The rule came after the emergence of a trend to follow the riders with a car packed with bikes on top of the roof at a close distance. In effect, the car stacked with bikes pushes more air in front of it, reducing the speed of the airflow around the rider and thus giving the rider a small advantage.
“I think the way it’s normally explained is that any object moving through the air pushes air with it,” Richard Kelso, the Adjunct Associate Professor at the University of Adelaide with specialities in fluid mechanics, aerodynamics, and sports engineering told Cyclingnews earlier this year. “The pressure distribution around the object – in this case, the car – leads to the air immediately in front being pushed forwards slightly.
“So, it means that the larger vehicle behind the cyclist will actually be pushing the air ahead with the cyclist, so that the airflow speed around the cyclist will be smaller. It is only small but it’s enough [to make a difference].”
“The maximum effect is right in front of the car, where the air is essentially moving with the car, and the minimum effect is at an infinite distance ahead of the car. So, at 10 metres ahead, there’s a very small favourable wind moving with the cyclist, but it’s still enough to produce that reduction in drag.”
Belgian professor Bert Blocken did some research on the matter and showed the benefit could be as much as 3.9 seconds over 50 kilometres.
UCI didn’t go on to limit the number of bikes on the roof but went on to increase the distance to the rider instead. The newly installed 15-metre gap would eliminate any possible advantage.
The UCI Congress held at the Fairmont Hotel in Monaco also saw some changes made to bike fits for the time trials and discussed plans for pinless bib numbers for which they aim to have an industry standard solution by 2024.