Low speed shimmy?

Discussion in 'Cycling Equipment' started by Rick Onanian, Jul 7, 2004.

  1. Rick Onanian

    Rick Onanian Guest

    At 15+ mph with my hands off the bars, violent shimmy will start
    within a few seconds. Should I treat it just like the high speed,
    hands-on shimmy more commonly asked about here? I get no shimmy with
    my hands on the bar up to 45 mph (don't know beyond that).
    --
    Rick Onanian
     
    Tags:


  2. jim beam

    jim beam Guest

    in my experience, it happens in harmonics - e.g. one that happens at
    10mph will also be present at 20, but probably not of the same
    amplitude. just treat it the same.

    what kind of frame/wheel combo do you have?

    Rick Onanian wrote:
    > At 15+ mph with my hands off the bars, violent shimmy will start
    > within a few seconds. Should I treat it just like the high speed,
    > hands-on shimmy more commonly asked about here? I get no shimmy with
    > my hands on the bar up to 45 mph (don't know beyond that).
    > --
    > Rick Onanian
     
  3. Rick Onanian

    Rick Onanian Guest

    On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email protected]>
    wrote:
    >in my experience, it happens in harmonics - e.g. one that happens at
    >10mph will also be present at 20, but probably not of the same
    >amplitude. just treat it the same.


    Mine happens at any speed above 15. I ride no-hands at a steady
    speed, and the shimmy increases in amplitude pretty quickly.

    >what kind of frame/wheel combo do you have?


    http://members.cox.net/thc69/bikes/tcr2.jpg

    20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum compact
    frame. I believe my answer is actually in my tall stem, according to
    this parallel thread:
    http://groups.google.com/groups?&th=4771eb045db5278c

    I'm not sure how the stem can affect handling when riding no-hands,
    except maybe in how the weight of the handlebars affects steering.
    --
    Rick Onanian
     
  4. S o r n i

    S o r n i Guest

    Rick Onanian wrote:
    > Mine happens at any speed above 15. I ride no-hands at a steady
    > speed, and the shimmy increases in amplitude pretty quickly.
    >
    > http://members.cox.net/thc69/bikes/tcr2.jpg


    I think I've spotted your problem.

    You have a chainring in your front spokes.

    Bill "HTH" S.
     
  5. Rick Onanian

    Rick Onanian Guest

  6. Rick Onanian <[email protected]> wrote:
    > At 15+ mph with my hands off the bars, violent shimmy will start
    > within a few seconds. Should I treat it just like the high speed,
    > hands-on shimmy more commonly asked about here? I get no shimmy with
    > my hands on the bar up to 45 mph (don't know beyond that).


    does it happen with your aerobars removed? otherwise i'm partial to blaming
    it on that stem ;-)
    --
    david reuteler
    [email protected]
     
  7. Rick Onanian

    Rick Onanian Guest

    On 08 Jul 2004 16:41:43 GMT, David Reuteler <[email protected]>
    wrote:
    >Rick Onanian <[email protected]> wrote:
    >> At 15+ mph with my hands off the bars, violent shimmy will start

    >
    >does it happen with your aerobars removed? otherwise i'm partial to blaming
    >it on that stem ;-)


    I'm too lazy to remove the aerobars to find out. I was thinking I'd
    fool with the headset preload, which may not be perfect.
    --
    Rick Onanian
     
  8. jim beam

    jim beam Guest

    Rick Onanian wrote:
    > On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email protected]>
    > wrote:
    >
    >>in my experience, it happens in harmonics - e.g. one that happens at
    >>10mph will also be present at 20, but probably not of the same
    >>amplitude. just treat it the same.

    >
    >
    > Mine happens at any speed above 15. I ride no-hands at a steady
    > speed, and the shimmy increases in amplitude pretty quickly.
    >
    >
    >>what kind of frame/wheel combo do you have?

    >
    >
    > http://members.cox.net/thc69/bikes/tcr2.jpg
    >
    > 20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum compact
    > frame. I believe my answer is actually in my tall stem, according to
    > this parallel thread:
    > http://groups.google.com/groups?&th=4771eb045db5278c
    >
    > I'm not sure how the stem can affect handling when riding no-hands,
    > except maybe in how the weight of the handlebars affects steering.
    > --
    > Rick Onanian


    frame & wheel in isolation should be fine. but waht about that rack???
    conventional racks are firmly attached to eyelets at the stays, both
    top & bottom. the bottom clip arrangement you have should be ok, but
    that top attachment is going to offer no lateral stiffness whatsoever -
    any lateral movement of the bike is going to have that rack acting like
    a textbook reciprocating mass.

    sure, check into the handlebar situation, but i'd address the rack
    situation first. personally, i commute with a back pack.
     
  9. Right, jb. Putting a rear rack on a bicycle has caused a shimmy in my
    personal experience, thouggh it came on at 30 mph.


    "jim beam" <[email protected]> wrote in message
    news:[email protected]
    > Rick Onanian wrote:
    > > On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email protected]>
    > > wrote:
    > >
    > >>in my experience, it happens in harmonics - e.g. one that happens at
    > >>10mph will also be present at 20, but probably not of the same
    > >>amplitude. just treat it the same.

    > >
    > >
    > > Mine happens at any speed above 15. I ride no-hands at a steady
    > > speed, and the shimmy increases in amplitude pretty quickly.
    > >
    > >
    > >>what kind of frame/wheel combo do you have?

    > >
    > >
    > > http://members.cox.net/thc69/bikes/tcr2.jpg
    > >
    > > 20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum compact
    > > frame. I believe my answer is actually in my tall stem, according to
    > > this parallel thread:
    > > http://groups.google.com/groups?&th=4771eb045db5278c
    > >
    > > I'm not sure how the stem can affect handling when riding no-hands,
    > > except maybe in how the weight of the handlebars affects steering.
    > > --
    > > Rick Onanian

    >
    > frame & wheel in isolation should be fine. but waht about that rack???
    > conventional racks are firmly attached to eyelets at the stays, both
    > top & bottom. the bottom clip arrangement you have should be ok, but
    > that top attachment is going to offer no lateral stiffness whatsoever -
    > any lateral movement of the bike is going to have that rack acting like
    > a textbook reciprocating mass.
    >
    > sure, check into the handlebar situation, but i'd address the rack
    > situation first. personally, i commute with a back pack.
    >
     
  10. Rick Onanian

    Rick Onanian Guest

    On Fri, 09 Jul 2004 06:09:51 -0700, jim beam <[email protected]>
    wrote:
    >> http://groups.google.com/groups?&th=4771eb045db5278c
    >>
    >> I'm not sure how the stem can affect handling when riding no-hands,
    >> except maybe in how the weight of the handlebars affects steering.

    >
    >frame & wheel in isolation should be fine. but waht about that rack???
    > conventional racks are firmly attached to eyelets at the stays, both
    >top & bottom. the bottom clip arrangement you have should be ok, but
    >that top attachment is going to offer no lateral stiffness whatsoever -
    >any lateral movement of the bike is going to have that rack acting like
    >a textbook reciprocating mass.


    Great observation! I would have never considered that something
    attached to the rear of the bike [seemingly firmly] could cause
    front-end oddness, but I'll definitely have to look into it.

    I have a couple extra clamps like the ones on the bottom which I
    could use at the top too; maybe I'll try them, or some other method
    for stiffening the rack.
    --
    Rick Onanian
     
  11. Rick Onanian

    Rick Onanian Guest

    On Fri, 09 Jul 2004 06:09:51 -0700, jim beam <[email protected]>
    wrote:
    >> http://groups.google.com/groups?&th=4771eb045db5278c
    >>
    >> I'm not sure how the stem can affect handling when riding no-hands,
    >> except maybe in how the weight of the handlebars affects steering.

    >
    >frame & wheel in isolation should be fine. but waht about that rack???
    > conventional racks are firmly attached to eyelets at the stays, both
    >top & bottom. the bottom clip arrangement you have should be ok, but
    >that top attachment is going to offer no lateral stiffness whatsoever -
    >any lateral movement of the bike is going to have that rack acting like
    >a textbook reciprocating mass.


    Great observation! I would have never considered that something
    attached to the rear of the bike [seemingly firmly] could cause
    front-end oddness, but I'll definitely have to look into it.

    I have a couple extra clamps like the ones on the bottom which I
    could use at the top too; maybe I'll try them, or some other method
    for stiffening the rack.
    --
    Rick Onanian
     
  12. It sure surprised me too, but I found this phenomenom on several frames,
    always with alloy racks. My current ride has a steel K-Mart rack, and no
    shimmy, whether there is any connection, I don't care to suppose.

    There are many things which can cause shimmys, also see:

    http://groups.google.com/groups?q=shimmy&hl=en&lr=&ie=UTF-8&start=0&sa=N

    "Rick Onanian" <[email protected]> wrote in message
    news:[email protected]
    > On Fri, 09 Jul 2004 06:09:51 -0700, jim beam <[email protected]>
    > wrote:
    > >> http://groups.google.com/groups?&th=4771eb045db5278c
    > >>
    > >> I'm not sure how the stem can affect handling when riding no-hands,
    > >> except maybe in how the weight of the handlebars affects steering.

    > >
    > >frame & wheel in isolation should be fine. but waht about that rack???
    > > conventional racks are firmly attached to eyelets at the stays, both
    > >top & bottom. the bottom clip arrangement you have should be ok, but
    > >that top attachment is going to offer no lateral stiffness whatsoever -
    > >any lateral movement of the bike is going to have that rack acting like
    > >a textbook reciprocating mass.

    >
    > Great observation! I would have never considered that something
    > attached to the rear of the bike [seemingly firmly] could cause
    > front-end oddness, but I'll definitely have to look into it.
    >
    > I have a couple extra clamps like the ones on the bottom which I
    > could use at the top too; maybe I'll try them, or some other method
    > for stiffening the rack.
    > --
    > Rick Onanian
     
  13. Bob Flumere

    Bob Flumere Guest

    Please......

    Get rid of the wheel reflectors..

    If you don't think that they are capable of causing your shimmy, spin
    a suspended wheel with shop air and see what the effect of the
    reflector weight is at speed. You'll be surprised a how much the fork
    and bars will jump around even a low rpm.. (15 mph)..

    I am told by others here that this cannot be the cause of a shimmy,
    but I found this to be the total problem with an old Trek 750 cross
    bike that almost threw me into the woods the first time I got it up to
    25 MPH on a downgrade.

    My motorcycle experience with wheel balancing to eliminate the deadly
    "Speed Wobble" suggests that some attempt at balancing bike wheels is
    not a wasted effort when dealing with shimmy.

    Get rid of the reflectors for one ride and let me know please!

    Bob Flumere
    [email protected]



    On Thu, 08 Jul 2004 08:36:36 -0400, Rick Onanian <[email protected]>
    wrote:

    >On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email protected]>
    >wrote:
    >>in my experience, it happens in harmonics - e.g. one that happens at
    >>10mph will also be present at 20, but probably not of the same
    >>amplitude. just treat it the same.

    >
    >Mine happens at any speed above 15. I ride no-hands at a steady
    >speed, and the shimmy increases in amplitude pretty quickly.
    >
    >>what kind of frame/wheel combo do you have?

    >
    >http://members.cox.net/thc69/bikes/tcr2.jpg
    >
    >20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum compact
    >frame. I believe my answer is actually in my tall stem, according to
    >this parallel thread:
    >http://groups.google.com/groups?&th=4771eb045db5278c
    >
    >I'm not sure how the stem can affect handling when riding no-hands,
    >except maybe in how the weight of the handlebars affects steering.


    Bob Flumere
    [email protected]
     
  14. On Sun, 11 Jul 2004 23:58:43 GMT, Bob Flumere
    <[email protected]> wrote:

    >Please......
    >
    >Get rid of the wheel reflectors..
    >
    >If you don't think that they are capable of causing your shimmy, spin
    >a suspended wheel with shop air and see what the effect of the
    >reflector weight is at speed. You'll be surprised a how much the fork
    >and bars will jump around even a low rpm.. (15 mph)..
    >
    >I am told by others here that this cannot be the cause of a shimmy,
    >but I found this to be the total problem with an old Trek 750 cross
    >bike that almost threw me into the woods the first time I got it up to
    >25 MPH on a downgrade.
    >
    >My motorcycle experience with wheel balancing to eliminate the deadly
    >"Speed Wobble" suggests that some attempt at balancing bike wheels is
    >not a wasted effort when dealing with shimmy.
    >
    >Get rid of the reflectors for one ride and let me know please!
    >
    >Bob Flumere
    >[email protected]
    >
    >
    >
    >On Thu, 08 Jul 2004 08:36:36 -0400, Rick Onanian <[email protected]>
    >wrote:
    >
    >>On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email protected]>
    >>wrote:
    >>>in my experience, it happens in harmonics - e.g. one that happens at
    >>>10mph will also be present at 20, but probably not of the same
    >>>amplitude. just treat it the same.

    >>
    >>Mine happens at any speed above 15. I ride no-hands at a steady
    >>speed, and the shimmy increases in amplitude pretty quickly.
    >>
    >>>what kind of frame/wheel combo do you have?

    >>
    >>http://members.cox.net/thc69/bikes/tcr2.jpg
    >>
    >>20mm 110 psi tire on CXP21 rim on 105 hub, Giant aluminum compact
    >>frame. I believe my answer is actually in my tall stem, according to
    >>this parallel thread:
    >>http://groups.google.com/groups?&th=4771eb045db5278c
    >>
    >>I'm not sure how the stem can affect handling when riding no-hands,
    >>except maybe in how the weight of the handlebars affects steering.

    >
    >Bob Flumere
    >[email protected]


    Dear Bob,

    Your plea raises an interesting question.

    It's often been stated here that wheel-balancing is
    pointless on bicycles because the wheel mass is so small
    compared to the bike and rider.

    How heavy would an unbalanced weight on a wheel have to be
    before wheel-balancing became worthwhile in the eyes of the
    naysayers?

    Carl Fogel
     
  15. Rick Onanian

    Rick Onanian Guest

    On Sat, 10 Jul 2004 06:01:51 -0700, "Dale Benjamin"
    <[email protected]> wrote:
    >It sure surprised me too, but I found this phenomenom on several frames,
    >always with alloy racks. My current ride has a steel K-Mart rack, and no
    >shimmy, whether there is any connection, I don't care to suppose.


    It is a lightweight alloy rack. Sure enough, it is definitely
    involved; this weekend, put a trunk on it, with a few pounds of
    stuff in it, and the shimmy is barely detectable. I also had two
    full 32oz bottles in the rear bottle cages that hang off the end of
    the rack.

    It seems strange to me that the rack would do that when unweighted,
    and behave when loaded; unweighted, it would seem to not have enough
    mass to have such an effect. However, who am I to argue with
    results?

    >There are many things which can cause shimmys, also see:
    >http://groups.google.com/groups?q=shimmy&hl=en&lr=&ie=UTF-8&start=0&sa=N


    Yeah, I see in-depth discussions constantly about it, which is why I
    haven't asked how to troubleshoot it; I just wanted to know if the
    troubleshooting process is the same, as the shimmy is under
    different conditions than usually discussed (usually, high speed
    with hands on the bars).
    --
    Rick Onanian
     
  16. Rick Onanian

    Rick Onanian Guest

    On Sun, 11 Jul 2004 23:58:43 GMT, Bob Flumere <[email protected]>
    wrote:
    >Get rid of the wheel reflectors..
    >If you don't think that they are capable of causing your shimmy, spin
    >a suspended wheel with shop air and see what the effect of the
    >reflector weight is at speed. You'll be surprised a how much the fork
    >and bars will jump around even a low rpm.. (15 mph)..


    I haven't given this attention to the front wheel, but removing the
    reflectors from my rear wheel does not result in a balanced wheel. I
    had observed a few months ago that spinning my rear up to a good
    speed while holding the bike in the air produced quite a strong
    reciprocation force where I held the bike.

    In a recent discussion regarding tires, traction, handling, and
    testing of all three, after I suggested that the force would load
    and unload the tire a little bit each revolution, resulting in
    uneven traction, Jobst asserted that it couldn't affect handling,
    and gave the impression that such a force is so trivial in the grand
    scheme of things as to have no effect whatsoever in a bicycling
    context. I am not entirely convinced.

    It did require a few steel 1/2" nuts taped to the rim before I got
    it reasonably balanced.

    >I am told by others here that this cannot be the cause of a shimmy,
    >but I found this to be the total problem with an old Trek 750 cross
    >bike that almost threw me into the woods the first time I got it up to
    >25 MPH on a downgrade.


    I'm not sure how vertical forces could cause a horizontal/rotational
    shimmy, but I also wasn't sure how a rear rack could cause front
    shimmy -- when in fact, weighting my rear rack with some extra
    tools, a couple apples, and a single-serving applesauce, as well as
    two water bottles, almost entirely eliminated the shimmy.

    Actually, while typing that bit above, I realized another major
    difference. In the shimmy-prone rides, I'm pretty sure I only had
    one bottle in the rack's bottle cages. In the shimmy-free ride on
    Saturday, I had bottles in both cages. Maybe I need to bring two
    half-full bottles instead of one full bottle.

    >My motorcycle experience with wheel balancing to eliminate the deadly
    >"Speed Wobble" suggests that some attempt at balancing bike wheels is
    >not a wasted effort when dealing with shimmy.


    See, mine is not a "speed" wobble, it's more of a "slow" wobble, and
    only with no hands. As such, I was just wondering if the
    troubleshooting process is the same as for hands-on high-speed
    wobble, for which there exists truckloads of information to be found
    in the archives of this newsfroup.

    >Get rid of the reflectors for one ride and let me know please!


    I might give it a try, but I think it's something to do with the
    rear rack.
    --
    Rick Onanian
     
  17. Bob Flumere

    Bob Flumere Guest

    On Sun, 11 Jul 2004 19:17:52 -0600, [email protected] wrote:


    >
    >Dear Bob,
    >
    >Your plea raises an interesting question.
    >
    >It's often been stated here that wheel-balancing is
    >pointless on bicycles because the wheel mass is so small
    >compared to the bike and rider.



    >Carl Fogel


    Hi Carl:

    I do wish that I did know more about the theory involved here. My
    statements here are based more on experience (which may not carry much
    weight here.. G).

    I know that when you spin a bike or cycle wheel at speed, such as we
    used to do with a stroboscopic automotive wheel balancer machine, that
    the forces on the free wheel are not all in the plane of the wheel and
    that some side to side motion is generated. You can easily
    demonstrate this by spinning a freely suspended bike wheel with a shop
    compressed air nozzle and you will see a "shimmy" component as well as
    the vertical out of balance forces.

    I am told, ( as were you, it seems - G), that this can not effect a
    bicycle at speed. But, we used to balance the motorcycle wheels by
    wrapping heavy gauge solder on the spokes at the "light" point as
    indicated by the stroboscopic balancer (or simply by letting the
    wheel seek its own heavy spot if the bearing and brake drag would
    permit. This would usually eliminate the deadly "speed wobble" which
    surely was a form of what we are refering to as "shimmy".

    I agree, it happens at harmonics and can be very exagerated if
    occuring at a resonant frequency of the structure of the machine
    involved.

    >
    >How heavy would an unbalanced weight on a wheel have to be
    >before wheel-balancing became worthwhile in the eyes of the
    >naysayers?
    >


    An out of balance condition of 1/2oz. on a car at the wheel rim can
    easily be felt at road speed as a vibration (probably mostly in the
    vertical plane), with a much heavier wheel and tire than the bike, so
    I feel that the reflector weight on a bike tire is sure to cause some
    effect even if mounted opposite the valve stem, which is supposedly
    the "heavy spot".

    In my case, with one of my first pedal powered bikes, a Trek 750
    "Cross", I recognized what was happening just before it shimmied me
    off of the road into the woods. After spinning the wheels with shop
    air to see what the wheel balance was like at speed, and removing the
    reflectors, which made a big improvment in the amount of vertical
    movement (and the side to side as well), I never had the shimmy event
    occur again in many thousands of miles of riding this bike. I realize
    that this is purely emperical and therefore of little value here.

    So while I am admitting that I cannot argue this point in theory, I
    ask only that doubters put a reflector ( or an equivalent weight) on a
    front bike tire, suspend the bike so that the fork can turn freely,
    spin at road speed by whatever means (shop compressed air nozzle is
    great for this) and observe the effect and then surely someone here
    can (and most likely will), theorize. BG.

    Bob..
    [email protected]

    P.S. Something to do with gyroscopic preccesion as the out of balance
    mass revolves around center creating a force at right angles to the
    primary out of balance force... rambling now..sorry ??????






    Bob Flumere
    [email protected]
     
  18. Rick Onanian

    Rick Onanian Guest

    On Mon, 12 Jul 2004 23:09:01 GMT, Bob Flumere <[email protected]>
    wrote:
    >effect even if mounted opposite the valve stem, which is supposedly
    >the "heavy spot".


    IIRC, the valve stem is opposite the rim weld or joint, for balance.
    --
    Rick Onanian
     
  19. pinnah

    pinnah Guest

    "Dale Benjamin" <[email protected]> wrote:

    >It sure surprised me too, but I found this phenomenom on several frames,
    >always with alloy racks. My current ride has a steel K-Mart rack, and no
    >shimmy, whether there is any connection, I don't care to suppose.
    >
    >There are many things which can cause shimmys, also see:
    >
    >http://groups.google.com/groups?q=shimmy&hl=en&lr=&ie=UTF-8&start=0&sa=N



    I'm not an engineer but I find this FAQ confusing. It seems to
    describe what is happening during a shimy but not what causes some
    bikes to shimy and other not to.

    Is it the set up of the cockpit, frame geometry, loads on racks or
    what?

    Call me confused.


    -- Dave
    ==============================================
    "It is impossible, or not easy, to do noble acts
    without the proper equipment."
    Aristotle, <<Politics>>, 1323a-b, trans Jowett
    ==============================================
     
  20. jim beam

    jim beam Guest

    pinnah wrote:
    > "Dale Benjamin" <[email protected]> wrote:
    >
    >
    >>It sure surprised me too, but I found this phenomenom on several frames,
    >>always with alloy racks. My current ride has a steel K-Mart rack, and no
    >>shimmy, whether there is any connection, I don't care to suppose.
    >>
    >>There are many things which can cause shimmys, also see:
    >>
    >>http://groups.google.com/groups?q=shimmy&hl=en&lr=&ie=UTF-8&start=0&sa=N

    >
    >
    >
    > I'm not an engineer but I find this FAQ confusing. It seems to
    > describe what is happening during a shimy but not what causes some
    > bikes to shimy and other not to.
    >
    > Is it the set up of the cockpit, frame geometry, loads on racks or
    > what?
    >
    > Call me confused.
    >
    >
    > -- Dave


    you're not confused - that's a remarably astute observation.
    unfortunately, if the faq authors are merely content to address symptoms
    rather than ailments, they're not going to be much help.

    my personal experience with resolving a shimmy issue was done partially
    by using a "stiffer" rear wheel, one built with unbutted spokes drive
    side rear, and ultimately replacing the frame with one built to the same
    spec, but with oversize tube to give much better torsional stiffness.
    cured my problems completely.

    ymmv, but the idea is to address the frame/wheel springiness issue so
    that they do not resonate with each other. if you're carring luggage,
    the rack-induced shimmy cited here is another perfect example of a
    reciprocating mass and its effects.
     
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