Originally Posted by
canyoneagle
Most original mountain bikes could take pretty hefty rubber, so anything up to 2.3 or 2.4 inches should fit. constriction points will be the chain stays and seat stays (where the tire passes the frame) and the fork crown.
My Ross Mount Hood will not take tires that wide in the rear. It has IIRC 1.8s in it now. Might take a slightly wider tire, depending on how agressive the nobs on the side are. Not a ton of clearance.