The load bed (2) of a trailer (1) is supported on a number of trolleys (4), each of which has an axle (5) having an intermediate portion (6), two hubs (7) rotating about a common axis of rotation (5a), and a suspension (13) having a connecting structure (14), a mechanical transmission (18) interposed between the connecting structure (14) and the axle (5), and a hinge pin (26) allowing the axle (5) to oscillate with respect to the connecting structure (14) about an axis (27) perpendicular to the common axis (5a); the transmission (18) having at least a first arm (19) and at least a second arm (20), both hinged to the connecting structure (14) and converging with each other and with the connecting structure (14); the first arm (19) being hinged directly to the hinge pin (26); and the second arm (20) being connected to the intermediate portion (6) by an angular relative-motion device (29).