A new study carried out at Eindhoven University has found that pro riders gain a greater aerodynamic advantage from riding behind race motorbikes than previously thought. A motorcyclist 30 metres in front was found to reduce a rider’s drag by 12 per cent, while even a gap of 50 metres can result in a seven per cent reduction.
Professor Bert Blocken said he had not previously investigated the phenomenon due to the difficulty of predicting the strongly fluctuating airflow between motorcyclist and rider, especially at larger distances.
“This makes the calculation so complex that standard calculation models were no longer sufficient,” he explained.
To overcome this, Blocken used the Dutch national supercomputer Cartesius at SURF as well as wind tunnel measurements.
He found that a rider 2.5 metres from a motorcyclist experiences up to 48 per cent less drag. If the rider would otherwise be riding at 54 km/h without the motorbike, the motorbike’s presence would allow a speed of about 67 km/h.
That would provide a time gain of 14.1 seconds every minute and while the advantage becomes smaller as the distance increases, the seven per cent drag reduction at a distance of 50 metres would still represent a gain of 1.4 seconds per minute at the same reference speed of 54 km/h.
“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,” said Blocken. “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.”
Dr Fred Grappe, Performance Director at Groupama-FDJ, agreed and said that current UCI rules are therefore not sufficient to prevent riders gaining an advantage from race motorbikes.
“It is therefore necessary to define a kind of ‘free zone’ around the rider 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.”
He found that a cyclist in the middle or rear of the peloton will encounter between five and seven per cent of the air resistance a solo rider would.
“It is as if a rider is cycling at 12 to 15 km/h in a peloton that is speeding along at 54 km/h,” he explained.
Comparing it to positions adopted by Marco Pantani, Fabian Cancellara, Peter Sagan and Vincenzo Nibali, he found that Sagan’s position – sitting down on the top tube, but pushed further back than Froome’s position – was the most aerodynamically efficient. Nibali’s and Pantani’s positions were also found to be faster.