I've been running 27"x11"x14" Ripsaws for over a year. I'm using STI HD3 5+2 offset rims, and have never had any rubbing issues. From the retailer (Rocky Mountain), with 10 psi, they were 26 7/8" tall and 10 3/4" wide. I didn't have to do the frame mod ( I was prepared to.), or have to use wheel spacers (sent them back). I have put almost 3,000 miles on this setup, over every type of terrain imaginable. I wouldn't be able to run 28s without doing the frame mod, however. My clearance is 1/4" to 3/8" at best. I have always had enough power to do anything I wanted, and my P500 has never failed to impress me, or anyone I was riding with.