I've always used balo rotors on my BMWs, but I found a pair of Ate Power Disc rotors on ebay for half of what the balos cost. My front discs, after three years and 8 track days, still weren't completely worn, but with a track day coming up next month, I decided I might as well install the Power Discs, and let them get broken in. After driving on them for a week, they work just fine -- no excess noise, no excess dust. We'll see how they hold up at Lime Rock next month.

Also, the rotors are spec'ed for the single-piston E31 calipers. If you look closely at the picture, you can see that the 4-piston calipers have a different pad coverage area than the single-piston calipers. If you're switching (like I did) from E31 single-pistons to the 4-pots, you can keep the same rotors. You can not use the rotors spec'ed for the 4-pots with the single-piston calipers.

Drew Zacharda
6-speed Touring