Abstract: The hub (3) of the bicycle (1) is connected to a chain-driven sprocket (10, 12) through a sleeve (11) carrying the sprocket(s), and through a driving mechanism which comprises a driving member (15) slidable inside the sleeve (11) and driven in rotation by this sleeve, and a driven member (16) slidable on the fixed axle (8) of the hub. The driving member (15) and the driven member (16) which is linked to the hub (3) through a free-wheel device (19, 24, 25) both carry cams (27) producing an axial thrust which pushes these members (15, 16) apart when they are rotated. This axial thrust is applied through a thrust bearing (33-36) to a sensing device comprising a strain gauge (29) mounted on a flexible non-rotating disk (28) carried on the fixed axle (8). Signals from the sensor are processed by a measuring and display device (6) attached to the handlebar, so that the rider may know at all times the value of the torque transmitted to the wheel.