Need Boardman's drag coefficient & frontal area

Discussion in 'Cycling Training' started by wwuster, Sep 29, 2006.

  1. wwuster

    wwuster New Member

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    I'm trying to calculate the watts vs speed curve for Chris Boardman. I've read conflicting information about his constants for the 1996 hour record.

    watts = .5*rho*Cw*A*v^3 + M*9.8*Crr*v

    I have rho as 1.226 kg/m^3. I've read that his frontal area at that time was .34 square meters but I'm not sure if that is accurate. v is measured in meters per second. I've also read that his weight was either 67, 68, or 69 kg and the bike weighed 7.15 kg (http://www.bikecult.com/bikecultbook/sports_recordsHour.html). This web page also says that his Cw is .165. I would like to verify that these constants are correct since this is the only page that I've been able to find that says what these constants are. Also, does anyone know what value to use for Crr? I was thinking that .004 would be the value for the wood floor at Manchester.

    thanks,
    William
     
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  2. acoggan

    acoggan Member

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    No need to reinvent the wheel, really. Peter Keen has already provided an estimate of his average power during that hour as being 442 W, and you can find his entire power-velocity curve in an old article in one of the British magazines.

    As for the CRR for a wood track, it's probably closer to 0.002...
     
  3. acoggan

    acoggan Member

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    BTW, that equation isn't entirely complete, as you're missing terms for chain and bearing friction...the latter really isn't significant, but the former clearly is.

    EDIT: an additional note: it's worth keeping in mind that the Cd that you derive from performances on a circular track tend to slightly underestimate the true value, since you get credit for how far/fast your wheels travel, not how far/fast your center of resistance (i.e., torso) travels.
     
  4. doctorSpoc

    doctorSpoc New Member

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  5. acoggan

    acoggan Member

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    Actually, if you look at Eq. 1 there you'll see that Jim simplified things by leaving out the bearing and chain friction terms (which make a minor contribution). The complete equation is in our paper:

    Martin JC, Milliken DL, Cobb JE, McFadden KL, Coggan AR. Validation of a mathematical model for road cycling power. J Appl Biomech 1998; 14:276-291

    (Posting just so people understand the origin of things...)
     
  6. wwuster

    wwuster New Member

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    For now I was intentionally ignoring the chain drive / bearing term since I don't yet know what it should be and it is relatively minor. I'm also ignoring headwind / tailwind and grade factors. I want to see the curve for Boardmans hour record where I think that the grade and wind would be 0.

    I've put together a graph here with the curve and constants that I used. Do these constants seem to be the correct choices?

    http://geocities.com/wwuster/boardman.jpg

    It would be nice if someone could post the info about the chain drive / bearing term, since I haven't been able to find that yet. I think that I've seen a reference that this is a function of the square of the speed. Is that right?

    thanks,
    William
     
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