rear end gets light, how can i fix it?

[Eric]

So the E30 popped her cherry at the ring this weekend. it was a ton of fun, and the car is pretty good to drive. braking is scary without ABS and huge brakes. a few times the rear end wanted to come around when under hard braking.

my biggest problem though is the back end starts to dance around pretty bad on high speed corners (80-110MPH). A friend suggested i'm hitting the bump stops and that is bouncing the rear up faster than the shock can control.

I've also read about removing the rear swaybar, can give more grip with the TA rear end. I dunno if this applies to high speed courses or just cone hunters.

On my 7th lap in the car, i got a real clean run, and a passenger who wanted to know how fast we were going. we recorded a 9:04:zzz: on his iPhone. I scrubbed about 30mph in a corner ( Mutkurve) i can usually take at speed (115mph) for a stupid NL driver who didn't use his mirrors. Without that dissapointing slowdown, it was a pretty fast lap.

here is a list of all the mods i bolted onto the undercarriage.

Front

Vorshlag camber plates (-4 camber, 7 1/2 caster, 2mm toe out)
Ireland chineese sparoc rippoff strut bar
H&R coil overs from an E30 M3.
Massive 26mm offset bump steer spacers (tie rods and CA's are still horizontal, can i stack more spacer there)
THR eyeballs
OEM control arms
OEM tie rods
E30 M3 steering rack
Ireland engineering 25mm hollow swaybar on the softest setting.
IE sway adjustable sway bar end links (strut mounted)
25mm wheel spacers
17x8 ET20 Msystem II wheels
215/40/17 Falken Azenis RT615 tires

Rear
H&R coil overs
E30 M3 subframe/trailing arms
Powerflex purple TA bushings
new OEM subframe bushings with holes filled with hard silicone
Ireland engineering 22MM sway bars slid all the way to the ends (soft)
10mm wheel spacers
17x8 ET20 Msystem II wheels
215/40/17 Falken Azenis RT615 tires


Brakes-
Front Willwood SL6 calipers with 330x32mm willwood discs
Rear - Willwood SL4R calipers with 300x32mm discs
unknown brake compound
bimmerworld stainless steel brake lines
25mm master cylinder
ATE super blue fluids
ABS computer/sensors removed

So with what i have to work with (adjustable ride height, adjustable front settings, adjustable sway bars settings, change tire pressure) what can i do to tone down the tendency the car has to step out.

Note - the car is firmly planted in most all corners. just some fast off camber, or corners that are in the middle of a crest (eiskurve) that creep me out a bit.

and here are some shots of the car in action!

[jlevie]

Have you had the car corner weighted and the coil overs adjusted for corner balance?

The nervousness of the rear end could be just a weight imbalance or the brake bias could be wrong, or both wrong.

[kilgojr]

Jim is a better source than I am with car set up...what pressures are you running with the Azenis? Have you tried to set the front sway bar stiffer so that it has a greater tendency to push the front through a corner?

I'm not sure, but the fact there is 30mm of difference from stock in track width front to rear could cause some issues....Jim, enlighten?

With the stiffness of your swaybars (car in general) and BIG brakes with no ABS you are going to have an oversteer tendency anytime you get on the brakes when the car is not fully settled.

[Jean]

What Jim said, and also not having a rear sway can also help "settle" the rear end.

I believe Wider rear track = understeer, wider front = more towards oversteer if the car was neutral.

Do you have true coilovers in the back or is the spring/shock in the stock e30 location?

[jlevie]

The first thing I'd do is to adjust the coil overs to corner balance the car. If the rear is still nervous, I'd stiffen the front sway to shift weight to the rear tires. If that isn't enough, I'd add weight to the center of the trunk. Somewhere along there the oversteer under power should be conquered. If the rear is still nervous under braking, stiffer springs up front are an option as would be twiddling the front to rear brake bias.

[Dave]

that sounds like a LOT of neg camber in the front. Not saying it is a factor on being "loose".

Jim (as always) has good ideas on how to address that.

[SkinnyVT]

what spring rates are you running?

[Massive Lee]

Hi Eric

It seems your rear end is too stiff. Could be the spring rate, the swaybars, the shocks or tires.

Also, a car that has too much front brake can have a twitchy rear end under braking. But also if the rear brakes are too strong. Let me know if you still run the OEM brake pressure valve. Front SL6R/332mm and rear SL4R/310mm is the ideal set-up with stiff suspension and stock pressure valve.

Lee

[Wh33lhop]

There's a reason lots of guys run no rear sway bar.

As everyone else has said, Try stiffening up the front sway or loosening up the rear (depending on if you want more or less overall roll stiffness, if the rear is dancing around you might want to give the rear some more compliance).

Car looks fucking awesome by the way.

[87e30]

So I know nothing about tracking cars and the above responses all seem helpful, but just thought I'd ask about this.

Can I just throw out the idea of a rear spoiler? Or is 100mph not fast enough to give any benefit?

[Erick]

Sorry, I dont have much to contribute to this thread. But I'm massively jealous.

If I buy another set of rims do I get a free ride around the ring? :p

[JeffRR]

What ride height are you running? Its very possible that you are bottoming on the jounce bumper, which would show itself as nervous/busy on the offending axle.

Make sure that you aren’t bottoming and then work on balancing with spring / bar adjustment.

I think you mentioned that your having trouble with a crest as well, that’s a rear shock issue. The rebound damping isn’t allowing the wheel to drop fast enough, soften up the rebound damping on your rear shocks. This should help with the crest as well as the tendency to OS under braking. The wheel just isn’t dropping.


Have fun at the ring

[Gnarles]

I don't have anything to contribute about your problem, but do you have any pictures of your bumpsteer spacers? I am interested in how you have that setup.

[Massive Lee]

... but do you have any pictures of your bumpsteer spacers?

13mm thick


26mm thick


Offset 26mm thick


Extra camber and wider track.

[Wh33lhop]

Mmmmmmmmmmmmm, lack of bumpsteer. :)