Ok, flat four wheels have a clear coat on them so unless you stopped that off then your not painting bare metal. If you did, then spray a light coat of a product called "bulldog" on them. It's an adhesion promoter, then spray a coat of black DTM, you don't need a sanding primer as you're not going to be block sanding them, the DTM is a sealer as well so a topcoat as soon as it "flashes" with whatever you're going to use, don't recommend rustoleum, but they're your wheels, so use what you want, I used acrylic enamel on mine
nice, dint know they have clear coat on them.