speed wobbles

Discussion in 'Road Cycling' started by Brian Schlachta, Aug 17, 2003.

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  1. Friend of mine has a Colnago Master X-Lite. It's a sweet looking machine even tho it has Dura-Ace
    on. Prob is is that he gets a wobble at around 65 km/h when in the drops, and around 70 km/h with
    his hands in the tops. I seem to remember reading something about rider weight, top tube flexibility
    and rider position as possible causes of a wobble and that it can (sometimes) be fixed by altering
    ones setup on the bike. Any ideas, or does he have a nice looking cuiser.

    tkx, Brian
     
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  2. Scribe2b

    Scribe2b Guest

    1--- check frame alignment
     
  3. [email protected] (Brian Schlachta) writes:

    > Friend of mine has a Colnago Master X-Lite. It's a sweet looking machine even tho it has
    > Dura-Ace on. Prob is is that he gets a wobble at around 65 km/h when in the drops, and
    > around 70 km/h with his hands in the tops. I seem to remember reading something about rider
    > weight, top tube flexibility and rider position as possible causes of a wobble and that it
    > can (sometimes) be fixed by altering ones setup on the bike. Any ideas, or does he have a
    > nice looking cuiser.
    >
    > tkx, Brian

    Quoting from a faq at http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html (a great URL/URI that you should
    bookmark):

    I will just add that besides taking the weicht off the fulcrum (saddle), the spped wobble can be
    stopped by clamping the top tube between the knees - one is usually spun out descending when the
    phenomenon manifests itself.

    Subject: 8h.5 Shimmy or Speed Wobble From: Jobst Brandt <[email protected]>

    Shimmy is not related to frame alignment or loose bearings as is often suggested. Shimmy arises from
    the dynamics of forward motion and the elasticity of the frame, fork, and wheels, and the saddle
    position. Both perfectly aligned bicycles and ones with wheels out of plane to one another shimmy
    nearly equally well. The same is true for bearing adjustment. In fact shimmy is more likely with
    properly adjusted bearings than loose ones. The bearing or alignment concept is usually offered as a
    cause of shimmy and each airing perpetuates the idea.

    Shimmy, the lateral oscillation at the head tube, depends primarily on the frame and its geometry.
    The inflation of the tire and the gyroscopic effects of the front wheel make it largely speed
    dependent. It cannot be fixed by adjustments because it is inherent to the geometry and elasticity
    of the components. The longer the frame and the higher the saddle, the greater the tendency to
    shimmy, other things being equal. Weight distribution also has no effect on shimmy although where
    that weight contacts the frame does.

    In contrast to common knowledge, a well aligned frame shimmies more easily than a crooked one
    because it rides straight and without bias. The bias force of a crooked frame impedes shimmy
    slightly. Because many riders never ride no-hands downhill, or at least not in the critical speed
    range, they seldom encounter shimmy. When it occurs with the hands on the bars it is unusual and
    especially disconcerting. There is a preferred speed at which shimmy initiates when coasting
    no-hands on a smooth road and it should occur every time when in that critical speed range. Although
    it usually does not initiate at higher speed, it can.

    Pedaling or rough road interferes with shimmy on a bicycle that isn't highly susceptible. When
    coasting, laying one leg against the top tube is the most common way to inhibit it. Interestingly,
    compliant tread of knobby tires give such high lateral damping that most bicycles equipped with
    knobbies do not shimmy.

    Shimmy is caused by the gyroscopic force of the front wheel that acts at 90 degrees to the axis of
    the steering motion. The wheel steers to the left about a vertical axis when it is leaned to the
    left about a horizontal axis. When the wheel leans to the one side, gyroscopic force steers it
    toward that side, however, the steering action immediately reverses the lean of the wheel as the
    tire contact point acts on the trail of the fork caster to reverse the steering motion.

    The shimmy oscillates at a rate that the rider's mass on the saddle cannot follow, causing the top
    and down tubes to act as springs that store the energy that initiates the return swing. The shimmy
    will stop if the rider unloads the saddle, because the mass of the rider is the anchor about which
    the oscillation operates. Without this anchor no energy is stored. The fork and wheels may store
    some energy, although it appears the frame acts as the principal spring.

    Shimmy can also be initiated with the hands firmly on the bars by shivering, typically in cold
    weather. The frequency of human shivering is about the same as that of a typical bicycle frame.

    --
    le vent a Dos

    Davey Crockett
     
  4. Excellent reply. Thank you!

    "Davey crockett" <[email protected]> wrote in message
    news:[email protected]rs.com. ..
    > [email protected] (Brian Schlachta) writes:
    >
    > > Friend of mine has a Colnago Master X-Lite. It's a sweet looking
    > > machine even tho it has Dura-Ace on. Prob is is that he gets a wobble at
    > > around 65 km/h when in the drops, and around 70 km/h with his hands in
    the
    > > tops. I seem to remember reading something about rider weight, top tube flexibility and rider
    > > position as possible causes of a wobble and that
    it
    > > can (sometimes) be fixed by altering ones setup on the bike. Any ideas,
    or
    > > does he have a nice looking cuiser.
    > >
    > > tkx, Brian
    >
    > Quoting from a faq at http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html (a great URL/URI that you
    > should bookmark):
    >
    > I will just add that besides taking the weicht off the fulcrum (saddle), the spped wobble can be
    > stopped by clamping the top tube between the knees - one is usually spun out descending when the
    > phenomenon manifests itself.
    >
    > Subject: 8h.5 Shimmy or Speed Wobble From: Jobst Brandt <[email protected]>
    >
    > Shimmy is not related to frame alignment or loose bearings as is often suggested. Shimmy arises
    > from the dynamics of forward motion and the elasticity of the frame, fork, and wheels, and the
    > saddle position. Both perfectly aligned bicycles and ones with wheels out of plane to one another
    > shimmy nearly equally well. The same is true for bearing adjustment. In fact shimmy is more likely
    > with properly adjusted bearings than loose ones. The bearing or alignment concept is usually
    > offered as a cause of shimmy and each airing perpetuates the idea.
    >
    > Shimmy, the lateral oscillation at the head tube, depends primarily on the frame and its geometry.
    > The inflation of the tire and the gyroscopic effects of the front wheel make it largely speed
    > dependent. It cannot be fixed by adjustments because it is inherent to the geometry and elasticity
    > of the components. The longer the frame and the higher the saddle, the greater the tendency to
    > shimmy, other things being equal. Weight distribution also has no effect on shimmy although where
    > that weight contacts the frame does.
    >
    > In contrast to common knowledge, a well aligned frame shimmies more easily than a crooked one
    > because it rides straight and without bias. The bias force of a crooked frame impedes shimmy
    > slightly. Because many riders never ride no-hands downhill, or at least not in the critical speed
    > range, they seldom encounter shimmy. When it occurs with the hands on the bars it is unusual and
    > especially disconcerting. There is a preferred speed at which shimmy initiates when coasting
    > no-hands on a smooth road and it should occur every time when in that critical speed range.
    > Although it usually does not initiate at higher speed, it can.
    >
    > Pedaling or rough road interferes with shimmy on a bicycle that isn't highly susceptible. When
    > coasting, laying one leg against the top tube is the most common way to inhibit it. Interestingly,
    > compliant tread of knobby tires give such high lateral damping that most bicycles equipped with
    > knobbies do not shimmy.
    >
    > Shimmy is caused by the gyroscopic force of the front wheel that acts at 90 degrees to the axis of
    > the steering motion. The wheel steers to the left about a vertical axis when it is leaned to the
    > left about a horizontal axis. When the wheel leans to the one side, gyroscopic force steers it
    > toward that side, however, the steering action immediately reverses the lean of the wheel as the
    > tire contact point acts on the trail of the fork caster to reverse the steering motion.
    >
    > The shimmy oscillates at a rate that the rider's mass on the saddle cannot follow, causing the top
    > and down tubes to act as springs that store the energy that initiates the return swing. The shimmy
    > will stop if the rider unloads the saddle, because the mass of the rider is the anchor about which
    > the oscillation operates. Without this anchor no energy is stored. The fork and wheels may store
    > some energy, although it appears the frame acts as the principal spring.
    >
    > Shimmy can also be initiated with the hands firmly on the bars by shivering, typically in cold
    > weather. The frequency of human shivering is about the same as that of a typical bicycle frame.
    >
    > --
    > le vent a Dos
    >
    > Davey Crockett
     
  5. Davey crockett <[email protected]> wrote in
    news:[email protected]rs.c om:

    > [email protected] (Brian Schlachta) writes:
    >
    >> Friend of mine has a Colnago Master X-Lite. It's a sweet looking machine even tho it has
    >> Dura-Ace on. Prob is is that he gets a wobble at around 65 km/h when in the drops, and
    >> around 70 km/h with his hands in the tops. I seem to remember reading something about
    >> rider weight, top tube flexibility and rider position as possible causes of a wobble and
    >> that it can (sometimes) be fixed by altering ones setup on the bike. Any ideas, or does
    >> he have a nice looking cuiser.
    >>
    >> tkx, Brian
    >
    > Quoting from a faq at http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html (a great URL/URI that you
    > should bookmark):
    >
    > I will just add that besides taking the weicht off the fulcrum (saddle), the spped wobble can be
    > stopped by clamping the top tube between the knees - one is usually spun out descending when the
    > phenomenon manifests itself.
    >
    > Subject: 8h.5 Shimmy or Speed Wobble From: Jobst Brandt <[email protected]>
    >
    > Shimmy is not related to frame alignment or loose bearings as is often suggested. Shimmy arises
    > from the dynamics of forward motion and the elasticity of the frame, fork, and wheels, and the
    > saddle position. Both perfectly aligned bicycles and ones with wheels out of plane to one another
    > shimmy nearly equally well. The same is true for bearing adjustment. In fact shimmy is more likely
    > with properly adjusted bearings than loose ones. The bearing or alignment concept is usually
    > offered as a cause of shimmy and each airing perpetuates the idea.
    >
    > Shimmy, the lateral oscillation at the head tube, depends primarily on the frame and its geometry.
    > The inflation of the tire and the gyroscopic effects of the front wheel make it largely speed
    > dependent. It cannot be fixed by adjustments because it is inherent to the geometry and elasticity
    > of the components. The longer the frame and the higher the saddle, the greater the tendency to
    > shimmy, other things being equal. Weight distribution also has no effect on shimmy although where
    > that weight contacts the frame does.
    >
    > In contrast to common knowledge, a well aligned frame shimmies more easily than a crooked one
    > because it rides straight and without bias. The bias force of a crooked frame impedes shimmy
    > slightly. Because many riders never ride no-hands downhill, or at least not in the critical speed
    > range, they seldom encounter shimmy. When it occurs with the hands on the bars it is unusual and
    > especially disconcerting. There is a preferred speed at which shimmy initiates when coasting
    > no-hands on a smooth road and it should occur every time when in that critical speed range.
    > Although it usually does not initiate at higher speed, it can.
    >
    > Pedaling or rough road interferes with shimmy on a bicycle that isn't highly susceptible. When
    > coasting, laying one leg against the top tube is the most common way to inhibit it. Interestingly,
    > compliant tread of knobby tires give such high lateral damping that most bicycles equipped with
    > knobbies do not shimmy.
    >
    > Shimmy is caused by the gyroscopic force of the front wheel that acts at 90 degrees to the axis of
    > the steering motion. The wheel steers to the left about a vertical axis when it is leaned to the
    > left about a horizontal axis. When the wheel leans to the one side, gyroscopic force steers it
    > toward that side, however, the steering action immediately reverses the lean of the wheel as the
    > tire contact point acts on the trail of the fork caster to reverse the steering motion.
    >
    > The shimmy oscillates at a rate that the rider's mass on the saddle cannot follow, causing the top
    > and down tubes to act as springs that store the energy that initiates the return swing. The shimmy
    > will stop if the rider unloads the saddle, because the mass of the rider is the anchor about which
    > the oscillation operates. Without this anchor no energy is stored. The fork and wheels may store
    > some energy, although it appears the frame acts as the principal spring.
    >
    > Shimmy can also be initiated with the hands firmly on the bars by shivering, typically in cold
    > weather. The frequency of human shivering is about the same as that of a typical bicycle frame.
    >

    Tkx, I'll send him the info. Hopefully, he''l be able to find a solution. It's pissed him
    off a bit. Paying top $ for such a nice bike and having it go all silly on him is pretty
    aggrivating.

    Brian
     
  6. Deeznuts

    Deeznuts Guest

  7. try some cheap traditional wheels with 25's on the front, and I'll doubt if you have a shimmy.
     
  8. Kyle Legate

    Kyle Legate Guest

    Brian Schlachta wrote:
    >
    >
    > Tkx, I'll send him the info. Hopefully, he''l be able to find a solution. It's pissed him off
    > a bit. Paying top $ for such a nice bike and having it go all silly on him is pretty
    > aggrivating.
    >
    The solution is spelled out quite explicitly in Jobst's explanation. I certainly hope your friend
    can find it.
     
  9. Gwhite

    Gwhite Guest

    Aarron Canino wrote:
    >
    > Learn how to follow a thread, dipshit. The thank you was not aimed at you.

    Welcome back Mr. Canino. You are as in as fine a style as ever.

    Dizzle is is trying to say how much he has missed you.

    http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=f8f34113.0212091340.3f272b3d%40posting.goog-
    le.com http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=f8f34113.0302250907.39abf64b%40posti-
    ng.google.com

    > "Deeznuts" <[email protected]> wrote in message
    > news:[email protected]...
    > > "Aarron Canino" <[email protected]> wrote in message
    > news:<RXV%[email protected]>...
    > > > Excellent reply. Thank you!
    > >
    > > No problem, Tuba-boy!
    > >
    > >
    > > Deez
     
  10. Wow! I didn't know that Deeznuts cared so much! What does that say about him that his life is so
    incomplete without someone for whom he has so little respect and whom he would consider to be a
    loser in his narrow-mided view of the world? Sad to see that in his own special, ignorant way, Deez
    has proclaimed to the group that he is so far lower than me in this world.

    By the way, Deez, if you are reading this, if you are that bored and lonely without me around, I am
    sure you are proficient enough with Google that you could probably locate a picture of me somewhere
    that, if you can find your prick, you could probably masturbate to during those lonely nights when
    even good porn can't make it happen for you.

    "gwhite" <[email protected]> wrote in message news:[email protected]...
    >
    >
    > Aarron Canino wrote:
    > >
    > > Learn how to follow a thread, dipshit. The thank you was not aimed at
    you.
    >
    > Welcome back Mr. Canino. You are as in as fine a style as ever.
    >
    > Dizzle is is trying to say how much he has missed you.
    >
    >
    http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=f8f34113.0212091340.
    3f272b3d%40posting.google.com
    >
    http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&selm=f8f34113.0302250907.
    39abf64b%40posting.google.com
    >
    >
    > > "Deeznuts" <[email protected]> wrote in message
    > > news:[email protected]...
    > > > "Aarron Canino" <[email protected]> wrote in message
    > > news:<RXV%[email protected]>...
    > > > > Excellent reply. Thank you!
    > > >
    > > > No problem, Tuba-boy!
    > > >
    > > >
    > > > Deez
     
  11. What would 25mm tires do to help prevent the shimmy? Cheap traditional wheels? Lanny "Callistus
    Valerius" <[email protected]> wrote in message news:[email protected]...
    > try some cheap traditional wheels with 25's on the front, and I'll doubt
    if
    > you have a shimmy.
     
  12. "Kyle Legate" <[email protected]> wrote in
    news:[email protected]:

    > Brian Schlachta wrote:
    >>
    >>
    >> Tkx, I'll send him the info. Hopefully, he''l be able to find a solution. It's pissed him off
    >> a bit. Paying top $ for such a nice bike and having it go all silly on him is pretty
    >> aggrivating.
    >>
    > The solution is spelled out quite explicitly in Jobst's explanation. I certainly hope your friend
    > can find it.
    >
    >
    >

    hehe, I hope so to. I think he's getting a print-out of it tonight. We'll see what
    happens. If he ends up in the ditch with a wrecked bike I sure ain't taking responsibility
    for it lol.

    later, Brian
     
  13. Voltaire

    Voltaire Guest

    "Lanny R. Levenson" <[email protected]> wrote in message
    news:[email protected]...
    > What would 25mm tires do to help prevent the shimmy? Cheap traditional wheels? Lanny "Callistus
    > Valerius" <[email protected]> wrote in message news:[email protected]...
    > > try some cheap traditional wheels with 25's on the front, and I'll doubt
    > if
    > > you have a shimmy.
    > >

    Your expensive bike will be so self-conscious of the cheap wheels and big tyres, it will refuse to
    shimmy, thereby not drawing attention to its embarrassing problem.

    Or maybe the heavier wheel and tyre will increase the stabilizing gyroscopic effect, thereby
    decreasing the lateral oscillation? But what the hell to I know about shimmy and lateral
    oscillation?

    Vol
     
  14. Deeznuts

    Deeznuts Guest

    "Aarron Canino" <[email protected]> wrote in message
    news:<[email protected]>...
    > Wow! I didn't know that Deeznuts cared so much! What does that say about him that his life is so
    > incomplete without someone for whom he has so little respect and whom he would consider to be a
    > loser in his narrow-mided view of the world? Sad to see that in his own special, ignorant way,
    > Deez has proclaimed to the group that he is so far lower than me in this world.

    Aarroon,

    It's good to have your fat ass back, man. This NG has really sucked without your Tuba-playing
    expertise. I know you are pretty busy between your job at the mall and pimping on all of your
    Tuba-groupies, but we need your presence here.

    > By the way, Deez, if you are reading this, if you are that bored and lonely without me around, I
    > am sure you are proficient enough with Google that you could probably locate a picture of me
    > somewhere that, if you can find your prick, you could probably masturbate to during those lonely
    > nights when even good porn can't make it happen for you.

    I did see a picture of you once. I have been trying to forget it ever since.

    Deez
     
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