Abstract: A bicycle transmission with one or two driving sprockets on a pedal shaft, selectively connectable with any one of several driven sprockets of progressively varying diameters on a rear-wheel axle, is controlled by a gear-shifting lever rigid with one or two cam disks each coacting with a cam follower on an associated rocker arm. Each rocker arm is tied to a flexible link, such as a Bowden cable, serving for the relative axial shifting of the chains and a respective sprocket set to let the chain jump from one driven (or driving) sprocket to an adjoining one. Each cam disk has a plurality of peripheral lands whose distances from the disk axis determine the engagement of the chain with one of the sprockets of the associated group.

Abstract: A demountable rear-wheel axle of a bicycle, carrying a set of sprockets of progressively decreasing diameters, is detachably held in a forked frame member next to a generally crescent-shaped stationary supporting element secured to that frame member, the supporting element having an arcuate edge generally paralleling about half the periphery of the adjoining smallest diameter sprocket. A guide bracket movable generally parallel to the wheel axle, engaging the driving chain of the bicycle, can be aligned not only with the several sprockets but also with the stationary supporting element to let the chain embrace that element when it is desired to remove the rear wheel; the movement of the guide bracket is controlled by a hand lever which normally is blocked by a releasable latch from aligning that bracket with the supporting element.