Production pic…	…and working prototype

Designed as part of the new Dura-Ace 7900 groupset and offered as an alternative to the mechanical shift components already shown, the electronic Dura-Ace 7970 series employs state-of-the-art Di2, or ‘Digital Integrated Intelligence’, shifting.

This innovative technology is still based on the ergonomics of the seminal Shimano Index System (SIS), which started the trend for dual-control braking and shifting almost two decades ago. The big difference in the case of Di2 is that the shifting action is taken care of by electronic instead of mechanical operation.

The electronic shifting system has been tested extensively over the past two years by professional riders in severe conditions including rain, mud, high and low temperatures and pave.

The Dura-Ace 7970 series comprises Dual Control Levers, electronically operated front and rear derailleur mechanisms and a battery kit. All other components such as the crankset and brakes are taken from the new mechanical Dura-Ace 7900 group.

We tried this one	Carbon fibre in evidence here

Dual Control Levers

Shifting is executed by simply pressing the relevant button. There are two on each brake lever, corresponding in operation with conventional SIS to avoid potential confusion. Front button equals main lever, rear button equals secondary (rear) lever. No hand power is needed anymore to shift beyond that required to press on the button. The system allows accurate and effortless shifting in challenging conditions such as cold, numb hands or exhaustion. Furthermore, the shifting performance will never be affected by contaminated or stretched cables since the shifting signal is transferred electronically.

The Dual Control Levers have been provided with a reach adjustment mechanism to make them suitable for people with smaller hands. They are compatible with the new SC-7900 FlightDeck computer, which measures data such as heart rate, altitude, cadence, gear position and battery condition and which can be used to make a wireless connection with a PC to analyze riding data. An optional ‘satellite’ switch allows shifting from multiple positions on the handlebar.

Derailleurs

The most remarkable improvement over mechanical operation is noted when shifting the front derailleur. RCUK tried the system out back in February and was immediately impressed with the effectiveness of both front and rear systems. Simply pushing the button moves the front derailleur smoothly and effortlessly, even under high load. So enjoyable is the sensation it is easy to find yourself ridiing around shifting up and down the chainrings simply for the fun of it. An additional feature is the automatic trim function; to prevent chain rub, the front derailleur chain plate positions itself automatically in response to the sprocket position of the rear derailleur.

The rear derailleur also offers remarkably quick and smooth shifts. It features a carbon pulley plate and titanium B axle for increased weight savings.

Production front mech…	…closest to prototype

Battery

Dura-Ace Di2 is powered by a long-life, compact 7.4V Li-Ion battery. Reliability and battery run time have been proved through repeated field tests in various riding conditions over the last two years. The battery, which fits any road bike, has been designed to be easy to mount and remove for charging. The shifting system is not wireless, since that would need additional power and therefore a heavier battery. It would also be less reliable than the technology that Shimano has chosen.

Time Trial/Triathlon

Dura-Ace Di2 is also suited to Time Trial and Triathlon riding thanks to the provision of multi position shifters. Dual Control Lever ST-7971 with electronic shift buttons for time trial and triathlon usage is introduced alongside an electronic satellite switch SW-7971 that can be integrated into time trial handlebar extensions. The shift wires can be guided through the bars for optimal aerodynamics.

More info at www.dura-ace.com. Availability in the market: January 2009