Speed changer with pre-determined gears, particularly for cycles

Speed changer (1) with predetermined gears, especially for a cycle, for control by cables (3, 4), based on a single rotating grip (2), of gearshifts (5, 6) connected respectively to an elastic return means, such as a spring, said changer (1) comprising at least two cable operating mechanisms (7, 8) located within a case (18), one operating mechanism (7) of the cable (3) of the front gearshift (5) or chainwheel gearshift, the other operating mechanism (8) of the cable (4) of the rear gearshift (6) or cog gearshift, this second mechanism (8), jointly in rotation with the grip (2), being able to induce release or pulling of the rear cable (4) during rotation of the grip (2) in the same direction, characterized in that the rotary assembly formed at least from the operating mechanism (8) of the rear cable (4) and the grip (2) can be rotationally coupled intermittently to the operating mechanism (7) of the front cable (3) of the chainwheel gearshift (5), this operating mechanism (7) of the front cable (3), when coupled, being able to induce pulling or release of the front cable (3) of the chainwheel gearshift (5) depending on the direction of rotation of the grip (2).