I was able to fit an AVON zr160 under mine with out any modifications. If you wanted to go fatter you would need to design a new rear brake support strut to suppor the rear caliper. It would need to be curved away from the tire itself to prevent it from rubbing the sidewall. You also may want to upgrade your slack adjusters to a stronger design as well do to the extra bite they tend to suck into the rear swing arm at launch and under heavy shifting. As for the front.......... your screwed. Good luck!