Inside the cycling realm, “to Everest” involves riding up and down the identical mountain until your ascents total the elevation of Mt. Everest — 8,848 meters.
After a brand new cycling “Everesting” record was set just a few years ago, a debate ensued on social media in regards to the strong tailwind the cyclist had on climbs — 5.5 meters per second (20 kilometers per hour or 12 miles per hour) — when he set the record. To what extent did the tailwind help him? Should limits be set on the allowed windspeed?
Martin Bier, a physics professor at East Carolina University in North Carolina, became intrigued by this debate and decided to explore the physics, and slightly project ensued. Within the American Journal of Physics, from AIP Publishing, he shares his finding that, ultimately, the wind seems to be of negligible consequence.
First, slightly background: From a physics perspective, cycling is less complicated to understand than running. “In running, the motion of the legs is repeatedly accelerated and decelerated, and the runner’s center of mass moves up and down,” said Bier. “Cycling uses ‘rolling,’ which is way smoother and faster, and more efficient — all the work is solely against gravity and friction.”
But there’s something odd about air resistance. The force of air friction you fight goes up with the square of your speed. If air resistance is the foremost thing limiting your speed — which is true for a cyclist on flat ground or going downhill — then to double your speed, you would like 4 times the force. Tripling your speed requires nine times as much force. But, however, when cycling uphill, your speed is way slower, so air resistance is not an enormous factor.
“If you’re riding up a hill and fighting gravity, doubling your power input means doubling your speed. In bike races, attacks occur on climbs since it’s where your extra effort gets you a much bigger gap.”
On a solo Everesting effort, calculations are straightforward. A rider is not getting an aerodynamic draft from one other rider ahead of them. The inputs are simply watts, gravity, and resistance.
“Naively, you could think that a powerful tailwind can compensate for an uphill slope,” said Bier. “You then ride up the hill as if it is a flat road, and on the best way down the headwind and downward slope balance out and again offer you the texture of a flat road. Nevertheless it doesn’t work — the square I discussed earlier wreaks havoc!”
His work shows the tailwind may help slightly on the climb, but many of the work on the best way up is the fight against gravity. The following descent is fast and lasts a much shorter time, while the headwind there actually has an enormous effect. And the speed on a descent is high — about 80 kph (49.7 mph).
“Air resistance goes with the square of the speed, which ends up in the headwind on the descent and causes an enormous reduction in speed,” Bier said. “The wind boost on the ascent is canceled out.”
The apparent implication of Bier’s work is there is not any point in waiting for the perfect wind if you ought to improve your Everesting time. “There aren’t any easy tricks,” he said. “If you ought to be a greater Everester, you could shed pounds and generate more watts (exercise). That is what matters — there is not any way around it.”
