Motorcyclists — stay away from cyclists in races, say scientists

Trailing cyclists make them go faster due to aerodynamics, researchers find


In May 2016, Belgian cyclist Stig Broeckx collided with a motorcycle during the Tour of Belgium. Doctors induced a coma due to severe head injuries; he was one of 11 cyclists hospitalized because of the incident.

There have been many such accidents between cyclists and motorcycles. The tragic climax was on 27 March 2016, when Antoine Demoitié, a young Belgian cyclist, died as a result being hit by a motorcycle in the Pro Tour race Gent-Wevelgem. Cyclists are calling on the International Cycling Union (ICU) to revise their rules for motorized vehicles, as world champion Tony Martin tweeted:

What we need NOW is a round table with UCI, race organisers and riders to force changes and decide one safety standard for EVERY race!

These calls are strengthened by new research that suggests as well as being dangerous, motorcycles could also be giving some cyclists an unfair advantage – and not in the way you might expect.

Surprising aerodynamics

When you look at cyclists in a race peloton, it’s easy to imagine that those in the lead have to work harder to cycle fast, giving the cyclists behind them an aerodynamic advantage. You’d be right in thinking this, but a new study reveals that the reverse is also true: if a motorcycle is riding closely behind a cyclist, that cyclist will have an advantage.

A team of researchers from Eindhoven University of Technology (TU/e) in the Netherlands and KU Leuven University and the University of Liege in Belgium have found that when a cyclist is followed by a motorcycle they will experience an aerodynamic advantage with up to almost 9% less air resistance, making them faster.

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

Motorcycles perform various tasks during a race, including carrying photographers or extra wheels in case riders break down. There are also motorcycles that have to watch the race to make sure nothing out of the ordinary happens; ironically, these very motorcycles could be influencing the outcome. Time trials are often won by tiny margins – literally every (split) second counts. Depending on the distance being raced, a following motorcycle could impact a cyclist’s time by several seconds.

This isn’t the first time the researchers have shown the effect: in a 2015 study published in the Journal of Wind Engineering and Industrial Aerodynamics, the team showed that a car following a cyclist at the regulation 10-meter distance could make them almost 4 seconds faster over a 50-kilometer distance – a decisive impact in a race. While the result wasn’t a big surprise to the researchers, it will certainly be news to many people, including cyclists.

Prof. Bert Blocken, PhDThe study’s lead author, Dr. Bert Blocken, is a professor in the Department of the Built Environment at Eindhoven University of Technology (TU/e) and the Department of Civil Engineering at KU Leuven University in Belgium. He’s also a keen cyclist who recognizes the difficulty in accepting the new findings:

There are very strong misconceptions about aerodynamics in the peloton. It’s counterintuitive, people really don’t expect it to happen. Even now I have heated discussions with people – a minority of professionals refuse to believe it. And even when people do believe the effect, it’s much bigger than they expect.

When it comes to aerodynamics, Dr. Blocken’s message is: Don’t trust your intuition.

All cycling teams do the same thing but it’s not necessarily optimal in terms of aerodynamics. Many aspects of aerodynamics are really counterintuitive; in every project even we as experienced scientists see things we didn’t expect. The problem is we’re totally submerged in aerodynamics but we can’t see it. And it’s also very complicated. If you haven’t seen simulations or wind tunnel tests, it’s impossible to guess the reason behind certain things.

Safe, fair races

The researchers used models in a wind tunnel to show how motorcycles can give cyclists a boost by following them. (Image © Dr. Bert Blocken, Eindhoven University of Technology)The researchers examined the aerodynamics of motorcycles in cycling races using numerical simulations and wind tunnel tests with scale models. The results showed that a motorcycle traveling 0.25 meters behind a cyclist can reduce their aerodynamic resistance by nearly 9%, increasing to 14% with three motorcycles. The aerodynamic resistance of the cyclist decreases by 6.4% at 0.5 m, 3.8% at 1 m, 1.2% at 2.5 m, 0.3% at 5 m and 0.1% at 10 m.

This might not seem like much, but if a motorcycle follows a cyclist at a distance of 2.5 m for just 2% of a 50 km race, that cyclist will have a time advantage of 0.40 seconds – this time difference has been decisive in several races.

The UCI has rules in place for motorcycles involved in races: one sentence specifies that motorcycles need to stay 10 m away from cyclists, another that they can’t allow cyclists to ride behind them. However, these contradict another rule that says press motorcycles are free to maneuver around cyclists.

In addition to the safety reasons for making the rules stricter, Dr. Blocken and the team say motorcycles should be required to stay 20 to 30 meters away from cyclists to ensure they don’t have an impact on the results. They have added their voices to those of the professional cyclists in calling for motorcycles to be fewer and further from cyclists. Dr. Blocken said:

This study is important to us. We did this work – unfunded – to support the cyclists and their teams in their discussion with the International Cycling Union to radically change the rules of professional cycling towards more safety concerning in-race motorcycles. Races should be safe and fair. Our research provides an additional compelling reason why the International Cycling Union should change its rules and enforce larger distances between cyclists and in-race motorcycles.

Read the study

Elsevier has published this article open access:

Blocken, Bert et al: “Aerodynamic benefit for a cyclist by a following motorcycle,” Journal of Wind Engineering and Industrial Aerodynamics (August 2016)

The lead author

Dr. Bert Blocken is Full Professor in the Department of the Built Environment at Eindhoven University of Technology (TU/e) in the Netherlands and part-time Full Professor in the Department of Civil Engineering at KU Leuven University in Belgium. His main areas of expertise are urban physics and environmental wind engineering. He has published more than 120 papers in international peer-reviewed journals. He developed TU/e’s first Massive Open Online Course, Sports & Building Aerodynamics. He has received the 2013 Junior Award from the International Association of Wind Engineering, six best paper awards from the Elsevier journal Building & Environment (2009, 2011, 2012) and at international conferences and a top-cited author award from the Elsevier journal Atmospheric Environment (2010). Several of his papers are top-cited papers in their respective journals. He is currently supervising a team of three senior researchers, 28 PhD students and 10 MSc students.

The journal

The official journal of the International Association for Wind Engineering (IAWE), the Journal of Wind Engineering & Industrial Aerodynamics provides a means for the publication and interchange of information, on an international basis, on all those aspects of wind engineering that are included in the activities of the IAWE: social and economic impact of wind effects, wind characteristics and structure, local wind environments, wind loads and structural response, diffusion, pollutant dispersion and matter transport, wind effects on building heat loss and ventilation, wind effects on transport systems, wind power generation, and codification of wind effects. This journal is published by Elsevier.


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