Pressure wash them real good, wipe them down with enamel reducer and wipe them dry again with clean rags (leave it all sit to dry for another 20 minutes), use the playing card trick described above, and paint. If you are taking the tires off...Clean up the bead and inside of the rim with a wire brush if necessary, and do the same for cleaning, then paint. If you want absolutely cleaned and painted, get them blasted, epoxy primer and a paint job.
