Engineering Dead-Ends

Part 1: The Triumph Sprung Hub

- Harry Fisher

In the dawn of motorcycling, many things that we now take for granted on a motorcycle either hadn’t been invented or were deemed unnecessary. Chain drive, electric lighting, gearboxes and noloss lubrication, to name but a few, were all developments that were quickly adopted, however, once they had been developed.

In the area of suspension development, the motorcycle manufacturers were notably backward. Front suspensions were almost universally adopted before World War One - mainly of the ‘girder’ type - but it wasn’t until after World War Two that rear suspension became widely utilised. Prior to that, rigid rear ends were the norm, with the saddle being sprung to insulate the rider from road shocks.

In the late 1930s, ‘plunger’ suspension was starting to make an appearance on the rear wheel. The vertical movement of the rear axle was controlled by sets of springs above and below it, mounted in extensions of the rear frame either side of the wheel, to control movement both up and down. It could be quite sophisticated, with springing and damping in both compression and rebound but there were problems with the system. Wheel travel was limited, the wheel could move out of the vertical axis and it was expensive to produce and difficult to maintain.