First of all, I wouldn't paint wheels. I know that seems to be a pretty popular pass time amoungst many posters here, but I think it looks like shit and within about 5,000 miles, they're fucked. Spend the money and get them powder coated. But if your insistent on painting them, sand them down with some fine sandpaper, wash with a wax & grease remover like PPG DX330, prime and paint with a rattle can of your choice. Viola, painted wheels that look like shit.