I would avoid the use of steel wool, no matter how many zeros were on the package. It leaves fine scratces that never go away, and can also serve to let dirt stick more readily. A really good degrasing cleaner, such as Westley's Bleche White and a car cleaning brush will do a fantastic job. I just cleaned years of brown crud off a friends wheels yesterday.

A brush like this is a must for cleaning wheels, and makes cleaning wire wheels and wheel covers about 95% easier-

 

Yep...I saw some scratches on the few flat spots an began to use a lighter touch. I need to get a nice long bristle brush like that for general hubcap upkeep.

 

Oof. I don't envy that job.