Unless you're only doing a small number of reps with each setup, it's very unlikely that someone with poor test protocol will find little to no difference between two setups. Suppose two setups differ by 10W, and someone does 4 reps per setup, and they all come out at around the same CdA. That would require 4 reps to have a random error of almost exactly 10W, while the other 4 were all spot on, or some similar alternative way of getting the same result. It's really very very unlikely. How poor test protocol typically manifests is with implausibly large differences between setups, because if your distribution has a large standard deviation the likelihood of the sample mean being a long way from the true mean is quite high, even with e.g. 4 reps per setup. If someone frequently tests changes and keeps finding only small differences between things, it's most likely that their testing is pretty good, whereas if someone keeps finding large differences between everything they test, it's most likely that their testing is poor.

Another way to get a handle on the your test protocol quality is take the "Tom Compton Challenge" :-)

http://bikeblather.blogspot.com/...ng-chung-method.html

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http://bikeblather.blogspot.com/

All I am saying is that there seems to be some pretty good evidence that shaving legs saves you a few watts. Looking at the pictures, it is pretty clear the time savings does depend on position but the data shows a savings nonetheless! I don't buy 15W but while everyone quibbles about how many watts that might be based upon position or chewbacca factor, shaving your legs = FREE SPEED. Keeping track of all the little details does add up!

Looking forward to seeing what other studies these guys do in their spare time in the wind tunnel!

This is why scientific papers are peer reviewed by anonymous referees that are expert on the given field (though that system is not perfect either and there are lots of abuse).

Maybe that result is correct, maybe not, I'm not familiar enough to pass on a judgement, I would love other experts to reproduce the experiment and analyze the data independently.

Verry interesting! I whanted to test it on several occasions but in the end I allways didn't have the time and the mood to shave my legs in the velodrom. Anyway, I will ckeck it the next time on the track in automn or spring. Anything bigger than 5W at 45 km/h should be no problem with our protocol.

I ask me whether it is due to a boundary layer phenomenom? Or how do the aerodynamic Experte call it, drag crisis? The answer could give a cda measerement with variing air velocity.

One comment to peer review process. I get a paper to review about every week, guess how good I can do my job? I also get back lots of papers of your research group from reviewers in order to correct them. There are many stupid reviewers out there!

http://www.trainingandracingwithapowermeter.com/...aerodynamicists.html

Is that your way of telling me my link was broken? All fixed now, thanks! ;-) I link to your blog post pretty early on in that...

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http://bikeblather.blogspot.com/

I'll be in the parking lot just east of here tomorrow morning (7/5) at 5:30 am with a razor:

33.1256658,-117.1579207


I'll be doing a small # of reps. this is what I will execute on my TT bike with both PT and SRM installed:




1) baseline ~50 psi lower tire pressure
2) hoods/sitting up
3) baseline

...shave...


1) baseline
2) hoods/sitting up
3) baseline ~50 psi lower tire pressure


if you are local, come out and join me. i'd be happy to help reduce your power meter data using the WLB method and chat about anything else you'd like to. runs will be 2 slow laps, 3 fast, 2 slow. I'll have cones out to help maintain lines - hopefully the wind will be calm. Should take a little over 75 minutes to complete things.


cheers,
-k


PS - I'm a 7/10 on the sasquatch scale - not sure how this compares to the wookie scale, though

PPS - I did some preliminary sniffing on this topic here - if it is this big, it should be detectable via field test. i'm curious to see what sorts out!

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Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
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I shaved my legs in a parking lot...



I had to cut the last one short because there was a motorcycle riding class trying to set up, and overall not my best most cleanest riding (it's been maybe 5 years since I was on the TT bike!?!). Also, conditions were not perfectly dead calm, and I should have started 30 minutes earlier (sun came up and warmed up the pavement). I'm not super happy with Crr values as a result. But, these data are what they are. If someone wants the SRM file and PT file to do their own analysis we'll figure something out.

Who's next to test the shaving claim?

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Kraig Willett
http://www.biketechreview.com - check out our reduced report pricing
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So shaved legs = faster, but I don't know how to convert your numbers into watts or time.

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/kj

http://kjmcawesome.tumblr.com/

What he said ^^^

If CxA is aero drag then it looks like the tests ranged from around 2% to 7-8% drag reduction?

Here's my "test" from today. Last week I rode a 50 mile TT, and this week I rode a 25 mile TT on the same course against many of the same competitors. Conditions were much slower today due to wind speed and direction, so I don't think there is much point comparing aerolabbed CdAs, but for the 50 I had perhaps 3 months of hair growth on my legs, and I shaved them for today's 25. I took the gaps to all the riders in the top 15 of the 50 who also rode the 25, and halved them to compare against the gaps in the 25:
Rider 1: 3:56 unshaved, 2:50 shaved, swing = 1:06
Rider 2: 0:31.5 unshaved, -0:07 shaved, swing = 0:38.5
Rider 3: -0:22 unshaved, -0:32 shaved, swing = 0:10
Rider 4: -0:23 unshaved, -0:29 shaved, swing = 0:06
Rider 5: -0:24 unshaved, -0:47 shaved, swing = 0:23
Rider 6: -0:32 unshaved, -0:33 shaved, swing = 0:01
Rider 7: -0:46 unshaved, -1:10 shaved, swing = 0:24


So I performed better today relative to everyone in the top 15 who rode both events, with a swing ranging from 1 second to 66 seconds per 25 miles. The mean swing was 24 seconds.


My NP for the 25 mile TT was 7.4% higher than for the 50 mile TT, which I'd have thought would be reasonably average for relative power.


Obviously I'm not claiming this is particularly strong evidence, it was just something fairly simple to look at.

The reported numbers imply a reduction in both air and rolling resistance after shaving. Not sure how much Crr would really have changed, and normalizing for that would amplify apparent aero changes. So there's likely other things going on with the data. Environmental, positional, power measurement controls. As well as a real effect of course. Crr calcs can sometimes be pretty sensitive to minor measurement changes.

> air and rolling resistance after shaving.

OK, now someone do an FTP test after shaving. I bet it increases FTP by another 15W.

There's no such thing as "Free Speed". Or "free lunch".
It's called "opportunity cost" in economics.

Shaving takes time and commitment. Once you commit you have to keep doing it, regularly. It itches. You get ingrown hairs.
All this time and effort can be put to other things. Like training. Or family time. Or work.

Therefore it matters whether the savings are 7%, as Specialized claims. Or if it's 0.6% as previous research indicates. Or maybe less.

Frankly, the 7% numbers seem way high to me. Many of us have a gut feeling for what 7% in drag or power savings feels like. So it's 7% for shaving legs, probably another 5% for shaving arms. Really?! That doesn't sound wrong to anyone? Think about it. To save 7% on the climb you need to lose like 14 lbs. But shaving legs can do that for you in ITT?!

So then when riders who don't shave put on leg warmers they all of a sudden drop all others by huge margins - 7% and they never realized it? When Specialized testers found this amazing result, have they bothered to test leg warmers?

Extraordinary claims require extraordinary proof. I will wait till other labs reproduce the results but this doesn't pass a gut-check.

The "opportunity cost" of shaving? Seriously?

God this place is ridiculous sometimes.

I've never shaved either. Not a fan of the idea. But rather than waiting for sixteen peer-reviewed, double-blind, wind-tunnel tests, I'lll probably just try it and do a few TTs that I've done without saving and see what happens. One or two aren't enough but in the aggregate, it shouldn't be that hard to see if there's actually a significant savings.

Why? Why not just shave before races?

Unless you can "feel" the results of the Navier-Stokes Equations, I'll take measured data in a wind tunnel over what someone "feels"

Fluid flows are incredibly complex, and often times are counter intuitive. We may intuitively understand things like the motion of a projectile, but fluids are not intuitive, especially compressible flows like air moving around a moving rider.

It all makes sense to me now. I always used to think any good race results I had were due to training and a moderate amount of talent.

Now I know it is simply due to the fact that my legs are naturally almost completely hairless. (We are talking about .01 on the Chewbacca scale. ) My wife envies me.

Not the best result in the genetic lottery, but at least I got something.

https://www.youtube.com/watch?v=DZnrE17Jg3I

We all deal with Navier-Stokes every day when we ride our bikes. You don't need wind tunnels to tell you that when you tuck in behind another rider or when you are in the drops you have less drag. Or do you?

Sure, I will believe scientific results. But which ones? The ones that say leg hair is worth 0.6 percent, or the ones that say it is 7%?

What's really much more disturbing to me is that these tests are an order of magnitude off. How can we believe anything if for whatever reason (protocols, etc.) the same experiment comes off different by a factor of 10? Makes me question any wind tunnel tests. It's like if you go to one doctor and he says - you weigh 160 lbs. But then another one says - my super-precise scientific measurements say you weigh 1,600 lbs, yes, I was surprised too, but... science!

Would you trust any doctor after that?

The three minutes it takes me to shave from waist to ankles every couple days pays dividends from the GF, don't care what it does for speed or not.

Also I like looking at my legs.

All talk, and no game.

You don't evaluate studies based on results; you evaluate them on test protocol and methodology, and sample size. Hint: when you have a small base, ratios can be really big. And you're comparing gross measurements to to % change? And you think drafting and drops are only 7% decreases in total drag?

Do us all a favor and go back to figuring out the difference between "to" and "too" instead of trying to analyze studies.

Key point is comparison. When you tuck behind a rider, you feel the difference. You compare somebody's wake to free-flowing air.

So until you start shaving mid-ride, this analogy doesn't really hold water.


And that's before we consider that 30% >> 1-7% and how imprecise we are in evaluating these changes based on feel.

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ZONE3 - We Last Longer

"All this time and effort can be put to other things. Like training. Or family time. Or work."

..how long does it take you to shave? man I'll knock it out in 5minutes..enter in log as "Active Recovery"..

cheers
S.

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// qui audet adipiscitur