The bicycle chain is a marvel of technology that efficiently transmits your efforts into turning the rear wheel; in fact, the chain is far more efficient than the shaft drives used in cars and this is the reason that motorbikes are still mainly equipped with them. But which chain to choose? Like all cycling products there seems to be lots to choose from; if you ride a derailleur-geared bike (the bit that hangs off the rear axle) then a multi-speed chain that is compatible with your drive train is the correct choice. If you have a nine speed cassette (nine cog wheels) then you'll need a chain designed to fit it. It's also a good idea (although not imperative) to match the brand of your chain with the manufacturer of your gears.