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Re: Bicycle dynamics vs. motorcycle dynamics

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01 / Original postRe: Bicycle dynamics vs. motorcycle dynamicsChalo · 5 Jun 2005 02 / This pagePosts 1–9Page 1 of 1 · chronological order 03 / Latest replyPost #9Blair P. Houghton · 7 Jun 2005

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Road Cycling
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5 June 2005
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7 June 2005
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Chalo
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  1. Original post
    Chalo
    Archived post
    #1
    Blair P. Houghton said:


    They're exactly the same, except for the enormous differences
    caused by the dichotomy between the mass ratios of rider and
    mount.

    On a bicycle, you're 80-90% of the mass, which gives you
    all the control.

    On a motorcycle, you're 10-50% of the mass, which means
    you're just along for the ride, making suggestions.

    Counterweighting and countersteer exist in both paradigms.
    As do gyroscopic effects, but I don't think they're the
    real story for either.

    Braking is only different in that a motorcycle/rider
    system's lower center of gravity lets you use the front
    brake more aggressively.

    There is another factor you have not addressed-- that of the staggering
    differences in gyroscopic forces between bicycles and motorcycles.

    Each wheel of a motorcycle can weigh more than a bicycle, and so can
    the crank assembly. And they all three turn at a multiple of the
    speeds typical for a bicycle wheel. This is a major reason for both a
    motorcycle's impressive stability and the force required at the bars to
    steer a motorcycle.

    Having ridden bicycles for transportation for 18 years and motorcycles
    for 10, I don't find that much about riding them that is directly
    comparable. But all my bikes have been 600+ lbs with lots of
    horsepower, and I'm willing to believe that a very lightweight
    motorcycle would feel more bicycle-like.

    Chalo Colina

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  2. Email address hidden
    Archived post
    #2
    Blair P. Houghton said:


    So far, I haven't needed to induce gyroscopy. But I
    haven't written out the equations myself yet....

    One of these days I'll get a hair up and put the whole system
    down on paper.

    Before you do the equations, take a look at what others have attempted.

    AFAIK, nobody has succeeded in a complete mathematical model of bike
    stability and handling, and many have tried. It's an excellent example
    of something that's simple in practice and devilishly difficult in
    theory.

    You might want to start with _Bicycling Science_ by Wilson et. al.

    - Frank Krygowski

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  3. Brian Wax
    Archived post
    #3

    As far as gyroscopic goes, the spinning mass of the wheels adds a great deal
    of stability. That is why many of the after market wheels are pounds lighter
    and the more exotic motorcycles have much lighter wheels. The lighter the
    wheel, the easier it is to change direction. This also has a big effect on
    the suspension characteristics.

    The dynamics of the bike and motorcycle are very similar as Blair has
    pointed out. Steering trail and rake make for more or less rider input for
    tuning. This also means stability. The more slack geometries or laid back
    seat tube make for a more solid platform. You pick what works best for you
    or what you feel more comfortable on. My CR 250 Honda and my Ducati have
    short wheel bases and steeper steering angles. These bikes turn well but are
    much more nervous at speed. I had to put steering dampeners on both bikes.
    While accelerating out of turns, the front wheel would shake back and forth
    violently.

    My Colnago is a much more stable and predicable steerer in contrast to my
    Crit geometry Serotta. Under hard braking I put my butt way over the back
    wheel of the Serotta to compensate for the steeper seat post angle. The
    rider will/should address his/her inputs according to the geometry.

    Brian

    <[email hidden]> wrote in message
    news:[email hidden]...

    Quoted message said:
    Blair P. Houghton said:


    So far, I haven't needed to induce gyroscopy. But I
    haven't written out the equations myself yet....

    One of these days I'll get a hair up and put the whole system
    down on paper.

    Before you do the equations, take a look at what others have attempted.

    AFAIK, nobody has succeeded in a complete mathematical model of bike
    stability and handling, and many have tried. It's an excellent example
    of something that's simple in practice and devilishly difficult in
    theory.

    You might want to start with _Bicycling Science_ by Wilson et. al.

    - Frank Krygowski

    Report
  4. Benjamin Lewis
    Archived post
    #4
    Quoted message said:
    Blair P. Houghton said:


    So far, I haven't needed to induce gyroscopy. But I
    haven't written out the equations myself yet....

    One of these days I'll get a hair up and put the whole system
    down on paper.

    Before you do the equations, take a look at what others have attempted.

    AFAIK, nobody has succeeded in a complete mathematical model of bike
    stability and handling, and many have tried. It's an excellent example
    of something that's simple in practice and devilishly difficult in
    theory.

    You might want to start with _Bicycling Science_ by Wilson et. al.

    This is the best I've found:

    http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/overview_papers_and_links.htm

    or equivalently:

    http://tinyurl.com/a37v5

    --
    Benjamin Lewis

    Although the moon is smaller than the earth, it is farther away.

    Report
  5. Just zis Guy, you know?
    Archived post
    #5

    At Mon, 06 Jun 2005 11:08:18 -0700, message
    <[email hidden]> was posted by Benjamin Lewis
    <[email hidden]>, including some, all or none of the following:

    Quoted message said:

    Although the moon is smaller than the earth, it is farther away.

    From what?

    Guy
    --
    May contain traces of irony. Contents liable to settle after posting.
    http://www.chapmancentral.co.uk

    85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

    Report
  6. Benjamin Lewis
    Archived post
    #6
    Just zis Guy said:

    At Mon, 06 Jun 2005 11:08:18 -0700, message
    <[email hidden]> was posted by Benjamin Lewis
    <[email hidden]>, including some, all or none of the following:

    Quoted message said:

    Although the moon is smaller than the earth, it is farther away.

    From what?

    I don't know. Is there any possible answer to your question that would
    make the statement useful in any way?

    --
    Benjamin Lewis

    Seeing is deceiving. It's eating that's believing.
    -- James Thurber

    Report
  7. Just zis Guy, you know?
    Archived post
    #7

    At Mon, 06 Jun 2005 11:55:10 -0700, message
    <[email hidden]> was posted by Benjamin Lewis
    <[email hidden]>, including some, all or none of the following:

    Quoted message said:
    Quoted message said:
    Quoted message said:

    Although the moon is smaller than the earth, it is farther away.


    From what?


    I don't know. Is there any possible answer to your question that would
    make the statement useful in any way?

    I feel the need to consult the magic 8-ball.

    "Reply hazy, try again"

    Well that was a lot of use! I'm beginning to wish I hadn't asked, now.

    Guy
    --
    May contain traces of irony. Contents liable to settle after posting.
    http://www.chapmancentral.co.uk

    85% of helmet statistics are made up, 69% of them at CHS, Puget Sound

    Report
  8. Leo Lichtman
    Archived post
    #8

    Well that was a lot of use! I'm beginning to wish I hadn't asked, now.
    ^^^^^^^^^^^^^^^
    Which one of you wrote the letter to "Car Talk," objecting to their
    reference to the "third half of the show?"

    Report
  9. Blair P. Houghton
    Archived post
    #9
    Brian Wax said:

    As far as gyroscopic goes, the spinning mass of the wheels adds a great deal
    of stability. That is why many of the after market wheels are pounds lighter
    and the more exotic motorcycles have much lighter wheels. The lighter the
    wheel, the easier it is to change direction. This also has a big effect on
    the suspension characteristics.

    But what I've seen (the book by the Aprilia engineers)
    says that the gyroscopic effect is supposed to *aid*
    turning, not *oppose* it.

    I believe what you seem to say, that we don't want so much
    gyroscopic effect.

    The bike geometry makes it inherently stable while it's
    rolling, and the gyroscopic effect hampers controllability.

    Quoted message said:

    short wheel bases and steeper steering angles. These bikes turn well but are
    much more nervous at speed. I had to put steering dampeners on both bikes.
    While accelerating out of turns, the front wheel would shake back and forth
    violently.

    Makes sense. Like a shopping-cart wheel, which has trail but no rake.

    This is a situation where the gyro effect would be a good thing.

    One other thing to note is that with intended precession of a gyroscope
    often there is unintended nutation because the forces are not always
    balanced.

    If nutation were a strong effect (and it's usually more
    noticeable than the precession in gyroscopic systems
    responding to imperfectly applied torques) then turning
    a motorcycle would always involve high wobble amplitudes,
    and we'd all notice.

    --Blair
    "It's falling...with style."

    Report

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