Hub gear

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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

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 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 exist. For example, Vélib', the public bicycle rental programme in Paris, uses bikes with 3-speed hub gears.

Unlike derailleur gears, where the gears and mechanism are exposed to the elements, hub gears and lubricants are sealed 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.

[edit] History

The Wanderer company (Germany, Chemnitz) were granted the first Patent for a hub gear in Germany in 1902. The British Sturmey Archer company developed and marketed a hub gear in 1903. In 1904 the Fichtel und Sachs (Germany, Schweinfurt) produced a hub gear under license to Wanderer.

By the 1930s hub gears were used on bicycles all over the world. Since the 1950s they have become less popular than derailleur gears which offer a wider gear range for a lower price, although hub gears have undergone a small revival in recent years.

Though most hub gear systems use one rear sprocket, SRAM's DualDrive system combines an epicyclic 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 foul 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 steps). Hub gears have in the past also been used on motorcycles, although this is now rare.

[edit] Advantages

14-speed hub cutaway diagram

• Because the mechanism is sealed within the hub and bathed in lubricant it is not exposed to dirt or weather. Hub gears consequently need less maintenance than derailleur gears and are more reliable, making them suitable for utility bicycles.
• Internal hub gears are not susceptible to impact damage in use or when the bicycle is being shipped.
• The gear can be shifted when the bike is stationary; derailleurs need the chain to be moving, which takes some trouble if the bike has stopped while in a high gear.
• Shifting is smoother than in external rear derailleurs.
• As the chain does not move sideways it can be covered with a chainguard or even fully enclosed, protecting the rider's clothing from grease and damage, useful for utility cycling. A fully encased chain will maintain clean lubrication and last much longer than if exposed.

[edit] Disadvantages

• Hub gears offering a wide range of ratios are very expensive, costing more than a frame and forks of reasonable quality.
• They are less efficient than derailleurs, although derailleurs become less efficient when dirty and worn.
• They are heavier than a derailleur system.
• They are considerably more difficult to repair than derailleur gears, (where every component is accessible and can be individually replaced).
• Lower number of gears (up to 14, derailleur can have up to 30 gears).

[edit] See also

A bicycle with a hub gear.

• Rohloff Speedhub 14-speed hub gear

[edit] External links

Wikimedia Commons has media related to:

Hub gear

• Flash Animation of Hub Gear
• Sturmey Archer's website
• The Speedhub at the Rohloff AG website
• Sram, American manufacturer of gearhubs and other bicycle parts
• Shimano, Japanese manufacurer of gearhubs and other bicycle parts
• overview of gear ratios and ranges for existing internal gear hubs by Sheldon Brown
• Tony Hadland's Bicycle Gear History and Technical pages

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