A gear-shifting device for means of transport comprising: a pair of shafts parallel to and spaced from each other each comprising a plurality of transmission units, each transmission unit of a tertiary shaft being driven to rotate by a respective transmission unit of the other shaft, the transmission units of the shaft rotating integrally with it; the transmission units of the tertiary shaft being arranged according to a predetermined sequence along an axis of rotation of the tertiary shaft and each transmission unit of the tertiary shaft being rotatable on itself about the axis; each transmission unit of the tertiary shaft being positioned axially at a respective transmission unit of the shaft and meshing together in such a way as to establish a predetermined transmission ratio between the shaft and the shaft; each transmission unit of the tertiary shaft being configurable between a non-selected condition in which it is freely rotatable about the tertiary axis and a selected condition in which it is rotatably integral with the tertiary axis; activation means operatively associated with the tertiary shaft and the transmission units of the tertiary shaft for selectively rotating in an integral fashion a transmission unit of the tertiary shaft with the tertiary shaft; characterised in that the activation means comprising a plurality of slowing disks each operatively connected to a respective transmission unit of the tertiary shaft; each slowing disk being rotatably mobile relative to the respective transmission unit around the tertiary shaft between a first position and a second position; each slowing disk being configured in such a way as to selectively rotate in an integral fashion the respective transmission unit with the tertiary shaft from the non-selected condition to the selected condition by generating a transient difference in the speed of rotation between the transmission unit selected and the respective slowing disk in such a way as to bring the latter from the first position to the second position; each slowing disk comprising along its perimeter edge a portion made of at least one deformable material; the device comprising at least one rotary unit operatively mobile towards a slowing disk for deforming the portion of deformable material in such a way as to generate the transient speed difference. a pair of shafts parallel to and spaced from each other each comprising a plurality of transmission units, each transmission unit of a tertiary shaft being driven to rotate by a respective transmission unit of the other shaft, the transmission units of the shaft rotating integrally with it; the transmission units of the tertiary shaft being arranged according to a predetermined sequence along an axis of rotation of the tertiary shaft and each transmission unit of the tertiary shaft being rotatable on itself about the axis; each transmission unit of the tertiary shaft being positioned axially at a respective transmission unit of the shaft and meshing together in such a way as to establish a predetermined transmission ratio between the shaft and the shaft; each transmission unit of the tertiary shaft being configurable between a non-selected condition in which it is freely rotatable about the tertiary axis and a selected condition in which it is rotatably integral with the tertiary axis; activation means operatively associated with the tertiary shaft and the transmission units of the tertiary shaft for selectively rotating in an integral fashion a transmission unit of the tertiary shaft with the tertiary shaft; characterised in that the activation means comprising a plurality of slowing disks each operatively connected to a respective transmission unit of the tertiary shaft; each slowing disk being rotatably mobile relative to the respective transmission unit around the tertiary shaft between a first position and a second position; each slowing disk being configured in such a way as to selectively rotate in an integral fashion the respective transmission unit with the tertiary shaft from the non-selected condition to the selected condition by generating a transient difference in the speed of rotation between the transmission unit selected and the respective slowing disk in such a way as to bring the latter from the first position to the second position; each slowing disk comprising along its perimeter edge a portion made of at least one deformable material; the device comprising at least one rotary unit operatively mobile towards a slowing disk for deforming the portion of deformable material in such a way as to generate the transient speed difference.