Here's our little 650B Monster Crosser. With 650B 2.0 knobby tires on disc brake wheels, I'd say that this is pushing the envelope for 700C to 650B conversions. And all we did was swap the wheels! Really, it was just that simple - we pulled out the 700C disc brake wheelset with the 700x31 cross tires, and put in a pair of 650B wheels with the new Pacenti Quasi-Moto 2.0 tire. Yes, disc brakes are good like that!