Low speed shimmy?

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 said:

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 <[email hidden]>

Quoted message said:

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.

Quoted message said:

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 said:

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.

S o r n i said:

Quoted message said:

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 said:

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 hidden]

On 08 Jul 2004 16:41:43 GMT, David Reuteler <[email hidden]>

Quoted message said:

Rick Onanian said:

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 said:

On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email hidden]>

Quoted message said:

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.

Quoted message said:

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

Quoted message said:

Rick Onanian said:

On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email hidden]>

Quoted message said:

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.

Quoted message said:

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 <[email hidden]>

Quoted message said:

Quoted message said:

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

On Fri, 09 Jul 2004 06:09:51 -0700, jim beam <[email hidden]>

Quoted message said:

Quoted message said:

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

Quoted message said:

On Fri, 09 Jul 2004 06:09:51 -0700, jim beam <[email hidden]>

Quoted message said:

Quoted message said:

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
[email hidden]

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

Quoted message said:

On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email hidden]>

Quoted message said:

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.

Quoted message said:

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 hidden]

Bob Flumere said:

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 hidden]

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

Quoted message said:

On Wed, 07 Jul 2004 20:15:22 -0700, jim beam <[email hidden]>

Quoted message said:

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.

Quoted message said:

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 hidden]

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

Dale Benjamin said:

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?

Quoted message said:

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 <[email hidden]>

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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 hidden]

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 hidden]

On Mon, 12 Jul 2004 23:09:01 GMT, Bob Flumere <[email hidden]>

Quoted message said:

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

Dale Benjamin said:

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
==============================================

pinnah said:

Dale Benjamin said:

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.