CFR Wobble

Same as on any other bike - rest your knee on the top tube.

"Phil Cox" <[email hidden]> wrote in message
news:[email hidden]...
| Any thoughts on how to correct a speed wobble in a Scattante CFR (2002)?
Any
| thoughts are appreciated.
|
| Phil
|
|

doesn't that just address the symptoms, not the cause?

Doug Huffman said:

Same as on any other bike - rest your knee on the top tube.

"Phil Cox" <[email hidden]> wrote in message
news:[email hidden]...
| Any thoughts on how to correct a speed wobble in a Scattante CFR (2002)?
Any
| thoughts are appreciated.
|
| Phil
|
|

i've had success with changing wheels to one with slightly less dish &
stronger spokes. others report tires, headset bearings, shifting
saddle/handlebar positions, etc. other suggestions are googleable.

my thoughts on the cause are that you're looking at a dynamic system
with two primary resonators - wheels & frame. if they're in tune, you
can get this speed-wobble harmonic. try tuning them out, with a
different frame if necessary. resonance killers like "knee on the top
tube" will get you out of trouble, but clearly that's less than ideal -
you should be in a position where it doesn't arise in the first place.

Phil Cox said:

Any thoughts on how to correct a speed wobble in a Scattante CFR (2002)? Any
thoughts are appreciated.

Phil

Phil Cox said:

Any thoughts on how to correct a speed wobble in a Scattante CFR (2002)? Any
thoughts are appreciated.

Phil

I think if you did a Google search you'll find that the cause(s) of
speed wobble has to do with harmonics. Something like the way tuning
forks work. These harmonic variables at work are very elastic and
conditional, behaving differently for each rider+bike combo. Even the
weather has a big influence on wither or not you get speed wobble for
that particular moment. I encountered speed wobble only once with my
road bike. It was scary and I thought I would get seriously injured.
Managed to stop without incident by pumping the brakes. After this
incident I approached downhills with more caution by using the "knee on
top tube" procedure. I tried once to induce speed wobble while my knee
was on the top tube and going down the same hill as before but it never
appeared. This experiment with speed wobble happened three years ago.
Now a days I go downhill without fear of speed wobble and without using
the "knee on top tube" procedure. The only difference between now and
then is that when I go downhill I like to ride in the drops with my ass
hanging off the back-end of the saddle. Others in this thread have
suggested changing components to cure speed wobble. This will probably
work for the speed wobble on the bike, but what about the speed wobble
in one's heart?

May the "Force" be with you. Be one with the bike and in harmony with
the world around you.

Kenny Lee

jim beam said:

i've had success with changing wheels to one with slightly less dish &
stronger spokes.

How does wheel dish affect shimmy? Also, what affect would
that have on the front, since only the rear wheel is dished?

How does the strength of the spokes affect shimmy
(especially since I've never heard of a shimmy causing
broken spokes)?

Mark McMaster
[email hidden]

Mark McMaster said:

jim beam said:

i've had success with changing wheels to one with slightly less dish &
stronger spokes.

How does wheel dish affect shimmy?

it's the classic weight suspended in the middle of a rope scenario.

X-----------------------X
^
w

the closer the angle at the end of the ropes gets to horizontal, the
greater the tension on the rope. at perfect horizontal, tension is
infinity. for a wheel, if you want to prove it to yourself, take a
dished wheel, but it on the floor so the load is on the axle, then
_gently_ lean with your hands on opposite sides of the rim. if you have
the non-dished side towards you, you'll find the wheel fairly stiff
against your weight. if you have the dished side towards you however,
you'll find the wheel noticably more flexible. if you can maximize the
bracing angle, you can therefore maximize lateral stiffness. if the
wheel has significant lateral flex & springiness, togther with rider
weight & load, there will be a natural resonant frequency.

Quoted message said:

Also, what affect would that have on
the front, since only the rear wheel is dished?

i'm not sure it does affec the front /wheel/ significantly. frame
torsion will however cause significant steering "adjustments" as the
castor of the fork seeks center.

Quoted message said:

How does the strength of the spokes affect shimmy (especially since I've
never heard of a shimmy causing broken spokes)?

i don't think it does cause broken spokes. i've never heard of it at
any rate. thickness of the spokes affects stiffness, and stiffness
affects the degree of flex, spring rate and therefore resonant frequency.

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

Quoted message said:

Any thoughts on how to correct a speed wobble in a Scattante CFR (2002)? Any
thoughts are appreciated.

Phil

Bonjour

If you don't mind me asking, what height and weight are you, and what
size is your bike? Also how violent was the wobble, and what were the
riding conditions.

Merci

LGF

Quoted message said:

If you don't mind me asking, what height and weight are you, and what
size is your bike? Also how violent was the wobble, and what were the
riding conditions.

Ht: 5'10
Wt: 175
Sz: 59cm Scatatne CFR (bought a 59 to get "stretched out" for longer rides)
Wobble: I was going a fairly steep hill and it felt like the front end of my
bike was gonna blow up. I was ging about 42 MPH, and I was SURE that I was
going to endo and crash at that speed. A combination of pulse braking and
prayer was the only thing that hept me from being a splat.

I was told that I liekly did not have enough weight over my front tire, but
when I put the weight over my front, the rear seems to float. I always
thought a longer bike would/should be more stable, but I am starting to
think the bike is just too big for me, and that I need about a 54 to 56 cm.

Phil

jim beam said:

Mark McMaster said:

jim beam said:

i've had success with changing wheels to one with slightly less dish
& stronger spokes.

How does wheel dish affect shimmy?

it's the classic weight suspended in the middle of a rope scenario.

X-----------------------X
^
w

the closer the angle at the end of the ropes gets to horizontal, the
greater the tension on the rope. at perfect horizontal, tension is
infinity. for a wheel, if you want to prove it to yourself, take a
dished wheel, but it on the floor so the load is on the axle, then
_gently_ lean with your hands on opposite sides of the rim. if you have
the non-dished side towards you, you'll find the wheel fairly stiff
against your weight. if you have the dished side towards you however,
you'll find the wheel noticably more flexible. if you can maximize the
bracing angle, you can therefore maximize lateral stiffness. if the
wheel has significant lateral flex & springiness, togther with rider
weight & load, there will be a natural resonant frequency.

Ah, I see you're still confused about how the spoke tension
affects wheel stiffness (which means you're probably still
confused about how spoke tension affects wheel strength).
Wheels are linearly elastic, so they have the same lateral
stiffness from both sides (unless and until the spokes
become slack). See Damon Rinard's test on wheel lateral
stiffness, question 3, "Do dished wheels flex differently
from one side to the other."

Quoted message said:

Quoted message said:

How does the strength of the spokes affect shimmy (especially since
I've never heard of a shimmy causing broken spokes)?

i don't think it does cause broken spokes. i've never heard of it at
any rate. thickness of the spokes affects stiffness, and stiffness
affects the degree of flex, spring rate and therefore resonant frequency.

But you didn't say anything about spoke stiffness, you only
said spoke strength. If you want to increase stiffness, a
better way might be to increase the number of spokes, as
this tends to make the wheel more durable also.

It does seem odd that your two suggestions for addressing
shimmy actually have opposite affects. Decreasing the rear
wheel dish tends to make the wheel less stiff - the only
practical way to decrease wheel dish on modern 8/9/10spd
road wheels is to move the left flange inward, which
decreases the bracing angle, and makes wheels more flexible.
On the other hand, your suggestion to using thicker spokes
will make the wheel stiffer.

Mark McMaster
[email hidden]

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

Quoted message said:

Quoted message said:

If you don't mind me asking, what height and weight are you, and what
size is your bike? Also how violent was the wobble, and what were the
riding conditions.

Ht: 5'10
Wt: 175
Sz: 59cm Scatatne CFR (bought a 59 to get "stretched out" for longer rides)
Wobble: I was going a fairly steep hill and it felt like the front end of my
bike was gonna blow up. I was ging about 42 MPH, and I was SURE that I was
going to endo and crash at that speed. A combination of pulse braking and
prayer was the only thing that hept me from being a splat.

I was told that I liekly did not have enough weight over my front tire, but
when I put the weight over my front, the rear seems to float. I always
thought a longer bike would/should be more stable, but I am starting to
think the bike is just too big for me, and that I need about a 54 to 56 cm.

I agree with the weight over the front tyre - I have been advised this
myself and tried it out. Also keeping your weight forward puts your
arms in a better position to act as steering dampers - further back
and your arms are in a very strong position and can react too forcibly
and too quickly, which can add to and perhaps actually cause the
problem. Add to this an understandable increased nervousness, things
can may get worse.

People who say placing your knee on the top-tube quickly abates the
sort of speed wobble you report have never experienced one!

LGF

Mark McMaster said:

jim beam said:

Mark McMaster said:

jim beam wrote:

> i've had success with changing wheels to one with slightly less dish
> & stronger spokes.

How does wheel dish affect shimmy?

it's the classic weight suspended in the middle of a rope scenario.

X-----------------------X
^
w

the closer the angle at the end of the ropes gets to horizontal, the
greater the tension on the rope. at perfect horizontal, tension is
infinity. for a wheel, if you want to prove it to yourself, take a
dished wheel, but it on the floor so the load is on the axle, then
_gently_ lean with your hands on opposite sides of the rim. if you
have the non-dished side towards you, you'll find the wheel fairly
stiff against your weight. if you have the dished side towards you
however, you'll find the wheel noticably more flexible. if you can
maximize the bracing angle, you can therefore maximize lateral
stiffness. if the wheel has significant lateral flex & springiness,
togther with rider weight & load, there will be a natural resonant
frequency.

Ah, I see you're still confused about how the spoke tension affects
wheel stiffness (which means you're probably still confused about how
spoke tension affects wheel strength). Wheels are linearly elastic, so
they have the same lateral stiffness from both sides (unless and until
the spokes become slack). See Damon Rinard's test on wheel lateral
stiffness, question 3, "Do dished wheels flex differently from one side
to the other."

please do the geometry. please do the experiment i describe. please
explain how all damon's results are "slanted upward toward the right in
every case".

Quoted message said:

Quoted message said:

Quoted message said:

How does the strength of the spokes affect shimmy (especially since
I've never heard of a shimmy causing broken spokes)?

i don't think it does cause broken spokes. i've never heard of it at
any rate. thickness of the spokes affects stiffness, and stiffness
affects the degree of flex, spring rate and therefore resonant frequency.

But you didn't say anything about spoke stiffness, you only said spoke
strength. If you want to increase stiffness, a better way might be to
increase the number of spokes, as this tends to make the wheel more
durable also.

in the following statment: "thickness of the spokes affects stiffness,
and stiffness affects the degree of flex, spring rate and therefore
resonant frequency." where do i talk about spoke strength?

Quoted message said:

It does seem odd that your two suggestions for addressing shimmy
actually have opposite affects. Decreasing the rear wheel dish tends to
make the wheel less stiff - the only practical way to decrease wheel
dish on modern 8/9/10spd road wheels is to move the left flange inward,
which decreases the bracing angle, and makes wheels more flexible. On
the other hand, your suggestion to using thicker spokes will make the
wheel stiffer.

where i'm from, decreasing dish usually means increasing bracing angle,
or moving the flange outward. perhaps we have a terminology problem?

jim beam said:

Mark McMaster said:

jim beam said:

Mark McMaster wrote:

Ah, I see you're still confused about how the spoke tension affects
wheel stiffness (which means you're probably still confused about how
spoke tension affects wheel strength). Wheels are linearly elastic, so
they have the same lateral stiffness from both sides (unless and until
the spokes become slack). See Damon Rinard's test on wheel lateral
stiffness, question 3, "Do dished wheels flex differently from one
side to the other."

please do the geometry. please do the experiment i describe. please
explain how all damon's results are "slanted upward toward the right in
every case".

You should probably read Rinard's report before commenting
on it. He says:

"A dished wheel might deflect slightly more due to loads
applied from the flatter side than it does due to equivalent
loads applied from the other, but it is unclear from this
data whether this is really the case. It may be true in
theory, because of the difference in bracing angle between
the right side spokes and the left side spokes: the more
favorable bracing angle of the left side spokes may be
better able to restrain the rim against deflection to the
right than the right side spokes might brace the rim against
deflection to the left.

"If it exists, the difference is very small: on the order of
just a few thousandths of an inch, i.e. within the error of
my measurement, even under the larger-than-life load of
25.78 pounds that I used for this test. Even if a small
difference exists in this artificially high load case, no
one will notice the even smaller difference the wheel might
display while riding."

So yes, there may be a small change in lateral stiffness as
the wheel is flexed due to the change in bracing angles of
the spokes - but the change is smaller than would be
detected by flexing the wheel by hand, as in your
experiment. Even the small changes in stiffness measured by
Rinard where in response to relative large loads. In the
smaller range of loads more likely to be experienced, there
will only a be a minor change in stiffnesses.

Here is a better experiment than laying the wheel on the
ground and pressing with your weight on opposites sides:
With the wheel in the frame, press the right back and forth
laterally between the seat stays. This is a better
representation of both the application of lateral load and
the amount of deflection that the rim experiences in use. I
doubt that you'll be able to detect a difference in the
right or left stiffnesses.

Quoted message said:

Quoted message said:

But you didn't say anything about spoke stiffness, you only said spoke
strength. If you want to increase stiffness, a better way might be to
increase the number of spokes, as this tends to make the wheel more
durable also.

in the following statment: "thickness of the spokes affects stiffness,
and stiffness affects the degree of flex, spring rate and therefore
resonant frequency." where do i talk about spoke strength?

The google record of this thread can be found at:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=adff4513.0407200116.6e8f6c61%40posting.google.com&rnum=1&prev=/groups%3Fq%3Dphil%2Bscattante%2Bcfr%26hl%3Den%26lr%3D%26ie%3DUTF-8%26scoring%3Dd%26selm%3Dadff4513.0407200116.6e8f6c61%2540posting.google.com%26rnum%3D1

The direct quote from your post (number four in the thread
above):

"i've had success with changing wheels to one with slightly
less dish & stronger spokes."

Quoted message said:

Quoted message said:

It does seem odd that your two suggestions for addressing shimmy
actually have opposite affects. Decreasing the rear wheel dish tends
to make the wheel less stiff - the only practical way to decrease
wheel dish on modern 8/9/10spd road wheels is to move the left flange
inward, which decreases the bracing angle, and makes wheels more
flexible. On the other hand, your suggestion to using thicker spokes
will make the wheel stiffer.

where i'm from, decreasing dish usually means increasing bracing angle,
or moving the flange outward. perhaps we have a terminology problem?

Moving which flange outboard? The dish in rear wheels is
created because the left flange is further outboard than the
right flange. But on modern 8/9/10spd wheels, the right
flange can not be moved further outward, or the derailleur
will interfere with the spokes. The only flange that can be
moved outward is the left flange, which would only further
increase the imbalance between the right and left bracing
angles. While this will increase the lateral stiffness, it
will also increase dish.

Mark McMaster
[email hidden]

mark, you're twisting what i say. play it straight please.

Mark McMaster said:

jim beam said:

Mark McMaster said:

jim beam wrote:

> Mark McMaster wrote:

Ah, I see you're still confused about how the spoke tension affects
wheel stiffness (which means you're probably still confused about how
spoke tension affects wheel strength). Wheels are linearly elastic,
so they have the same lateral stiffness from both sides (unless and
until the spokes become slack). See Damon Rinard's test on wheel
lateral stiffness, question 3, "Do dished wheels flex differently
from one side to the other."

please do the geometry. please do the experiment i describe. please
explain how all damon's results are "slanted upward toward the right in
every case".

You should probably read Rinard's report before commenting on it. He says:

"A dished wheel might deflect slightly more due to loads applied from
the flatter side than it does due to equivalent loads applied from the
other, but it is unclear from this data whether this is really the case.
It may be true in theory, because of the difference in bracing angle
between the right side spokes and the left side spokes: the more
favorable bracing angle of the left side spokes may be better able to
restrain the rim against deflection to the right than the right side
spokes might brace the rim against deflection to the left.

"If it exists, the difference is very small: on the order of just a few
thousandths of an inch, i.e. within the error of my measurement, even
under the larger-than-life load of 25.78 pounds that I used for this
test. Even if a small difference exists in this artificially high load
case, no one will notice the even smaller difference the wheel might
display while riding."

So yes, there may be a small change in lateral stiffness as the wheel is
flexed due to the change in bracing angles of the spokes - but the
change is smaller than would be detected by flexing the wheel by hand,
as in your experiment. Even the small changes in stiffness measured by
Rinard where in response to relative large loads. In the smaller range
of loads more likely to be experienced, there will only a be a minor
change in stiffnesses.

Here is a better experiment than laying the wheel on the ground and
pressing with your weight on opposites sides: With the wheel in the
frame, press the right back and forth laterally between the seat stays.
This is a better representation of both the application of lateral load
and the amount of deflection that the rim experiences in use. I doubt
that you'll be able to detect a difference in the right or left
stiffnesses.

Quoted message said:

Quoted message said:

But you didn't say anything about spoke stiffness, you only said
spoke strength. If you want to increase stiffness, a better way
might be to increase the number of spokes, as this tends to make the
wheel more durable also.

in the following statment: "thickness of the spokes affects stiffness,
and stiffness affects the degree of flex, spring rate and therefore
resonant frequency." where do i talk about spoke strength?

The google record of this thread can be found at:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=adff4513.0407200116.6e8f6c61%40posting.google.com&rnum=1&prev=/groups%3Fq%3Dphil%2Bscattante%2Bcfr%26hl%3Den%26lr%3D%26ie%3DUTF-8%26scoring%3Dd%26selm%3Dadff4513.0407200116.6e8f6c61%2540posting.google.com%26rnum%3D1

The direct quote from your post (number four in the thread above):

"i've had success with changing wheels to one with slightly less dish &
stronger spokes."

Quoted message said:

Quoted message said:

It does seem odd that your two suggestions for addressing shimmy
actually have opposite affects. Decreasing the rear wheel dish tends
to make the wheel less stiff - the only practical way to decrease
wheel dish on modern 8/9/10spd road wheels is to move the left flange
inward, which decreases the bracing angle, and makes wheels more
flexible. On the other hand, your suggestion to using thicker spokes
will make the wheel stiffer.

where i'm from, decreasing dish usually means increasing bracing angle,
or moving the flange outward. perhaps we have a terminology problem?

Moving which flange outboard? The dish in rear wheels is created because
the left flange is further outboard than the right flange. But on
modern 8/9/10spd wheels, the right flange can not be moved further
outward, or the derailleur will interfere with the spokes. The only
flange that can be moved outward is the left flange, which would only
further increase the imbalance between the right and left bracing
angles. While this will increase the lateral stiffness, it will also
increase dish.

Mark McMaster
[email hidden]