5 inch rear springs and suspension travel with GC weight jacks and Koni S/A on e36

[xvxax]

I purchased ground control weight jacks this season in order to be able to corner balance my car and the added bonus of eliminating coil bind.

I did not realize the design does not allow me to fully lower the height adjuster due to interference with my thicker design m3 axle shafts. With as minimal clearance between the adjuster and axle shaft as I feel comfortable, my rear end sits really high. 13" high, or higher. This means I need to run 5" springs.

So, does anyone run 5" springs on the rear with or without weight jackers with GC valved Koni single adjustables? I am concerned about reducing my suspension down travel with such a short spring. I am currently running 600# rear springs and my car is an autocross/ occasional DE car.

Before you tell me to call GC, they recommended the 6" long springs in the first place. I am looking for real world advice.

[jcrist]

These are Ground Control and worked fine, untill T3 at Road Atlanta for a weekend. The good news is that the perch screws are aluminum and were no match for the half-shaft. My rear lower CA was bent and once replaced, the perch screw clears just fine. I set the "new to me" LRCA next to the one I took off of the car on the ground and VERY CLOSELY examined. I could not tell a difference and thought there was something else wrong. It wasn't, the bend was not visible, problem fixed when I installed the new/used part.

[xvxax]

Hmm, not sure it's my LCAs. I have some heavy duty chromoly ones. I would say my clearance perch screw to axle is very similar to yours. I wasn't very confident in running the perch screw 2mm from the axle shaft. Are those the oversized m3 axles (The 32mm ones?)

[GotCone?]

get a 4" spring

[jcrist]

If they are the same on both sides I would agree that there is nothing wrong with them.
Mine are Ground Control, purchased from BW. I don't have very much clearance but enough. The stress put on mine would far exceed HPDE or street driving and I've been running that setup with #1000 springs for a couple of years.

[B.Watts]

I don't think I've ever seen a car running these rear adjusters that doesn't have scars on their halfshafts. FWIW, we've run the smaller style halfshafts (I believe they came on the 95 M3) with a lot more power/torque than the average BMW track/race car without any problems.

[jcrist]

Yeah, the torque rating is probably 1000% any instantaneous or sustained load calcs.....
Maybe some of the drag racing guys with slicks and turbos would have issues. OF course, BW had a rash of failures in the WC cars (E90/2??)

[badmonkey]

Doubtful OP wants to run 600# 5" springs, potentially too soft for the length.

Call GC, they could tell you for sure.

[xvxax]

Thanks for the replies.

B. Watts: I was afraid of that, on the scarring. Going to try to avoid purchasing half shafts unless completely necessary.

So: anyone running 5" springs on the back of their e36? Jcrist, are you? I don't think the clearance bolt to half-shaft would be an issue with a spring that short. I run my rear around 11.75-12", and if the car is going to be bottomed out on the spring all the time then I will just return them and my newly acquired collection of 6" 2.25ID springs.

[jcrist]

I run 2.25x5" at the following rates depending on set-up
#875
#950
#1000

[MINIz guy]

Bumping this instead of creating my own, as there's some good information here. Installing JRZ's on my car and trying to run the GC weight jacks. Currently have a 5" 1000lb spring w/ a helper and my rear is jacked up sky high. It's around 7.5" from ground to the jack point and I want it closer to 6.5". Can't pull the helper as I have too much droop.

How low are people able to get, ground to jack point w/o pad, with a 5" spring and helper? Are 4" springs to the go-to to get low?

[jonb94118]

900 lb, 5" rear spring. @6.25 to jack point. Don't use helper springs, but my dampers are at the correct length to not allow the spring to flop around at full droop. Not that it really matters. Take out the helper spring and see what you get. Also, you would be surprised how much that spring will compress from static under cornering loads and how close it gets to coil bind at too low of a ride height. Zip ties on your damper shafts will tell you much it compresses.

[MINIz guy]

900 lb, 5" rear spring. @6.25 to jack point. Don't use helper springs, but my dampers are at the correct length to not allow the spring to flop around at full droop. Not that it really matters. Take out the helper spring and see what you get. Also, you would be surprised how much that spring will compress from static under cornering loads and how close it gets to coil bind at too low of a ride height. Zip ties on your damper shafts will tell you much it compresses.

Awesome, thanks for a number to reference. I did slam the perches down and managed a ride height of 6.25" with the helper in place. Happy-ish with it and can work with it. Will have to do more testing and see how much it travels at the next TnT.