Well, I got them cleaned off with a little bit of elbow grease and full-strength Simple Green. I used a wire brush first to get off the excess and then followed that with the Simple Green and it seemed to work pretty well although it took a lot of work with a nylon brush and a rag. The tires are Armadillos so I wasn't too worried about using the wire brush as long as I didn't get too rough with it. The tires seem to be fine now and no slick stuff left over.