A two-mass-skate bicycle (TMS) is a theoretical model created by a team of researchers at Cornell University, University of Wisconsin-Stout, and Delft University of Technology to show that it is neither sufficient nor necessary for a bike to have gyroscopic effects or positive trail to be self-stable. The two-mass and skates aspects of the model were chosen to eliminate design parameters so that the nine that remain, the locations of the masses and the steering geometry, could be more easily analyzed. Instead of full inertia tensors, the total mass of the bike is reduced to just two point masses, one attached to the rear frame and one attached to the front fork. Instead of rotating wheels, the non-holonomic ground contacts are provided by small-radius skates.