Hub gear


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 lubricants are sealed within the shell of the hub gear, in contrast with derailleur gears where the gears and mechanism are exposed to the elements. Changing the gear ratio was traditionally accomplished by a shift lever connected to the hub with a Bowden cable, and twist-grip style shifters have become common.
Hub gear systems generally have a long and largely maintenance-free life though some are not suitable for high-stress use in competitions or hilly, off-road conditions. Many commuter or urban cycles such as European city bikes are now commonly fitted with 7-speed gear-hubs and 8-speed systems are becoming increasingly available. Older or less costly utility bicycles often use 3-speed gear-hubs, such as in bicycle sharing systems. Many folding bicycles use 3-speed gear-hubs. Modern developments with up to 18 gear ratios are available.

History

Before epicyclic gears were used in bicycle hubs, they were used on tricycles. Patents for epicyclic hubs date from the mid-1880s. The first patent for a compact epicyclic hub gear was granted in 1895 to the American machinist Seward Thomas Johnson of Noblesville, Indiana, U.S.A. This was a 2-speed but was not commercially successful.
In 1896, William Reilly of Salford, England patented a 2-speed hub which went into production in 1898 as 'The Hub'. It was a great success, remaining in production for a decade. It rapidly established the practicality of compact epicyclic hub gears.
By 1902, Reilly had designed a 3-speed hub gear. He parted company with the manufacturer of 'The Hub' but had signed away to them the intellectual rights to his future gear designs. To circumvent this problem, the patents for Reilly's 3-speed were obtained in the name of his colleague, James Archer. Meanwhile, well-known English journalist and inventor Henry Sturmey had also invented a 3-speed hub. In 1903, Frank Bowden, head of the Raleigh Bicycle Company, formed The Three-Speed Gear Syndicate, having obtained the rights to both the Reilly/Archer and Sturmey 3-speeds. Reilly's hub went into production as the first Sturmey Archer 3-speed.
In 1902, Mikael Pedersen patented a 3-speed hub gear and this was produced in 1903. This was said to be based on the "counter shaft" principle but was arguably an unusual epicyclic gear, in which a second sun was used in place of a ring gear. In 1904 the Fichtel & Sachs company produced a hub gear under license to Wanderer, and by 1909, there were 14 different 3-speed hub gears on the British market.
By the 1930s, hub gears were used on bicycles all over the world. They were particularly popular in the UK, the Netherlands, the German-speaking countries and Scandinavia. Since the 1970s, they have become much less common in English-speaking countries, but in many parts of northern Europe, where bicycles are regularly used as daily transport rather than merely for sport or leisure, hub gears are still widely used. The cheaper and stronger derailleur systems, which offer a wider gear range, have now started to appear.
By 1987, Sturmey-Archer made only 3- and 5-speed hubs, and Fichtel & Sachs and Shimano made only 2- and 3-speed hubs. In that year, the first book for some 80 years dealing solely with epicyclic bicycle gears was published. Since then, there has been a slow but steady increase in interest in hub gears, reflected in the wider range of products now available.
In 1995, Sachs introduced the Elan, the first hub gear with 12 speeds, and an overall range of 339%. Three years later, Rohloff came out with the Speedhub 500/14, a gear hub with 14 speeds and a range of 526%, comparable to that of a 27 speed derailleur gear system, and also sufficiently robust and lightweight for mountain biking. In 2007, NuVinci started manufacturing continuously variable transmission ∞-speed hubs for commuter bicycles, with an increasing range of about 380%.
As of 2008, Sturmey-Archer makes 3-, 5- and 8-speed hubs, SRAM make 3-, 5-, 7- and 9-speeds and Shimano make 3-, 7- and 8-speeds. In February 2010, Shimano announced the introduction of the Shimano Alfine 700, an 11-speed model.
Though most hub gear systems use one rear sprocket, SRAM's Dual Drive system combines an epicyclic hub with a multi-speed rear derailleur system to provide a wide-ranging drivetrain concentrated at the rear wheel. In 2010, Canyon presented the 1.442-concept, a hybrid hub which uses a similar epicyclical/derailleur combination.
Brompton Bicycle have their own design, with a two-speed derailleur coupled to a special three-speed wide-ratio Sturmey-Archer hub, the "BWR". The system is useful for folding bicycles, in recumbent bicycles, and cargo bikes. Hub gears have in the past also been used on motorcycles, although this is now rare.

Principle of operation

The simplest 3-speed hubs use a single planetary epicyclic gearset. The sun gear is mounted solidly to the axle and is thus fixed relative to the bicycle frame.
  • In low gear, the sprocket drives the annulus, and the planet carrier drives the hub, giving a gear reduction.
  • In middle gear, the sprocket drives the hub directly.
  • In high gear, the sprocket drives the planet carrier, and the annulus drives the hub, resulting in a gear increase.
The hub axle of a hub gear will carry torque in all gears except direct drive, and so must be securely braced against rotation. While anti-rotation washers between the dropout and axle nut have often proved adequate, wider-ranging modern systems use a reaction arm affixed to the chain stay. Rear wheels with drum brakes require a reaction arm anyway.
Most hub gears are operated in a similar manner, with a single twist, trigger or thumb-shifter. An exception is the older style of Sturmey-Archer 5-speed, which used a second shift cable to change between close and wide-range sun gears, effectively giving two 3-speed hubs in one unit. The middle gear in both ranges was direct drive, so there were five distinct gears. They could either be controlled with a special 5-speed shifter which operated both cables, or with a regular 3-speed shifter and a friction shifter.

Advantages

  • Hub gears are sealed within the hub, which protects them from water, grit, and impacts. Thus hub gears usually require less maintenance and can be more reliable over time than comparable external derailleur gear systems, which may require more adjustments and replacement of parts.
  • Hub gears completely avoid the danger of collision with the spokes and wheel-collapse that derailleur systems can suffer.
  • Hub gears can change gear ratios when the rear wheel is not rotating. This can be useful for commuter cycling with frequent stops and for mountain biking in rough terrain.
  • Hub gears can be simpler to use for inexperienced riders, because there is generally only a single shifter to operate and there are no overlapping gear ratios. By contrast, modern derailleur systems often have two shifters, and require some forethought to avoid problematic gear combinations.
  • Hub gears can be manufactured to include a coaster brake. This is not possible with derailleur systems, because the chain cannot transmit a backwards pull.
  • Hub gears provide a means for shifting gear ratios on drivetrains incompatible with external derailleurs such as belt drives and shaft drives.
  • The single chainline allows for a full chain enclosure chain guard, so the chain can be protected from water and grit, and clothing can be protected from contact with the lubricated chain.
  • The single chainline does not require the chain to bend or twist. As a result, the chain can be constructed differently, with parallel pins instead of barrel-shaped ones. Line-contact between the bearing surfaces, instead of the point-contact of a derailleur chain, greatly extends the working life of all components.
  • On bicycles with fixed chain-lines, no chain tensioner is required, eliminating a part that could otherwise become damaged in rough terrain- an advantage for off-road cyclists. Where a tensioner is required, a short cage is usually sufficient to take up the chain slack.
  • The single external sprocket means that the wheel can have a hub with more distance between its flanges and be built with no or much less dish, making it laterally stronger than a similar wheel with narrower flange spacing and more dish to accommodate multiple sprockets. The hub shell of gear hubs is also often of a larger diameter than that of derailleur hubs, meaning the spokes on such wheels may be shorter.

    Disadvantages

  • It can be hard or impossible to select another gear while pedalling, because a release of pressure is required to enable a change in this case.
  • The rear wheel cannot be completely separated from a bicycle with hub gears without also disconnecting the gear cable, which complicates the process of replacing an inner tube.
  • The hub gear is an integral part of the wheel and it is not possible to change the wheel without also changing the hub gear.
  • Hub gears are more complex and usually more difficult for the rider to repair, which is nearly impossible by the roadside.
  • Hub gears are typically more expensive than derailleur systems.
  • At commuter/recreational power levels, current hub gears are typically about 10% less efficient than reasonably maintained derailleur gears.
  • Hub gears tend to be heavier than derailleur systems with equivalent gearing characteristics, and the additional weight is concentrated at the back wheel. For this reason, they are not a primary choice for rear-suspension bicycles in sporting use as the extra unsprung weight may adversely affect traction and braking.
  • Hub gears are generally incompatible with quick release mechanisms/skewer axles.
  • It is sometimes possible to select no gear when changing gears with a poorly adjusted gear cable, which results in a complete loss of drive.