Innovation: Shimano's Bicycle Parts Get Smart

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The reason: When a rider flipped the switch there was a delay before the electronic derailleurs responded with a high-pitched whine. "Even when we told them the electronic shifter was faster, some riders weren't convinced," says Fujii.

Over the next two years Fujii's crew used carbon fiber to shave a few grams off the weight. They also made the system revert to a "sleep" mode so a small battery sent power to the derailleurs only when they were moving.

Improving the durability and water resistance was more challenging. Early on, vibrations caused the derailleur motors to misfire and shift inadvertently, and moisture triggered a short circuit. After some tweaking, Shimano again asked riders to use the prototypes in races on pavement, grass, wooded trails, and cobblestones. Whenever a cable came loose or a short circuit occurred, the prototypes were shipped back for X-ray analysis at Shimano headquarters in the western city of Sakai. At one point the team studied using wireless technology and a wheel hub that used friction instead of a battery to generate power but later tossed out those ideas.

The Di2's biggest test was the 2008 Paris-Roubaix race. Passing that would help Shimano persuade other riders to use the derailleurs at the Beijing Olympics and other major races. Weeks before the Paris-Roubaix, Fujii's team had received complaints that the toggle switch was too hard to operate during bumpy rides. So they reverted to a paddle-shaped switch that operated just like previous Dura-Ace systems. "You have to design it so it's familiar enough for riders to use right away, or they will reject it," says Jimbo, Shimano's marketing director.

That was one of the last things to be changed. "I think it shifts much faster and much easier than the mechanic one," says Posthuma, who rides on the Rabobank team and used the Di2 at last year's Tour de France. Manufacturers agree. The Di2 is a "big step forward and it would be a mistake for other component manufacturers to not follow," says Specialized Bicycle Components' Chris D'Alusio, who heads advanced research and development.

Hall is BusinessWeek's technology correspondent in Tokyo.