Seat for a motor vehicle

The seat has a tiltable backrest (1) linked to u-shaped support frame (3) and back support flange (9). The support frame has an extruded section with upper/lower belt brace (5,4) connected at front end to the landed belt brace (6) and at the distal end to profile brace (8), which has smaller cross section than the support frame. The central brace (7) is connected between landed belt brace and profile brace.