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An electronic gear-shifting system is a method of changing gears on a bicycle, which enables riders to shift with electronic switches instead of using conventional control levers. The switches are connected by wire or wirelessly to a battery pack and to a small electric motor that drives the derailleur, switching the chain from cog to cog. An electronic system can switch gears faster, and because the system does not use Bowden cables and can calibrate itself, it may require less maintenance. ==History== In 1990 the Japanese bike component manufacturer SunTour introduced the Browning Electronic AccuShift Transmission (''SunTour BEAST'') - a triple chainset system for mountain bikes in which one quarter of the circle is hinged along a radius. During shifting, this segment is pushed sideways by a relay operated mechanism like a railroad switch and picks up the chain that is currently running on the next cog.〔(【引用サイトリンク】 Browning )〕 In 1992 the French manufacturer Mavic introduced their first electronically controlled gear shift mechanism called ''Zap'' at the 1992 Tour de France. It was a prototype, but it achieved neither technical success nor commercial application. A development of this was used by Chris Boardman to win the opening time trial (''prologue'') of the 1997 Tour de France.〔 In 1994 Sachs introduced the Speedtronic.〔(【引用サイトリンク】 SRAM History )〕〔 In 1999 Mavic introduced the ''Mektronic'', its second electronic shift system, which suffered from reliability issues and was subsequently discontinued.〔 During the 2000s both Shimano and Campagnolo (2005) experimented with electronic shifting in professional cycle races.〔 The first commercially successful electronic gear shift system for road bicycles was introduced by Shimano in 2009, the ''Di2''.〔 Three professional teams used the Di2 in the 2009 Tour of California: Columbia High Road, Garmin Slipstream, and Rabobank;〔 and several teams and riders, including George Hincapie, used it during the 2009 Tour de France Also in 2009 Giant released a bicycle equipped with the Shimano Di2〔〔(【引用サイトリンク】 TSR Advanced SL LTD )〕 and Trek began providing a battery mount and Di2-specific cable routing and stops on its Madone frames.〔(【引用サイトリンク】 Madone 6 Series )〕 In 2015 SRAM announced its wireless electronic groupset called, SRAM RED eTap. The group is scheduled for release in Spring of 2016 and will be available on complete bikes and through aftermarket SRAM component dealers.〔https://sramroadsupport.zendesk.com/hc/en-us/articles/206573428-When-is-SRAM-RED-eTap-available-〕〔https://sramroadsupport.zendesk.com/hc/en-us/articles/206573508-Where-is-SRAM-RED-eTap-available-〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Electronic gear-shifting system」の詳細全文を読む スポンサード リンク
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