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Hub gears or internal-gear hubs are a type of gear system used on bicycles. Hub gears are used mostly on utility bikes and various types of small wheeled bicycle, such as folding bikes. Hub gears work by internal planetary or epicyclic gearing, which means that the outer case of the hub gear unit (which is attached to the spokes) is made to turn at a different speed relative to the rear wheel's sprocket depending on which gear is selected.
In this simple epicyclic gear mechanism, the inner gear or "sun gear" (green) provides the input rotation. The two "planet gears" (blue) rotate freely about the planet gear carrier (yellow) which is fixed. As the planet gears rotate about the sun gear, they propel the outer ring gear or "annulus" (red), which provides the output rotation
In this simple epicyclic gear mechanism, the inner gear or "sun gear" (green) provides the input rotation. The two "planet gears" (blue) rotate freely about the planet gear carrier (yellow) which is fixed. As the planet gears rotate about the sun gear, they propel the outer ring gear or "annulus" (red), which provides the output rotation

In the United States and United Kingdom, hub gears are less common than derailleur gears which are the dominant gear system on most modern bicycles in these countries. In most of continental Europe, however, hub gear systems are dominant. Hub gear systems have in the past also been used on motorcycles, although this is now quite rare.

Unlike derailleur gears, where the gears and mechanism are exposed to the elements, hub gears are enclosed within the hub of the bicycle's rear wheel. Gears are changed by a cable which is tightened or loosened by a lever or twist grip on the handlebars.

Hub gears were invented in 1903 by an English company Sturmey Archer, and by the 1930s they had become common on bikes across the world. Their popularity has been much diminished by derailleur gears which, since the 1950s, have become the most common type of gear system on bicycles, due to their lower price and wider gear range, although hub gears have undergone a small revival in recent years.

The main advantage of hub gears is that because the mechanism is enclosed within the hub, it is not exposed to dirt or weather. This means that, unlike derailleur gears, hub gears need very little maintenance and are very reliable. Bicycles built with internal hub gears instead of derailleurs also are less vulnerable to damage in shipping. The other advantage is that the gear can be changed when the bike is stationary, which makes them suitable for riding in city traffic with lots of stops and starts.

The main disadvantage of hub gears is that, because of the limited space available in the hub, they have only a limited range of gears, typically just three or four speeds. Recently, however, seven speed internal hubs have become common and models are available which have as many as fourteen speeds. Hub gears are also heavier and more expensive than derailleur gears.

Though most hub gear systems use one rear sprocket, SRAM's DualDrive system combines an epicilic hub with a multi-speed rear derailleur system to provide a wide-ranging drivetrain concentrated at the rear wheel. The system is useful for folding bicycles (where a multiple front chainset could run afoul of the bike's folding mechanism) and in recumbent bicycles and freight bicycles (where small wheels and/or increased weight require a wider range of gears with smaller individual steps between each ratio).

8-Speed hub gear

The Rohloff Speedhub is a 14 speed internal hub gearing system. It is considered by many as a great leap forward in gearing system for bicycles. 14 equally-spaced gears are operated by one twistgrip with no overlapping ratios. The gear range is as wide as a mountain bike's 27-speed derailleur system.

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SEE ALSO:

* Sturmey Archer's website
* The Speedhub at the Rohloff GmbH website
* Sram, German manufacturer of gearhubs and other bicycle parts
* Shimano, Japanese manufacurer of gearhubs and other bicycle parts