Shifter (bicycle part)
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A bicycle shifter or gear control or gear levers is a component used to control the gearing mechanisms and select the desired gear ratio. Typically, they operate either a derailleur mechanism or an internal hub gear mechanism. In either case, the control is operated by moving a cable that connects the shifter to the gear mechanism. Shifters are mounted on the down tube of the frame, on the handlebars, or at the ends of triathlon bars. Major manufacturers of shifters include Shimano, Campagnolo, and SRAM.
The controls are mounted so that the right shifter controls the rear derailleur and the left shifter controls the front derailleur. For hub gears, the control is also mounted on the right.
Over the years, many different kinds of shifters have been used. The trend in development has been to reduce the need for the rider to direct attention away from riding. Friction shifters gave way to index shifters, which do not require fine-tuning during a gear change. In the 1990s, shifters were placed closer to the hand positions on the handlebars, up to the point of being integrated with the brake lever control.
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[edit] Friction shifting
Originally, gear control levers consisted of a simple lever. Changing gears required pushing or pulling the lever so that the derailleur would move the chain to a different sprocket on the rear hub. The cyclist would need to adjust the lever to center the chain on the sprocket.
This system started out with 2 or 3 sprockets, and by the 1970s had developed to 5 and 6 sprockets. Many inexperienced cyclists, especially those who started in the US 1970s bike boom, found it difficult to change gear accurately. Typical difficulties included gear changes that left the chain in between two sprockets, which causes noisy rattles, or undesired and unexpected gear changes. However, many experienced cyclists still prefer friction gears for its simplicity and long-term reliability, as well as the ability to mix and match components from different manufacturers without the compatibility issues of indexing systems. In addition, the introduction of ramped freewheel sprockets (such as Shimano's Hyperglide system) and derailleurs with floating jockey wheels has made accurate gear changes much easier than previously.
[edit] Index shifting
Index shifting is a system where the control has discrete stops. Hub gears by design are indexed, so for derailleur systems, indexing was an innovation. Each stop corresponds to one position of the derailleur. This allows the cyclist to change gear without having to adjust each time, as in friction shifting.
The first successful indexed shifting system was the Shimano Index Shifting or SIS, introduced in 1984 on the 6-speed Dura-Ace racing groupset. This made it near impossible to misshift, but at the expense of having more difficult initial adjustment. Most modern bikes made today are equipped with index shifting. Prior to this Shimano had sold a system called Positron which placed the 'clicks' in the derailleur, however this system was only targeted at cheaper bicycles and gained a bad reputation. All modern indexed shifting places the clicks in the shifters.
Index shifter styles include twist shifters, trigger shifters (such as Shimano's Rapidfire design), shifters integrated with brake levers, levers mounted on the downtube, and bar-end controls. A twist shifter is mounted in line with the handlebar grips. Shifting is controlled by rotating the grip of the shifter. Trigger shifters have separate levers that change gears to the next gear up or down. Early indexed shifters could be used in friction mode for backwards compatibility, but this feature is no longer common.
New mountain bicycles use either twist shifters or trigger shifters. Older mountain bicycles may have thumb shifters, either indexed or non-indexed. Shimano's Deore, LX, XT, and XTR mountain groupsets include combined brake/shift controls, called Dual-control. Moving the brake lever perpendicular to the direction to control the brakes operates the shift mechanism.
Given that friction shifters were compatible with almost any derailleur, index shifting systems have been criticized for their non-interchangeability. For example, Shimano indexing components are often incompatible with SRAM or Campagnolo components, because the amount of cable pulled between each "click" is different in each system. In addition, newer components are often not backward compatible with older systems from the same manufacturer, so finding spares for older systems is often difficult, and stocking all of the possible combinations (shifters, derailleurs, chainrings, freewheels, and cassettes) is a challenge for the local bike shop. Some components can be mixed and matched between systems, but it can a bit of a kludge to do so. Component manufacturers have been accused of planned obsolescence for introducing more and more complicated shifting systems--and withdrawing support for older systems--to a riding public which generally doesn't need so many gears for basic transport, utility, or recreational cycling.
One notable exception to the lack of compatibility in modern shifters is the fact that none of Campagnolo's front shifters are indexed, so they are compatible with all double or triple cranksets, even those of different manufacturers. Campagnolo rear shifters are also partially backwards compatible because a mechanic can upgrade them for use with a different number of rear sprockets by replacing a small part, the shift disc.
[edit] Brake/Shift Levers
Older road bike shifters may be down tube gear levers, mounted on the down tube of the frame. These have been available both non-indexed (friction) and indexed. If the levers are not mounted on the handlebar, the rider would have to move a hand from the handlebars to the gear lever to change gears. They could also maintain one hand on the handle bars and another on the gear lever, while accelerating. This made changing gears difficult while turning, going up hill, maneuvering in traffic, or during a race, as the rider would lose some stability from having only one hand on the handle bar, while adjusting the lever. Friction shifters had the added disadvantage of having to be trimmed every time the gear was changed, which might take a few moments. This led riders to usually stay in one gear, unless they were about to rapidly change their speed. Indexed shifters addressed the trimming issue, but the stability issue remained.
With the introduction of systems like Shimano STI and Campagnolo Ergo, and the more recent SRAM system, the majority of these issues have been addressed. These systems combine an index shifter into each brake lever, and are were sometimes referred to as brake/shift levers, for their ability to combine the brake and shift functions into a single unit for use with one hand. However, in recent times, the term brake has been dropped, and the levers are referred to simply as shifters. These shifters when combined with gear ramps and teeth shaping on the cassette address all of the issues with friction and index shifters.
[edit] Advantages
Shifters allow for rapid and precise shifting, without removing the hands from the handlebars. Because the shifter is a combination of gear lever and brake, the cyclist does not have to move their hands, and has both in easy reach. This addressed one of the principle disadvantages of previous designs. Shifter technology has been combined with gear ramps and tooth shaping on the cassette, to allow for the chain to transfer power while shifting. This allows the cyclist to shift more frequently to match the desired cadence. This makes shifters greatly superior to friction or index shifters in traffic or during a race. As the cyclist can accelerate more rapidly (thanks to rapid down shifting while pedaling), maintain a straighter line while accelerating (such as while riding along a curb in traffic, or during a race), and downshift while approaching an intersection or a hill. The ability to rapidly shift allows a cyclist to better maintain a good cadence and therefore cycle faster with less effort, as the gear is better suited.
For touring cyclists and recreational riders who use drop bars, brifters may make riding easier and more comfortable as they allow the rider to use more hand positions and also retain access to both the brakes and gear shifters at the same time.
In general, the additional weight, expense, and occasional maintenance of shifters on a road bicycle is far outweighed by the performance advantages in a racing context.
[edit] Disadvantages
Shifters are not without their disadvantages; the system is more complicated and subject to greater wear and tear than previous systems, especially friction shifters. Due to their greater number of parts shifters are more expensive and less reliable than index shifters. Index shifters and shifters rely on the cable tension to be maintained, but over time the derailleur cable will stretch, causing the system to slowly drift to the right of the gear. Periodic adjustments are required.
Because of the increased desire of the time trialist for an aerodynamic position on the bicycle, a time trial bike uses triathlon bars, a different bar arrangement to a road bicycle's drop handlebars. The controls are mounted at the end of the triathlon bars and are called bar-end levers or barcon, for bar control. Bar-end gear levers can also be used on the ends of drop handlebars.
