Abstract: An automatic transmission for a linked chain driven wheel includes a plurality of chain-engaging sprockets disposed coaxially with and spaced apart along the axis of rotation of the wheel. Each of the sprockets has a predetermined diameter which differs from that of the other sprockets. The sprockets are drivingly connected to the wheel. A chain guide, which is axially movable relative to the sprockets, is provided. The chain guide, when aligned with a given sprocket, will guide the drive chain into engagement with that given sprocket. A chain guide actuator is operatively connected to the chain guide for varying the axial position of the chain guide automatically in response to the angular speed of the wheel.

Abstract: An automatic transmission for a bicycle comprising a sprocket wheel of variable diameter, for receivably engaging a linked bicycle chain, drivingly connected to a bicycle wheel. The diameter of the sprocket wheel can be varied in relation to the angular speed of the bicycle wheel. Variation in the diameter of the sprocket in response to drive pressure applied by the linked bicycle chain is prevented by a locking mechanism.