You could get a 2.25 or maybe (?) a 2.5 in there... but I am not sure what the point of that would be. Beyond the 47b range and it doesn't make a lot of sense unless you are riding on the beach.The site says the A4X frame will take a 24 x 2.6" tire and gives specs for a 650b wheel. What width tire can the frame accommodate for a 26" wheel?