A traction-drive system that in one embodiment comprises an idler rotatable about a longitudinal axis, a plurality of rotatable and generally disc-shaped planet rollers each having an inner contact surface, a case contact surface and an idler contact surface, the inner contact surface being of a first diameter, the case contact surface being of a second diameter, and the idler contact surface being of a third diameter, the planet rollers distributed about the idler and each planet roller contacting the idler at its respective idler contact surface. The traction drive system of this embodiment also comprises an inner ring rotatable about the longitudinal axis adapted to contact the inner contact surface of each of the planet rollers, and a case ring adapted to contact the case contact surface of each of the planet rollers. In some embodiments, the inner contact surface of each roller only contacts the inner ring, the case contact surface of each roller only contacts the case ring and the idler contact surface of each roller only contacts the idler.