Millions of Americans haven't been on a bike since they were kids. Here's how Trek set about getting them back.

Trek Bicycle has built a $600 million-a-year business making wheels for serious cyclists. But with sales flattening, Trek turned its attention to the casual bike market. The challenge: Trek's usual R&D was soliciting feedback from the likes of Lance Armstrong. "We didn't know how to design for Sunday riders," admits Hans Eckholm, Trek's lead designer on this project.

Trek hooked up with Shimano, a $1 billion maker of gear and brake systems, which had an automatic gear-shifting technology popular in Asia and Europe but not yet embraced in the U.S. Trek and Shimano bet that the three-speed system -- a computer nestled under the crankshaft that changes gears based on the velocity of the bike -- would appeal to uneasy riders. "We originally built the system to run on batteries," says Matt Robertson, a Shimano product manager. "We redesigned it to be pedal-powered, because we knew if riders went out and the battery was dead, we'd be too."

In focus groups with people who hadn't ridden a bike as an adult, Trek learned that no one equated bike riding with exercise. "They didn’t see themselves in Lycra," Eckholm says. To appeal to the casual rider, Trek designed a frame based on its comfort-bike series that also took cues from old-school beach cruisers and design icons like the KitchenAid mixer. The emphasis: comfort and stability when turning at low speeds.

Trek discovered that one of the first things non-riders do when shopping for a bike is to feel the handlebars. So Trek designed the grips with a large, squishy bulge (to limit vibration). Casual riders also tend to carry stuff with them -- such as a camera or an iPod -- but don't want saddlebags. The seat became a storage compartment.

Trek's designers battled with company execs about whether to expose the wires that let the front wheel communicate with the onboard computer. Designers worried that the wires would make the bike look too high tech, but routing them through the frame required reinforcing the front tube and moving a major ball bearing. That would increase costs. The company displayed the two alternatives at a trade show early this year. People gravitated toward the hidden-wire prototype. "There was something magical about how it worked," Eckholm says.

Kickstands are normally sold separately; they’re an easy source of additional revenue for bike dealers. But Trek designers insisted that one be built in to eliminate another barrier for nonriders.

"Whenever people talk about their childhood bicycles, they talk about the color first," says Eckholm. "We felt the color would make or break this bike." But offering lots of colors was costly -- and impractical, given the three model sizes for men and two for women. The solution arose during testing, when designers noticed that the chrome hubs scratched easily and could use a protective cover. The team then realized that any point of contact -- handlebar grips, chain guards, pedals -- presented an opportunity to customize the bike’s color through removable "peels." After a buyer picks his favorite of seven colors, the plastic strips can be changed by the dealer in about five minutes.

Since releasing the Lime earlier this year, Trek has sold around 10,000 (at just under $600 apiece), but it's not yet a blockbuster. Just as Trek didn't know how to build bikes for casual riders, the company worries that many bike shops don’t know how to sell to them. So Trek and Shimano are working to educate shops about that market. Trek is also wooing female buyers with a new frame that's easier to mount and with additional frame colors such as light green and light blue.