Every cyclist knows an aerodynamic tuck reduces drag. But a new study coming out of Eindhoven University in the Netherlands (see part 1 and part 2) suggests some tucks are better than others, while challenging assumptions about which position works best.
Case in point: Chris Froome’s dramatic Peyresourde descent on Stage 8 in the Pyrenees of last year’s Tour de France. Over the course of nearly 10 miles, the eventual Tour victor put a stunning 13 seconds on his rivals while alternately pedaling and coasting in a radical forward-seated position on his top tube.
Within moments, Tour followers exploded with speculation crediting Froome’s “super tuck,” where his torso rested on his stem and his entire head extended beyond the axis of his front hub. See it here:
But wait, says a team of researchers led by Bert Blocken, a Netherlands physics professor who has studied bike aerodynamics for several years. Scientifically, it turns out Froome’s riding position is only fourth fastest among six pro rider styles that were analyzed. And the differences aren’t necessarily slight: Had Froome adopted the fastest tuck, modeled after two-time defending World Champion Peter Sagan, he might have padded his margin by an additional minute and seven seconds.
“Froome did not win because his descent position was aerodynamically superior,” Blocken wrote in a post on LinkedIn. Froome won because he accelerated at the crest, and because his chasers used inferior aerodynamics.
Besides Froome and Sagan, the study compared positions used by Italian standout Vincenzo Nibali — perhaps the peloton’s most acclaimed descender — Swiss time trial and stage specialist Fabian Cancellara, and the late Marco Pantani, known for his climbing prowess. Using a traditional riding position (Cancellara’s “back upwards”) as the baseline measure, the study found Nibali’s “back horizontal” and “back down” positions (butt on the saddle with neck and chin aligned roughly with the stem) to be 8 percent and 12 percent faster, respectively.
By comparison, Froome’s tuck was 9 percent faster. And Pantani’s classic (and very awkward looking) behind-the-saddle crouch was 14 percent faster.
At 17 percent faster, Sagan took the laurels with a position the study labeled “top tube safe” — seated on the top tube but with rear end abutting the seat post, which puts the chin in direct line with the front hub.
Had Froome’s chasers used Sagan’s style, they might’ve caught Froome, Blocken noted. As it was, they were in the inferior “back upwards” position far too often.
As a follow-up, Blocken noted none of these can touch the YouTube-popular “superman” position, where the rider flattens out by perching his lower abdomen atop the saddle and extending his legs rigidly straight out behind. It’s a whopping 24 percent faster — 7 percent faster than Sagan’s.
But Blocken warned it’s “dangerous and irresponsible,” even suggesting it should be banned by the UCI, because the rider can’t adequately control the bike. Although slightly slower, Sagan’s centered position has the plus of safety because “it allows a fairly even distribution of the weight of the cyclist over the two wheels.”
Blocken’s team couldn’t do real-life simulations of Froome’s triumph because his rivals weren’t filmed during their runs and other variables like air turbulence were not recorded. Instead, they used software drawing from wind-tunnel tests and computational grids based on a brain-cramping 36 million calculation cells in the air pocket around the cyclist.
In the end, comfort and security may contribute most to aerodynamic choices for any given cyclist, the study suggests. The fastest descenders also tend to be the least cautious, as Froome and Nibali showed in back-to-back crashes during rainy conditions at Mont Blanc, the 19th stage of last year’s Tour. Froome’s Team Sky subsequently chided him for taking unnecessary chances.
Blocken, professor of building physics at Eindhoven University of Technology, invited cyclists wanting to try out new aero tucks to approach his team for testing “before taking any risk on the road.” The study team also included Thierry Marchal, global industry director at ANSYS International; Thomas Andrianne, University of Liege’s wind-tunnel lab director; and doctoral students Yasin Toparlar and Thijs van Druenen.