If Tom Dumoulin wins the first time trial of the Tour de France with a few seconds, a couple of Delft engineers in a wind tunnel, will play a crucial supporting role. The rider of Team Giant-Alpecin wears a new aerodynamic corrugated suit in that time trial of 37.5 km, from Bourg-Saint-Andéol to La Caverne du Pont-d’Arc, that is developed by the Technical University of Delft in the Netherlands.

Dumoulin’s body is scanned with dozens of cameras.

The tests were not performed on the rider himself, but on a doll from a 3D printer that has exactly his size and riding position. “So we had to measure Dumoulin only once, and then we   could experiment for weeks with various substances in the lab,” Daan Bregman, coordinator sport research at TU Delft, said.

In 1974 the Swiss skater Franz Krienbühl was the first who wore a tight, sleek suit that astounded his competitors with his lap times. Since that time the sports world is aware of the fact that aerodynamics matter. Time trial cyclists with a speed of about 50 kilometers per hour have to fight against the wind which is responsible for more than eighty percent of the total air resistance. Especially in the individual time trial, special clothes can result in substantial time savings. The cyclists then ride in the same constant posture and cannot hide themselves in the wheel of other cyclists.

Dumoulin´s suit contains a combination of rough and smooth areas that cause air particles to keep sliding longer down his body. The wake behind the body – similar to the wake right behind a boat – is thereby reduced.


`Other teams don´t use a dummy that is an exact copy of the rider in  the wind tunnel  , so we could  do  better studies and our results are therefore just a little better`. According  to Daan Bregman,  coordinator sport research at TU Delft.


The researchers brought soap bubbles filled with helium in the air flow in the wind tunnel, which they lighted with a laser to properly map the flow. They calculated that the outfit that Dumoulin wears during the time trial produces one-half to one percent less air resistance   than a smooth racing suit. That seems not much, but the scientists have calculated that it yields between 5 and 10 seconds profit with a trial of 37.5 kilometers. Bregman: “Other riders in the Tour also wear special aerodynamic suits of course, so the time savings compared to competitors may be very small. `Other teams don´t use a dummy that is an exact copy of the rider in  the wind tunnel, so we could  do  a better study and our results are therefore just a little better`.

Harry Hoeijmakers, professor of technical fluid mechanics at the University of Twente  is not involved in the project in Delft, says the half-percent gain in air resistance is “a realistic assessment.” Hoeijmakers helped to develop faster suits for the Dutch skating team at the Olympic Games in Sochi in 2014.

The Dumoulin dummy

The airflow with cyclists has more variety however, said Hoeijmakers. “Skaters ride indoor and thus have nothing to do with, for example side winds or rain. The flow around a wet suit is a different story. The scale model did fine in a dry wind tunnel, but during rain when the suit gets wet everything changes. “

The Delft researchers are aware of this and ride the Dumoulin doll again soon in the wind tunnel for new tests. “Maybe it is worth to put on another suit in bad weather. Or it can just slightly better connecting the helmet on the back. That kind of detail we shall discover in the coming years. “

Tom Dumoulin in real cycling life.

End of the story
Tom Dumoulin was the winner of the first time trial in the Tour de France of 2016.

Results: Etappe Bourg-Andeol naar Chaverne du Pont 37.5 km:
1: Tom Dumoulin              50 min 15 sec
2: Chris Froome                51 min 18 sec
Rohan Dennis                    51.56
Bauke Mollema                 52.09
Tony Martin                       52.50
Adam Yates                        53.16
Nairo Quintana                 53.23
Fabian Cancellara             53.30

Tom Dumoulin prepares himself for the Olympic time trial in August 2016 in Brasil.

Time trial bike in wind tunnel
TU DELFT, Nederland.