After all the spy shots, prototypes, anticipation and debate over Shimano’s foray into electronic gear shifting, the lid has finally been officially lifted on the new electronic Dura-Ace ‘Di2’ (Digital Integrated Intelligence) groupset which will be available to the public come this January.

The Dura-Ace Di2 7970 package will include wired STI Dual Control levers, front and rear derailleurs and a battery pack; the rest will be filled in with standard 7900 componentry. Even with the additional electronic hardware, the complete Di2 group will still be approximately 113g lighter than the current 7800 groupset - but around 68g heavier than the standard 7900 mechanical group, according to Shimano.  

Many have questioned the wisdom of electronic shifting what with its modest weight disadvantage and perceived increase in complexity – not to mention failed attempts by other manufacturers. So, what are the purported advantages of electronic over mechanical shifting?

• Relatively lengthy shift lever throws are now just ultra-short button clicks
• Optional remote shift buttons for time trial or other applications
• Faster and more precise servo motor derailleur movements
• No adjustment of the derailleurs after initial setup (adjustment and accuracy are monitored with each shift)
• True all-weather performance thanks to the removal of cable and/or housing contamination
• The future option for frame manufacturers to internally route the cables  

We’ll have an opportunity soon enough for a first-hand test ride but in the meantime, here are the details:

Image:Shifter (side view).: shifter (side view).

STI Dual Control levers (ST-7970) – 255g/pair

Although the entire 7970 package is heavier than the standard 7900, the STI Dual Control levers themselves will shed over 155g, meaning the additional weight is at least located down low and the bike might actually feel a bit lighter when swinging side-to-side. Button placement is analogous to mechanical units so shifting should be intuitive for current Shimano users.

As with the new 7900, the 7970 levers will also have a reach adjustment and will be compatible with the new FlightDeck computer (SC-7900).

Image:Rear derailleur.: rear derailleur.

Derailleurs (RD-7970 & FD-7970) – 225g & 124g

Save for the replacement of a spring with a servo motor, the Di2 rear derailleur will share many of the mechanical version’s changes such as the carbon fibre pulley cage and 27T cog compatibility.  A built-in mechanism protects the servo motor in the event of a crash, too, and the system supposedly recalibrates itself afterwards

Image:Front derailleur.: front derailleur.

The front derailleur’s more powerful internal guts supposedly deliver quicker and smoother shifts than mechanical systems, especially under load. The system CPU is also housed here and a self-trimming function automatically adjusts the cage in response to the position of the rear derailleur on the cassette to eliminate chain rub.    

Image:Battery pack.: battery pack.

Battery (SM-BT79) – 68g

Dura-Ace Di2 uses a compact 7.4V Li-ion battery that will last for approximately 1000k (621mi) of “heavy use” and will recharge in just 1.5 hours. Extensive testing has also reportedly shown excellent sealing and reliability “in challenging conditions”.  

Shimano says it ultimately went with a wired system to save weight as a wireless setup would require three (or even four) separate batteries: one for the rear derailleur, one for the front derailleur, and one or two for the Dual Control levers. Moreover, the wired configuration should prove more reliable over the long-term.

Time Trial & Triathlon (ST-7971 & SW-7971) – weights TBD

Shimano will also introduce a Dual Control lever that is bar-end mounted for use with time trial and triathlon setups although it won’t be available until some time after the rest of groupset is introduced. Like the standard drop bar-mounted levers, the TT/Tri version will also be reach-adjustable and compatible with the new coded wireless FlightDeck computer.   

Finally, a satellite shift unit (SW-7971) will be available that can be mounted onto the end of time trial aero bar extensions (or elsewhere depending on your requirements) and optional internal wire routing will maintain a clean look.

Image:Shimano's 2009 di2 electronic gruppo.: shimano's 2009 di2 electronic gruppo.

And how much will Dura-Ace Di2 7970 cost? US pricing is still to be finalized but the tentative UK costs should at least provide some indication. Let’s be frank; it’ll be expensive:

• STI Dual Control levers - £349.99/pair
• Rear derailleur - £349.99
• Front derailleur - £249.99
• Cable set - £99.99
• Battery - £49.99
• Charger - £49.99
• Chainset (Dura Ace FC7900) - £319.99
• Cassette - £129.99

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