A2Z, let it sit for about 30 sec a wheel, then scrub lightly with a bristle brush. I have polished Mille Miglia wheels, and I haven't noticed any scratching or discoloring of the metal. The only thing is that if you let this stuff dry on the wheels, it turns white, but that can be washed off with thurough rinsing. It evan cleaned the carbon residue off mty exhaust tip!