How Chains Wear

Motorcycles and bicycles both use what is called a 'bushing' chain. Bicycles over five speeds must use a 'bushingless' chain, due to the great angular displacement between cogs.

Chains do not stretch, they wear. Strech of the materials in the chain is impossible given the relatively small forces that a motorcycle or bicycle can generate. The wear takes place where the pin from one link meets the bushing (or plates) of the next link. Interestingly, Since on every other link two pins are shared by one outer plate, The chain changes length only between every other link.

Rohlhoff - Theoretical initial schematic

Rohlhoff - Worn schematic