Electronic gear-shifting system (English Wikipedia)

James Huang (Aug 2009). "Shimano Dura-Ace Di2 transmission". BikeRadar.com. Retrieved 2010-02-13.
Cole, Matthew (2008-08-01). "Shimano unveils Dura-Ace Di2 electronic groupset". BikeRadar.com. Retrieved 2010-02-09.
Richard Tyler (Jun 20, 2011). "Shimano Ultegra Di2 – First look". BikeRadar.com. Retrieved 2012-09-10.
Stephen Farrand (Oct 25, 2010). "Campagnolo show off new electronic gear system". BikeRadar.com. Retrieved 2012-09-10.
Robin Wilmott (Jul 17, 2012). "Campagnolo Athena EPS 11-speed launched". BikeRadar.com. Retrieved 2012-09-10.
Warren Rossiter (August 26, 2015). "SRAM Red eTap ushers in wireless shifting era". BikeRadar. Retrieved 2015-09-12.

bikerumor.com

Tyler Benedict (November 2, 2016). "X-Shifter's universal wireless shifting kit goes live". Bike Rumor. Retrieved 2017-06-04.

Lennard Zinn (September 15, 2009). "Campagnolo's Magic Lives on in Vicenza". VeloNews. Retrieved 2010-02-17.

Best, Paul (2009-04-08). "Shimano's Dura-Ace Di2 electronic shifting to give road racers a time advantage". Gizmag. Retrieved 2010-02-10.
Ben Coxworth (December 18, 2012). "Tiso unveils wireless electronic gear-shifting for road bikes". GizMag. Retrieved 2015-09-12. Shift signals are transmitted from the shifters to the control unit via Bluetooth and/or another unspecified type of radio protocol – Shimano and Campagnolo's systems, by contrast, use electrical wiring.

Ben Coxworth (December 7, 2016). "The 10 best cycling innovations of 2016". New Atlas. Retrieved 2017-06-04.

David Arthur (9 July 2009). "Pro riders on Shimano Dura-Ace Di2". RoadCyclingUK. Retrieved 2010-02-12.

Crowe, Paul. "Electronic Shift By Wire on Bicycle". The Kneeslider. Retrieved 2010-02-09.

"SRAM History". Archived from the original on 2009-10-06. Retrieved 2010-02-17.
Phillips, Matt (9 Feb 2010). "The Shift to Electric". Bicycling Magazine. Archived from the original on April 17, 2009. Retrieved 2010-02-10.
"When is SRAM RED eTap available? – SRAM Road Electronic Groupset FAQ". Archived from the original on 2015-09-07. Retrieved 2015-09-11.
"Where is SRAM RED eTap available? – SRAM Road Electronic Groupset FAQ". Archived from the original on 2015-09-19. Retrieved 2015-09-11.

"When is SRAM RED eTap available? – SRAM Road Electronic Groupset FAQ". Archived from the original on 2015-09-07. Retrieved 2015-09-11.
"Where is SRAM RED eTap available? – SRAM Road Electronic Groupset FAQ". Archived from the original on 2015-09-19. Retrieved 2015-09-11.
"SRAM Road Electronic Groupset FAQ Batteries Batteries". SRAM Corporation. Retrieved 2015-09-12. Are the front and rear derailleur batteries interchangeable? Yes. Additionally, shifters use one CR2032 coin type battery each.
"SRAM Road Electronic Groupset FAQ Batteries Batteries". SRAM Corporation. Retrieved 2015-09-12. The complete SRAM RED eTap groupset is 137 grams heavier than SRAM RED mechanical with the same crankset, bottom bracket, and a short cage rear derailleur.