Abstract: Trailer of the type which can be widened out or retracted when required, made of a frame on which there is mounted a wheel assembly. The frame comprises a traction bar, a rear transverse member fixedly mounted at one end of the traction bar, a front traction member which is parallel to the rear traction member and is also fixedly mounted on the traction bar, along the latter, short of its opposed end. The portion of the traction bar between the front transverse member and the opposed end thereof constitutes a traction rod. A movable framework is disposed on both sides of the traction bar between the rear and front transverse members. The wheels of the trailer are mounted on the movable frameworks, which can laterally extend thereby widening out the trailer, or they can be retracted in the narrow position of the trailer. This trailer can easily be attached to a four- or three-wheeler of the sporting type and, when it is widened out, it can be used to carry the four- or three-wheelers.