concern being to preserve the passenger cell whatever the consequences for the vehicle until now efforts have been limited to working on the parts which are not very likely to buckle since they are not very slender in the sense of euler or they are well supported at various places along their length such as the front side bars supported by the various bracing functions of the components which are connected thereto wheel housings gearbox support for example or the rear side bars supported by the wheel housings the rear chassis the crossbar for example the applicant has taken a different approach by concentrating on structural elements such as the extensions mounted at the end of a short cradle instead of the long cradle most frequently used in this case such structural elements are not generally supported over their length which is considerable they are therefore capable of being subjected to buckling the formula i of the appendix 1 gives a definition of the slenderness in the sense of euler where l is the length of the element s is the area of its straight section and imin is the minimum modulus of inertia in the section being considered to return.