Rear coil over suspension

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Rear coil over suspension

Postby pbeck » Sat Sep 08, 2018 9:18 pm

I'm sure there are some of you out there that are running rear coil over shocks. I need some help/information getting my set up right. What rear weight are you running and what # rating are your springs ? I've had a horrible issue trying to get mine right. I've reduced the spring weight 3 times and still the only suspension movement I get is flex in my rear wheel sidewalls. My rear weight is about 1750#, with an overall weight of 3160#, although I don't have any way to check corner weights. What are you running and how does it work ?
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Re: Rear coil over suspension

Postby Richard Miller » Mon Sep 10, 2018 9:45 am

what spring rate are you running right now ? I tried to find stock rate for a corvair but so far no luck ,, I might guess about 350 ,, if your car has 1750 on rear ,, half is 875 what is your motion ratio ,, probably 1:1 if shock attached to trailing arm ,, effectiveness reduced if shock is mounted at an angle ,,and total suspension travel ? lets say 4 inches ,, and your ride height is half of that ,, then 2 inches of compression needs to support 875 pounds ,,so a rate of 450 would compress 2 inches to 900 at 2 inches of travel with no preload ,, softer with some preload would center your travel and give a softer ride ,, so is my WAG ( wild ass guess ) anywhere near what you are running ?
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Re: Rear coil over suspension

Postby Richard Miller » Mon Sep 10, 2018 10:43 am

spent some time trying to find stock rate with no luck ,, looking at some coil over charts in speedway catalog it looks like rates around 300 are common
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Re: Rear coil over suspension

Postby pbeck » Tue Sep 11, 2018 7:53 pm

I've probably tried 4 different weights, currently have 175# springs on QA1 single adjustable shocks. I am running about 20 degrees or a little less angle from the trailing arms to the upper mount. I had it all torn down a couple of weeks ago, switching to the 175's and I did check the axle tire movement with no spring, but only on the right side (the longest) and it had good motion with very little in/out movement on the inner cv joint. I get all my stuff from Speedway but I'm going to check on the QA1 website and see if I can pick up some additional info.
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Re: Rear coil over suspension

Postby Richard Miller » Tue Sep 11, 2018 9:24 pm

wow I see your dilemma ,, 175 # rate isn't high at all .. suspension should be compressing ,, would sag an inch if I leaned on your fender ..good luck and let us all know what you find
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Re: Rear coil over suspension

Postby pbeck » Sun Nov 18, 2018 10:25 pm

After a lot of measuring and watching the movement of the suspension without the springs, I finally determined that my shocks weren't long enough. Where I should have had about 2" of compression travel, I didn't have any. Don't know how that happened since all the measurements were taken with a set of mockups from Speedway Motors. At any rate I ordered another set of shocks, 2" taller ride height. I ordered them with 175# springs, but after installation, decided that they needed a little more. Ordered 200# rating springs and they turned out just right.

One of the things I learned from all the U tube bits I watched was that the spring rating is really pretty simple. If the spring is rated at 200#, that means that for every 200# weight you apply to the spring, the spring will compress 1". The spring rate remains the same all through the compression.

I still don't know or understand very much about suspension, but sometimes I just get lucky !
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Re: Rear coil over suspension

Postby 66VairV8 » Mon Nov 19, 2018 9:19 am

Good information. I am converting my car to a C5 diff and C5 suspension and will be going to coil overs. I was able to scale my current Crown setup and the total weight is 2874 (1/2 tank gas without me in the car) LR= 836 and RR=795. This is the base line and will possibly change once the conversion is completed.
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Re: Rear coil over suspension

Postby pbeck » Tue Nov 20, 2018 9:49 pm

The closest I could get (with Ag scales) was 3140 total with approximately 1300# front and 1800# rear. That still sets up the rear spring rate at over 400#. Add to that the shocks mount at about an 80 degree angle. I'm still not sure how I got this lucky, but I'll accept it................
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Re: Rear coil over suspension

Postby 66VairV8 » Tue Dec 25, 2018 3:33 pm

I had a senior moment and forgot to post all the numbers. FL 608, FR 635, LR 836, RR 795 1243 front, 1631 rear. I currently have Koni adjustable shocks but will go to coil over with the C5 suspension. Qal1 was what I was looking at. Hopping to expand the wheel well to fit a wider tire.
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Re: Rear coil over suspension

Postby pbeck » Sat Jan 05, 2019 10:57 pm

If I had it all to do over (the body work) I would install wheel tubs. It would make a much neater installation and I doubt it would have required much more labor.
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