Lifting Inner Front and Rear Wheels at Autocross

[Caius]

Hello,

I have been a member for some time, but this is my first post. I really appreciate all of the information I have been able to gather that you guys have provided! So thanks a lot for that.

I have been doing quite a bit of searching and am really having trouble finding the answer to my problem. First of all the car: It is an e36 with the s50 in it, stripped down, no cage, and weighs in at 2236lbs. I am running 285/30/18 Hoosier A7 all around. Currently I have 700lb springs in the front and 900lb in the back, TC kline shocks front and back, UUC front sway bar on the stiffest setting and currently no swaybar in the rear.

I have tried a variety of spring/sway bar combinations in the rear including none, stock e36 325i sway bar, and the UUC rear on the soft setting. For springs I have tried 750 in the back and 900 in the back.

All of the aforementioned combination cause the front wheel to lift off (which I am generally ok with). The problem is that the rear also lightens and If I try to put some power down mid corner it just spins the inner rear. The car has an 3.38 LSD from an automatic M3.

The car is generally well balanced it doesn't understeer or oversteer too much. I feel like the suspension setup is close to where I want it to be, but I am just trying to work out this bad behavior without buying another set of springs or sway bars on a "gut feeling"

I appreciate any help you guys can provide. Thanks.

[DenKare]

What trailing arm bushings do you have?

[Caius]

I have spherical bushings on the trailing arms and the control arms. I moved the suspension up and down without the springs or swaybar attached to check for binding, and I didn't feel any.

[olemiss540]

I have spherical bushings on the trailing arms and the control arms. I moved the suspension up and down without the springs or swaybar attached to check for binding, and I didn't feel any.

If you have that issue in the rear, it would seem like you eigther don't have enough roll stiffness for that combo of wheel/tire grip, or not sufficient droop travel in your shocks. No expert but my humble opinion for what it's worth.

[aeronaut]

285 Hoosier A7s, an (old?) OEM LSD, and autocross (aka some tight turns). And you're getting inside tire spin.
The fix *may* be a new (and modified) LSD?

[Hofmeister]

Thats a pretty aggressive setup. I agree on rebuilding the LSD unit and maybe throwing an extra disk in there for the 40% lock, and if possible find a way of dropping the front roll center of the car (not sure if possible on e36) to help it keep the front planted.

[olemiss540]

Thats a pretty aggressive setup. I agree on rebuilding the LSD unit and maybe throwing an extra disk in there for the 40% lock, and if possible find a way of dropping the front roll center of the car (not sure if possible on e36) to help it keep the front planted.

Not sure there is any solution for the front given the camber gain with a smaller front bar and the roll center issues when dropping below parallel. Lifting inside front wheel is the nature of these beasts.... Mine clears atleast 3 inches...

[jakermac]

I too have this exact problem. I'm 800fr, 900rr, GC small front bar, 275/35-17 (never ran A7s, only 6s) on 10.5" wheels. I'm convinced that I need a bigger front bar. I'm going to try the medium GC front bar. And I have about 28mm of front roll center correction - SLR Speed mini kit.

Have you checked the clearance between the rear upper control arm and the chassis? Is there any chance you're getting contact between the spring centering nubs on the frame/control arm? I've cut mine down to 1/2 their height on both the arm and the chassis.

I have made a bunch of changes to try and correct some of this, and then I took a sabbatical from autocross for the last 3 years. I am almost certain that it's the lack of front roll stiffness. I'm a little heavier at just under 2,400 lbs (Street Mod legal) but I'm pushing 270/240 at the wheels with a built motor.

[olemiss540]

I too have this exact problem. I'm 800fr, 900rr, GC small front bar, 275/35-17 (never ran A7s, only 6s) on 10.5" wheels. I'm convinced that I need a bigger front bar. I'm going to try the medium GC front bar. And I have about 28mm of front roll center correction - SLR Speed mini kit.

Have you checked the clearance between the rear upper control arm and the chassis? Is there any chance you're getting contact between the spring centering nubs on the frame/control arm? I've cut mine down to 1/2 their height on both the arm and the chassis.

I have made a bunch of changes to try and correct some of this, and then I took a sabbatical from autocross for the last 3 years. I am almost certain that it's the lack of front roll stiffness. I'm a little heavier at just under 2,400 lbs (Street Mod legal) but I'm pushing 270/240 at the wheels with a built motor.

Flares or bodywork? Just curious....

[jakermac]

Hard Motorsports flares shimmed out for more clearance. Extensive mods/body work under the flares.

285/30-18 on 10.5:



275 Hoosiers:

[SLA]

I've been fighting the same issues all season. The inside rear won't get the power down out of corners. The car feels pretty good otherwise. 650/800 springs on JRZ RS D/A. Eibach F-ARB. 255/40/17 RE71R. I tested LSD breakaway torque at 39ft-lbs. I have not been able to locate a definitive answer on what breakaway torque for the OEM 188 diff should be.

My car is not corner balanced though, but I have an appointment finally on the 26th. I've been putting it off for 2 years so i can get the car down in weight first and have to miss a day of work to get to the shop (far). I'm hoping after I'll be able to put down the power much earlier.

[Caius]

Thanks guys, I appreciate all of the input. Although I had thought of the diff being part of the problem, I was really hoping to point fingers at something less expensive... lol But I guess such is the nature of the beast.
In a recent update, I have done two more events since I posted this, and I found a setup that shows some improvement. I dropped the car all around about another 3/4". Went with the 900lb rear springs and a UUC rear roll ball on the soft setting.. This still allows the inner rear to spin, but seemingly not as much... Now the problem is that off the start I spin the tires all the way through 1st and partway through second gear. Its really hard to get it to hook up on launch due to all of the stiffness back there.