A physicist’s analysis reveals that contrary to popular belief, tailwinds do not significantly boost cycling speeds during Everesting challenges, where cyclists ride up and down the same mountain until they’ve climbed the equivalent of Mount Everest’s elevation.
The Physics Behind Cycling
Biking is less physically demanding and more efficient than running. As opposed to the centre of mass moving up and down like in running, cycling utilises a ‘rolling’ motion which is more fluid and thus uses less energy.
But the wind is special in that a steep uphill puts a cyclist only against gravity; air resistance remains constant. The faster you ride, the stronger air friction is pushing back and this force increases with every mile per hour your speed as it does with the square of your speed (which means that if you double your speed, it takes four times more force to overcome the air friction! For cyclists on the flat or at speed descending a hill, where air resistance is the dominant limiter this matters greatly.
As a result, air resistance is less of a problem when cycling uphill on the contrary. Gravity is the main force resisting the progress of a cyclist, instead of air resistance when speeds are faster. That is why attacks tend to come on the climbs during bike races – you put out more power and thus go faster.
The Myth of the Tailwind
Our final argument sprang to life in recent days when a new Everesting record fell, and so it should, for the rider in question had an almighty tailwind at his back on the climbs. Several questions were asked whether or not the tailwind was unfair for the cyclist;
Instead, one man — physics professor Martin Bier — went on a quest to investigate just how much tailwinds were actually helping. Howden’s analysis shows that having a tailwind may offer some small advantages going up, but these will be more than outweighed by the significant headwind one encounters during the descent.
This is because speed and air resistance have an exponential relationship. If the tailwind allows the cyclist to climb a little faster, then he will expend less energy but those are relatively low speeds compared to what another would be able to reach on steep descent going against that precious headwind. They pretty much cancel out any benefit from climbing and gliding.
Conclusion
The Bier study underscores that there are no magic beans one can take to make Everesting more efficient. As you do so, remember: the answer to becoming faster is more fitness + less weight = higher power. When there are minor tailwinds, these probably help a little bit but nothing enough to really change the bigger picture of what you need to accomplish. Ultimately, this is a reminder to fall back to basics of training and preparation rather than looking for something external as an extra bit.
