I have not done this, but I am quite sure you would need something along the lines of 4.5-5 inches to get the tires away from each other far enough so as not to have heat build up from them. The tires bulge past a regular rim by 2", so if you double that it would have you at 4" and that would have the tires on each other. You may have to see about finding a different off set for the bud wheels to get that size on the back. Good luck