Shimano Dura-Ace Di2 Groupset
According to various news sources, Shimano has formally announced plans to release its Dura-Ace Di2, a new electronic shifting option for the all-new 7900 series Dura-Ace, in January 2009.
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 synchronised shifts.
Shimano Dura-Ace Di2 Shifter
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.
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.
Shimano Dura-Ace Di2 Rear Derailleur
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 analysing 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-synchronises the shifter and rear derailleur.
Shimano Dura-Ace Di2 Front 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.
Shimano Dura-Ace Di2 battery pack
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.
And just how much will Dura-Ace Di2 7970 cost, I hear you ask? Well, US pricing is still to be finalised. But, let’s be honest, it’s going to be expensive.