Following the stir caused by a team car full of spare bikes in the time trial this year, the UCI has moved to clean up the aerodynamic trickery with a rule change.

Starting in 2023, support cars must stay 15 meters behind the riders participating in the time trial.

This change is intended to reduce the possibility of riders benefiting from aerodynamic drag reduction due to the presence of a following car.

While the benefits of having a car in front of you while driving are obvious, there are also benefits (albeit much smaller) from having an object behind you.

"Objects moving through the air push air out with them. The pressure distribution around the object, in this case a car, pushes the air immediately in front of it slightly forward," Richard Kelso, adjunct associate professor at the University of Adelaide, explained to Cycling News earlier this year.

"This means that the airflow velocity around the cyclist is smaller, as the larger vehicle or following vehicle behind the cyclist pushes the air forward with the cyclist. That's just a small thing, but it's enough (to make a difference)."

For this reason, some riders and teams have in recent years begun stacking multiple bikes on the roof of their following vehicle to maximize surface area and drag. two-time world champion Filippo Ganna (Ineos Grenadiers) used to ride with a one spare bike on the roof, but since mid-2021 he has been stacking multiple bikes.

The UCI has not moved to limit the number of bikes that can be placed on the roof of a car, but has stipulated that cars must be further back than the previous 10 meter rule.

"Rear vehicles must follow at least 15 meters behind the rider and must never pass the rider or approach the same height as the rider," the new 2023 regulations stipulate.

"In the event of a breakdown, technical assistance may only be provided while the rider and vehicle are stationary, and the following vehicle must not interfere with anyone else.

It is unclear whether there is any real aerodynamic advantage left in attaching a car with a bike 15 meters behind; the advantage at 10 meters is already marginal, and the UCI is hoping that the 50% increase in distance will level the playing field.

Belgian professor Bart Brocken calculated that if a standard car were to travel 10 meters backward, the drag coefficient would decrease by 0.23%, or 0.078 seconds per kilometer.

The issue has already sparked debate this year, with time trial specialist Alex Dowsett suggesting that stacking support cars is a "gray area."

"It's a gray area between the spirit of fair play and the UCI rule book," Dowsett said.

"If there's no rule against it, then it's not cheating," he added. We understand a lot about aerodynamics now," Dowsett said. Skin suits are an aerodynamic advantage that make riders faster, but pushing from behind is ......" He added. Is this in the spirit of fair play?