Forensic Investigations of Low-Clamp-Force Type Wheel Separations

Wheel separations are a common non-operator cause of damage and injury in road transport systems. Forensic investigators are often engaged to determine why a wheel separated from a moving vehicle. In 100 investigations, the authors observed wheel separations due to axle, bearing, or fastener system failures. Fastener system failures dominate, and the authors show that low fastener clamp force is their necessary and sufficient condition. Examples of physical evidence of low fastener clamp force commonly found in forensic investigations are presented. The reasons for low fastener clamp force are explored using known wheel installation-to-separation times and distances, torque audits, and interface corrosion. From these, it is often possible to form a sound explanation for a low-clamp-force type wheel separation. Finally, wheel nut re-torquing is identified as a probable effective measure in preventing low-clamp-force type wheel separations.