I use the Zep brand purple degreaser, I picked up a gallon of it from Home Depot.
I diluted it to the "weakest" listed on the label, and I use it to clean tires. Spray it on, let is sit about a minute or so, then scrub away. It works great for me, doesn't take a lot, and gives you nice, clean, bare rubber to apply your coating to.
I'm sure there are other uses for it, but I haven't experimented much. I would shy away from interior use, but it should work great on an engine bay, and possibly wheel wells.
(For the record, I do by best to keep it off of wheels and paint. I don't think a bit would hurt it, but why take the chance? For really dirty wheels I like diluted Simple Green, for relatively clean wheels I'll use a car wash soap)