That said, trikes have started to invade more traditional two-wheeled events, purring down highways from Laconia, N.H. — home to the longest-running bike rally in the country — to Ruidoso, N.M., site of this week’s Golden Aspen Motorcycle Rally, where organizers expect about a third of the bikes to be three-wheelers.

“Our predominant crowd is 60 and over, and without a doubt, the trikes are taking over,” said Patric Pearson, owner of the Golden Aspen rally.

Three-wheelers are even a common sight at Harley-happy events like the giant motorcycle rally in Sturgis, S.D., that draws hundreds of thousands of people to the Black Hills every August, including Monte Hochhalter, a 68-year-old truck driver from Longmont, Colo., who decided to switch to three wheels after some pressure at home.

“My equilibrium isn’t so good anymore,” Mr. Hochhalter said. “My wife wouldn’t ride with me.”

Mr. Hochhalter was riding a converted 2006 Harley, which cost him $18,000. But the company’s 2013 trike can go for almost twice that, complete with cruise control and a good set of high beams (perfect for older eyes, of course). It also comes with an ample trunk, something Tim Buche, the president of the Motorcycle Industry Council, a trade group, said was important to baby boomers — who make up a third of motorcycle owners.

“Boomers travel,” he said. “And they like to take all their stuff.”

A collection of independent companies has long offered kits to convert two-wheel bikes made by major manufacturers. But in 2008, Harley-Davidson — the industry leader in large touring bikes — announced that it would enter the market with the Tri Glide, working with a smaller company called Lehman Trikes. (In 2010, Harley moved production in-house.) The Tri Glide is now a consistent top-10 seller in several demographic groups, said Scott Habegger, the company’s director of product planning, including the company’s core customers: white men over 35.

But the three-wheelers are tapping into another market: women, including those who may not have been comfortable handling a touring bike, which can weigh nearly 1,000 pounds, or were just tired of being relegated to the role of passenger.