“We can showcase really innovative stuff,” Mr. Nielsen said. “Our customers have come to expect that.”

Buying a bicycle online is not as simple as buying a T-shirt. High-end bikes, which can cost well over $5,000, come in as many as 10 sizes. Buyers choose from frames made of carbon fiber, certain types of steel or other metals. There are single-speed, fixed-gear, road, time-trial, cyclocross, hybrid, commuter and many types of mountain bikes. Bike shops have long helped cyclists find the right fit.

Charles McCorkell, who owns Bicycle Habitat, which has two stores in Brooklyn and two in Manhattan, is part of Trek’s direct-to-consumer sales program. Customers choose a bike on Trek’s website, pay for it and pick a shop to receive it. (Trek, like most major manufacturers, will not send the bike directly to consumers). Trek sends the bike to the store, where it is assembled for the customer, who must pick it up in person.

Of the 15 Trek orders Mr. McCorkell has received this way, about five turned out to be the wrong size or bike for the customer, he said. That presents a problem because the bike is not part of the shop’s inventory, and the store earns much less on these sales. Mr. McCorkell said that so far he has been able to return the bike and get the customer another Trek bike. Mr. Bjorling said Trek was improving the consumer education portion of its website to help its customers make better choices.

In an industry looking for ways to reach out to consumers who are accustomed to buying online, this model is only growing. Beeline Bikes assembles and delivers bikes bought on Raleigh’s and Diamondback’s websites as well as those bought through Backcountry and Competitive Cyclist. (Accell and Backcountry are investors in Beeline.) Velofix, which has similar arrangements with about a dozen small brands, including Eddy Merckx, will also help fit customers to a bike before they order one. Beeline and Velofix also provide services for bikes bought on Amazon.

Manufacturers like that customers have a point of contact with a certified mechanic for repairs and adjustments. The convenience of receiving that service at home is an added bonus. But in an effort to avoid undercutting local shops, most companies do not discount bikes when they sell them directly; in fact, buyers may find better prices in their local shop.

Many bike shops are already reacting to these changes. Richardson Bike Mart, a three-store chain in the Dallas area, started its own mobile repair service. Though many shop owners worry that such a service could cannibalize their business, that has not been the case, said the store’s owner, Woody Smith. So far, 65 percent of his mobile repair customers are new.