an extended position shown in fig2 the first frame portion 10 comprises a first beam 12 and a second beam 13 which are parallel and parallel to a direction of longitudinal movement of the trailer as indicated at 14 the beams 12 and 13 are indicated by a first transverse beam 15 and a second rear transverse beam 17 at the front of the beams 12 and 13 is provided a pair of inwardly inclined beam portions 18 and 19 which converge to central apex at which is provided a hitch pole 20 extending forwardly from the frame for attachment to a towing vehicle the rear or second frame portion comprises a first beam 21 and a second beam 22 each of first and second beams 21 22 is formed of a first tubular portion 23 of the same dimensions as a tubular portion forming the beam 12 13 and a second tubular portion of reduced dimensions for sliding inside of the tubular portion defining the beam 12 13 thus in the retracted position shown in fig1 the end 24 of the portion 23 lies substantially immediately adjacent the end 25 of the beam 12 the beam 13 and the corresponding beam 22 of the second portion of the same construction at the forward end of the smaller beam portion of the rear frame is provided a pair of guide rollers 25 26 which roll on the inside surfaces of the top and bottom wall of the beam 12 13 as best shown in fig3 at the rear end of the beams 12 and 13 is provided a pair of rollers 27 28 which roll on the outside surface of the smaller portion of the beams 21 22 thus the smaller.