Abstract: An automatic transmission for a bicycle includes a rotatably supported wheel, an endless drive chain which is manually driven and held against axial movement relative to the wheel, a shift member which is rotationally and axially movable relative to the wheel and has thereon two axially spaced sprockets of different size which can each be engaged and driven by the chain, an arrangement responsive to the speed of the wheel for urging the shift member to move in respective axial directions as the wheel speed increases and decreases, and an arrangement responsive to the amount of force being applied by the cyclist for offering increased resistance to axial movement of the shift member in a direction which would upshift the transmission to a higher gear in response to an increase in bicycle speed. The arrangement responsive to the magnitude of the force applied by the cyclist also forces the transmission to downshift when the cyclist is applying a relatively large force to the pedals.