If it hadn’t been for the sight of Chris Froome running up Mont Ventoux, the most unexpected moment of the this year’s Tour de France might have been Froome attacking on the descent of the Col de Peyresourde, pedalling with his bum on the top tube and his chest pressed against the top of the bars.
The logic behind this descending seems simple: you get the aerodynamic benefit of sitting low on the top tube, but are also able to pedal for a little extra speed. However, academics in Belgium and the Netherlands have put their serious work to one side for a week to show how this position might not be as fast as it looks.
In an article posted on Linkedin, Bert Blocken of the Eindhoven University of Technology in the Netherlands shows how he and other academics at KU Leuven, the University of Liège in Belgium, and ANSYS International used Computation Fluid Dynamics to compare four different riding positions: a time trial position, seated on the top tube (like Froome), seated in the saddle with your chest close to the bars, and a normal cycling position sitting upright with your hands on the hoods.
Unsurprisingly the time trial position was the fastest and the normal cycling position was the slowest, generating 19.9 per cent more air resistance than the time trial position. However, descending in the saddle was only 1 per cent less aerodynamic than the time trial position, while the Froome descending style was 1.6 per cent less aerodynamic. Not a big difference then, but we’re sure with their marginal gains philosophy Team Sky will be paying attention.
However despite apparently not being in the optimum aerodynamic position, Froome did of course manage to take 13 seconds on his rivals. According to Blocken this was due to a number of factors, such as the gap he had opened up over the top of the Peyresourde, the hesitation of the chasing group before the finish, and the fact that Froome’s rivals may have been descending in an even less aerodynamic position.