A trailer to be attached to a cycle such as a bicycle, or a trailer-cycle set includes a device for controlling the steering and speed or deceleration of the trailer according to input control commands, the controlling device being equipped with means for measuring signals representing the longitudinal force and transverse force applied by the cycle to the trailer, the measuring means comprising sensors, including at least one deformation sensor for measuring the signal representing the longitudinal force applied by the cycle to the trailer and two sensors on the wheels of the trailer for measuring the signals representing the transverse force applied by the cycle to the trailer.