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In Reply to: Tire scrub at the track posted by Skid on October 15, 2000 at 15:31:19:
After a few recent track events I note I'm getting wear too far around the shoulders of my AVS Sports. This despite a) camber measured at -0.9deg L/-1.3deg R thanks to H&R lowering springs, .5 deg negative camber plates, strut brace, and tires @ 41psi cold & 45psi hot. Observers note I'm still getting a fair bit of lean, again despite RD sway bars, H&R's, Bilstein Sports.
E28's gain a great amount of camber in the rear, especially when you lower the car. It's really great at the track, because the rear end just sticks. Beautiful. Unfortunately the fronts are a different story. It doesn't get ENOUGH negative camber for the front end. The result of this is that a lowered car (without front mods to increase camber) ends up understeering and scrubbing. This is inherint in the design of the suspension.
My questions are: Although the measured camber is outside the manual's -.83deg spec, is the measured camber value sufficient for track use?
Yes, perfectly allright. It's surprising (to me) that you have a 0.4 degree difference in camber between the left and right side. I don't know what mine was at the top of my head. (This could be the cause of many things, not just the car being hit or chassis flex). If you really want more camber, in which case you can go for adjustable camber kits.
Incidently, I do feel the onset of straightline shimmy at exactly 80kph (50mph) and will replace the front stock bushings & arms this winter. Could this looseness also somehow translate into the loss of negative camber under hard cornering?
No. You'd notice "scalloping" or other forms of tire wear. Not the wear of the outside edge more than inside middle of the tire as I presume you're describing. Though it's not good either way. Replace the upper control arm bushings with machined 750 ones, or get poly (though if you're using your car on the street, I recommend rubber, not poly).
When the upper bushings go, you end up having the car gain toe-out under braking. I know that the strut tower is inclined at an angle towards the rear of the car anyway, but that change in angle is minimal for the camber. The tire tread wear the way you describe it is more of not enough camber, but watch for the scalloping anyway.
Or is there just a natural limitation imposed by chassis flex as to how hard these cars can be driven?
Strut braces are always a good idea. And if you really want more negative camber up front, go for adjustable camber kits. My website has a link to Ed Walters who's designing a top-side adjustable camber kit. REALLY NIFTY! I checked it out on his car it works wonders. Though the BMP and others are ok too.
I was going to prep the car for SoloI next year but am now wondering if the E28 chassis is up for it.
If you put in a roll cage, sure. But you have to consider that they are 12+ years old, and will end up having more chassis flex than your brand new out of the box E46 330i's. There's no competition.
My recommendation is to make sure all your bushings are new and that your front end is tight. Then go out to the track and see what happens. If you're still not happy, then go to adjustable camber kits.
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