Quote:
Originally Posted by Varinn
I did my second autocross of the season today, and I've got 6 more to go. I spent my entire day battling absolute gobs of understeer and I'm hoping I can get some pointers on what I might be doing wrong.
If you asked me where I was running into it, I'd say that it was from turn in to apex. Holding steady speed didn't seem to help and I tried trail braking in, slow in fast out (best result) and diving in hard after braking (no good, just plows hard). I'm not quite capable of maneuvering the car consistently with the throttle to counteract the understeer. Our local autocross pad has a lot of small transitions between pavement sections and the ground sort of rises and falls like small waves, attempting to throttle steer in a big way had me running the course backwards on one go at it. My best runs were hard braking, gentle turn in, and wrestle on the edge of understeer through the turn with a hard throttle out and some oversteer through exit. My times were not great (good, not great. Competitive for my class) and controlling the back end was difficult.
Local shop aligns in degrees/minutes, BMW specialist and they strongly advised not going too far negative. Not sure I agree my e30 is around -3°/-3° and behaves well on track but I've been trying it as they suggested.
Front specs
-1°25' camber / 6° caster / 0°05' toe (per wheel, 0°10' total)
Rear specs
-0°53' camber / 0°15' toe (per wheel with 0°30' total) / 0°00 thrust angle
Tires
Michelin Pilot Super Sports 245/275 front and rear, have tried various pressures between 30/32 f/r to 35/36 f/r. Higher pressure seemed to have the best result in feel from the seat but wasn't totally utilizing the tire width (barely touching the michelin man. Low pressures had massive sidewall flex that had the fronts scrubbing the tire "shine" off half way down the Michelin letters.
Suspension
Bone stock, zero mods except for RTAB limiters when I re-did the rear and bushings. Car has 100,000km, I suspect my shocks may be a strong factor in this at this mileage.
I'm open to suggestions on things I can change in driving style, or replacement parts/alignment settings. I am not afraid to run large camber if need be but would like to keep my suspension street-able (max would be H&R street performance at max ride height)
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Lots of old threads on this but running -2.0 up front isn't going to eat tires as long as you keep the toe-in minimal and/or zero. I can't imagine driving this car close to stock settings. For track and Autox I'm using two camber washers up front, -1.8 street with IIRC 1/16th total toe-in. I mark the positions of each strut for reference, then move the struts full inboard for track or autoX. That gives me about -2.5 to -2.6 and a bit of toe-out. (Hack's idea, not mine!) Poor man's camber plates. Just move things back to "stock" for street use. Torque on bolts is ~20 Ft. Lbs. (note, torque wrenches are not particularly accurate at the ends of their scales, and these bolts can sheer if over-torqued).
Many of us have found going with stock rear toe range towards the max toe-in and using RTAB limiters helps put down the power exiting the corners. -1.7 to -2.0 rear (YYMD) also works nicely. -1.7 is more street friendly with the toe settings for wear as the rear isn't easily swapped between settings like the front.
Now, with AutoX (I run fun only, not comp) what you can do and stay in your class is another question. You may be limited there or going with changes may bump a class--in which case stock might be it. You know the rules better than I!
Search on alignment with Ship, Ian, The Hack, or me--lots out there if you want more detail. Here's a few.
http://www.zpost.com/forums/showthread.php?t=706698
http://www.zpost.com/forums/showthread.php?t=422123
http://www.zpost.com/forums/showthread.php?t=536407