THE PHYSICS OF A PURSUIT AND HOW TO APPLY THIS
To group your ride
- Tom Shanney
Drafting is an important part of cycling whether it be charging along the French countryside in the Tour, lapping the velodrome in the team pursuit or just on a Sundayclub ride. If you draft behind another rider who is cutting the wind you obviously gain a significant advantage. Not only are you no longer pushing against the wind, but you are literally being ‘carried’ along by the eddying flow of the air pocket created behind. This can save you between 20 and 40 per cent of your energy expenditure, depending on how close you are and how strong the wind is. The low pressure helps moves you forward. As a cyclist moves forward he produces a turbulent wake of air behind creating a low pressure area behind the rider and an area of wind that moves along with him.
A less known fact is that drafting not only helps the cyclist who is behind, but it also gives an advantage to the lead rider as well. The first cyclist enjoys up to a 3.1 percent reduction in wind resistance as the trailing rider reduces the turbulence coming off the lead rider and in effect makes him more aerodynamic. If somebody pulls in behind you to draft, they fill this void of space behind you, the movement of air flows past you and then continues to flow past the second person, resulting in less turbulence and swirling air behind you. Obviously the lead cyclist still needs to expend much more energy than the cyclist who is following, but both gain an advantage.
There are several tips to consider when drafting, firstly to get the maximum benefit, keep your wheel as close as possible to the one in front of you. Ideally, ride in a staggered position with your front wheel just behind the rear wheel of the rider ahead of you. If you’re not okay with taking that risk, don’t worry you can be as far back as about 3/4 of a wheel length and still save some energy. The benefit of drafting gradually increases from the second rider to the fifth before starting to level off. In groups up to five, the last rider enjoys the most aerodynamic benefit. In a group of six to eight (roughly the number in a team time trial), the next-to-last position feels the least wind resistance. In a big peloton, the best position is between fifth and eighth. As being to near the back can put you in danger of playing an exhausting game of yo-yo. Any changes of pace that occur at the front will be magnified at the back of a group, forcing you to accelerate harder out of bends or after junctions to catch back up.