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Easier to balance on a bicycle when you are cycling faster

  1. May 11, 2008 #1
    Why is it easier to balance on a bicycle when you are cycling faster rather than slow?
    Does it have something to do with angular momentum?
    Thanks.
     
  2. jcsd
  3. May 11, 2008 #2

    dx

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    Yes. When youre cycling faster, the wheels have more angular momentum.
     
  4. May 11, 2008 #3
    I would like to know the effect of spin angular momentum in this case. Is there anything related to precession in play here?
     
  5. May 11, 2008 #4
    Oh ye I understand that you have greater angular momentum, but how does that link to your stability?
     
  6. May 11, 2008 #5

    Cthugha

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    This is a common, but wrong myth. If you fasten the complete front of the bicycle, so that it is impossible to steer, a fast bike will not be more stable than a slow bike.

    In a nutshell, as soon as you tend to fall to one side the front wheel turns a bit into this direction and makes the bike follow a curved path. On the curved path, the bike is subject to a velocity dependent centrifugal force, which stabilizes the bike and lifts it up again.
     
  7. May 11, 2008 #6

    tiny-tim

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    Is it? Surely the stabilisers on a ship work in the same way as the wheels of a bike … and make the ship more stable? :confused:
     
  8. May 11, 2008 #7

    rcgldr

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    It's due to the steering geometry. If you extend an imaginary line through the pivot axis of the front wheel to the ground the contact patch will behind where this imaginary line intercepts the pavement. For bicycles and motorcycles, it's called trail, for cars it's called caster.

    When a bicycle is leaned over, gravitational downforce is applied to the center of the front wheel at the horizontal axis of the front wheel, while a opposing upwards reaction force is applied from the pavement at the contact patch. Since the contact patch is "behind" the pivot axis, this creates a inwards turing torque on the front wheel, and is designed create a corrective steering response that returns the bicycle to a vertcial position as long as the speed is above a crictial minimum speed. The critical minium speed depends on the amount of trail; the longer the trail, the lower the minimum speed.

    Trail results in vertical stablity, a tendency towards veritcal orientation. Gyroscopic reaction results in roll stability, a tendency to hold the current lean (roll) angle. As speeds increase, the gyroscopic reaction becomes more significant, and at around 100mph on a motorcycle, the gyroscopic reaction of holding a lean angle is the dominant one and there's virtually no tendency to return to vertical. This consequence of high speed riding experienced by motorcycle racers is that it takes virtually the same amount of counter-steering effort to return to a vertical orienation as it does to lean over.
     
    Last edited: May 11, 2008
  9. May 11, 2008 #8

    Cthugha

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    Well, gyroscopes on ships surely can rotate rather freely and do not roll on the ground, which is a huge difference.
     
  10. May 12, 2008 #9

    rcgldr

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    Gyroscopic reactions create roll stability, which is the purpose of the stabilisers. In the case of bicycles and motorcyles, the purpose of steering geometry is vertical stability as opposed to roll stability. At high speeds on a motorcycle, the gyrocopic reactions dominate, and you end up with roll stability, but it's not a problem as long as the rider counter steers to change lean (roll) angle.
     
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