Well, I was washing the Bimmer today, and got to the rims. Problem is, the rear driver's rim is coated in some black, gritty, grimy stuff. It comes off with bug and tar remover, but only grudingly.
Weirdly enough, the other rims are clean.
Any idea of something a little stronger to clean this darn rim? I'm not looking forward to standing on my head with a toothbrush.