Derailleur
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A derailleur is specifically a device that moves a bicycle chain from one sprocket to another, and more generally the entire gearset on a multiple-speed bicycle with such a mechanism.
Shimano 600 front derailleur (1980)
Campagnolo Super Record rear derailleur (1983)
Shimano XT rear derailleur on a mountain bike
Pulley wheels for a rear derailleur
Hub gear
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A hub gear, internal-gear hub, internally geared hub or just gear hub is a gear ratio changing system commonly used on bicycles that is implemented with planetary or epicyclic gears. The gears and lub
Derailleur
…of the range ratio obtained. Derailleur gears generally have an efficiency around 95%, a few percentage points higher than other gear types such as hub gears. Bicycle drivetrain systems…
Sturmey-Archer S3X
early NuVinci hub
NuVinci internals
A Sturmey-Archer AM bicycle hub gear mechanism with the ring gear removed to show the compound (stepped) planet gears.