Abstract: An automatic transmission system for a cycle including a belt member having a fixed width and extending from a first pulley connected to the pedals of the cycle to a second pulley in driving connection to a wheel of the cycle and an actuator contacting the belt member. The second pulley has a belt-receiving slot of tapering width such that the slot is widest adjacent an outer diameter of the second pulley. The actuator applies the pressure to the belt member in relation to a rate of rotation of the wheel. The actuator causes the belt member to move radially in the tapered slot. The actuator includes an arm member which extends outwardly from the actuator and is in interactive contact with the belt member. The second pulley includes a first pulley half, a second pulley half, and a spindle connecting the first pulley half to the second pulley half. The first pulley half is in resilient relationship to the second pulley half.