A shock absorber for motor vehicles, comprising: a deforming body (2) comprising a first portion (3) and a second portion (4) which are fixed to one another such as to identify a tubular member (5) which has a first axis and comprises a first wall (6) and a second wall (7) adjacent to one another, which intersect to identify an edge (8), each portion (3, 4) comprising a half-shell (9) and two fixing tabs (10) arranged respectively at opposite ends of the half-shell (9), at least a portion (3, 4) comprising at least a bead (11, 12) which develops along a perpendicular development with respect to the first axis. The bead (11, 12) develops continuously at least along a part of the first wall (6) and at least along a part of the second wall (7) of the tubular member (5), following at least the edge (8) identified between the first wall (6) and the second wall (7), the bead (11, 12), when it follows the first wall (6), being orientated projecting with respect to the zone of the external surface of the first wall (6) which surrounds the bead (11, 12), the bead (11, 12), when following the second wall (7), being orientated retracted with respect to the zone of the external surface of the second wall (7) which surrounds the bead (11, 12), the bead (11, 12), at the edge (8), varying orientation thereof between projecting and retracted.