They are essentially brushed aluminum with a clearcoat (paint) over top, so whatever you do, use products that are safe for painted surfaces. I've used a (outdoor) tub with warm water and soap before to loosen up nasty stuff. Soft bristle brushes and patience are good too. Once you get most of the goo off and have just some specs and spots, try a claybar. They lift debris off wheels the same way they do off painted surfaces and glass.
Dan
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2005 Silver CRD Limited

245/75R16 GoodYear Duratracs
Fumoto drain | ProVent CCV Filter
Stanadyne FM100 filter | Cummins fuel pump
GDE Eco | SEGR | BoulderBars | FrankenLift | Frankenskids