The Specialized video[1] is worth watching - it's pretty funny how astonished they were over how much power it saved.
If you are interested in this, then the book Faster: The Obsession, Science and Luck Behind the World's Fastest Cyclists by Michael Hutchinson is really good (and very well written).
He notes that human intuition about aerodynamics just isn't very good (you have to test) and that the current state of the art is no longer wind tunnel testing but computational fluid dynamics (CFD) followed by testing with a power meter on the road.
CFD lets designers iterate much quicker on designs and try things outside the norm (avoiding the local maxima problem). Power meters plus riding is better than wind tunnel testing because things like variable cross winds are very hard to test in wind tunnels.
The annoying thing with CFD with analyzing viscous phenomena is the question of reproducibility. Flow structures in this regime (low Re, that is low speed and small length scales) are notoriously sensitive to surface defects, e.g. the hairs being analyzed. A CFD sim will show nearly the same results for a given problem, and current CFD lacks the fidelity to really model tiny turbulent features at these scales as well as the necessary fine surface definition. Experimental results may show drastically different results depending on the minute upstream flow variations, and surface quality: in this case, legs with hair/sweat/dust/oils could all trip the boundary layer to varying degrees. Stories abound of clumsy wind tunnel technicians who left skin grease on a wing model for a low-speed test and neglected to polish it with a rag...
I had thought that it was already established by swimmers that hair was a detriment to speed. Why would it be surprising to cyclist? I do ride, but not competitively so I will keep the razor to my face only, thank you.
Exactly this, its already well established that skin hair causes drag. Firstly it acts as insulation. Secondly, it works remarkebly well to evaporate sweat and being originally savanna dwelling primates that endurance hunted our pray it would only make sense that drag not only exchanged for, but contributes directly to our ability cool our body temperature.
> The tests showed that shaving his legs reduced Thomas’s drag by about 7 per cent, allowing him to exert 15 watts less power and still go at the same speed. In theory, that translates to a 79-second advantage over a 40-kilometre time trial that takes about one hour.
Shaving reduces the drag, but the originally study measured the reduction around 0.6 percent while this one found a 7 percent reduction. So, about 10 times bigger than anticipated.
When I read this "Even more confounding was that the results contradicted earlier findings" it totally colored my reading of the article. (Emphasis mine.)
One thing they don't tell you in the Specialized video is that they're not testing someone who is pedaling. There's some much more turbulence from just moving your legs, that shaved or not shaved makes almost 0 difference. No one is coasting for 40 km. Even the time savings they do cite in perfect, almost platonic conditions is seconds over hours of riding.
Bicycling manufacturers always skew the numbers for how much savings (time, watts, whatever) their new top of the line frames will give you. It's all smoke and mirrors.
One thing they don't tell you in the Specialized video is that they're not testing someone who is pedaling.
This isn't true. Watch the video - he's pedaling when they test.
There's some much more turbulence from just moving your legs, that shaved or not shaved makes almost 0 difference.
That's almost exactly wrong. It's true that pedalling creates turbulence, but the speed your legs move and the turbulence created by that movement is almost entirely disguised by other effects.
For example, the fact a bike is asymmetrical (because of the drivetrain) is a much bigger factor than turbulence because of moving legs.
It is important that testing includes pedaling, because there can be particular positions that work better on some bikes (or for some people) than others.
But in this case the testing used sensible protocols and the difference is a real thing.
Bicycling manufacturers always skew the numbers for how much savings (time, watts, whatever) their new top of the line frames will give you. It's all smoke and mirrors.
That may be the case, but all Specialized is selling here is their aerodynamic expertise (at least until you can buy a Specialized razor blade).
IMHO, you're absolutely nuts to believe a bike company, when it comes to these sorts of things - that's what an independent research company is for - or at remembering a basic part of experiments: it needs to be reproducable (and then verified) - this "shaved legs" hasn't seen that.
Specialized has something to sell - their business practices, especially with their trademark protection, has been ridiculous, which has been a turn off to people who think clearly.
The market for high-end bikes are people who can afford the bikes, which is usually not the people who would see any difference in buying the $2k bike, rather than the $15k bike. Specialized really doesn't want you to understand this, so they make wildly exaggerated claims about their equipment. People who benefit from fractions of a percent better performance usually are people who are sponsored by the bike company (and thus, get the bikes for free). A difference of a few seconds, over a 50km course makes sense for the elite time trialist, in the Pro tour, it makes 0 difference to your weekend warrior, doing an hour long crit.
Who the heck am I? I'm someone that rides bikes, often for very long distances, to break records (which I do). Don't believe the hype, unless you don't especially have an interesting in holding onto your money.
I'll concede only that my views are unpopular, but that certainly doesn't mean they're incorrect.
I agree you need to be very careful when you evaluate claims by manufactures. Independent testing is very hard to find, too (outside the German Tour magazine which does a decent job).
But in this case it is unlikely their findings are particularly biased. It's worth noting that the point of the original article was that the Specialized testing actually verified an earlier finding that hadn't been tested properly since.
> One thing they don't tell you in the Specialized video is that they're not testing someone who is pedaling.
Yes they are. Chris Yu (running Specialized's wind tunnel; the only bicycle company with their own) is a CalTech/Stanford trained aerodynamicist and competitive cyclist. Give him some credit.
ah, that makes much more sense. If they had been pedaling I was wondering how they got rid of bias since it would be pretty hard to blind the rider as to whether their legs were shaved!
Another cycling company, Trek bicycles, has a pedaling mannequin that they use for some of their wind tunnel tests([1] page 14). That's an older report (2010), but they have another from 2013 if you're interested in that stuff[2].
In this case they measure the wind resistance of the rider directly in the wind tunnel. The fact the rider knows their legs are shaved doesn't seem to be a factor in that measurement.
If you are interested in this, then the book Faster: The Obsession, Science and Luck Behind the World's Fastest Cyclists by Michael Hutchinson is really good (and very well written).
He notes that human intuition about aerodynamics just isn't very good (you have to test) and that the current state of the art is no longer wind tunnel testing but computational fluid dynamics (CFD) followed by testing with a power meter on the road.
CFD lets designers iterate much quicker on designs and try things outside the norm (avoiding the local maxima problem). Power meters plus riding is better than wind tunnel testing because things like variable cross winds are very hard to test in wind tunnels.
[1] https://www.youtube.com/watch?v=DZnrE17Jg3I
[2] http://www.amazon.com/Faster-Obsession-Science-Fastest-Cycli...