I've done rims on older cars by removing the wheel from the car, scrubbing them with a harsh detergent and degreaser to get any possible grime off. Sanding them smooth with 320 grit paper. Clean them again and when dry, tape off the tire (if you use newspaper double up as newspaper can absorb paint). Spray on light coat of primer folowed by a heavier coat of primer every 10-15 minutes for about 3-4 coats. Then wet sand that with 600-800 grit wet sanding paper to smooth it out and then clean it well and when dry put a light coat of silver paint followed by 3-4 medium coats (not quite as heavy as primer as color coat runs more easily). Then do the same with clearcoat if you want that long lasting shine. I have pictures on my website of the bumper I painted on my car that gives you the steps and a place to buy higher quality paint than what you get at Pep Boys or Home Depot.
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