The best wheel cleaner I have used on BMW wheels is the BMW gel product, available from the dealer. It seems to work well dissolving the brake pad dust, and it doesn't harm the wheel finish.

The pad residue dust is black, because BMW puts carbon black in the pad material as a filler.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue