Cycling in a group has a large advantage over cycling all by yourself. Especially on a flat surface, aerodynamic drag resistance is the main contributor to the overall resistance you will experience during cycling. Therefore, in road races, cyclists generally ride in a peloton; ‘a group of cyclists riding closely together to reduce aerodynamic drag and energy expenditure’. Riding closely behind another cyclist to reduce aerodynamic drag is called drafting. Previous studies suggest a drop in drag resistance of 30 to 50% when drafting, compared to riding alone. However, some controversy exists in the magnitude of this advantage.
Previous studies have confirmed the reduction in aerodynamic drag when drafting. The aerodynamic drag experienced while drafting, was 50 to 70% of that of an isolated cyclist. Nevertheless, cyclists themselves say that it requires very little effort to ride in the belly of the peloton. Even less than the research data suggest. What causes this discrepancy between the data and the experience of the cyclists?
Wind tunnel testing
Aerodynamic drag resistance can be measured using computer model simulations (Computational Fluid Dynamics, or CFD) or in a wind tunnel. Previous studies investigated aerodynamic drag when riding in small groups. However, a normal peloton consists of over a hundred riders! What about the aerodynamic drag when cycling in a peloton that big?
To measure the aerodynamic drag in a peloton in a wind tunnel, 121 scaled dummy-cyclists were positioned in a wind tunnel (scale 1:4). Two types of pelotons were tested; one dense peloton and one peloton in which the riders were positioned further apart from each other. Drag was determined for each rider.
The aerodynamic benefits of drafting
The aerodynamic drag force in a dense/ packed peloton is the highest for the front cyclist. This can’t be a surprise. However, even he or she experiences less drag than an isolated cyclist! Due to upstream disturbances, a front cyclist of a peloton experiences just 86% of the aerodynamic drag compared to a lonely rider.
After the front cyclist, each cyclist benefits from the riders in front of him/her. The outer cyclists of the peloton experience between 59 and 67% of the drag an isolated cyclist experiences. For cyclists who ride in the centre of the last four rows of the peloton, the same number might be as low as 5%! Almost half of the peloton experiences a drag of 5-10% compared to an isolated cyclist.
In a less dense peloton, similar reductions where found. However, the front cyclist experiences somewhat more drag (94% compared to an isolated rider) than in a dense peloton, due to the increased distance between him/ her and the next rider.
To put things in perspective: the equivalent cycling speed, which is the experienced wind speed when drafting, might be 3.2-4.5 times lower than the peloton speed of 15 m/s!
Benefits vs. Tactics
It’s no surprise that a team leader will not ride at the front of the peloton, but will stay in the peloton to save energy for later. Especially during longer races, for example the grand tours, energy conservation is critical.
Therefore, when looking solely at aerodynamics, riding in the back of the peloton is very beneficial. However, there are some tactical consequences. You might miss attacks at the front, are more likely to be involved in a crash and have to deal with speed change amplifications due to the so-called accordion effect. A fine line exists between winning and losing. Being your team’s first man therefore puts a lot of weight on your shoulders!
Blocken B, van Druenen T, Toparlar Y, Malizia F, Mannion P, Andrianne T, et al. Aerodynamic drag in cycling pelotons: New insights by CFD simulation and wind tunnel testing. Journal of Wind Engineering and Industrial Aerodynamics. 2018;179:319-37.