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 short bursts.

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: computer simulations 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 % 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% 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.

Intermediate distance Drag reduction Speed increase Time gained per minute 0.48 m -71% 48.9% 29.3 s 2.64 m -48% 23.6% 14.1 s 4.8 m -36% 15.6% 9.3 s 10 m -23% 8.8% 5.3 s 15 m -18% 6.7% 4.0 s 20 m -15% 5.4% 3.3 s 30 m -12% 4.2% 2.6 s 40 m -10% 3.5% 2.1 s 50 m -7% 2.4% 1.4 s

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. Source: 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.