Last April, a team of Japanese engineers from Shimano flew to France to test a prototype derailleur (an electronic gear shifter for a bicycle) on an important focus group: professional cyclists. The venue was the Paris-Roubaix race, among the most bruising in Europe. The 161-mile course includes 28 stretches of jaw-rattling cobblestone roads as it winds through villages in the French countryside. In previous years, Shimano's battery-powered derailleur prototypes hadn't been up to the task. Some had shifted at the wrong time, others simply conked out. But the engineers were hoping that the latest version would be glitch-free. "One of main goals was to make the derailleurs tough enough to be used for the Paris-Roubaix race," says Kazuhiro Fujii, who led the Shimano engineering team.

They got their wish. Shimano now sells the derailleurs in the U.S. as the Dura-Ace 7970 Di2. Released in January, the Di2 looks like a traditional shifter. But instead of using steel cables, its rubber-coated wires send signals to computer chips in the derailleurs that guide the chain from one gear to the next. The Japanese bike parts maker says the system is faster and weighs 67 grams, or about 3 percent, less than the old Dura-Ace system (the chips, micromotors, and battery make it 68 grams heavier than the latest Dura-Ace mechanical parts). The company also says the shifting is so precise that chain derailments rarely occur, and that the system needs no tuning up.

The Di2 is an attempt by Shimano to maintain buzz around the brand even as the global economy hits the skids. Analysts say the market for road bikes has been resilient in recent years thanks to a boom fueled by American Lance Armstrong's record-breaking seven victories in the Tour de France. In the bike market, the $250 million company is a...