A “Toolbox” for Forensic Engineers

Establishing the Load Transfer Path 77
Figure 3.12 View from the rear of the racing motorcycle sidecar as recovered.
The sidecar wheel bracket is broken and completely separated from the chassis.
the best available, and used exclusively by a three-times-in-succession
national champion. Six machines roared off in the final race and the young
man was in fifth place as he entered the first curve. Suddenly, just as he started
the slide at the bend, his machine went “tail light” and somersaulted through
the air, twisting around and turning over as it did so. The sidecar passenger
was flung clear of the track, but the rider was thrown to the ground and his
machine appeared to land on his back before coming to rest several yards
further along the race track.
When the machine was recovered it was discovered that a triangular
bracket that held the sidecar wheel was broken and partially separated from
the sidecar chassis. This bracket was a unique design that allowed the
sidecar wheel to be adjusted forward and backward along the sidecar chassis
with the axle mounted in an eccentric hub that enabled the wheel to be set
at various angles of “toe-in” and inboard inclination. It was the ease of
making these fine adjustments, absolutely critical in a championship race,
that made it so popular with the racing motorcycle fraternity. The chassis
and the bracket were made from high strength steel tubing joined by bronze
welding, a conventional method at that time (early 1990s) for cycle and
motorcycle frames. The steel tube and joining method were those recommended
for cycle frames by Reynolds TI in its technical brochures. The
sidecar axle was a hardened and tempered alloy steel as used for stub axles
of small motor cars.
Figure 3.12 is a rear view of the machine, as recovered, with the sidecar
wheel offered up approximately in the position it was in when the bracket
fractured. The engineer for the defendant company was the first to examine
the damaged machine. A tie rod from the bracket to underneath the saddle