How long did you leave it on ? Did it get baked on from the heat the brakes put off ? I would start with a good all purpose cleaner then step up to a degreaser, you could also try whatever wheel cleaner you might have. I would find a good detailing brush something that wont hurt the clear coat and work the cleaner a little bit after letting it sit for a minute or two. Make sure you rinse off all the cleaner once your done.