Racing cyclists like to ride close behind the rider at the front. That shelters them from the wind, and allows them to save energy. But the rider at the front also benefits, with a 2.5% reduction in wind resistance. This has been shown in research carried out by prof. Bert Blocken (Eindhoven University of Technology, Netherlands), which was shown on Dutch TV yesterday, 7 March. Blocken’s findings are also interesting for riders in team time trials. The place in the line of riders where the least energy is required isn’t at the end of the line, but in next-to-last position.

The 2.5% reduction in wind resistance for the rider at the front arises when the gap between the riders is around 15 cm and at a speed of 54 km/h. This is the approximate top speed reached in a sprint on a gentle upward slope or in a team time trial. If the gap between the riders is 1 meter, the advantage for the rider at the front is still 0.6%. According to Blocken, his research shows in detail that two riders together both benefit, even if one of them refuses to take his share of working at the front. Of course the advantage for the second rider is much greater, with a saving of 34% in the amount of energy expended.

The scientific explanation of this effect is that the follower causes a reduction in the low pressure area behind the front rider, Blocken explains, thereby reducing the aerodynamic drag.

Team time trials

Blocken (37) also investigated longer lines of riders, such as in a team time trial. The results show that it is often not the rider in last place who enjoys the least resistance, but the one immediately in front of him. However this is not always the case; in a line of up to four riders the one in last place has the most benefit, although this is not the case when there are more riders in the line. In the future Blocken intends to carry out simulations of lines of riders of different sizes, to further improve the predictive value of his findings.

Tactics

Blocken draws a number of tactical conclusions from his research. “If you’re the better sprinter in a long breakaway of two riders, and your partner won’t take over at the front, it isn’t always the best strategy to try to leave him behind as soon as possible. Because even though he doesn’t share in working at the front, you still benefit if he stays behind you.” He also thinks that in team time trials, the teams could make changes in the order of their riders. “In a breakaway or a team time trial, just a few seconds often makes the difference between winning and losing”, Blocken explains.

High accuracy

Blocken’s research consists of computer simulations of the air flows around riders, together with wind tunnel tests. He tested different riding positions, with both real riders and models of racing cyclists fitted with 115 pressure sensors. The simulations have a degree of accuracy that has up to now never been achieved: he calculated wind resistance data in steps of 0.0003 seconds and over lengths of 0.014 mm. For example for a line of four riders he calculated data for 18 million points. This required a large amount of computing power: each simulation by a cluster of computer processors took around five days. Blocken’s research, carried out in partnership with KU Leuven (Belgium) and ETH Zurich (Switzerland), has already led to several publications in the Journal of Biomechanics.

TV broadcast

Blocken’s work was shown in this TV broadcast: http://www.uitzendinggemist.nl/afleveringen/1243040 (Dutch, no subtitles). This also covered his detailed aerodynamic research in the Port of Rotterdam, with PhD student Wendy Janssen and Herm Jan van Wijhe of the Port of Rotterdam, This involved four months of measurements over the entire port area for the Port of Rotterdam Authority. His team also carried out computer simulations of the airflows across the entire port area. This is the first time that the total wind field in a large port has been investigated in such detail. The findings are important for the dimensioning of shipping channels and docks, and for safe maneuvering, docking and loading and unloading of the largest cargo ships.



