Abstract: This invention is concerned with the problem of coupling a heavy close-coupled four-wheeled trailer to a vehicle.The coupling system provided includes a tubular member (1) pivotally mounted at the forward end of the trailer, and a draw-bar (4) slideable within the tubular member. A king pin (9) is provided on the rear end of the draw-bar (4) and, when the draw-bar is in its forwardmost position, the king pin can be locked in the jaws (10) of a fifth wheel coupling. If the coupling is released, the draw-bar can be moved rearwardly, and can also be moved laterally, within a range determined by cooperation of the king pin (9) with rails (12). The area through which the forward end of the draw-bar (4) can be moved is indicated by the hatched area (14) FIG. 3. When the draw-bar is moved to its rearwardmost position, it is again held on the fore-and-aft axis of the trailer by two further rails (13).