The often-heard complaint that motorcycles can influence the outcome of races is justified

The often-heard complaint that motorcycles can influence the outcome of races is justified
Experiment with a rider cycling behind a motorcycle in the wind tunnel of Eindhoven University of Technology. Credit: Bart van Overbeeke

In professional cycling, in-race motorcycles such as TV motorcycles drive in between the riders. In the slipstream behind the motorcycle, cyclists can gain time. For the first time, the exact extent of this advantage has been scientifically investigated. It turns out to be even more advantageous than expected. Using computer simulations and wind tunnel measurements, Professor Bert Blocken of Eindhoven University of Technology and KU Leuven—in collaboration with software company ANSYS—investigated the effect. He found that a motorcyclist 30 meter in front of a rider reduces drag by 12 percent. A rider who cycles behind this motorcyclist for one minute therefore can gain 2.6 seconds.

In recent years, many cycling teams, riders and commentators have complained that the motorcycles influence the races, and sometimes even determine the results. However, the exact extent of the advantage for a rider cycling behind a motorcycle had not been investigated before. It is not uncommon for motorcyclists to remain in front of a single rider or a group of riders at twenty to thirty meters for several minutes. Even distances of a few meters occur in .

Professor of Building Physics Bert Blocken is surprised at the enormous time gains that his research shows: "Even if a motorcyclist only rides for a few seconds in front of the riders, a considerable time advantage can still be gained. For a rider cycling for 10 seconds at 2.5 meters behind a motorcycle, this gain can exceed 2 seconds."

Winning or losing

Blocken investigated the drag using two methods that independently show the same results: and measurements in the TU/e wind tunnel. A rider who cycles at a distance of approximately 2.5 meters from a motorcyclist experiences up to 48 percent less drag. If he or she would ride at 54 km/h without motorcycle, the presence of the motorcycle will allow him or her to ride at about 67 km/h. This provides a time gain of 14.1 seconds every minute. This advantage becomes smaller as the distance increases, but at a distance of 50 meters a 7 percent reduction is still measurable. This represents a gain of 1.4 seconds per minute at a reference speed of 54 km/h. At reference speeds above 54 km/h, the time gain is even bigger.

The often-heard complaint that motorcycles can influence the outcome of races is justified
The decrease in drag, speed increase and time gained per minute for each measured distance between rider and motorcyclist. Assumption: rider without help of motorcycle rides at reference speed of 54 km/h. Credit: Bert Blocken

"We repeated the wind tunnel measurements and our calculations a few weeks after the first tests because I couldn't believe the size of the effects. But we always found the same results. Because races are sometimes decided by seconds, these differences can determine whether you win or lose. The often-heard complaint that motorcycles can influence the outcome of races is therefore justified," says Blocken.

The time gains cited above are calculated and measured without head wind, tail wind or crosswind. Blocken: "If there is head wind, the time gains are larger. If there is tail or crosswind, the time gains are smaller. The stronger the crosswind, the more difficult it is for a rider to get in the 's slipstream."

The often-heard complaint that motorcycles can influence the outcome of races is justified
Computer simulation of a rider cycling at a distance of 10 meters from a motorcyclist. The green and yellow colors in front of the rider show that the airspeed here is substantially lower than in front of the motorcycle. Credit: Bert Blocken

Insufficient and unenforced guidelines

The International Cycling Union UCI issued new guidelines for motorcyclists in 2017. Blocken's research shows that these are not sufficient to prevent time gain for the riders. Moreover, these rules are not enforced during the race, which means that in reality motorcycles are much closer to the riders.

Dr. Fred Grappe, performance director at the UCI World Tour Team Groupama-FDJ substantiates that the aerodynamic effects of the motorcycles affect the performance of the riders. "It is therefore necessary to define a kind of 'free zone' around the in which no motor vehicle is allowed for more than a few seconds. Bert Blocken's new scientific study in cycling dynamics provides the knowledge to determine such a zone effectively. Given the influence of even a few seconds on a ranking, it is unacceptable to ignore this knowledge and its importance."

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Citation: The often-heard complaint that motorcycles can influence the outcome of races is justified (2019, June 27) retrieved 17 September 2019 from
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User comments

Jun 27, 2019
I am a vigorous (tri)cyclist and a habitual wheel-sucker of upright bicycles, passing motorcycles and passing automobiles. There is great benefit in riding in the wake of another vehicle.

Jun 27, 2019
This is a bit of a drag

For how
In a few days time
The tour of frace begins
How are we supposed to get close up photographs
For the sport
For the viewers
For the sponsors
If we cannot get close up pictures
It's more than a bit of a drag
It's one of those things you have to live with
For without close up photography
The viewers will leave
The sponsors will leave
The teams will disappear
Cycling will be no more

Fore we have to suck it up and grit our teeth as life is not always fair!

Jun 28, 2019
Cycling will be no more
The Tour is a circus, it is not 'cycling'. The clowns stalled their car when they started using drugs and legislation to beat the best. The UCI ringmaster is not fair and the protest is to SHUN ICKY ugly people.

For speedy fitness I ride a recumbent tricycle (maybe fast being 70 y.o.). For clean sports entertainment I am enjoying Alex Honnold's Free Solo and Tommy Caldwell's Dawn Wall. "Imagine an Olympic event that if you don't take the Gold Medal then you die."

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