An air-conducting system for a tractor and/or trailer is described, wherein at least one of the vehicles has a wind deflector. The problem addressed by the invention was to improve the aerodynamic drag of tractors and/or trailers. The problem is solved according to the invention by an air-conducting system in which the wind deflector is arranged at the rear of the trailer and/or at the rear and/or in the front region of the tractor and can be adjusted depending on the driving speed.