Get some Bug & Tar spray and head to the car wash. Hose down the wheels with the B&T, then hit them with the high pressure water and a brush if you have one handy.
You'll probably have to do that a few times for each wheel to get everything off, but it's the most straightforward and least labor-intensive approach I have found to removing Plasti-Dip from odd shaped items which don't lend themselves to having it peeled off very well.
Plus, when you're done, you don't have to worry about any residue or cling-ons, everything should be nice, shiny, and clean!