Apparatus (7) for coupling a trailer (5) to a tractor (3) whereby the trailer (5) is adapted for charging forage material into an elongated tubular element (9) comprises a framework (6). Bearing plates (8) are carried on respective pairs of telescoping members (105) on the framework (6) and are urgeable by hydraulically powered drive rams (112) into engagement with the ground engaging threads (110) of the corresponding rear wheels (11) of the tractor (3) for braking the rear wheels (11) of the tractor (3), for in turn controlling the forward speed in the direction of the arrow (A) of the tractor (3) and the trailer (5), so that the forward speed of the tractor (3) and the trailer (5) is substantially matched with the rate at which the tubular element (9) is being charged with forage material from the trailer (5).
