My 3 Series BMW has built up thick black deposits on the rims again after four months, even though I just replaced the brake pads recently. Every time I clean them with a pressure washer, they're dirty again after two weeks.
Brake dust builds up on mine constantly too, even after a brake pad change - it's just normal with modern brake pads, especially with a sportier driving style or frequent braking in the city. What really helps: apply a protective sealant (wheel sealant or just regular car wax) after each cleaning, then dirt doesn't stick as stubbornly and washes off much easier next time. Long term you won't get around it, but with the sealant you need way less elbow grease and time when cleaning.
that's really annoying, but the good news: it probably isn't because you're doing something wrong. modern brake pads, especially on BMWs, just produce much finer distributed wear particles than they used to. a pressure washer helps short-term, but the dust settles again and again due to brake heat and electrical charge - it's basically physics.
what really helps: try a nano-coating specifically for wheels. that creates a protective layer where brake dust doesn't stick as well. then clean with mild soapy water (not high pressure!) - i do it that way every four weeks and the brake dust builds up much more slowly. important: **avoid high-pressure washers after that**, it destroys the coating faster. also don't spray right after driving when the wheels are still hot.
as an alternative (or additionally) ceramic brake pads might be worth considering if you replace them at some point - they produce less fine dust, but are more expensive. for in between: a microfiber cloth and car wax can work wonders without damaging the wheels. some people also swear by special wheel cleaners with acid, but i'm cautious about that because they can attack the painted surface if you're not careful.
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