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How to get super-aero on the descents while staying safe

Chris Froome’s curious descending position isn’t as aerodynamically efficient as he might hope, according to new research from the Netherlands and Belgium. 

Researchers led by Bert Blocken of the Eindhoven University of Technology in the Netherlands and KU Leuven (Leuven University) in Belgium investigated the aerodynamic performance of different descending positions in cycling, looking particularly at the positions of Chris Froome, the late Marco Pantani, Fabian Cancellara, Peter Sagan and two different positions adopted by Vincenzo Nibali.

Let’s cut to the chase here: Peter Sagan’s position – sitting down on the top tube, but pushed further back than Chris Froome’s position – comes out on top, based on the assumption that none of the cyclists in these positions would be pedalling, or they’d all be pedalling with the same power output.

Here are the results in full:

Bert Blocken, Eindhoven University of Technology, the Netherlands and KU Leuven, Belgium - 1.jpg

Pic courtesy of Bert Blocken, Eindhoven University of Technology, the Netherlands and KU Leuven, Belgium

Fabian Cancellara’s ‘back upwards’ position came out slowest with Nibali’s ‘back horizontal’ position 8% faster. Froome’s position was 9% faster than Cancellara’s, Nibali’s ‘back down’ position was 12% faster, while Pantani’s position, resting his chest on the saddle with his bum just over the back wheel, was 14% faster.

Sagan’s ‘top tube safe’ position, sitting on the top tube with his chest on the stem so that his weight is distributed quite evenly over the wheels, was calculated to be 17% faster than Cancellara’s.

How did Professor Blocken and his team work this out? 

First, through wind-tunnel testing. They scanned a cyclist in different positions, had models made at 1:4 scale and tested those models in the wind tunnel in Liège.

Check out the full paper for details on the testing methods. 

Then the team used computational fluid dynamics (CFD) simulations with extremely high-resolution models (36 million calculation cells).

The researchers acknowledge that it’s a crude calculation but say that Sagan’s ‘top tube safe’ position could have saved Froome 1:07mins over the position he actually used when he attacked on the Peyresourde descent on Stage 8 of last year’s Tour de France (he might not care; he won the race anyway). As well as being faster, the researchers believe that the top tube safe’ position is less risky – hence the name, obviously!

Froome’s position does have an advantage over the ‘top tube safe’ position in that it allows pedalling but not, the researchers say, with a large power output.

Superman 2.png

Interestingly, the so-called ‘Superman’ position (above), where a rider essentially lies forward on the bike with his torso on the saddle and legs stretched out behind him/her (not to be confused with Graeme Obree’s Superman position which was entirely different), was found to be 24% faster than Cancellara’s base time… But if you want to ride down the Peyresourde like that, well, you’re on your own.

For more info read the paper in full here.

As an aside, Peter Sagan Tweeted today that he was working on his aero position in California, so you can expect to see it making another appearance in one of the big races soon.

 

Mat has worked for loads of bike magazines over 20+ years, and been editor of 220 Triathlon and Cycling Plus. He's been road.cc technical editor for eight years, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a past winner of the Cycling Media Award for Specialist Online Writer.