Brake dust contains iron particles from the brakes creating friction against the rotors. Products like CarPro Iron X, Concours Purge, and Auto Finesse Ironout and General Fallout Remover will chemically react to these iron particles and dissolve them. The product is let to sit on the wheels for a certain dwell time between 2-10 minutes. While the chemical reaction takes place, the wheels will start to turn purple. This is the product dissolving the iron particles. You should use a brush to help agitate the dirt and spread the product to help it work. But in some cases, you can get away with a touch-less wheel clean. Iron remover wheel cleaners have great benefits with coated wheels.
Some wheel cleaners are on the acid side of the scale like Meguiars Wheel Brightener. Wheel cleaners that are acid based should not be used on polished aluminum or anodized wheels. They are however safe on clear coated and painted wheels. The wheel acids do a better job at eating away the brake dust than alkaline products do, but using them continuously isn’t a good idea. It’s a much better idea to use a neutral PH product for your regular maintenance washes or slightly on the alkaline side. You can use the acid for heavily oxidized wheels that have a lot of water spots on them. The acids will help break down the minerals left behind from the water.