This is stuff pretty amazing - I've had three BMWs over the past 20 years, among other cars, and have never found a solution to the brake dust problem until this spray. I cleaned the wheels and barrels thoroughly w/soap, water and a set of wheel woolies. Liberally sprayed the protectant on the face, on the spokes and into the barrel between the spokes. Let it sit for a couple of hours before driving. So far, this week, the wheels are pristine. It's a surreal thing to see clean BMW wheels after a week of driving.
Sounds like an infomercial, but I'm really impressed so far. Only downside is that the bottle is very small. Can't see more than two applications (4 wheels per application) coming out of the bottle - which cost $12. If it lasts 4 weeks, I think it will be worth it.
1993 e36 325i, 1999 e46 328i, 2005 ap2 s2000, 2007 WRX STi, 2008 g37s coupe, 2009 Audi a4 2.0T Avant