Too much negative not only wears the rear tyres, but also makes the rear a bit unpredictable when putting the power down.
Words of wisdom from Ess Three. I didn't do anything about the amount of rear camber...
Coming home on Friday night, the car started making an unearthly racket, managed to get home and upon removing the wheel centre cap, three sheared wheel bolts fell out, I removed the wheel, to remove the spacers and there is a crack all the way around the shouldered part where the wheel locates. The new tyres that I had on the rear four months ago were down to the wear markers (that's two rears to every front).
I've been to JBS today to order my adjustable tie-bars, whilst there I showed them my broken spacer, to discover that H & R won't sell them in ones, I'll have to buy a pair, so that'll have to go on hold.
I've also splashed out on four Goodyear F1 Asymetrics and they seem to have transformed the handling of my car, should be even better when the tie-bars come. All I've got to do now is the grumbling front wheel bearing and a 40,000 mile service (including the cambelt and water pump for peace of mind). Then everything should once again be hunky-dory, even though I'll be a grand lighter.
So the moral of this story is:- If you lower your S3 and you've got loads of negative camber, don't put on 20mm spacers, they'll only exaggerate the problem, make your back end twitchy, wear out your tyres at an unacceptable rate and shear your wheel bolts. Get some tie-bars fitted first...