A structural beam (20) includes a polymeric beam section (21) and a reinforcer (22) comprising a pattern of stranded wires (31) of high strength steel that selectively reinforces and stiffens the beam section (21) for increased strength. The reinforcer (22) can be positioned integrally within the beam (20), or attached to a rear beam where the beam has a rearwardly open section, or attached to a front (25D) of the beam such as to stiffen the front of the beam.