A motorbike behind the rider can provide > 9% drafting benefit

phreak

https://www.tue.nl/en/university/news-a ... ehind-him/

Research at TU Eindhoven, KU Leuven and the University of Liege has shown how a motorcyclist riding right behind a racing cyclist can reduce the air resistance for the cyclist by almost nine percent. In a time trial, such as this Friday’s forthcoming prologue in the Giro (Tour of Italy) in Apeldoorn, this could mean a decisive advantage. The researchers advise the UCI (International Cycling Union) to extend the minimum distance between motorcycle and cyclist, also from a safety perspective, to 20 or 30 meters.

In cycling races there are many motorcycles present, for instance for reporters and photographers, often riding very close to the riders. The discussion concerning the number of motorcycles in the race has once again been ignited by several incidents involving motorcycles, including the recent death of the 25 year-old Belgian cyclist Antoine Demoitié following a collision with a motorcycle in the Gent-Wevelgem race. Research by TU Eindhoven, KU Leuven and the University of Liege, supervised by TU/e professor and keen cycling fan Bert Blocken, reveals that motorcycles can also have 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 to calculate that a motorcycle at a distance of 0.25 meter 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 certainly not uncommon in elite races.


Graphs of the time gained (vertical axis) depending on the time trial distance (horizontal axis) for different following motorcycle distances (d). Credit: TU Eindhoven.
Up to a minute gained
The researchers calculated the time that can be gained in a time trial for various distances between the cyclist and following motorcycle. Depending on how long a motorcycle rides behind the cyclist in a short time trial like the Giro prologue (9.8 kilometer), 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.

Unprecedented research
Last year the TU/e researchers showed that a following car could give a rider a time advantage by driving close behind the rider. Now it appears that the aerodynamic benefit provided by a following motorcycle is even greater, mainly because motorcycles tend to ride much closer behind 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 greater than previously thought.

UCI must modify the rules
The researchers advise the UCI to modify the rules on motorcycles in cycling races not only from a safety perspective but also given the measured undesirable aerodynamic advantages that riders could gain. They are appealing for the regulatory ten meter distance to be increased to thirty meters and, moreover, to ensure there is compliance with this distance, something that almost never happens in reality. They join the riders in asking the UCI to take stricter action concerning in-race motorcycles.

joelsim

So, Nibbles with no doubt have 4 behind him and a car a-post to hang on to, whilst Landa will just have the heli in front of him at low level

Escher303

" ...0.25 meter 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 certainly not uncommon in elite races..."

0.25m? That's 25cm, are they really getting that close when behind? Side on maybe, and their evidence for them being that close behind is race pictures? Sure there is a very important case for getting motos out of the way, for safety and when riders are given an advantage when they are in front. But this case doesn't look particularly well researched based on that article.

ddraver

Groundbreaking research that Ned and Chris did last year...

bobmcstuff

Yeah sensationalist headline but then turns out they used a crazy distance. How they can advocate moving from 20 to 30m from that headline I don't understand- surely they should look at the effect from a moto at 20m vs a moto at 30m. Maybe the study has just been reported in the most sensational manner possible (as if).

DeVlaeminck

" If there are three motorcycles, the reduction can be as much as 14 percent. Race pictures suggest that such short distances are certainly not uncommon in elite races."

Is it even possible to get three motorcycles 25cm behind a bike rider !

The_Boy

Of course it is. It doesn't say that there are three motos in gap 25cm long.

I mean, it's highly unlikely but...