Metal pipes connect the fluid in the master cylinder to the brake mechanism in each wheel hub.

There are two main types of gear: derailleur, where a mechanism nudges the chain between different-sized sprockets; and hub gears that work inside the enclosed wheel hub.

Investigators say a broken wheel hub was the cause of the accident.

A third link runs from each rear wheel hub forward to the frame to transmit driving and braking thrust.

When replacing, a wheel hub assembly should be torqued to the vehicle's specifications to prevent failure.