September 20, 2014 Login  


these newfangled aero helmets...
Last Post 04/22/2014 04:16 PM by Keith Jackson. 95 Replies.
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Cosmic Kid

Posts:1105

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03/30/2014 08:08 PM
Posted By Keith Jackson on 03/30/2014 03:42 PM
Specialized helmet Powerpoint slide is equally misleading as the differences in terms of drag coefficient are so minute that they are easily overcome by other more important aerodynamic factors.


You are gonna have to back that claim up, Keith....please show me examples, backed up by data, where the aero advantages of an aero helmet are overcome by other aerodynamic factors.
Just say "NO!" to WCP!!!!
Orange Crush

Posts:1179

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03/30/2014 08:25 PM
Posted By Cosmic Kid on 03/30/2014 08:00 PM
@ OC:

"OK, show me some data"

*shown data*

"No, I don't like that data."

I can post umpteen white papers showing the aerodynamic advantage of aero helmets and you are just gonna say the same thing.

The data is there....I can't make you accept it.

Give me those umpteen white paper then...if they are good then I will accept them. 

I gave you the MIT data and the inferences that can be made from it...5W, not 20W.

You said you did not like that data but gave no actual reason. Who is calling the kettle black?

The MIT study is independent peer-reviewed. The Specialized data is what? Come on


http://dspace.mit.edu/bitstream/handle/1721.1/40486/191803811.pdf

http://www.biketechreview.com/index.php/blog/551-specialized-evade-aero-helmet-claims

The data is there, I can't make you accept it.



Orange Crush

Posts:1179

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03/30/2014 08:30 PM
Posted By Cosmic Kid on 03/30/2014 08:08 PM
Posted By Keith Jackson on 03/30/2014 03:42 PM
Specialized helmet Powerpoint slide is equally misleading as the differences in terms of drag coefficient are so minute that they are easily overcome by other more important aerodynamic factors.


You are gonna have to back that claim up, Keith....please show me examples, backed up by data, where the aero advantages of an aero helmet are overcome by other aerodynamic factors.

Actually, one of those guys working that damn MIT tunnel had this to say (they worked with Ivan Basso amongst others):

"How you put your race number on matters more than having an aero wheel; today, we glued on our numbers to get them to fit flatter. Then there's water bottle placement: On a round-tubed frame, having a bottle on your seat tube is more aerodynamic than not having one at all, and it's much more aero than putting it on the down tube. And wearing gloves in a time trial will slow you down more than using a nonaero front wheel."
Cosmic Kid

Posts:1105

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03/30/2014 08:40 PM
All those things are mutually exclusive of an aero helmet. Keith said that the advantages of an aero helmet can be "easily overcome" by other factors.

What factors overcome the advantages of an aero helmet?
Just say "NO!" to WCP!!!!
Cosmic Kid

Posts:1105

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03/30/2014 08:55 PM
Sorry, I confused the MIT w/ the Harvard study from years ago...I get those brainiacs mixed up all the time.

So in a study from 2007, they concluded that the "best" helmet offered an advantage for a recreational rider of between 9 - 14w (yaw dependent). Now, leaving aside the fact that the aerodynamics of helmets have improved in the last 7 years, let's go with that. Again, you guys must have powers spare if you can afford to cough up over 10w to the competition.

But from their conclusion:

by wearing an aero helmet, a rider can save a considerable amount of power and can also substantially reduce their overall drag.


Isn't that what I have been saying? I think it is.....
Just say "NO!" to WCP!!!!
Orange Crush

Posts:1179

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03/30/2014 09:00 PM
Lots of things CK...these guys explain it just nicely

http://cozybeehive.blogspot.ca/2009/01/further-explorations-in-aeroness-what.html

Cosmic Kid

Posts:1105

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03/30/2014 09:21 PM
No, sorry....they didn't test the "Jordan tongue" facial expression. Incomplete data.
Just say "NO!" to WCP!!!!
Keith Richards

Posts:735

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03/30/2014 09:34 PM
I have another problem with your "mutually exclusive" statement. Because they are not. When we do experiments at my job we use this term called an "aggregate" and we use to get a better picture of things. We talk of it in terms of risk, but the same thing applies here. You just cannot separate the various aspects of aerodynamics on an object they way you are. It paint an unrealistic picture. I will give you an example from cars and then one from cycling to make what I am saying more clear.

When aerodynamics started being taken seriously in NASCAR they suddenly had a problem with cars going airborne when spun as the same thing that kept them on the ground in the wind tunnel turned them into airfoils once the cars started spinning.

Just today in Ghent, I was watching as guys sat up and TURNED their head around while using these new aero helmets. At 25-30mph. The aerodynamic tails were sitting up like sails in the wind.

The irony is that it made me realize that at least Giro addressed the fact that a helmet on a cyclist is going to be subject to winds coming from different angles and that a TT type profile for a mass start helmet will end up causing as much trouble as they would fix aerodynamically.

But the thing still looks terribly hot on a long August day in the mountains.
----- It is his word versus ours. We like our word. We like where we stand and we like our credibility."--Lance Armstrong.
Cosmic Kid

Posts:1105

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03/30/2014 09:46 PM
They are mutually exclusive because they are not caused by you wearing the helmet. If you are gonna tug in your shorts, you are gonna tug on your shorts. The aero helmet is still faster when you tug in your shorts.

As for those guys turning their heads, that is exactly why they have been designed the way that they have....but let's take the extreme example - and Evade (which has a small tail) turned 90* for a second or two. That doesn't "overcome" the aero gains the rider has been experiencing the whole day....even if they turn their head multiple times during the race. Every minute you are wearing an aero helmet, you are saving power. Those advantages are not negated by a moment's glance to the side to check on your competition.

Just say "NO!" to WCP!!!!
Orange Crush

Posts:1179

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03/30/2014 10:23 PM
Am I the only one who finds it funny that while helmets may be the relative holy grail in cycling aerodynamics (I agree with that much), of course the powers that be first had to sell us those posh aero wheelsets and frames at much higher market value for considerable less effect (4x less at 10x price). Apparently the $ drive was greater than the innovation drive. It has been known for considerable time that the cyclist is a much greater drag than the bike

And it doesn't hurt to take a step back and realize that words like "substantial" and "considerable" or "significant" should be seen within the context of the limitations of improving cycling aerodynamics, which is unable to escape the T-Ford age.

T-ford age car: Cd = 0.7-0.9
Bike Racer: Cd = 0.88
Modern Car: Cd = 0.2-0.3
Time trialist: Cd = 0.7

And again, if I am to believe the MIT guys then our aerodynamics holy grail is about as important as glueing on your race number, ditching your gloves, and by all means shave.

OK, I extrapolated that last one

Cosmic Kid

Posts:1105

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03/30/2014 11:45 PM
Well, to be fair, until last year your only choices in helmets were a road helmet or a full-on TT lid (and really there weren't many viable TT lids until 2004). The idea of an aero road lid is very new. No one had thought of it before.

One additional thought re: riders looking around. Again, that is not caused by the type of helmet they are wearing. So you can't say that those actions negate the addy amid benefit of the helmet....unless you compare what they drag would be while wearing a standard road helmet. My guess (and it is admitedly just a guess) an aero road lid, fee men with a tail, is going to be more aerodynamic than a standard road lid when Travelling perpendicular to the wind, simply because you don't have vents to increase drag.
Just say "NO!" to WCP!!!!
Ride On

Posts:433

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03/31/2014 06:58 AM
It comes down to do you believe the numbers being presented or you don't. None of us have enough access to the data or testing to really know.

For me I tend to view data from a company that is trying to sell me something with a grain of salt. Not that they are out right making it up but that they are also not supplying me all the information. I understand they want to make a buck and to do that they have to present the data in a way that makes their product look good.

CK is on board with the data. I'm ok with that.
Cosmic Kid

Posts:1105

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03/31/2014 10:58 AM
More data to be dismissed ....Road Bike Action did a test of aero helmets (both road and TT versions). CdA numbers are below:



Note that the Evade is damn close to the CdA of some full aero lids. Rule of thumb for converting into time saved is .005 CdA=50gr drag=5 watts=.5sec/km. So, in this case the Evade would represent about a 40" time savings over a 40K TT, or 10w power savings.

Note - this data was for a single rider on a velodrome.
Just say "NO!" to WCP!!!!
Orange Crush

Posts:1179

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03/31/2014 11:34 AM
10W is a lot closer to the evidence I presented than the 20W you claimed earlier. I consider this a small victory for science and reason
Cosmic Kid

Posts:1105

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03/31/2014 12:09 PM
Meh....Plenty of tests still out there that show higher numbers....

And knowing how RBA has conducted tests in the past, I'm skeptical of their testing methods, but I'm more than willing to toss the data out there.

My own experience is more along the 20w number going from a Specialized Prevail to a Giro Selector. But the actual results will always be highly individual....but I have yet to see any tests that show either no, or a insignificant, gain in power.
Just say "NO!" to WCP!!!!
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