Try brake cleaner and a rag. Then wash the car with soap and water.

 

go to ur local parts store and pick up some "clay" its a finishing clay, awesome for removing brake dust tree sap and any major cake ons...meguires makes a excellent one and so does clay magic who makes both a medium and fine grit...the stuff works miracles

 

i just use a normal towel and water on my dads bmw (the brake dust on the front rims is rediculous after about 1 month or so the rims r black and they are the stock bmw grayish rims) it comes off perfectly fine

 

Concerned about the "theoretically" part.. Anyone wax their rims and if so what wax you use?