It is well-known that in the middle of a cycling peloton you ride “sheltered from wind” and, therefore, experience less air resistance. But how much less has never been thoroughly investigated. Earlier research with small groups of riders has shown that riders in the middle of the pack encounter 50 to 70 percent of the air resistance experienced by an individual rider. And this number has been extrapolated to the whole peloton. However, professional riders and coaches suggest that when you’re well-embedded in the belly of the peloton you “sometimes hardly have to pedal,” so the air resistance must actually be much lower.
My teams at Eindhoven University of Technology in the Netherlands and KU Leuven in Belgium, in close collaboration with ANSYS and supercomputer company Cray, found that in the middle of a peloton, racing cyclists experience just 5 to 10 percent of the air resistance they face when cycling alone. This is about 10 times less than was previously estimated, and was demonstrated by computer simulations and wind tunnel research on a peloton of 121 cyclists. Both methods, performed independently, produced the same results, which can explain why so few escapes in road cycle races are successful: The assumptions contained in the calculation models that race teams use to determine their strategies are incorrect.
This new study shows for the first time the distribution of air resistance for each rider in a peloton of 121 riders. The results show that in the middle and at the back of the peloton it’s as if a rider is cycling at 12 to 15 km/h in a peloton that is speeding along at 54 km/h. That’s why it feels right that riders expend so little energy at these positions.
We should not misinterpret these results: An amateur cyclist can ride along with a peloton of professional cyclists for a short distance and under the conditions of our study, if on a straight, flat road. But as soon as the rider takes a bend, the accordion effect sets in, the peloton stretches out and the resistance will become much greater. The conditions become impossible for the amateur. Our air resistance results (below) offer additional insight into just how exceptional elite cyclists’ performances are.
Riders can use this data to see where the best position is in a peloton. At the very back, the air resistance is very low, but there is less opportunity to react to attacks and falls happen more often. So, for classification riders or sprinters, I think the best position is in row six, seven or eight, where they are sufficiently shielded by other riders but near enough to the front to watch the race carefully.
Our teams examined two pelotons of 121 riders, where the distance between the rows differed slightly. Computer simulations amounted to 3 billion cells — a world record for a sports application — and required CRAY’s supercomputers and high-performance computing (HPC) licenses from ANSYS. The simulations ran continuously for 54 hours to complete the calculations and used a total of 49 terabytes of working memory.
Want to learn more about the world’s largest sports simulation? Watch this recorded.