Which cyclist hill descent position is superior?

Govt abstract

The truth that totally different skilled cyclists use very totally different hill descent positions signifies that there isn’t any consensus within the peloton on which place is admittedly superior, and that the majority cyclists didn’t take a look at totally different positions, for instance in wind tunnels, to seek out which place would give them the biggest benefit. With two totally different and independently utilized analysis strategies, wind-tunnel testing and CFD simulations, that every yield the identical conclusions, we show which bicycle owner hill descent place is aerodynamically superior, amongst a pattern of 6 positions utilized by skilled riders previously. We additionally talk about which positions are superior from the point of view of security and energy technology. The outcomes present that the notorious “Froome” place throughout the Peyresourde descent of the Stage 8 of the 2016 Tour de France will not be aerodynamically superior to a number of different positions. In reality, preliminary hesitation and an excellent much less aerodynamic descent positions adopted by most the main chasers precipitated Froome to win stage 8 of the Tour. The Froome place will not be quicker, not safer and less highly effective in comparison with different positions. Different positions are as much as 8% quicker, present extra equal distribution of physique weight over each wheels, and permit extra energy technology.

Analysis crew

This venture was led by Bert Blocken of the Eindhoven College of Know-how within the Netherlands and KU Leuven (Leuven College) in Belgium, and carried out along with Thijs van Druenen and Yasin Toparlar of the Eindhoven College of Know-how, the College of Liège in Belgium (Thomas Andrianne) and ANSYS Worldwide (Thierry Marchal).


An unbiased and unfunded investigation of the aerodynamic efficiency of various hill descent positions in biking. As well as, feedback are given about energy technology and security related to every place. Some misconceptions are defined.

Why this new investigation?

This work was incited by the top of stage 8 of the Tour de France (2016), wherein in all probability probably the most outstanding merchandise was the best way wherein Chris Froome descended the Peyresourde in the direction of the end line, took a 13” lead on Nairo Quintana, Adam Yates, Bauke Mollema and his different rivals, from which he broke away simply earlier than the highest of the Peyresourde, and gained the stage. The determine beneath reveals Chris Froome throughout his descent, sitting on the highest tube, along with his chest on the handlebar. Through the descent he was alternatively pedaling and holding the legs static. The descent coated 15.5 km, from an altitude of 1569 m to 632 m. Froome reached a median pace of 62.5 km/h and a most pace of 90.9 km/h. Some attributed this to the so-called “superior aerodynamic descent place” adopted by Froome. Inside 5 minutes after the end, I acquired three emails, from Yasin Toparlar, Thierry Marchal and Thomas Andrianne, suggesting we examine this to see whether or not this explicit place is admittedly aerodynamically superior.

Completely different hill descent positions

Completely different cyclists use very totally different hill descent positions. Determine 2 beneath reveals (a) Chris Froome; (b) the late Marco Pantani; (c) Vincenzo Nibali able adopted additionally by many others; (d) Nibali in his explicit descent place; (e) Fabian Cancellara able required for a technically troublesome descent with many sharp bends; and (f) Peter Sagan able we’ll denote as “Prime tube secure”. The latter identify is chosen as a result of versus the Froome place, on this place the physique weight is distributed extra equally over each wheels. These totally different descent positions, that are nonetheless utilized by skilled cyclists in a number of races, point out clearly that there isn’t any consensus within the peloton on which place is admittedly superior, and that in all probability most cyclists didn’t take a look at a number of positions intimately by both wind-tunnel investigation or CFD simulation to seek out which place would give them the biggest benefit.


Wind-tunnel testing

The primary methodology was wind-tunnel testing. We scanned a bicycle owner in 4 totally different positions, had fashions made by CSC slicing at scale 1:4 and the crew examined these within the wind tunnel in Liège. The checks had been carried out at 216 km/h for Reynolds similarity with the bodily actuality at full scale and 54 km/h (= 15 m/s). 216 km/h is a hurricane of class 4, so the fashions wanted to be strengthened with vertical bars within the wheels. Corrections had been made to take away their contribution to the aerodynamic resistance.


Our earlier analysis indicated that at and above 15 m/s, a adequate diploma of Reynolds quantity independence is obtained and the identical drag areas outcome at 20 and 25 m/s. The outcomes when it comes to drag space are proven in determine 4 beneath. The drag space is the product of frontal space A and drag coefficient Cd that each seem within the equation of the drag power:



Computational Fluid Dynamics (CFD) simulations

The second methodology was pc simulation with Computational Fluid Dynamics (CFD). The identical 4 positions and two extra positions had been analyzed with ANSYS Fluent CFD software program utilizing extraordinarily high-resolution fashions of 36 million calculation cells with sizes all the way down to 20 micrometer (= 0.020 millimeter) near the physique of the bicycle owner, which is required for correct and dependable outcomes as a result of the very skinny laminar sublayer near the floor of the bicycle owner and the bicycle must be resolved. These cells are so small they’d be inconceivable to see in actuality. Nevertheless, after greater than 6 months of testing, we discovered that this decision and likewise the typology of the grid additional away from the physique has a really massive influence on the accuracy of the outcomes. Based mostly on this expertise, we developed the ultimate grids.

We mixed these grids with the applying of the Transition SST-k-omega mannequin whose capabilities in boundary layer transition can solely be absolutely exploited by the kind of extraordinarily high-resolution grid as made right here. We did this for twenty bicycle owner fashions however solely outcomes for 6 of them are reported right here.

The wind-tunnel and CFD outcomes are mixed in Determine 8. Observations:

  • Wind tunnel and CFD give precisely the identical order of finest positions when it comes to lowest aerodynamic resistance: “Pantani” first, “Again down” second, “Froome” third, “Again horizontal” fourth.
  • Wind tunnel and CFD agree very properly (inside error vary for first three positions) due to each the cautious technology of a really high-resolution grid and the cautious utility of the Transition SST-k-omega mannequin.


Two extra positions

As a result of the comparability of the 2 unbiased strategies confirmed that each give the identical order of positions and that each strategies are dependable, the examine was prolonged with two different descent positions. The ultimate outcomes are proven within the determine beneath. Word that many of the percentages are bigger than the deviations between wind-tunnel outcomes and CFD outcomes, as was proven above. These percentages are based mostly on the idea that:

  • Both all cyclists experience down a really steep hill with out pedaling
  • Or all cyclists are pedaling with the identical energy provision

Feedback about this additional down.


Why are these outcomes so totally different?

One would possibly surprise why these outcomes are so totally different from one another and from what one would possibly intuitively anticipate. The aerodynamic resistance or drag power is decided by the equation proven above, wherein 4 components are discerned: the biking pace, the frontal space of the bicycle owner, the drag coefficient of the bicycle owner and the air density. Assuming the identical biking pace and air density, the frontal space A and drag coefficient Cd stay. The upper the values of A and Cd, the bigger the drag power. The principle motive for the distinction in outcomes on this examine is the totally different drag coefficients. The drag coefficient is the results of the strain distribution on the physique of the bicycle owner. The strain distribution in all positions examined may be very complicated and really totally different. Place of separation factors is essential right here. It can’t be obtained by instinct however must be studied by pc simulation. This distinction causes the totally different drag forces. The strain coefficients on the cyclists and bicycles as discovered by pc simulation are proven within the determine beneath.


4 conclusions

1.   Froome didn’t win as a result of his descent place was aerodynamically superior.

The place utilized by Chris Froome in stage 8 of the Tour de France of 2016 was not aerodynamically superior. A number of different positions are quicker. Chris Froome gained the stage as a result of he accelerated earlier than the hilltop and already had a considerable lead when he reached the hilltop. When you’ve gotten a lead if you begin descending whereas others are nonetheless climbing at decrease pace, your lead solely will increase till the others begin descending. Second, the chasers, like Nairo Quintana, even after they had been descending the hill, hesitated and had been using within the very non-aerodynamic place “Again upwards” for a really lengthy whereas, see photographs beneath. Later, they adopted the place “Again horizontal” and a few for a short whereas solely place “Again down”. So sure, Froome’s place was extra aerodynamic than that of the chasers, however not aerodynamically superior all-round. Descending “Again down” or “Prime tube secure” would have allowed the chasers possibly to meet up with Froome and stop him from profitable and taking the yellow jersey.

2. “Prime tube secure” place is quicker ànd safer.

The brand new analysis reveals that, if pedaling of the bicycle owner will not be wanted, the place “Prime tube secure” is the perfect place of the 6 positions examined. Additionally it is the most secure place of the 2 “Prime tube” positions because it permits a reasonably even distribution of the load of the bicycle owner over the 2 wheels.

3. Even contemplating pedaling, place “Froome” will not be superior.

When pedaling is essential, we must always deal with positions that enable pedaling of the bicycle owner with robust energy technology. Pedaling is hardly potential in place “Pantani” and place “Prime tube secure”. However pedaling with bigger energy output will in all probability be potential in place “Again down” and definitely in place “Again horizontal”, which makes these positions extra appropriate for descending than place “Froome”, wherein pedaling is feasible however not with massive energy output.

4. Don’t take dangers for no acquire.

Past the scientific outcomes supported by this investigation, there are skilled or leisure cyclists who is perhaps placing their probabilities of victory and possibly even their life in danger by adopting a extra harmful place with the injustified hope to enhance their aerodynamics. It isn’t unlikely that Alberto Contador misplaced Paris-Good in 2017 to Henao by adopting the Froome place. With the three main excursions, the Giro, the Tour and the Vuelta, simply across the nook, many is perhaps tempted to undertake this “Froome” place, taking threat for no acquire. We strongly advise towards that, from the viewpoints of pace, security and energy. We additionally encourage skilled cyclists prepared to contemplate new positions to first strategy us in order that we might safely examine them on the pc and within the wind tunnel earlier than taking any threat on the street.


Q1: How dependable are these outcomes?

We used two unbiased strategies (wind-tunnel testing and CFD) that each gave the identical outcomes, when it comes to rating of positions. It was not simple to get dependable outcomes, each in wind-tunnel testing and CFD. Each require quite a lot of experience. It took us 10 months to get each to the very excessive degree of accuracy we’ve got now, particularly within the simulations. That could be a huge funding, nevertheless it has given us distinctive experience and now we’re able to do the checks and simulations with the identical accuracy however a lot quicker.

Q2: I don’t consider your outcomes.

That’s okay. It isn’t our intention to persuade the world. We had two unbiased strategies giving the identical outcomes. We publish our leads to high scientific magazines based mostly on nameless peer overview. We respect all beliefs, additionally when they’re unsuitable. Many individuals (even some professionals in biking) motive based mostly on instinct. Instinct is commonly a foul advisor in aerodynamics. The controversy between instinct and science can and can go on for years and many years. It’s an attention-grabbing one, and retains our work very related.

Q3. Workforce Sky is a scientific crew that checks every little thing, so your outcomes can’t be true.

We get this query on a regular basis. Positive crew Sky do quite a lot of testing. Each respectable crew does. However no crew can take a look at every little thing, not even when they’d have limitless price range. It took us – as professionals with long-standing experience in wind-tunnel testing and CFD simulations – 10 months to get this work accomplished as we reported it now. So personally, we consider Chris Froome when he stated after stage 8: “I didn’t follow this, it was a hunch of the second”. No crew can take a look at every little thing. Aerodynamics is just too sophisticated for this. Mankind has been learning aerodynamics for greater than 2000 years, with 1000’s and in latest many years thousands and thousands of researchers all around the world. Nonetheless we don’t perceive every little thing. Scientists don’t even agree on the definition of turbulence (!). So analysis in biking aerodynamics will proceed for many years, possibly centuries. Sky are glorious but additionally terrestrial. They can not take a look at every little thing. No one can.

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