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The (Still) Mysterious Physics of Riding a Bike

A new study comes closer to cracking the code.

The partiers at the 2013 Santa Cruz Bike Party are balancing fine. (Flickr/Richard Masoner)

Science nearly has bicycles figured out. Researchers have a good grasp on why bikes can balance by themselves, and are getting better at keeping them standing up in bike share stations. What’s less understood, says Stephen Cain, a researcher at the University of Michigan’s Department of Mechanical Engineering, is how people stay on bicycles.

On the surface, it’s a strange space for scientific analysis. Most people know how to ride a bike—about 94 percent of Americans, according to a recent survey. There seem to be few big-budget industries that stand to gain by understanding the evidently complex biomechanics of riding. Furthermore, researchers already understand the most basic basics of biking: riders keep their center of mass over the wheels, using steering and body movements (a lean here, a lean there) to guide this, the most elegant of machines.

But what makes one bicycle rider good and another one bad? In fancier terms: What are the biomechanical differences between cycling pros and newcomers? For a new paper published in PLOS ONE this week, Cain and his University of Michigan colleagues invited 14 subjects into their lab to find out.

Half of the riders identified as “skilled”—they went on regular training rides, they belonged to a cycling club or team, and they competed several times per year. And half were classified as “non-cyclists”—they knew how to ride, but they did so only occasionally, for recreation or transport. Once inside a motion capture laboratory, Cain and his team took measurements as their participants cycled on a “roller,” a stationary bike that still requires riders to balance by pedaling and leaning, as one would do in the wild.

The research team’s roller setup, which subjects used in their lab trials. (Cain et al.)

Cain and team studied the movements and concluded that the big difference between newbie and expert riders comes down to body motions. Though everyone seemed to balance pretty much equally at slow speeds, better bikers used smaller and more effective body and steering movements to stay upright when the bike was moving quickly. It seems that because skilled cyclists are better at, you know, having bodies, they don’t need to make large corrective moves as often as their less-skilled peers.

There are still some bicycle physics mysteries, as Cain laid out in a piece in The Conversation: “Are the differences linked to a higher risk of crashing for the novice riders?” he wrote. “Or do the differences simply reflect a different style of control that gets fine-tuned through hours and hours of training rides?”

These questions matter because understanding how bodies behave on bikes could help researchers design safer bikes for novices or mobility-impaired riders—America’s graying population, for example. Cain, whose research focuses more generally on human movement, also suspects studies in this vein will illuminate more about human mobility in general. “The bicycle is an interesting testbed for understanding human balance,” he says. Climb aboard.

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