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Old 05-18-09, 08:54 AM   #1
merlinextraligh
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Time Trial Helmet position

There's lots of data that shows TT helmets reduce aerodynamic drag. My question relates to the aerodynamics of a TT helmet with your head dropped downward. Intuitively, one might think the TT helmet would actually increase drag. However, there is some indication that TT helmets, even with your head dropped are more aero, than a conventional helmet.
http://www.springerlink.com/content/k004r03534n626p1/

Because I'm too cheap to pay $25 to read one chapter of a book online, I thought I'd ask here.


The specific reason for my question is we're doing the tandem division of the State Time Trial championship ( I'm asking here rather than the tandem forum becasue there is a lot more racing knowledge here.)

My stoker in time trial position has her head pretty much straight down, which isn't worth changing given that the stoker doesn't need to see where we're going.

So, is it worth buying a TT helmet for the stoker, knowing that the rear of the helmet is going to be pointed upward the majority of the time. I'm tending to lean that way.

However, given a general a lack of fitness/talent, I don't want to pass up an opportunity to buy speed.
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Old 05-18-09, 08:56 AM   #2
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Couldn't she slide the TT helmet back so that its flush with her back while her head is down? Would look silly, but it'd work.
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Old 05-18-09, 08:57 AM   #3
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Have you looked on slowtwitch? There was some discussion about it there and I *think* John Cobb weighed in. I can't remember the outcome though, sorry.
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Old 05-18-09, 08:59 AM   #4
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If you look at pictures of Dr O'Donnell he subscribes to this.

He has to roll his eyes upward so he can see down the road.
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Old 05-18-09, 09:03 AM   #5
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buy her this.
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Old 05-18-09, 09:35 AM   #6
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I'm not a TT specialist, I'm a tri guy, and I have the Giro TT helmet. It pretty much requires you to keep your head up to maintain any "aerodynamic advantage". The Louis Garneau model appears to allow you to keep your head pointed a little more down.

I've looked into it a good bit, but from what I've gleaned from various forums & articles, the advantage you get is about equivalent to that of a disc wheel (and considerably cheaper).

Just intuitively I'd say that if you put your head down while wearing the Giro TT helmet - you're screwing yourself out of any benefit and probably hurting yourself to boot.
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Old 05-18-09, 10:06 AM   #7
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It's all about the vents.

http://www.trainingbible.com/joesblo...bb-clinic.html
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Old 05-18-09, 10:21 AM   #8
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I recall the thread on ST about this. Cobb said that even looking straight down the TT helmet retained a significant aero advantage over a regular helmet. Not quite as good as looking straight forward, but close, and still much better than a regular lid.
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Old 05-18-09, 11:05 AM   #9
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Originally Posted by Flak View Post
I recall the thread on ST about this. Cobb said that even looking straight down the TT helmet retained a significant aero advantage over a regular helmet. Not quite as good as looking straight forward, but close, and still much better than a regular lid.

I remember that thread and my post to it was something like:

The advantage gained by the tail up position is that the air vents of the aero helmet are now out of play. I forget who originally told me that. May have been on biketechreview.
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Old 05-18-09, 11:53 AM   #10
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I've read a little bit about this. From my limited understanding 2 things come into play. The vents on the front of the helmet and the style back that you have.

Flat backs:
We did test several things and in Brett’s case, because of his flat bike and shoulder shape, he was fastest with the helmet “tail down”.

Rounded Backs:
Another rider that I’m going to show for example, had the more common “B” style or rounded back and he was measureably faster with his head aimed down.

LINK HERE
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Old 05-18-09, 11:57 AM   #11
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Quote:
Originally Posted by K-S2 View Post
I'm not a TT specialist, I'm a tri guy, and I have the Giro TT helmet. It pretty much requires you to keep your head up to maintain any "aerodynamic advantage". The Louis Garneau model appears to allow you to keep your head pointed a little more down.

<a>I've looked into it a good bit, but from what I've gleaned from various forums & articles, the advantage you get is about equivalent to that of a disc wheel (and considerably cheaper).

<b>Just intuitively I'd say that if you put your head down while wearing the Giro TT helmet - you're screwing yourself out of any benefit and probably hurting yourself to boot.
a. Maybe at zero yaw.
b. not as much as you'd think according to some people in the tunnels.
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Old 05-18-09, 02:02 PM   #12
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If your stoker is smaller fairly smaller than you then she (I'm guessing it is your wife) will be in your wake and a TT helmet will probably be a negative (no aero advantage, but a heat transfer, i.e. cooling, penalty). You would probably do better aero-wise by swapping positions on the bike, but it may have marital relations repercussions and no bike race except for a top step on the TdF podium is worth that. (I will not tell you about the one time my wife and I played Bridge when I wasn't her partner. It was before we were married and it almost resulted in us breaking it off.)
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Old 05-18-09, 02:07 PM   #13
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There are definitely arguments for her to be captain. One is drivetrain efficiency. The captain only gets about 93% of power to the hub, where the stoker gets 98%.

Not sure about aerodynamics, given that she can pretty well hide behind me, and I couldn't behind her.

But as a practical matter, its not an option. I'm 6'1", and she's 5'8", and I outweigh her by 70lbs. Given the length of the stoker's compartment, i'd be pretty upright, and more importantly, she doesn't have the physical strength to deal with my weight if we get out of synch.
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Old 05-18-09, 02:23 PM   #14
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Quote:
Originally Posted by merlinextraligh View Post
Given the length of the stoker's compartment, i'd be pretty upright, and more importantly, she doesn't have the physical strength to deal with my weight if we get out of synch.
Then forget the TT helmet for her. It won't help and will probably hurt. Just make sure that you stay low and get as much of an aero advantage as you can. And you can quote me as a UF engineering prof for why you need a might new aero helmet and she doesn't. (PM me and I will explain it to her free of charge if it becomes an issue. Not a professional courtesy, but a bike racer courtesy.)
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