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Earlier this week, Belgian Tom Boonen (Quick-Step Floors) made a bit of cycling history on Stage 2 of the Tour de San Juan as the first rider to win a UCI road race while using disc brakes. The implementation of disc brakes in the pro peloton has been an unquestionably dramatic affair, so this latest development — especially by a racer of Boonen’s caliber — will likely be seen by many as something of a milestone.
Specialized deserves credit for supposedly offsetting the two major perceived downsides of disc brakes from a performance perspective. According to the company’s marketing claims, its S-Works Venge ViAS Disc is neither heavier nor significantly less aerodynamic than the standard rim-brake version. As such, for Boonen, there would have been no obvious downsides to accompany the superior braking performance that discs provide.
However, proponents of the technology perhaps shouldn’t go shouting from the rooftops just yet. Boonen’s win may have been historic, but Stage 2 of the Tour de San Juan was hardly the ultimate test of disc brakes’ strengths and weaknesses in the context of the pro peloton.
Even if you take Specialized’s claims of equal aerodynamics and weight at face value, that doesn’t account for how that mass is distributed. On a relatively flat and short parcours like the one on which Boonen won, that wouldn’t make much of a difference. However, climbers are notoriously finicky about rotating weight, particularly on queen stages of a Grand Tour where the race can literally be won or lost on a single attack on a steep pitch of road, and regardless of whether those extra grams have any real-world effect on climbing speed. Would someone like Chris Froome be willing to spin a couple hundred extra grams of stainless steel up Alpe d’Huez with the maillot jaune on the line? Maybe, or maybe not.
The question of mechanical support for disc brakes remains to be fully answered as well. Although it’s easy to set up disc brakes so that the rotor doesn’t rub on the pads in most situations, the minimal clearances still make it more difficult to consistently do so with a spare wheel; complete spare bikes are preferred.
That sort of thing would be relatively easy to manage at a smaller event like the Tour de San Juan where there are roughly 160 starters on hand and just four WorldTour teams. Compare that with the 200 riders and denser field of elite, big-budget teams in a Grand Tour, for example, or the utter chaos of the Tour of Flanders or Paris-Roubaix. Would the improved performance of disc brakes be enough to offset the potential headaches associated with an ill-fitting team spare or neutral wheel?
Not to discount the talents of fellow sprinter Elia Viviani, but it should perhaps also be said that Boonen also faced fewer obstacles to victory at the Tour de San Juan than he normally would. Discs or not, there was a good chance he was going to win that day.
Unquestionably, the first win on disc brakes at a high-level UCI road race is notable, at least for those who have been following the technology’s circus-like implementation over the past year.
Boonen’s win is historic, but it’s not a monumental occasion, and a sample size of one doesn’t constitute convincing data. It very much remains to be seen just how things will go as we get deeper into the season.