asgelle

Shaved Legs = 15 watts? (Page 7): Triathlon Forum: Slowtwitch Forums

So based on Coggan's rule of thumb ~20W, 80 sec for a 40 K.
https://forum.slowtwitch.com/gforum.c...thumb;#5096025

sced

The classical equations learned in engineering school are generally very, very poor predictors of phenomena of any complexity, as are controlled experiments that ignore the effects of all the variables that significantly affect a system's behavior under a broad spectrum of realistic conditions. The video should be considered at best only suggestive and nothing more. The real way to determine true or false on the leg hair thing would require a lot of field testing that accounted for the interactions of perhaps a dozen or more variables and then teased out the leg hair effect in this broader context. There is no other way.

asgelle

Don't you hate how one datum can destroy a beautiful hypothesis? Whatever you say about generalities, in the case of the bicycle performance model, literally hundreds of field tests have confirmed its accuracy. The same goes for wind tunnel measurements of CdA. You can list all the reasons why it shouldn't work, but that all falls apart in the face of the fact that field testing proves it does. As shown above, field test results are coming in and they are in line with the wind tunnel predictions.

Dunbar

I wonder if you need to shave your legs to save the watts? What about just slicking the hair down with sun screen or lotion?

Brad W

I just finished a 22 mile ride with a 16 mph average then for lunch I ate a burger and onion rings that weighed in at 2000 cal. and 2500mg sodium. Do you think if I shaved my legs it would negate the harm I've done to myself?
I'm feeling some guilt.

Brad

wphamilton

I saw a video in the 33 version of this thread where they checked the beard vs no beard. One second in a time trial, so don't bother shaving the beard.

But they asked for more questions, even those not involving body hair. Someone suggest socks. I want to know if socks slow you down. And shoe laces. I would ask myself but no one listens to me ...

sced

You can keep hand waving or revisit the scientific method. Lots of people confuse model predictions with reality - they are not the same at all. All models are wrong to some degree and at most the leg hair thing is a minor effect that could easily be confounded by other variables. Without credible confirmatory field data that video is forever speculative.

asgelle

Did you miss Kraig's test data or are you saying he isn't credible?

rpeterson

I went and tested arm hair today for the fun of it.

Saved me 4 watts, pretty interesting.

dwmckee

Nice to see actual science here instead of endless opinions. But alas the opinions still have to voice.

Wind tunnel testing, if done properly can lead to very predictable conclusions about real world results. That is why there are so many wind tunnels still in use today. I am an aerospace engineer and I can tell you that there are literally millions of hours of useful wind tunnel testing that have produced reliable predictions of real world impact.

dwmckee

The more common scientific approach would be to control all variables except one then test that way, not to test with a bunch of variables changing then trying to tease out the impact of changing one variable. This single variable approach is the engineering innovation that brought the Wright Brothers to success in designing the first practical aircraft. They changed only a single variable at a time to determine the impact on their design. Lilienthal and Langley in contrast often changes 10 or more variables at a time in developing competing aircraft designs, and failed miserably in the process.

dwmckee

Wow, that is a big statement. Do you have any examples to support this? I mean, I use my engineering equations all of the time to design real world structures and systems. If these things do not work, well, why are all of the bridges still standing and are aircraft producing predicted improvements in efficiency and, well, how does anything work as designed?

And this is really just a rhetorical question, no answer required...

wphamilton

The Jacobs laminar-flow airfoil design comes to mind ...

DXchulo

The sock thing is interesting because you'll see guys wear long sleeves in a TT, but not the same materials in a leg-warmer type of setup on their legs.

FLvector

+ 1,000

FLvector

Not many cycling shoes use shoe laces, but the straps/buckles must be enough of a concern that you'll see many racing in TT's wearing shoe covers to be more aero.

sced

What about DOE? What about systems affected by uncontrollable variables?

sced

Pardon me. Yes, there are lots of formulas and canned computer programs out there for ably predicting/designing all kinds of things, but I was thinking about chaotic/non-deterministic systems, like biking in all kinds of road, weather conditions etc.

1986raleigh

Now that the is almost over, here is my take.

I can prove that a 5 mph 90 degrees consistent cross wind will push a 168 grain areodynamic bullet with a certain BC traveling 2600 fps off a straight course by 1 1/2 inches in a distance of 300 yards traveled.

I do not doubt if I took that areodynamic bullet and put a few little hairs on it that it would definately change the wind effect (BC), I suspect it would slow the bullet, causing more effect to the cross wind in the same distance traveled. Ballistic coeffecient is a clearly measurable, preditable and totally repeatable measure of how bullets in flight react.

My conclusion is thus, I believe hairy legs and arms have a areodynamic effect on the velocity of a cyclist, how much is up for debate.
That being said I still ain't shaving my legs.

My boss says he keeps his arms and legs shaved because it allows more efficient cooling by allowing sweat evaporation to occur faster, I may shave for that but I gotta think about it a while....

himespau 

Never been interested in shaving in the past for any reason, but, as I'm covered in chigger bites from toe to waist (and above - chigger bites on sensitive areas like nipples and other areas are the worst) and seeing how the Caladryl clear just gums up in the hair and crusts over rather than efficiently reaching where it needs to go, I'm considering it. Couldn't care less about the aero benefits though.

bbattle

They are meaningful only in the theoretical sense. Extremely unlikely road conditions will ever approach wind tunnel conditions so the data is only suggestive.

bbattle

No! Not a skullet!

therhodeo

Does no one else shave just because they think it looks better?

merlinextraligh

Wind tunnel tests on aero equipment are typically run at 50km speeds. Its not an unreasonable speed to test given that elite athletes will be TTing that fast, and even non elite time trialers will be close to that speed for portions of a 40k.

Wind tunnel results using this protocal are verified every day in the real world by riders using the equipment so tested.

And it does scale. If you ride slower than 50km, your time savings actually go up. The smallest time gain was 50 seconds for a 50 minute 40k. Apply that to a rider doing a 60 minute 40k, and the time gains go up to 81 seconds. (See the author's comments).


I'm skeptical enough to believe that there may well be some differences applying the data to "the real world". However, given the dramatic time savings for all 6 riders, there's pretty good reason to believe that there is a measurable advantage in the real world, and it is virtually free speed.

2 seconds a KM is pretty irrelevant on your average club ride, but even 1 second a KM may be worth 10-20 spots in a typical TT.

achoo

I wonder if all the thousands of owners of wind tunnels the world over know their **** don't work because YOU say so.