Collapsible strut with controlled deformation for the frame of a road vehicle

A collapsible strut (10, 11) with controlled deformation for the frame (6) of a road vehicle (1); the strut (10, 11) consists of an internally hollow tubular body, which presents a closed transverse section, extends between an inner end (12) and an outer end (13), which are axially opposite to one another, is suited to be fixed in a projecting manner to the frame (6) of the road vehicle (1) at the inner end (12), and fulfils the function of deforming in a controlled manner in case of crash, thus collapsing axially; furthermore the strut (10, 11) presents a thickness (T) which axially varies from the inner end (12) to the outer end (13).