Groups of bike racers move like birds and fish

New Scientist : Human bicyclists in mass-start races, such as the Tour de France, tend to move as a cohesive unit, alternately clumping together and stretching out single file, much like flocks of birds or schools of fish. New research shows that the behavior is due more to certain physical principles than to individual wills. A former competitive cyclist named Hugh Trenchard studied videos of cycling races that took place in velodromes and collected statistics on cyclists’ speed and physical attributes. He found that the riders tend to group together, and the shape of the resulting peloton depends on the speed of the front rider, with the rest keeping pace by drafting, or riding directly behind another cyclist in order to take advantage of the reduced drag. Drafting helps slower riders stay with the rest of the group but makes it harder for them to pass the rider ahead. The speed of the entire group is limited by the individual cyclists’ inherent maximum abilities. The seemingly cooperative behavior that arises occurs regardless of team strategies or rider fatigue, says Trenchard.