Method for measuring a speed and/or a distance travelled by a bicycle while it is being used by a user, by means of at least one permanent magnet placed on a wheel of the bicycle and a measurement circuit comprising a magnetic sensor placed on a frame portion or a fork for mounting the rotation freewheel, the measurement circuit being placed on the frame portion or the fork at the same distance from the axis of rotation of the wheel as the permanent magnet to be facing the permanent magnet as it passes during rotation of the wheel, characterised in that the method comprises steps of: - moving the bicycle on a path with the wheel rotating with the permanent magnet, - detecting the passage of the permanent magnet facing the magnetic sensor of the measurement circuit by generating an induced-voltage pulse each time the permanent magnet rotates, - rectifying the voltage generated by the magnetic sensor by means of a rectifier and by storing the rectified voltage on a smoothing capacitor (C L) to power the measurement circuit, - computing a speed and/or a travelled distance of the bicycle in a computing unit, which is clocked by an oscillator, based on the induced-voltage pulses received over time from the magnetic sensor and in light of the value of the diameter of the bicycle wheel, and - wirelessly transmitting one or more speed and/or distance measurements computed in the computing unit of the measurement circuit to a mobile device carried by the user or on a part of the bicycle by a signal transmission-reception unit connected to an antenna of the measurement circuit, a direct transmission of instantaneous speed measurement to the mobile device being carried out to display this instantaneous speed measurement on a display element of the mobile device, and as soon as the power supply voltage level on the smoothing capacitor (C L) falls below a first low power supply voltage threshold, a deactivation of the signal transmission-reception unit is performed, and in that before the power supply voltage level on the smoothing capacitor (C L) falls below a second power supply voltage threshold lower than the first low threshold, a memorisation of the different computations of speed and/or distance travelled by the bicycle are performed in a non-volatile memory of the measurement circuit. - moving the bicycle on a path with the wheel rotating with the permanent magnet, - detecting the passage of the permanent magnet facing the magnetic sensor of the measurement circuit by generating an induced-voltage pulse each time the permanent magnet rotates, - rectifying the voltage generated by the magnetic sensor by means of a rectifier and by storing the rectified voltage on a smoothing capacitor (C L) to power the measurement circuit, - computing a speed and/or a travelled distance of the bicycle in a computing unit, which is clocked by an oscillator, based on the induced-voltage pulses received over time from the magnetic sensor and in light of the value of the diameter of the bicycle wheel, and - wirelessly transmitting one or more speed and/or distance measurements computed in the computing unit of the measurement circuit to a mobile device carried by the user or on a part of the bicycle by a signal transmission-reception unit connected to an antenna of the measurement circuit, a direct transmission of instantaneous speed measurement to the mobile device being carried out to display this instantaneous speed measurement on a display element of the mobile device, and as soon as the power supply voltage level on the smoothing capacitor (C L) falls below a first low power supply voltage threshold, a deactivation of the signal transmission-reception unit is performed, and in that before the power supply voltage level on the smoothing capacitor (C L) falls below a second power supply voltage threshold lower than the first low threshold, a memorisation of the different computations of speed and/or distance travelled by the bicycle are performed in a non-volatile memory of the measurement circuit.