Originally Posted by GregW / Oregon
It may fit on, but is likely to be about ~2" smaller in OD than stock. I wouldn't suggest it, especially in the rear.
My dealer tried the space saver available from LeatherZ. Even with a 15mm spacer it won't fit--the E9X M3's front brakes are too big. Then, of course, there is the diameter/handling issue.
My dealer will soon be trying the space saver from an X3/550i with the 15mm spacer. It's a bit larger in diameter and has different offset.