Force distribution on pedals...

Discussion in 'Cycling Equipment' started by Rocket69, Dec 23, 2003.

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  1. Rocket69

    Rocket69 New Member

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    Hi all... looking for a website or an answer to this question.

    If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the pedals? (in pounds or kilos)?

    Thanks to anyone who helps or gives direction...

    Rocket69
     
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  2. Andy Coggan

    Andy Coggan Guest

    "Rocket69" <[email protected]> wrote in message
    news:[email protected]...
    > Hi all... looking for a website or an answer to this question.
    >
    > If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
    > pedals? (in pounds or kilos)?

    Power (in W, or Nm/s) = torque (in Nm) x angular velocity (in rad/s)

    Therefore:

    300 Nm/s * 1/(90 rev/min * 6.18 rad/rev * 1 min/60 s) = 32.4 Nm

    Assuming a crank length of 170 mm, this means an average (around 360 degrees) effective (tangential
    to the crank) force on the pedal of:

    32.4 Nm * 1/0.17 m = 190 N, or 19.4 kg.

    Note that the actual force will vary in essentially a sinusoidal manner from close to zero when the
    cranks are vertical to close to twice the average when the cranks are horizontal.

    The following web page may provide you with some additional insight:

    http://home.earthlink.net/~acoggan/quadrant_analysis.html

    Andy Coggan
     
  3. Dave Lehnen

    Dave Lehnen Guest

    Rocket69 wrote:
    > Hi all... looking for a website or an answer to this question.
    >
    > If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
    > pedals? (in pounds or kilos)?
    >
    > Thanks to anyone who helps or gives direction...
    >
    > Rocket69
    >
    >
    >
    > --
    >
    >

    Do you mean the magnitude and direction of pedal force during one complete cycle? The average
    tangential force, for a crank throw of 170 mm, at 300W and 90 RPM, is 42.09 lb or 187.2 N or
    19.09 KgF. There is no unique answer for how the force is distributed through the cycle. Studies
    have been done with instrumented pedals to determine how force varies through the cycle with
    various riders and conditions. The book "High-Tech Cycling", 2nd Ed., has quite a bit on this in
    chapter 5. There is usually some downforce even on the upgoing pedal. As you would expect, the
    highest forces are from the downgoing leg, somewhat past mid-stroke. There are probably websites
    with similar information, which you can search for as well as I can.

    Dave Lehnen
     
  4. Peter Cole

    Peter Cole Guest

    "Rocket69" <[email protected]ngforums.com> wrote in message
    news:[email protected]...
    > Hi all... looking for a website or an answer to this question.
    >
    > If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
    > pedals? (in pounds or kilos)?
    >
    > Thanks to anyone who helps or gives direction...

    There's a pedaling vector model at www.analyticcycling.com.
     
  5. Ted Bennett

    Ted Bennett Guest

    Rocket69 <[email protected]> wrote:

    > Hi all... looking for a website or an answer to this question.

    If a rider
    > pedals at 90RPM and is generating 300 watts, what is the
    force distribution
    > on the pedals? (in pounds or kilos)?

    Thanks to anyone who helps or gives
    > direction...

    Rocket69

    First get your units right. Force = mass x acceleration, so a kilo can't be a measure of force.

    --
    Ted Bennett Portland OR
     
  6. Rocket69 wrote:

    > Hi all... looking for a website or an answer to this question.
    >
    > If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
    > pedals? (in pounds or kilos)?
    >
    > Thanks to anyone who helps or gives direction...
    >
    > Rocket69

    Depends on the size of the pedal circle, but for 170mm cranks it would be an average of 93N (9.5kgf)
    on each pedal, assuming the rider can produce a perfect couple. The pedals are travelling a distance
    of 1.6 metres per second. You can scale the force up for shorter cranks developing the same power.

    Of course, for most riders the peak force on each pedal will be much greater than this and there
    will be very little force at the top and bottom dead centres. For a highly trained rider using
    clipless pedals it will be closer to the average.
     
  7. Robert Chung

    Robert Chung Guest

    Andy Coggan wrote:
    > "Rocket69" <[email protected]> wrote
    >> If a rider pedals at 90RPM and is generating 300 watts, what is the force distribution on the
    >> pedals? (in pounds or kilos)?
    >
    > Note that the actual force will vary in essentially a sinusoidal manner from close to zero when
    > the cranks are vertical to close to twice the average when the cranks are horizontal.

    Rocket69 can plot the data available at http://www.isbweb.org/data/kautz to see the sine and to see
    that the max force is roughly twice the average.
     
  8. Zog The Undeniable <[email protected]> wrote:

    > Of course, for most riders the peak force on each pedal will be much greater than this and there
    > will be very little force at the top and bottom dead centres. For a highly trained rider using
    > clipless pedals it will be closer to the average.

    That doesn't seem to be the case in practice though.

    Andrew Bradley
     
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