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Old 09-23-13, 08:17 PM   #1
Creakyknees
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time trial headwind/tailwind formula

Ok geeks, have at it:

"On a closed track against a powerful head/tailwind, what racing strategy should a cyclist adopt? One engineer has derived a simple rule-of-thumb that gives the answer "

http://www.technologyreview.com/view...ilemma-solved/

arxiv.org/abs/1309.1741
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Old 09-23-13, 08:50 PM   #2
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Conventional advice is to go a bit above threshold into the wind, and recover slightly down wind. His answer seems basically consistent with that.

However, without diving into his model, it doesn't appear that he considers the match burning effect of going over threshold. In other words he just assumes as long as the average power is the same it doesn't matter wether its all at FTP, or half above and half below.
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Old 09-23-13, 10:29 PM   #3
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I agree that one can't just say you have x total power to use. But perhaps one could use training power data to come up with an excess energy curve as a function of time. Or as a function of time and time over power y. Or something along those lines.
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Old 09-24-13, 07:27 AM   #4
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Yeah, the (incorrect) "fixed amount of energy to spend" thing is an assumption that greatly impacts the accuracy of anything else he does. He's also oversimplifying the "essentially three strategies," and the third one is too broad. Lastly, it's absurd to assume that the wind at the start of the race has anything at all to do with the wind out on the course, up to an hour later, or even minute later.

The general strategy is sound (go harder when it's hard, and easier when it's easy), but the assumptions render anything beyond that useless.
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Old 09-24-13, 09:25 AM   #5
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The general strategy is sound (go harder when it's hard, and easier when it's easy), but the assumptions render anything beyond that useless.
speed = distance/time. distance = integral(velocity). both rolling and wind resistance increase with velocity, so very simply it's best to expend your energy in the "slow" parts, be they uphill or into a headwind. More speed-bang for the watt-buck, so to speak.

how much over threshold vs. under is going to vary with each rider.
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Old 09-24-13, 10:09 AM   #6
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speed = distance/time. distance = integral(velocity). both rolling and wind resistance increase with velocity, so very simply it's best to expend your energy in the "slow" parts, be they uphill or into a headwind. More speed-bang for the watt-buck, so to speak.

Accelerations out of corners and turnarounds too. You pretty much want to minimize any of your time going slow, and maximize your time going fast (which sounds silly, but is pretty much what we're talking about).

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how much over threshold vs. under is going to vary with each rider.
It's also going to vary with each course and each gust of wind.
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Old 09-24-13, 10:28 AM   #7
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Accelerations out of corners and turnarounds too. You pretty much want to minimize any of your time going slow, and maximize your time going fast (which sounds silly, but is pretty much what we're talking about).
^^ yes. I was indicating that the article is silly. There's a limit to power, and cycling has diminishing returns as speed increases so it's always better to minimize the slow period. Author's calculations miss a lot of things, but the principle is sound (and same as conventional wisdom) so precise calculations are unnecessary (and would be impossible) anyway. Regardless, I think we're all on the same page.
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