When a Tour de France cyclist rides behind their team car, they're not just following a support vehicle — they're getting a hidden aerodynamic boost. New research shows that the type of car following a rider could give them more than eight extra seconds in a time trial, enough to decide who wears the yellow jersey.
Scientists at Heriot-Watt University in Scotland ran wind tunnel tests and computer simulations to figure out exactly how team cars affect the cyclists riding ahead of them. The answer, it turns out, is a lot.
"When a cyclist rides, they create an area of overpressure in front of them that holds them back, and an area of suction behind them that pulls them back, causing resistance," said Bert Blocken, who led the research at the university's School of Engineering and Physical Sciences. "But a car creates the same effect on a much larger scale. It pushes a big bubble of overpressure ahead of it, and when the car drives close behind a cyclist, that bubble partly cancels out the suction behind the rider, providing the cyclist with a meaningful boost."
At just 1 meter (3.3 feet) behind a car, a rider's aerodynamic resistance drops by almost 14 percent — what Blocken called "massive." The benefit shrinks as distance grows, but it never completely disappears, even at 30 meters (98 feet).
The researchers tested eight different vehicles, from the tiny Smart Fortwo to boxy work vans. The results were clear: the bigger and more blunt the car, the bigger the push it gives the rider ahead. A rider followed by a typical estate car at 10 meters would gain 2.3 seconds over the Tour de France time trial course. But a rider followed by the larger Grenadier Station Wagon would gain even more.
"You might say these are small numbers, but elite time trials are sometimes decided by a tenth of a second, or even a hundredth," Blocken said. "In that context, these gains are enormous. They could determine who wins the Tour de France time trial."
This is the third study in a pioneering series by the team, and their work has already changed the sport. After their first research in 2023, cycling's world governing body, the UCI, extended the minimum distance between rider and car from 10 meters to 25 meters (82 feet) in individual time trials. A second study showed that piling bikes on a car roof actually increases the push effect, prompting the UCI to warn teams against exaggerating the practice.
Blocken's advice to the UCI is simple: set a maximum allowable drag area for team cars so no team can gain an unfair advantage simply by picking a bulkier vehicle. "The rules should simply be changed, and then we are done with it," he said.