im running a 225 all around, i dont seem to have problems, even at a full turn. but i dont doubt that its close. ive heard of people putting as much as a 255 on the rear without problems, but i wouldnt go over a 225 up front. This is with stock wheels though. get new wheels with correct spacing and you could probably go bigger.

 

hes just talking about rear tires. i think a 26x8 is the biggest ive heard of, but im not sure. but dont forget, the taller tire thereoreticly increases the gearing. im going to run a 20" tall slick on 14" rims so it reduces the gearing.

 

mine is 245 all around