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Racing Cyclist Can Gain Up To A Minute With Motorcycle Right Behind Him

FLI motorcycle-aero-advantage

A motorcyclist following close behind a racing cyclist can reduce the air resistance for the cyclist by almost 9 percent. In time trials such as the prologue of the Giro, this can give the cyclist the decisive advantage. That is the conclusion a study by TU Eindhoven, KU Leuven, and the University of Liège.  

Cycling races come with many motorcycles, for instance for reporters and photographers. In many cases, these motorcycles ride very close to the cyclists. The discussion about the number of in-race motorcycles was recently re-ignited by several incidents, including the death of the 25-year-old Belgian cyclist Antoine Demoitié after a collision with a motorcycle. Research by TU Eindhoven, KU Leuven, and the University of Liège, supervised by professor and keen cycling fan Bert Blocken (TU Eindhoven / KU Leuven), has now shown that motorcycles can also play a decisive role in the outcome of a race from an aerodynamic perspective.

Less air resistance 

The researchers used computer simulations and wind tunnel measurements of scale models of a time trial rider and a motorcyclist (see picture). Their calculations showed that a motorcycle at a distance of 0.25 metre behind the cyclist can cut the air resistance by almost 9 percent. If there are three motorcycles, the reduction can be as much as 14 percent. Race pictures suggest that such short distances are not uncommon in elite races.

The researchers calculated the time that can be gained in a time trial for various distances between the cyclist and following motorcycle. Depending on close the motorcycle is to the cyclist in a short time trial like the Giro prologue (9.8 kilometres), a few to several seconds can be gained. Time trials are often won by very narrow margins. In the longer time trials, the difference could be up to a minute.

Graphs of the time gained (vertical axis) depending on the time trial distance (horizontal axis) for different following motorcycle distances (d).
© TU Eindhoven

Last year, the researchers had already shown that a following car could give a cyclist a time advantage by driving close behind him. Now it appears that the aerodynamic benefit provided by a following motorcycle is even greater, mainly because motorcycles tend to ride much closer to the cyclist. But now, for the first time, this ‘following effect’ of motorcycles and following vehicles has been investigated in detail. Evidence suggests that the effect is much bigger than previously thought.

Recommendations for the UCI

The researchers advise the UCI to modify the rules for motorcycles in cycling races. This would help prevent accidents as well as unfair aerodynamic advantages for cyclists riding in front of a motorcycle. The researchers recommend increasing the regulatory 10 metre distance to 30 metres and ensuring that the rules are complied with. Their recommendations dovetail with cyclists’ call for stricter measures.

FLI Bycicle

Image of computer simulations with colours depicting different pressure levels. The motorcycle follower causes an overpressure in front of the motorcycle (red area) and a reduction in the low pressure behind it (blue area), thereby reducing the aerodynamic drag. © TU Eindhoven

Source: KU Leuven

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