The largest tire I was able to run without rubbing (after removing the factory flares) was a 265/75/17, on a 9.25" wide Moto Metal wheel.

The factory fender flare takes up a lot of room towards the inner lower area of the fender opening. I plan to trim the factory flare to allow the wider, taller tire on my Ramcharger. Currently running a 28/75/17 with a 440 and add-a-leaf in front.