you can use ALL kinds of setups, but the tires are really designed with a specific shape, which is definitly affected by rim width- big tires can be used on skinny rims, but the available traction suffers, as does the quickness of turn initiation-kind of defeats the purpose of putting on NEW tires,..those pro riders are actually putting on the "skinny" 125 tire, onto a 2.15 rim, so as to drive off the bottom of the ruts, rather than scrub off power on the sides of the ruts; it also makes the bike turn into the corners "quicker"; hope some of this is of help, jack