English: The invention concerns a new propulsion system for bicycles, comprising the use of a larger bicycle frame (02), provided with an intermediate bar (03), which together with a lower bar will serve as the support to a metallic block (04) which serves as the base and attachment for all the mechanism. The mechanism comprises the use of two levers (06), supported and attached in each side of the block (04), which are provided in one of its ends of a pedal (08) and in the other lever rack (07). The levers (06) have reciprocated and synchronised movements, moving each one along a short and elliptical path, driving through the crank gears (10) that make the rotative axle (09) to rotate, transmitting its movement to the chain wheel (11) which by means of a second chain (13), that in its turn transmits it to the conventional chain wheel (12) from whose axle the pedals were suppressed. From this point the common traction system is in use. The synchronisation system of the levers (06) is assembled inside of the block (04).