A sensor system is described, using self-mixing laser sensors (10) and an analyzer circuit (30) in order to determine the velocity of a vehicle, such as a car, and the rotational velocity of a wheel (20) of the car. Deviations between the velocity of the vehicle and the rotational velocity of the wheel (20) can be used to determine sliding of the wheel (20) and, finally, the traction or, more specifically, the coefficient of driving friction between the wheel (20) and the surface the car is driving on. Furthermore, a vehicle control system is described, initiating test accelerations of a wheel (20) by means of a control circuit (50) and control means (300, 400) in order to determine the coefficient of driving friction during driving. The test accelerations initiate short periods of sliding of the wheel (20) and the sliding is detected by means of the sensor system.