The device for the motion transmission onto cycles comprises: a connecting core able to be associated with a frame of a cycle in a rotatable way around an axis of rotation; and a ring gear lying on a lying plane surrounding the core and able to be coupled to a flexible transmission element closed on itself in a loop for starting said cycle along a direction of forward movement; oscillation means placed between the connecting core and the ring gear and able to tilt the lying plane with respect to the axis of rotation.