Adjusting device enabling aerodynamic resistance of a semi-trailer tractor to be reduced

It is an adjustment for a fifth wheel (5) having a displacement direction (21) with two on a vehicle, in particular on a tractor unit (1), in the longitudinal direction thereof guide rails arranged with a on the guide rails (27) slidable carriage and having an actuating device for displacing described the carriage, wherein the operating means when shifting while maintaining the positive engagement between the guide rails (27) and carriage (26) is formed. The actuator to move the carriage includes a first motor drive (23a, b). Furthermore, a first position sensor is at least S1 for detecting the slide position is provided, wherein at least the first position sensor S1 is connected to a control device (40).