Chain final drive

On a chain-drive motorcycle the gearbox output shaft carries a small front sprocket, the rear wheel carries a large rear sprocket, and a roller chain loops around both. The difference in tooth count is the final reduction: a 14-tooth front and a 42-tooth rear, for instance, make the engine turn three times for every wheel turn. Swapping sprockets is the cheapest way to change a bike's character, a bigger rear sprocket for quicker pull, a smaller one for a higher top speed.

• Each link is a pair of side plates joined by pins, with a bushing and a roller on each pin so the chain rolls onto the sprocket teeth instead of sliding.
• On most bikes above 150 cc the chain is sealed: O-rings or X-rings between the plates trap grease inside the pin and keep grit out, which multiplies its life.
• The top run pulls; the bottom run hangs with a little slack, which is necessary because the distance between the sprockets changes as the swingarm moves.
• Slack is adjusted by moving the rear axle backwards in its slots; stretched chains and hooked sprocket teeth are replaced as a set.

The chain runs along the left side of the bike, usually with a guard on top; commuters such as the Splendor or Shine enclose it fully in a case so it stays cleaner for longer.

What you notice: the chain needs cleaning and lubing every few hundred kilometres and adjusting every few thousand, more often in rain and dust. In return it is the lightest, cheapest and most efficient final drive, which is why racing bikes and 100 cc commuters alike use it.