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Bicycle gearing is the aspect of a bicycle drivetrain that determines the relation between the cadence, the rate at which the rider pedals, and the rate at which the drive wheel turns. On some bicycles there is only one gear and, therefore, the gear ratio is fixed , but most modern bicycles have multiple gears and thus multiple gear ratios.
A chain drive and rear derailleur gear change, the most popular system in use today A shaft-drive with crankset and rear gear hub. Bicycle drivetrain systems are used to transmit power on bicycles, tricycles, quadracycles, unicycles, or other human-powered vehicles from the riders to the drive wheels.
This is equivalent to doubling the size of the drive wheel; that is, it is like a directly driven bicycle with a 52-inch wheel. That gear is said to be "52 gear inches." A bicycle with a 26-inch wheel, a 48-tooth chainring, and a cassette with gears ranging from 11 to 34 teeth has a lowest gear of 26 × 48 / 34 = 37 gear inches and a highest ...
In the single-chain system, the chain runs from the top of a chainring attached to the cranks to the top of a sprocket attached to the rear wheel hub with a freewheel, as with most bicycle chain drives. The chain then, usually, wraps around the rear sprocket to an idler sprocket between the rear wheel and the cranks, then runs back to a second ...
Chain drive was the main feature which differentiated the safety bicycle introduced in 1885, with its two equal-sized wheels, from the direct-drive penny-farthing or "high wheeler" type of bicycle. The popularity of the chain-driven safety bicycle brought about the demise of the penny-farthing, and is still a basic feature of bicycle design today.
Shimano 600 front derailleur (1980). A derailleur (French pronunciation:) is a variable-ratio bicycle gearing system consisting of a chain, multiple sprockets of different sizes, and a mechanism to move the chain from one sprocket to another.
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From a mechanical viewpoint, up to 99% of the mechanical energy delivered by the rider into the pedals is transmitted to the wheels (clean, lubricated new chain at 400 W), although the use of gearing mechanisms reduces this by 1–7% (clean, well-lubricated derailleurs and a straight chainline), 4–12% (chain with 3-speed hubs), or 10–20% (shaft drive with 3-speed hubs).