Low speed shimmy?

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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

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

On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <nospam@example.net>
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

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.

On Thu, 08 Jul 2004 15:07:06 GMT, "S o r n i"
<sorni@bite-me.san.rr.com> wrote:
>> http://members.cox.net/thc69/bikes/tcr2.jpg
>
>I think I've spotted your problem.
>
>You have a chainring in your front spokes

I've been waiting for that one. ;)
--
Rick Onanian

Rick Onanian <spamsink@cox.net> 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 reuteler@visi.com

On 08 Jul 2004 16:41:43 GMT, David Reuteler <reuteler@visi.com>
wrote:
>Rick Onanian <spamsink@cox.net> 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

Rick Onanian wrote:
> On Wed, 07 Jul 2004 20:15:22 -0700, jim beam
> <nospam@example.net> 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.

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" <nospam@example.net> wrote in message
news:0eadnVHhNs29BHPd4p2dnA@comcast.com...
> Rick Onanian wrote:
> > On Wed, 07 Jul 2004 20:15:22 -0700, jim beam
> > <nospam@example.net> 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.

On Fri, 09 Jul 2004 06:09:51 -0700, jim beam <nospam@example.net>
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

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" <spamsink@cox.net> wrote in message
news:daete05shdgjo641b34ishld3ekindbh8e@4ax.com...
> On Fri, 09 Jul 2004 06:09:51 -0700, jim beam
> <nospam@example.net> 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

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 rflumere@comcast.net

On Thu, 08 Jul 2004 08:36:36 -0400, Rick Onanian
<spamsink@cox.net> wrote:

>On Wed, 07 Jul 2004 20:15:22 -0700, jim beam
><nospam@example.net> 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 rflumere@comcast.net

On Sun, 11 Jul 2004 23:58:43 GMT, Bob Flumere
<rflumere@comcast.net> 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 rflumere@comcast.net
>
>
>
>On Thu, 08 Jul 2004 08:36:36 -0400, Rick Onanian
><spamsink@cox.net> wrote:
>
>>On Wed, 07 Jul 2004 20:15:22 -0700, jim beam
>><nospam@example.net> 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 rflumere@comcast.net

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

On Sat, 10 Jul 2004 06:01:51 -0700, "Dale Benjamin"
<daleb@k-online.com> 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

On Sun, 11 Jul 2004 23:58:43 GMT, Bob Flumere <rflumere@comcast.net>
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

On Sun, 11 Jul 2004 19:17:52 -0600, carlfogel@comcast.net 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.. rflumere@comcast.net

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 rflumere@comcast.net