I would recommend lightly blasting the powder coating to roughen it. Hand sanding a wheel would probably not get at all the nooks and crannies. I assume that you're talking about NEW undamaged powder coating. If there's any rust that's started to creep underneath, you'd be better off removing the powder coating and starting from bare metal, IMO. I had a bracket that was powder coated that got a rock chip in it and started to rust, by the time I chased all the rust off, there wasn't any powder coating left. The coating peeled off pretty easily.
