Abstract: The present subject matter relates to a speed-change device for bicycles, enabling the user to change gear sequentially, from the lowest to the highest combination, which allows the cyclist to pedal without a drop in cadence (revolutions per minute), without noticing a difference in load (speed increase) and without a reduction in the performance (reducing, diminishing speed) of his bicycle. The objective of the system (combinations, mechanism) gives the cyclist this correct sequence enabling him to save time and not to unnecessarily waste energy. The actual cyclist can be certain that the mechanism is implementing the correct sequence for him and that his pedalling performance will be the most advantageous.