I hit those with a scrub brush and heavy duty detergent. My latest favorite is "Awesome" cleaner. Works real good, but any solvent type of shop detergent works. Once dry, I also use acetone and a rag, or a 3M "scrub pad." If that doesn't work, I use paint stripper only where needed with the 3M pad.
Once all that is done, and tire dry, I liberally wipe with a "Trim Restorer" product (I use Turtle Wax's offering) and let the tires sit with a rag over them, (dust) until ready to use. The trim restorer works way better than other rubber preservatives and cleaners.