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Work associated with different wheel sizes on bicycles

  1. Apr 22, 2010 #1
    Hello, I'm wondering if someone can help with a little question I have regarding bicycle wheel size and the work associated with keeping it moving. I'm trying to understand how changing the wheel size (effective circumfrance) from 26" to 29" may impact the ammont of effort required by a bicycle racer while on an incline. Assuming the wheel weight is constant and disregarding exterior forces other than gravity how might one go about comparing the two? What I mean is does the simple physics of size play a role in work? I assume it does because a large protion of a bicycle wheel's weight is in the rim and tire, which is near the outer edge of the wheel and should affect rotational inertia, right?

    Thanks,

    C
     
  2. jcsd
  3. Apr 22, 2010 #2
    Having a larger radius gives you more angular momentum which will make it a bit harder to turn with better stability r x p = L

    The larger wheel gives you a longer circumference. Which means your bike moves further across the ground with each petal rotation, and it takes more work, but you go further in less time (higher velocity). You will not get any free energy out of it though, it is no different than changing gears. This is why the original bikes had huge wheels, before gears where in place.

    The ride is smoother due to longer spokes which bend more and absorb shock. For road racing this may not be a good thing as there is a slight transfer of momentum to heat.

    The bike will be a bit heavier overall, gravity is a conservative force though.

    I ride with a guy who switched to 29ers about a year ago and thats all he talks about now. The extra angular momentum can be helpful in downhill mt biking. He is going to build another one and let me try it out soon.
     
    Last edited: Apr 22, 2010
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