I installed an RC components 18" x4.25 rim with 150-70 tire. I had to take a knife and cut a little clearance for the belt and I cleaned it up with a dremel grinder. It fits with no rubbing. This was done on an 07 street glide.
I've just installed a new set of Revtec wheels 21" and 16", I stayed with the factory width rim both front and rear I think I can just trim my lower belt guard and would work fine plenty of room between tire and belt itself.
