Physicists reveal that tailwinds have little effect on cycling speed

In the cycling world, “To Everest” means cycling up and down the same mountain, reaching a total altitude of Everest’s 8,848 metres.

After a new “Everesting” bicycle record was set a few years ago, social media erupted with debate about the strong tailwind (5.5 meters per second (20 kilometers per hour or 12 miles per hour)) that the cyclists experienced on the climb when setting the record. How much did the tailwind help? Should there be a limit to the wind speed that is allowed?

Martin Beer, a physics professor at East Carolina University in North Carolina, was intrigued by the controversy and decided to study it. So a small project was started. He published his findings in the American Journal of Physics that the effect of wind was negligible after all.

First, a little background: from a physics point of view, cycling is easier to understand than running.

“In running, the runner’s center of mass moves up and down as the legs repeatedly accelerate and decelerate,” Beer says. “In cycling, the motion is ‘rolling’, which is smoother, faster and more efficient – all motion is done purely against gravity and friction.”

But there’s something strange about air resistance: the force it causes grows as the square of your speed. If air resistance were the main limiting factor to your speed (as a cyclist riding on flat ground and downhill), you’d need four times the force to double your speed, and nine times the force to triple your speed. But on the other hand, when you’re riding uphill, you’re going much slower, so air resistance isn’t a big factor.

“When you go up a hill and you’re fighting gravity, if you double your power input, you double your speed. In bike racing, climbs are where you attack, because that extra force can make a bigger difference.”

In a solo Everest climb, the math is simple: you are not subject to an aerodynamic draft from the rider in front of you. The only inputs are watts, gravity, and drag.

“Naively, you’d think that a strong tailwind would compensate for the slope on the way uphill,” Beer says, “and then when you go uphill, it feels like a flat road, and when you go down, the headwind and the downhill slope balance each other out and it feels like a flat road again. But that doesn’t work. That square I mentioned earlier plays havoc.”

His research shows that while a tailwind may help a little on the climb, most of the work is done mid-way through the climb fighting gravity. The descent that follows is quick and takes much less time, but the headwind actually has a bigger effect there. And the speeds on the descent are high, around 80 kph (49.7 mph).

“Air resistance grows as the square of your speed, so on the way down you’re facing a headwind, which slows you down a lot,” Beer says. “On the way up, the wind pressure cancels out.”

Beer’s research makes it clear that if you want to summit Everest in less time, waiting for the perfect winds is pointless.

“There are no quick tricks,” he says. “If you want to be a better Everester, you have to lose weight and produce more power. That’s the thing. There’s no way around it.”