A “Toolbox” for Forensic Engineers

Establishing the Load Transfer Path 69
Figure 3.6 Bead of a front tire showing the kink where the steel bead has been
deformed by the tire being impacted against the wheel rim.
of abrasion or wear. Assembling the pieces revealed that the fractures spread
out from a single point on the left rim, consistent with a forceful impact
concentrated at one spot. The impact had been cushioned by the tire, as there
was no deep indentation in the metal of the rim itself. Figure 3.5 shows the
major pieces juxtaposed, and Figure 3.6 shows the inside of the tire with a
pronounced kink in the bead consistent with being flattened against the outer
flange of the rim.
It was a tubeless tire and no evidence of puncture could be found, so the
air must have either escaped through cracks in the metal wheel or by displacement
of the tire bead from the wheel rim by an external force. The
bundle of high tensile steel wires inside the rubber forming the bead (which
holds the tire onto the wheel rim) had been deformed to the profile of the
outer rim, as evident in Figure 3.6. This forceful impact had clearly occurred
when the wheel hit the tree, as there were several small splinters of bark
embedded in the fracture of the major part of the wheel still attached to the
hub, which could only have occurred after the tire had been displaced from
the disintegrating wheel.
This big force against the front tire had been reacted to by the magnesium
alloy wheel and must, in turn, have been reacted to by the axle in order for