Shimano Dura-Ace 7970 Di2

Shimano Dura-Ace 7970 Di2
Perfect shifting, electronically

For years, the increased accuracy, smoothness and reliability of electronic shifting has been perhaps the ultimate goal for high-performance-bike designers. After several companies’ attempts failed—suffering from breakdowns in bad weather, poor battery life or unbearable complexity—Shimano’s Dura-Ace Di2 has finally delivered it.
The Di2’s black carbon-fiber setup looks traditional, but what appears to be a standard shifter is actually a switch that sends gear changes via a wire to sensors in the front and rear derailleurs (the parts that guide the chain up and down the gears). A CPU in the front derailleur, in turn, signals motors that move the chain across the bike’s front and rear cogs. Steel cables, a source of frustration in shifting, have been eliminated. They probably won’t be coming back.
The electronic system makes gear changes faster and virtually eliminates missed shifts, which can interrupt pedaling rhythm or even cause the chain to fall off. And the Di2 is two ounces lighter than last year’s mechanical Dura-Ace group.
Shimano spent three years testing the system, and it was used extensively in this year’s Tour de France. Available now on high-end 2009 bikes, electronic shifting should work its way into most bike makers’ entire product lines over the next five years. $2,100; bike.shimano.com
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