Shimano released its first electronic derailleur in 2001. It could be argued that, by 2014, it was on its fourth generation. Despite starting so much later, this, very first, SRAM electronic derailleur was technically interesting in a number of ways:

• It was fully wireless.
• It used an easily swapped li-ion battery that was used throughout the system.
• SRAM mounted all the motors etc. in the p-knuckle. Shimano placed all the action in the b-knuckle and Campagnolo chose to mount the actuator diagonally across the parallelogram.

it was called 'SRAM Red eTap'. The word 'eTap' implies that it uses an 'e' (electronic) version of SRAM's mechanical 'DoubleTap' system. DoubleTap has only a single blade on the brake lever. A short push changes to a higher gear, a longer push changes to a lower gear.

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This is a used, but tidy, SRAM Red eTap (RED-E-A1) with a medium length, WiFli, pulley cage. It is a racinmg derailleur that is very much in the modern, wide ratio, idiom. Some of its attributes are:

• The b-knuckle has the b-pivot bolt fairly distant from the top of the parallelogram plates. The b-knuckle has a very different geometry from the short cage version.
• The pulley cage is a full 80mm long.

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• Derailleur brands: SRAM
• Categories: SRAM - the derailleur in Red
• Themes: Electric Avenue
• Country: USA, manufactured in Taiwan
• Date of introduction: 2016
• Date of this example: manufactured 2015? (serial number starts 1537... possibly indicating week 37 of 2015?)
• Model no.: RD-RED-E-A1
• Weight: 243g including battery
• Maximum cog: 32 teeth (SRAM)
• Total capacity: 34 teeth (bikeshop folklore)
• Pulley centre to centre: 80mm
• Index compatibility: 11 speed
• Chain width: 3/32”
• Logic: top normal
• B pivot: unsprung
• P pivot: sprung
• Materials: largely aluminium with a composite p-knuckle and a carbon cage

Ref. 1659