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Inertia/Momentum of a bicycle

  1. Dec 22, 2009 #1
    Hi everyone, happy christmas

    I am working on a project looking into the inertial feel of a bicycle. The overall aim of this part is to calculate the inertia of a bike and rider and to consider how this inertia feel can be recreated in an exercise bike and to quantify the differences through testing. In order to do this I need to caluclate the inertia/momentum of a real bike and caluclate the inertia/momentum of a cycling ergometer.

    The thing I am unsure about is what is the inertia, (is it a wuantity or is it something that a cyclist feels) and how can it be calclated? Do I need to calculate inertia and momentum for example and how do I combine them. My intial thoughts are:
    Frame and cyclist (momentum = mass x velocity)
    Rotating wheel and crank (disc) (inertia =(mass x (radius)2)/2

    The other issue is that I need to work out the inertia feel of a cycling ergoemter. Knowing that they have large mass fly wheels can I treat this as a disc and calcualte inertia in the same way and compare it to the above?

    Thanks for you help in advance, it is much appreciated

  2. jcsd
  3. Dec 31, 2009 #2
    Having raced bikes for 10-years, I can perhaps point you in the correct direction with some ideas:

    1. a lot of the feel comes through the feedback behavior of the bars. A cyclist always has some amount of side-to-side rocking motion due to the pedaling motion and this translates into some minor swinging of the handlebars to compensate. The effect you want to replicate is self-correcting trail where the momentum of the bike swings the handlebars back into a straight-ahead position. The faster you go, the stronger this self-correcting feedback.

    2. coasting represents a certain amount of cycling time. Coming down a hill, going around a corner. Coastdown measurements can be used to measure the ratio of aero-drag to drivetrain & rolling-resistance drag at various speeds.

    3. drag-versus-speed. Rolling-resistance and drivetrain drag goes up fairly linearly with speed while aero-drag increases to the square-power of speed and the power-required to overcome that drag increases to the cube-power. You'll want to be aware of gearing, speed and the resultant drag

    4. wind. Relates to above point. The cooling effect of wind cannot be discounted. Cyclists can generate some of the highest continuous power-outputs of any athlete, 250watts+ for hours on end. This requires a lot of cooling to keep the muscles working effeciently. Without that, a lot of the realism effect is completely gone.
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