Technical FAQ: Could aero brakes win a Tour sprint?
Clean front ends and drag
In the finish-line photos of the sprint finishes of stages 2 and 4 in the Tour de France, it was notable to me that the riders who came in second (Sonny Colbrelli in stage 2) and third (André Greipel in stage 4), were riding bikes with exposed front brakes and cables, while the riders who finished just 1-2 feet ahead of them (Peter Sagan and Fernando Gaviria) were both riding bikes with much cleaner-looking front ends. Could the drag associated with the exposed cables have made up that 1-2 foot difference in a 200-meter sprint, particularly considering the very high speeds the pros can sprint at?
I actually believe that it could make that much difference. In this article, a Cannondale aerodynamicist calculates that “in a 200-meter, 60kph sprint with similarly-sized riders both putting out 1,000 watts, the rider on the SystemSix would finish four bike lengths ahead of the rider on the SuperSix EVO.” While I am not sure how much you can hang your hat on a calculation like that, we are also talking about a much smaller distance than four bike lengths.
Cannondale’s calculation is referring to the total bike, and you’re only talking about exposed cables. However, it is the front of the bike that makes the most difference aerodynamically, especially at those kinds of speeds, and a significant part of cleaning up the aerodynamics of the front end is to conceal the cables.
A mysterious spinning wheel at the Tour
I respect your opinion on all matters physics and bike related. If you tell me that there is a non-assisted reason that the rear wheel on the white bike (the polka-dot jersey wearer’s bike) spins the way it does in this video, I will believe you. I don’t believe that a wheel spins like that just from the momentum of moving the bike from a stopped position. No way!!
While watching the Tour de France stage unfold on the cobbles, there were several crashes. With about 17km to go, there was one crash that involved Tom Skujins getting tied up off the road.
Did you notice anything strange about his bike when he went to remount? Specifically, when he lifted the bike and then put it back down again to point it in the right direction, the rear wheel was spinning fast. I never saw him turn the crank arm or anything. I’m not proposing mechanical PED, but it’s very curious and I was looking for a reasonable explanation.
Dear Todd and John,
I think there is a very reasonable explanation for this not having to do with hidden motors. And yes, I agree with Todd that there is no way that the wheel would spin “like that just from the momentum of moving the bike from a stopped position.”
We are missing the correct angle on the first few seconds of the video to see the critical thing that I think Skujins did to make the wheel go like that. I think we get a hint during the first two seconds. Between seconds one and two, as Skujins’s head just becomes visible above the running cameraman’s right shoulder, Skujins seems to be coming up from a bent-over position to an erect one.
In my opinion, Skujins has done what many riders would do in that situation; he has bent over and spun the crank for one of three possible reasons. And even though it may look like he is rolling the bike, I believe he has it slightly off the ground in the tall grass as he carries it forward to the road after spinning the crank. I believe that he has either: (1) shifted the chain onto a larger cog (lower gear) so that he can start up again, since they were going fast at the time of the crash, and he would have been in too small of a cog to easily get started; (2) shifted to his smallest cog in order to prepare the wheel for a rear wheel change, or, (3) turned the crank to make sure that the chain is in gear (rather than about to start clunking around once he starts pedaling due to either the derailleur having been pushed inward to a larger cog while the shifter is still set for a smaller cog, or to the shifter having been clicked during the crash while the cranks were not turning).
This Twitter video seems to support my explanation.
For those interested in the motorized cheating issue, you might find Andrew Hood’s recent article interesting.
More on rider weight and coasting speed
I read your posts about how weight affects downhill speed, and I agree that heavier riders go downhill faster. As a shorter rider around 5-foot-6, I am usually smaller than most riders. With a weight that averages 135 pounds but has been between 125 and 140 pounds over the decades, I can attest that I get passed most of the time going downhill unless I put out major power efforts to keep up. To test how weight impacts descending without affecting air drag and other variables like wheel mass, I attached a 7-pound weight case from Rock Bar Cycling to my road bike. The weight case has a low profile, so air drag changes are minimal.
Using the case on the bike in solo rides and on group rides, I can attest that adding the extra weight made descending easier and less effort was required to keep up on descents. As the weight impacted descending, in reverse, it made climbing harder. The weight has more of an impact on long climbs than on rollers, where the mass can push you up the early part of the hill.
I have been experimenting with the weight to test how location affects the ride as well. I found that moving the weight higher on the bike affects the ride and effort. When the weight is under the bottom bracket and down tube, less power is needed to move the bike than when the weight is under the top tube. When the weight is increased at the top tube, the effort is a bit harder. I attribute the difference to the slight swaying of the bike as one pedals. As the bike sways from side to side slightly, it takes slightly more strength to keep the bike stable while pedaling.
Using the weight on the bike had positive results as far as strength training goes. The first couple of weeks of riding with the weight on the bike made the ride much harder of course, and I actually felt like I went to the gym to do weight workouts at the end of the ride. After many months of using the weight on the bike, I gained strength quicker doing the same type of rides versus riding without weight.
To test for different variables, I added weight to other bikes types such as a mountain bike and to a 20-inch wheel folding bike. As those bikes are heavier, the weight was up to 35 pounds for the mountain bike and 30 pounds for the folding bike. The road bike was about 25 pounds using one weight case. I did try two weight cases on the road bike, which added 14 pounds. It was really hard on uphill roads and even quite noticeable on flat roads.
One of the interesting outcomes of the testing was that the weight of the bike after adding the weight case under the bottom bracket and down tube did not affect the ride quality of the bike as much as wheels do. The folding bike, for example, still felt nimble and good for climbing. Reducing wheel size or wheel weight really does have more of an impact on ride quality and effort than reducing frame weight as far as bike performance and feel are concerned. I don’t think I would want to add seven pounds of weight to the wheel of a bike.