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Bicycle Balance

  1. Nov 5, 2009 #1

    I am just thinking: why it is hard to balanca a (2-wheel) bicycle when it is not moving, while it is easy balanced when it is moving?

    I hope that I am asking in the right forum.

    Thanks in advance
  2. jcsd
  3. Nov 5, 2009 #2
    It is a cruel trick played by God to make life difficult for cyclists
    Either that or it's the gyroscope effect but I think it's the first one :-)

    If you take your front wheel off the bike and hold it on the axle while somebody spins it for you you can actually feel the forces if you try and move the axle up or down at either side, it's actually really weird but quite good fun too
  4. Nov 5, 2009 #3


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    Gold Member

    In a way one can say that the process of riding a bicycle is a self-balancing process. Let me explain.

    The crucial factor is the geometry of the steering. A bicycle with a vertical steering column would be an awful ride, it needs that angle.

    The wikipedia article about
    http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry" [Broken] tells about the head angle, the rake and the trail.

    - First effect of the steering geometry: when the bicycle is not leaning the front wheel is pushed to alignment with the frame. (This effect is lacking in a frame with a vertical steering column.)
    - Second effect of the steering geometry: when the bicycle is leaning gravity pulls the front wheel to a slight angle with the frame - just a slight angle.

    So if you are on the move, and you begin to go into an accidental lean, the front wheel automatically turns towards that direction, and the bicycle rolls back underneath you. it happens automatically, all you need is allowing it to happen.
    Steering is almost not necessary; riding with no hands on the handlebars is very easy and straightforward (on a bicycle with a sufficiently stiff frame.)

    Many people come to a supposition that some gyroscopic stabilizing effect is at play. Now, the englishman David Jones has actually tested that hypothesis. He built himself a bicycle with a second wheel mounted alongside the front wheel, in such a way that at all times it is counterrotating. Because of that counterrotation the gyroscopic effects from the two wheels cancel each other. Jones found that the non-gyroscopic bicycle was just as stable to ride as the standard bicycle. That is strong evidence that gyroscopic effect is not important.

    Last edited by a moderator: May 4, 2017
  5. Dec 31, 2009 #4
    Yes, due to the extremely low mass of a bicycle front wheel (500-800gm), it imparts very little gyroscopic effect.

    The reason it's easier to balance at higher speeds is the self-correcting trail that forces a non-straight front-wheel back to dead-ahead. The faster you go, the more momentum you have with the bike+rider system to push the steering back to straight-ahead. Actually, it's the ground that pushes the front wheel back to centre.
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