Shifter (bicycle Part) - Index Shifting

Index Shifting

Index shifting is a system where the control has discrete stops. Hub gears by design are indexed, but 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 in which the indexing mechanism was placed in the derailleur; however this system was only targeted at cheaper bicycles and gained a bad reputation. In all modern indexed shifting systems, the indexing mechanism is placed 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, often indexed for the rear derailleur and friction for the front. 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. For example, a typical Shimano (2:1), 7-speed shifter changes the cable length by 2.9mm between each gear, while a similar 7-speed SRAM (1:1) shifter changes the cable length by 4.5mm; some other SRAM units, (that differ only by an MRX designator), are compatible with Shimano units. 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 be 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.