Abstract: A toothed wheel for a chain transmission system for a bicycle, intended to be coupled with at least one other toothed wheel in a group of crowns or of sprockets rotating as a unit has a plurality of teeth that follow one another on the radially outer periphery of the toothed wheel, alternating with grooves. Each tooth has a thickness, a width and a height and has an idle flank, passive in the exchange of torque with a bicycle chain, and a pressure flank, active in the exchange of torque with the same chain. The toothed wheel has at least one gearshifting helping tooth the height of which, measured from the bottom of an adjacent groove, decreases in the direction of the pressure flank, in any case being greater than or equal to 90% of the radius of the pin.

Abstract: A control device for a derailleur of a bicycle is described, comprising a support body, a cable-winding bush supported for rotation with respect to the support body, an indexer mechanism housed in the support body and suitable for controlling the angular position of the cable-winding bush, and a single manual actuation lever, the indexer mechanism comprising a toothed wheel integral in rotation with the cable-winding bush and having a first and a second plurality of slanting teeth, a first pawl integral with a driven arm of the lever and brought into thrusting engagement upon the first teeth while the lever is manually moved in a first direction beyond a predetermined rotation threshold, and a second pawl driven out of retention engagement with the second teeth by the driven arm of the lever while the lever is manually moved in the first direction up to the predetermined rotation threshold.