Shimano’s electronic Dura-Ace

• Photos

By Lennard Zinn

Shimano has formally announced plans to release Dura-Ace Di2, a new electronic shifting option for the all-new 7900 series Dura-Ace, in January.

Composed of dual control shift/brake levers, front derailleur, rear derailleur, a wiring harness and battery pack, the new Dura-Ace Di2 7970 components integrate with components from the upcoming 7900 series Dura-Ace group, while adding only 68 grams.

Electrically actuated shifting eliminates cable friction and contamination. The shifters are now merely switches, which also allows for creative placement of optional remote shifters while reducing the weight and profile of the main shifting units. For example, a rider could place remote switches out on the ends of aero bars as well as on the top of drop bars near the stem.

Derailleur movements are computer-controlled and servo motors in both front and rear derailleur create synchronized shifts.

ST-7970 Dura-Ace Di2 Dual Control Levers
By eliminating mechanical shifter parts and using unidirectional carbon fiber brake lever blades, the new Dual Control lever is 155g lighter than the mechanical version. The levers are slimmer, and the ergonomics are further refined for a comfortable grip.

Wiring harness
Except when it comes to downloading the on-board computer to a PC, the system is not wireless. It powers each derailleur through a wiring harness rather than adding the complexity of wireless transmitters and receivers. To have been wireless, each component would have required a separate battery, which would have added weight, and each receiver/transmitter would have consumed battery life at a higher rate.

The shifter wiring harness accepts an all-new FlightDeck computer (SC-7900). The new FlightDeck features heart rate, altitude, grade, cadence, estimated caloric consumption, gear position, and battery life and is directly downloadable data via a wireless connection.

RD-7970 Dura-Ace Di2 rear derailleur
Like the 7900 mechanical derailleur, the 7970 has a new carbon fiber rear pulley cage, and the new design is compatible with wider-range cogsets, accommodating up to 27 teeth. Driven by a servo motor instead of a cable and spring, shifts are identical and precise due to the computer control unit analyzing each shift.

The rear derailleur has a similar profile to standard rear derailleurs, rather than incorporating an oversized housing containing a reciprocating notched bar driven by the upper jockey wheel, which provided shifting power for Zap and Mektronic. Already less vulnerable due to its shape, Shimano built a mechanism into the rear derailleur that allows it to move inward under impact to reduce the potential for damage in the case of a crash. After being bumped inward, cycling through the shifting a couple of times automatically re-synchronizes the shifter and rear derailleur.

FD-7970 Dura-Ace Di2 front derailleur
The front derailleur is the “brains” of the system. This is a departure from Mavic Zap and Mektronic systems that preceded it; these had cable-actuated front derailleurs. The integrated ultra-compact CPU not only ensures shifting precision for both the front and rear derailleurs individually, but also monitors the position of each. The front derailleur tracks the chain and requires zero manual trim while maintaining shifting speed. The front derailleur logic also performs the inward shift from the big chainring in two split-second movements to eliminate chain drop.

SM-BTR1 Dura-Ace Di2 battery pack
The 7.4V, high performance lithium ion battery is designed to deliver reliable, long life even in the worst conditions. In conditions requiring consistent and frequent shifting, the battery is capable of 1000 kilometers of use. That’s not much relative to the battery life in a bike computer, but fortunately, this battery is rechargeable. Lithium ion batteries are lighter, more compact and better performing than other types.

Shimano Dura-Ace Di2 7970 specs

ST-7970 Dura-Ace Di2 Dual Control levers
? Unidirectional carbon fiber lever blades reduce weight without loss of durability

? Shifting positions mimic Dual Control with the ease of an electric switch
? Titanium clamp and fixing bolt
? Enhanced perch shape is more comfortable over longer distances
? Integrated reach adjuster provides a custom fit for even smaller hands
? Shift impulses transmitted in fractions of a second
? Revised brake cable pivot location provides better braking modulation
? Optional satellite shifter
? Wiring harness is FlightDeck ready
? 255g

RD-7970 Dura-Ace Di2 rear derailleur
? Carbon fiber rear pulley cage for lighter weight without loss of durability
? New geometry allows for use of 27 tooth max cog
? Servo saving feature allows derailleur body to move inward on impact to reduce or eliminate damage to the component and servo motor
? 225g

FD-7970 Dura-Ace Di2 front derailleur
? Integrated CPU monitors both front and rear shifting for precise and consistent derailleur alignment
? Computer integration allows the front derailleur to track the chain eliminating the need for manual trim and also eliminates chain drop when shifting inward from the big ring.
? 124g

SM-BTR1 Dura-Ace Di2 battery
? High performance Lithium Ion composition
? Rechargeable (1.5 hours for full charge)
? Mounting bracket to easily adapt to most bikes
? Approximately 1000 kilometers of heavy use between charges – 7.4V
? 68g

SC-7900 Flight Deck cycle computer
? Gear indicator with virtual cadence
? Heart rate monitor
? Estimated caloric consumption
? Altitude & inclination
? Battery life indicator
? Wireless PC connection

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