Why does Cavs chain keep coming off after sprints?
When Mark Cavendish crossed the line in Chteauroux to take his second stage win in the 2021 Tour de France, it was a dream come true. The 36-year-old Manxman won his first-ever Tour stage here 13 years ago - his career had come full circle. Image 1 of 2 Sprinting to victory on Stage 6 of the Tour de France. Click right for a closer crop. (Image credit: Tim de Waele via Getty Images) Image 1 of 2 Sprinting to victory on Stage 6 of the Tour de France. Click right for a closer crop. (Image credit: Tim de Waele via Getty Images) Image 2 of 2 (Image credit: Tim de Waele via Getty Images)  But something that didn't come full circle as he put both hands on his head exactly as he had done in 2008 was his chain. Victory number 32 was in the bag but his chain was flapping uselessly underneath the chainstay. This isnt even the first time Cavendish has rolled across the line with his drivetrain disengaged. The same thing happened back in April, at the end of stage two in the 56th Presidential Cycling Tour of Turkey in another closely fought sprint with Alpecin-Fenix's Jasper Philipsen. So folks, why did Mark Cavendishs chain drop the moment he stopped sprinting?Watch.Video from GCN+. We asked Dov Tate of Parcours wheels, an Oxford engineering graduate who last conducted a groundbreaking study into the way wheels behave in real-world conditions. "Interesting question!" said Tate. "First thing to note is that Deceuninck-Quick-Step are running Rovals Rapide CLX wheels I believe. These use a DT Swiss EXP ratchet system on the freehub, so different to the pawl-based design that we use. Im not 100 per cent sure on exactly how that freehub would respond under the (pretty extreme) conditions in a sprint. "My instinct is that if you watch the sprint back in slo-mo, Cav is noticeably more 'violent' in his sprint body movement, then hes the only one who has quite such an abrupt halt in his pedalling motion (when he posts up for the win)." Tate explains: "He locks his left knee as he sits up, which probably puts a small amount of backpedal momentum into the drivetrain, whereas everyone else just rolls through the line in the drops. So his is a more jerky motion at the point of crossing the line versus the other sprinters who are smoother on their drivetrain. Given his chain will already have been 'sloshing' all over the place during the sprint, it really wouldnt take much at all to cause it to jump and drop." Image 1 of 2 Taking his first of four wins at the Tour of Turkey. Click right for a closer crop. (Image credit: Anadolu Agency) Image 1 of 2 Taking his first of four wins at the Tour of Turkey. Click right for a closer crop. (Image credit: Anadolu Agency) Image 2 of 2 (Image credit: Anadolu Agency via Getty Images)  Add to this the motion of the freehub, which will have been travelling very fast before the sudden stop. Tate says: "There is probably also a small amount of rotational momentum in the freehub, so as he stops pedalling, the freehub is likely still rotating forwards, along with the wheel. Plus theres a non-zero amount of friction between freehub and wheel which will also contribute to this forward rotational momentum. "So altogether, theres likely a combination of some forward momentum in the chain, combined with either a complete stop at the cranks (or even a small reverse motion), which is enough to make the chain drop, given its already moving around violently from the sprint." Tate sums up: "Id say its not one single cause, rather the 'perfect storm' of several micro contributors." We've asked for a comment from Deceuninck's technical staff on the ground at the Tour and will update this story as soon as we have one. Although in slo-mo it looks as though Cav has had a lucky escape, as long as he only sits up and celebrates when there's no more pedalling to be done it shouldn't cause him a problem.