Power to Weight Chart?

Discussion in 'Road Cycling' started by [email protected], Mar 16, 2006.

  1. Does anyone know of a chart that shows how much additional speed can be
    expected upon a given reduction in weight, assuming power and other
    variables remain constant? I seem to recall hearing about Johan
    Bruyneel running such numbers pre-1999 on Lance's power to determine
    how much weight he'd need to lose to win the Tour. There would be some
    imprecision based upon the reality that body drag is likely to decrease
    from weight loss, but there should be some good approximation. Anyone?
     
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  2. Ron Ruff

    Ron Ruff Guest

    In a nutshell, on steep climbs your speed will be a little less than
    proportional to power to weight ratio. In other words increasing P/W
    (that is total weight) by 10% will get you maybe 8-9% faster speed. On
    the flat, weight hardly matters... P/CdA being the more important
    consideration.
     
  3. Donald Munro

    Donald Munro Guest

    gkaton wrote:

    > Does anyone know of a chart that shows how much additional speed can be
    > expected upon a given reduction in weight, assuming power and other
    > variables remain constant? I seem to recall hearing about Johan
    > Bruyneel running such numbers pre-1999 on Lance's power to determine
    > how much weight he'd need to lose to win the Tour. There would be some
    > imprecision based upon the reality that body drag is likely to decrease
    > from weight loss, but there should be some good approximation. Anyone?


    I seem to recall Lafferty's Italian friend has a theory using a term
    called VAM to measure climbing speed improvement vs weight. Its probably
    on 53x12.com (but the secret subscription site 55x11.com might also have
    some orange juice on sale).
     
  4. Phil Holman

    Phil Holman Guest

    "Ron Ruff" <[email protected]> wrote in message
    news:[email protected]
    > In a nutshell, on steep climbs your speed will be a little less than
    > proportional to power to weight ratio. In other words increasing P/W
    > (that is total weight) by 10% will get you maybe 8-9% faster speed. On
    > the flat, weight hardly matters... P/CdA being the more important
    > consideration.
    >

    Yes, but there is a general correlation between weight and CdA. In
    theory, surface area will increase to the 2/3 power of weight increase.
    For a 10% weight change, the drag will change by approx 7% and the speed
    by 3.5% for the same power output.

    Phil H
     
  5. Dan Connelly

    Dan Connelly Guest

    Phil Holman wrote:

    >
    > Yes, but there is a general correlation between weight and CdA. In
    > theory, surface area will increase to the 2/3 power of weight increase.
    > For a 10% weight change, the drag will change by approx 7% and the speed
    > by 3.5% for the same power output.


    2/3 would be true only if BMI was proportional to height^3. Since height
    tends to scale more rapidly than mass^(1/3), the actual power is more than
    (2/3). From the paper I read, it's closer to 0.75.

    Dan
     
  6. Phil Holman

    Phil Holman Guest

    "Dan Connelly" <[email protected]_e_e_e.o_r_g> wrote in message
    news:[email protected]
    > Phil Holman wrote:
    >
    >>
    >> Yes, but there is a general correlation between weight and CdA. In
    >> theory, surface area will increase to the 2/3 power of weight
    >> increase. For a 10% weight change, the drag will change by approx 7%
    >> and the speed by 3.5% for the same power output.

    >
    > 2/3 would be true only if BMI was proportional to height^3. Since
    > height
    > tends to scale more rapidly than mass^(1/3), the actual power is more
    > than
    > (2/3). From the paper I read, it's closer to 0.75.
    >
    > Dan


    Let's think about this some more. When people gain weight, their height
    doesn't change :)

    Phil H
     
  7. Ron Ruff

    Ron Ruff Guest

    Phil Holman wrote:
    > Yes, but there is a general correlation between weight and CdA. In
    > theory, surface area will increase to the 2/3 power of weight increase.
    > For a 10% weight change, the drag will change by approx 7% and the speed
    > by 3.5% for the same power output.


    I can't agree that "A" is proportional to .7*W. Surface area is not the
    "A" in CdA... it is frontal area. True, this is correlated somewhat
    with weight... but probably less than height. An even bigger factor is
    the shape of the rider's body.
     
  8. Phil Holman

    Phil Holman Guest

    "Ron Ruff" <[email protected]> wrote in message
    news:[email protected]
    >
    > Phil Holman wrote:
    >> Yes, but there is a general correlation between weight and CdA. In
    >> theory, surface area will increase to the 2/3 power of weight
    >> increase.
    >> For a 10% weight change, the drag will change by approx 7% and the
    >> speed
    >> by 3.5% for the same power output.

    >
    > I can't agree that "A" is proportional to .7*W. Surface area is not
    > the
    > "A" in CdA... it is frontal area.


    Cross sectional area and surface area increase in the same proportion.
    It's the effect of a volume change on area. As Dan pointed out, not all
    dimensions scale equally so the effect does not fit exactly.

    >True, this is correlated somewhat
    > with weight... but probably less than height. An even bigger factor is
    > the shape of the rider's body.
    >

    Duh! Especially if that extra weight can be sculpted into a NACA
    symmetric profile :)

    Phil H
     
  9. Ron Ruff

    Ron Ruff Guest

    Phil Holman wrote:
    > Duh! Especially if that extra weight can be sculpted into a NACA
    > symmetric profile :)


    I think the lower legs could really benefit from this... imagine
    squashing the calves into an airfoil shape...?

    Having a wide butt wouldn't be good... that trailing edge needs to
    taper as much as possible.
     
  10. "Ron Ruff" <[email protected]> wrote in message
    news:[email protected]
    >
    > Phil Holman wrote:
    >> Duh! Especially if that extra weight can be sculpted into a NACA
    >> symmetric profile :)

    >
    > I think the lower legs could really benefit from this... imagine
    > squashing the calves into an airfoil shape...?
    >


    About 30+ years ago Jerry Ash was a pretty fair sprinter and a tandem
    partner with Leigh Barczewski. Somehow a rumor got passed to the Soviets
    that Ash had gotten deer tendons grafted onto his legs to improve his
    sprinting ability. Obviously not true, but good for a laugh.

    > Having a wide butt wouldn't be good... that trailing edge needs to
    > taper as much as possible.
    >


    Didn't seem to hurt Felicia Ballanger.
     
  11. In article <[email protected]>,
    "Carl Sundquist" <[email protected]> wrote:

    > "Ron Ruff" <[email protected]> wrote in message
    > news:[email protected]
    > >
    > > Phil Holman wrote:
    > >> Duh! Especially if that extra weight can be sculpted into a NACA
    > >> symmetric profile :)

    > >
    > > I think the lower legs could really benefit from this... imagine
    > > squashing the calves into an airfoil shape...?
    > >

    >
    > About 30+ years ago Jerry Ash was a pretty fair sprinter and a tandem
    > partner with Leigh Barczewski. Somehow a rumor got passed to the Soviets
    > that Ash had gotten deer tendons grafted onto his legs to improve his
    > sprinting ability. Obviously not true, but good for a laugh.
    >
    > > Having a wide butt wouldn't be good... that trailing edge needs to
    > > taper as much as possible.
    > >

    >
    > Didn't seem to hurt Felicia Ballanger.


    <http://slam.canoe.ca/2000GamesGallerySep20/cycling3.html>

    --
    Michael Press
     
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