Magic Erasers use a really really fine celled structure to break the surface tension of stuck on soiling, grease, etc. This is why they're great, because it creates more resistance between the sponge and the soiling than the soiling contains in adhesion to whatever its stuck on in most cases.
Things like brake dust, road grit and dirt come off pretty easily because they don't have the kind of adhesion to the surface that paint would to the metal on your wheels, so It'll definately do the job. If you were taking off large ammounts of rough dirt and things like that off yor wheels and you had to scrub and scrub, you'd more than likely just be sratching tons of little marks into the paint or enamel thats on your wheels. For something like that I'd rather use some mild soap or wheel cleaner to help it along instead of dragging tons of particles across my wheels with the Magic Eraser alone. So I would say the sponge itself WONT damage your wheels at all, but any dirt, grime, gravel, etc thats being pushed around by the sponge definately could scratch your wheels if you really scrub.
Thats just my view on things though, maybe I think too much. haha.
More info please.
