Slipstreaming Science: Cycling Drafting Aerodynamics


In the first of our Tune Your Ride series, our friends at Trek have done some expert research on the science behind drafting (also known as ‘slipstreaming’), and have found out how close cyclists and racers should be to that wheel in front:

The test was conducted using Alphamantis Aerosticks, which have been used by a host of riding royalty such as Team Sky, British Cycling, Zipp and Team Europcar. These sensors measure airflow and deliver a huge amount of data, to help tune bikes to be as aerodynamically efficient as possible.

Trek mounted a sensor to the front of some brand new Emondas for the study (pictured), along with GPS and power monitors.  To keep things realistic, all of the trials were conducted on a normal, flat road that was open to the wind. Additionally, real-world road race conditions were implemented, with formations studied ranging from a two-man break to a nine-rider peloton.

Previous studies have found that the positioning of the Aerostick on the bike corresponds with the best possible drafting position, however Trek describe it as: “Only one point of reference in the chaotic wake impinging upon the drafting rider.” To overcome this obstacle, a second Aerostick was mounted to the front which validated the initial, one-stick tests, as they provided good agreement.

Significant effects were found on airspeed at the Aerostick when the gap between the drafting rider and the lead was zero bike lengths, and this benefit quickly disappeared the further the drafting rider was from the lead. This means that being close to the man in front’s wheel does have a benefit. This won’t come as a surprise to anyone who has experienced a wheel-sucker in a group ride who doesn’t take a turn at the front.

The results also show the benefits of the diagonal positioning seen in the pro peloton at events such as the Tour of Oman, where crosswinds can cause havoc. In these situations the study shows that a drafting rider can gain a large advantage from not being directly behind the lead rider, but at the half-wheeling position.

In summary, it may come as no surprise to seasoned riders that the most efficient place to be is just off the wheel of the man in front. However, when introducing new cyclists to formation riding, you can back up good technique with scientific evidence!