Sorry for the length of it but thought this info would help:
Wheel Surface Cleaning:
It is important to keep wheel surfaces clean, as well as improving the overall look of the vehicle leaving them dirty can have many adverse effects; the black powder coating on the surface of your wheel has four components; a static friction charge (caused by the pads contact with the rotors) that attracts dirt, road tar and other contaminants kicked up by both your vehicle and others. Friction heats the pads and callipers to extremely high temperatures, and causes tiny particles of hot metal to wear off and sent flying in different directions.
Many of these hot metal particles land on your rim and literally fuse themselves to the surface. Finally there is brake pad adhesive, modern brake pads are complex compounds of metals, synthetic materials and adhesives (the binder system) which is designed to wear away under friction like the rest of the pad. The adhesives used in brake pads can be very difficult to remove and they are also corrosive and will etch the wheel surface, the metal particles from the pads and rotors will become a conduit for rust compromising the paint surface of your wheel
Wheel cleaning is not that difficult, especially if you use the correct tools, they have to work safely but effectively. Wheel cleaners that contain acid are the most dangerous, there are wheel acids that are safe if used with care and the directions are followed precisely. Accidents and expensive wheel replacements can always be avoided if you do some research and are smart about your choices. Always check the products MSDS and its pH value before you use it. It is always preferable that you use a 100% acid-free product with a pH of 7.5 – 8.0
Cleaning Clear Coated Wheels:
•Ensure wheels and rotors are cool before applying cold water as this may cause them to warp. Hose off as much initial grime as you can. Rinse up into the wheel well to wash away road kill, mud and other debris.
•Use detailing clay to remove any imbedded contaminants
•Use a solvent based cleaner to remove any road tar
•Apply a solution of P21S Total Auto Wash to wheel-wells and tyres, and let soak in, agitate with a long-handled boars haired brush before rinsing
•Spray P21S Wheel Cleaner (Gel or Liquid) this cleaner is 100% acid-free and will not damage any type of wheel finish. (Gel for badly soiled and regular for normal soil) onto wheel rims and lat soak in (for badly soiled surfaces us P21S-Red (422)
•Before finally removing cleaner, agitate with a soft brush and then rinse off (See Wheel Brushes)
•Rinse wheel surface thoroughly with clean water (to avoid splashing paint surface rise by pouring a bucket of water over each wheel from the top down
•Remove any surface imperfections with a suitable clear coat polish (dependant upon extent of damage)
•Dry wheels with a towel, apply a polymer sealant (ZoopSeal) to the surface of the wheels, it will protect the finish from brake dust and the elements and also make them easier to keep clean.