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If they are the plastic chrome clad, use whatever you use on your paint. Clean them well, polish to get a shine, then go with a heavy protective coating. Either wax or synthetic.
the detailer at the shop i'm at uses an acid etching solution. Its diluted to a working concentration and then sprayed on the rim. let sit for 1 min and then rinsed off with water.
I had brake dust on my rims that could not be cleaned off. polishing did not work well. With the acid soln, the rims are like new.