.ridetech.com/info/spring-rate-calculator/

[Custom 68]

Thanks oesman, I will get some measurements and see where I am on mine. That last site has a pretty cool calculator.

[Custom 68]

ok so I have ran thru some numbers based on that ridetech site. It looks like I need to be somewhere around 500 lbs/inch. My current springs are 800. That is a big difference. I am going to reweigh and get some better or more measurements and decide What I should try.

[OESMAN]

I have some investigating to do as well.. I have not been factoring in the weight of the C4 rear as it is attached to the frame and should actually increase my sprung weight and decrease the un-sprung.

[OESMAN]

Sorry forgot to add that I am building a short stepper, C4 rear with a 540 Caddy.

[69cummins]

So you are going to need a pretty good estimate of the sprung weight of the rear to start. Then if it is independent suspension you are going to need the distance from the inner pivot of the arm the coil over mounts to to the mounting point. You will also need the distance from the mounting point on the arm to the point where the arm pivots at the wheel. Now you need the angle from vertical that the coil over is mounted. Once you have all that you can plug that into a calculator and that should get you pretty close.

[OESMAN]

I ordered a front cross member from Flat Out so I can run front and rear C4 with coil overs. My buddy is going to bring over his 4 wheel scale for weight. Once I have that I will give Flat Out my rear angle and weights for them to supply me with correct coil overs.

[Custom 68]

Here is what I found running some calculations.
Using the ridetech calculator and my measurements I should be using a 425 lb/inch for a 12 inch long spring.
I had purchased a used coil over setup and it came with 12 inch long 825 lb/inch spring. I currently have this on there as it was a guess and didn't know what I needed. I measured mine today and raising it up taking the weight off the front I have 3 inches of spring deflection. so now I am questioning what I should try. I know I dont want to drop all the way to the 425 but I don't know what how much static deflection I should have.
Does anybody have any opinions on where I am and what I should run?

[Custom 68]

anybody else before I order some springs and give it a shot?

[OESMAN]

AFCO has a good price on springs. What was your rear weight? 425# seems a bit stiff.

[Custom 68]

This is actually for the front. I am not using coil overs on the rear.

[Custom 68]

In light of all the confusion I am going to stick with what I have for now. Currently I have 825 lb/inch springs. My lower shock mount is 13 inches from the inner lower pivot connection and my shock is at 80 degrees so it is only 10 off from vertical. I am using a 12 inch free length spring and is compressed with the weight of the truck approximately 3 inches.
I will continue to explore and look for input. Good springs will cost me about 120 dollars for both. I would like to try 650 springs and don't know how it will change the ride and handling. Off to another project...

[Custom 68]

bringing this back up.
I had made a mistake on my original rates. I was confused on another sping rate post from the past I believe. That said I just purchased a known rate of 600 lbs/inch a good brand Hypercoil. I installed have a measured static deflection of 2.75 inches on the springs. I am thinking these are still too stiff. I can swap them for a different rate if that is what I need to do. Are there any thought on how much the springs should be compressed? These are 12 inch springs.

[Custom 68]

I will update one last time on this. I have now swapped out to some 500 lb/inch Hypercoil springs. These are nice springs and are considerably lighter than my original Carrera ones. I could probably drop down to a 450 lb/inch rate spring and be even better but I am done swapping around for now. with my setup they are fairly easy to swap.
My ride and stability is great. I am glad I dropped down a rate.
Like said above each design is going to be different. Since I built mine they are custom. I was able to get my lower mount close to the lower ball joint so that allowed my spring rate to be lower than some other setups.