Pulsing Rear Wheel

Steve Spencer said:

I just noticed this behavior and am wondering if its a problem. I'm
standing next to my bike, pick the rear wheel off the ground, and hold
it there by the saddle. With my other hand, in a big gear, I spin the
wheel as fast as I can with my other hand.

After I stop pedaling, the wheel is spinning rapidly. It is also pulsing
up and down about 2 times a second. Any idea what could cause this?

The wheel is slightly unbalanced, which is entirely normal.

Quoted message said:

I don't notice anything when riding.

Therefore it is not a problem and there is no need to do anything about it.

Steve Spencer said:

I just noticed this behavior and am wondering if its a problem. I'm
standing next to my bike, pick the rear wheel off the ground, and
hold it there by the saddle. With my other hand, in a big gear, I
spin the wheel as fast as I can with my other hand.

Quoted message said:

After I stop pedaling, the wheel is spinning rapidly. It is also
pulsing up and down about 2 times a second. Any idea what could
cause this?

Quoted message said:

I don't notice anything when riding. The rim, a Velomax Tempest, is
within 2mm of lateral and vertical true, and the hub feels very
smooth. Could it be the freehub?

The imbalance is typical of bicycle wheels where the heavy spot is
usually opposite the valve stem because there is a splicing insert
where the rim is joined. If it isn't there than it is at the valve
stem because the tube is heavier there. In either case it has no
bearing on riding because the forces are so small, even at 60mph
speeds, that there is no point in balancing the wheel.

I suspect most children, in the days when one rode a bicycle to
school, knew this because it was fun to turn the bicycle upside down
and hand crank the wheel up to a speed that nearly lifted the saddle
off the ground. In fact this is probably the only thing that is
better done with a bicycle upside down rather than right side up...
although one sees bicycles this position on occasion when someone
changes a flat. It looks more like durability testing for saddles and
spedometers to me.

Jobst Brandt
[email hidden]

Quoted message said:

Steve Spencer said:

I just noticed this behavior and am wondering if its a problem. I'm
standing next to my bike, pick the rear wheel off the ground, and
hold it there by the saddle. With my other hand, in a big gear, I
spin the wheel as fast as I can with my other hand.

Quoted message said:

After I stop pedaling, the wheel is spinning rapidly. It is also
pulsing up and down about 2 times a second. Any idea what could
cause this?

Quoted message said:

I don't notice anything when riding. The rim, a Velomax Tempest, is
within 2mm of lateral and vertical true, and the hub feels very
smooth. Could it be the freehub?

The imbalance is typical of bicycle wheels where the heavy spot is
usually opposite the valve stem because there is a splicing insert
where the rim is joined. If it isn't there than it is at the valve
stem because the tube is heavier there. In either case it has no
bearing on riding because the forces are so small, even at 60mph
speeds, that there is no point in balancing the wheel.

have you ever balanced one to see if it affected shimmy?

Quoted message said:

I suspect most children, in the days when one rode a bicycle to
school, knew this because it was fun to turn the bicycle upside down
and hand crank the wheel up to a speed that nearly lifted the saddle
off the ground. In fact this is probably the only thing that is
better done with a bicycle upside down rather than right side up...
although one sees bicycles this position on occasion when someone
changes a flat. It looks more like durability testing for saddles and
spedometers to me.

Jobst Brandt
[email hidden]

old crow said:

Quoted message said:

The imbalance is typical of bicycle wheels where the heavy spot is
usually opposite the valve stem because there is a splicing insert
where the rim is joined. If it isn't there than it is at the valve
stem because the tube is heavier there. In either case it has no
bearing on riding because the forces are so small, even at 60mph
speeds, that there is no point in balancing the wheel.

Quoted message said:

have you ever balanced one to see if it affected shimmy?

Yes, and you can find it in the Google archives, I'm sure Carl Fogel
could help you. However, instead of alluding to homework assignments
for readers of this newsgroup, how about offering your own findings on
subjects instead of sniping from cover.

Jobst Brandt
[email hidden]

Does the freewheel or cassette float around while the
wheel spins.

Quoted message said:

old crow said:

Quoted message said:

The imbalance is typical of bicycle wheels where the heavy spot is
usually opposite the valve stem because there is a splicing insert
where the rim is joined. If it isn't there than it is at the valve
stem because the tube is heavier there. In either case it has no
bearing on riding because the forces are so small, even at 60mph
speeds, that there is no point in balancing the wheel.

Quoted message said:

have you ever balanced one to see if it affected shimmy?

Yes, and you can find it in the Google archives, I'm sure Carl Fogel
could help you. However, instead of alluding to homework assignments
for readers of this newsgroup, how about offering your own findings on
subjects instead of sniping from cover.

Jobst Brandt
[email hidden]

in this instance, i'm not sniping, [unlike your passive-aggressive
header] - i'm asking whether you investigated. and i have google
bookmarked on my own browser, thanks for being so helpful.

Quoted message said:

old crow said:

Quoted message said:

The imbalance is typical of bicycle wheels where the heavy spot is
usually opposite the valve stem because there is a splicing insert
where the rim is joined. If it isn't there than it is at the valve
stem because the tube is heavier there. In either case it has no
bearing on riding because the forces are so small, even at 60mph
speeds, that there is no point in balancing the wheel.

Quoted message said:

have you ever balanced one to see if it affected shimmy?

Yes, and you can find it in the Google archives, I'm sure Carl Fogel
could help you. However, instead of alluding to homework assignments
for readers of this newsgroup, how about offering your own findings on
subjects instead of sniping from cover.

Jobst Brandt
[email hidden]

Dear Jobst,

Frankly, I can't figure out what you were doing from your
description of how you prepared your wheel for your
wheel-balance experiment:

"After hearing so much about results with balancing wheels,
I balanced my front wheel, that was 3 grams out of balance,
by wrapping solder wire around the appropriate spoke. At
the same time I wrapped about 10 grams of solder on the
opposite spoke 180 degrees away but slid the wire to the hub
inside the spoke crossing by pushing the spokes apart to let
the coil pass. A 36x3 wheel has crossings close to the hub
so the weight was essentially ineffective in wheel balance
that was essentially perfect with the 3 gram weight on the
other side."

http://groups.google.co.uk/groups?q=jobst+shimmy+%22out-of-balance%22&hl=en&lr=&group=rec.bicycles.tech&scoring=d&selm=911a4m%246ut%243%40hplms2.hpl.hp.com&rnum=2

It sounds as if you wrapped 3 grams of solder wire around
the appropriate spoke (opposite the heavy spot on your
wheel, presumably at the nipple?).

So far, so good.

But then you wrapped 10 grams of solder around the spoke
opposite that one ("the opposite spoke"😉 at the hub.

What was the reason for the second weight at the hub?

Carl Fogel

Steve Spencer said:

I just noticed this behavior and am wondering if its a problem. I'm
standing next to my bike, pick the rear wheel off the ground, and hold
it there by the saddle. With my other hand, in a big gear, I spin the
wheel as fast as I can with my other hand.

After I stop pedaling, the wheel is spinning rapidly. It is also pulsing
up and down about 2 times a second. Any idea what could cause this?

I don't notice anything when riding. The rim, a Velomax Tempest, is
within 2mm of lateral and vertical true, and the hub feels very smooth.
Could it be the freehub?

Take off the spoke reflector if there is one. Get it rounder
than 2mm ( you have a dent? 2mm is a lot for a new wheel,
typical of an urban commuting wheel) if that pulsing bothers
you. It isn't noticeable once you're on the bike.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Carl Fogel said:

Quoted message said:

Quoted message said:

> The imbalance is typical of bicycle wheels where the heavy spot
> is usually opposite the valve stem because there is a splicing
> insert where the rim is joined. If it isn't there than it is at
> the valve stem because the tube is heavier there. In either case
> it has no bearing on riding because the forces are so small, even
> at 60mph speeds, that there is no point in balancing the wheel.

Quoted message said:

Quoted message said:

Quoted message said:

have you ever balanced one to see if it affected shimmy?

Quoted message said:

Quoted message said:

Yes, and you can find it in the Google archives, I'm sure Carl
Fogel could help you. However, instead of alluding to homework
assignments for readers of this newsgroup, how about offering your
own findings on subjects instead of sniping from cover.

Quoted message said:

Frankly, I can't figure out what you were doing from your
description of how you prepared your wheel for your wheel-balance
experiment:

# "After hearing so much about results with balancing wheels, I
# balanced my front wheel, that was 3 grams out of balance, by
# wrapping solder wire around the appropriate spoke. At the same time
# I wrapped about 10 grams of solder on the opposite spoke 180 degrees
# away but slid the wire to the hub inside the spoke crossing by
# pushing the spokes apart to let the coil pass. A 36x3 wheel has
# crossings close to the hub so the weight was essentially ineffective
# in wheel balance that was essentially perfect with the 3 gram weight
# on the other side."

http://tinyurl.com/5yqg3

Quoted message said:

It sounds as if you wrapped 3 grams of solder wire around the
appropriate spoke (opposite the heavy spot on your wheel, presumably
at the nipple?).

Yes.

Quoted message said:

So far, so good.

Quoted message said:

But then you wrapped 10 grams of solder around the spoke opposite
that one ("the opposite spoke"😉 at the hub.

Quoted message said:

What was the reason for the second weight at the hub?

That weight was moved to the center of the wheel where it had no
effect so that it could be shifted to the periphery of the wheel or to
the hub to crate a large imbalance on the balanced wheel or not, an
imbalance greater than the one that most wheels have naturally.

As explained in that item, I rode down the smooth test road balanced
and unbalanced. There was no perceptible difference.

In a similar comparison test I also tested Rolf, Bontrager and an MA-2
36-spoke wheel for shimmy. All three of these wheels shimmied
identically which was subsequently verified by instrumentation at a
test lab.

I also tested my wheel with a water filled tire (to the exclusion of
air) and found that the bicycle shimmied as well as with the same
wheel and the tire air filled. I had no instrumentation to measure
frequency although I felt that it might possibly have had a lower
frequency than with air.

Jobst Brandt
[email hidden]

Steve Spencer said:

I just noticed this behavior and am wondering if its a problem. I'm
standing next to my bike, pick the rear wheel off the ground, and hold
it there by the saddle. With my other hand, in a big gear, I spin the
wheel as fast as I can with my other hand.

After I stop pedaling, the wheel is spinning rapidly. It is also pulsing
up and down about 2 times a second. Any idea what could cause this?

I don't notice anything when riding. The rim, a Velomax Tempest, is
within 2mm of lateral and vertical true, and the hub feels very smooth.
Could it be the freehub?

Thanks,
Steve

Normal balance issue.
2 mm of true sounds like it could be improved by 4 times to be in more typical range.

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

Quoted message said:

In a similar comparison test I also tested Rolf, Bontrager and an MA-2
36-spoke wheel for shimmy. All three of these wheels shimmied
identically which was subsequently verified by instrumentation at a
test lab.

Hey Jobst-

I always thought - possibly in error - that "shimmy" referred to a lateral
oscillation - such as when a tie rod end is worn out on an automobile. Am I
wrong?

Dan

Quoted message said:

Carl Fogel said:

Quoted message said:

>>The imbalance is typical of bicycle wheels where the heavy spot
>>is usually opposite the valve stem because there is a splicing
>>insert where the rim is joined. If it isn't there than it is at
>>the valve stem because the tube is heavier there. In either case
>>it has no bearing on riding because the forces are so small, even
>>at 60mph speeds, that there is no point in balancing the wheel.

Quoted message said:

Quoted message said:

>have you ever balanced one to see if it affected shimmy?

Quoted message said:

Quoted message said:

Yes, and you can find it in the Google archives, I'm sure Carl
Fogel could help you. However, instead of alluding to homework
assignments for readers of this newsgroup, how about offering your
own findings on subjects instead of sniping from cover.

Quoted message said:

Frankly, I can't figure out what you were doing from your
description of how you prepared your wheel for your wheel-balance
experiment:

# "After hearing so much about results with balancing wheels, I
# balanced my front wheel, that was 3 grams out of balance, by
# wrapping solder wire around the appropriate spoke. At the same time
# I wrapped about 10 grams of solder on the opposite spoke 180 degrees
# away but slid the wire to the hub inside the spoke crossing by
# pushing the spokes apart to let the coil pass. A 36x3 wheel has
# crossings close to the hub so the weight was essentially ineffective
# in wheel balance that was essentially perfect with the 3 gram weight
# on the other side."

http://tinyurl.com/5yqg3

Quoted message said:

It sounds as if you wrapped 3 grams of solder wire around the
appropriate spoke (opposite the heavy spot on your wheel, presumably
at the nipple?).

Yes.

Quoted message said:

So far, so good.

Quoted message said:

But then you wrapped 10 grams of solder around the spoke opposite
that one ("the opposite spoke"😉 at the hub.

Quoted message said:

What was the reason for the second weight at the hub?

That weight was moved to the center of the wheel where it had no
effect so that it could be shifted to the periphery of the wheel or to
the hub to crate a large imbalance on the balanced wheel or not, an
imbalance greater than the one that most wheels have naturally.

As explained in that item, I rode down the smooth test road balanced
and unbalanced. There was no perceptible difference.

In a similar comparison test I also tested Rolf, Bontrager and an MA-2
36-spoke wheel for shimmy. All three of these wheels shimmied
identically which was subsequently verified by instrumentation at a
test lab.

what testing? what instrumentation? what lab? where are the results?

Quoted message said:

I also tested my wheel with a water filled tire (to the exclusion of
air) and found that the bicycle shimmied as well as with the same
wheel and the tire air filled. I had no instrumentation to measure
frequency although I felt that it might possibly have had a lower
frequency than with air.

Jobst Brandt
[email hidden]

There are two reasons I can see why a wheel that vibrates in the "inverted
bike" position would not do so while being ridden:

1.) People seldom ride as fast as the bike can be pedalled up-side-down.
2.) When you are riding, your body weight and frame weight combine, to
produce a much lower resonant frequency than the inverted bike without a
rider. If the resonant frequency and the rotational frequency are closer
together (bike inverted) the amplitude will be greater.

Dan said:

I always thought - possibly in error - that "shimmy" referred to a lateral
oscillation - such as when a tie rod end is worn out on an automobile. Am I
wrong?

Yes! It is apparently a teenage mating ritual accompanied by loud music :-)

Seriously fellas - I don't really understand what all this discussion about
balancing a damned bicycle wheel is all about. I ride wheels that are "true" in
terms of no lateral wobble on roads that are full of pot-holes, cracks and
uneven slabs of concrete. The wheels are on either 26" MTBs or old 27" road
bikes

Besides watching out for inattentive drivers as I ride during the summer, I'd
be damned if I could ever notice any unbalanced effect on any of my bicycles
(mind you I only ride (so far) cheap Chinese built MTBs and 30 y.o. Peugeots
(10 speed). I never noticed any unbalance on my old CCM single speed with the
big 28 X 1 1/2 tires either.

Should I expect anything different (ie no NOTICEABLE balance shimmy/pulse) with
my soon to be built touring bicycle with 48 spoked wheels?

Leo Lichtman said:

There are two reasons I can see why a wheel that vibrates in the
"inverted bike" position would not do so while being ridden:

Quoted message said:

1.) People seldom ride as fast as the bike can be pedalled
up-side-down.

That is definitely not the case with most active bicyclists. I
regularly see riders spinning downgrade at rates that you cannot
achieve by hand on an upturned bicycle. They do this in 52-13 gears
and the like.

Quoted message said:

2.) When you are riding, your body weight and frame weight combine,
to produce a much lower resonant frequency than the inverted
bike without a rider. If the resonant frequency and the
rotational frequency are closer together (bike inverted) the
amplitude will be greater.

I don't believe resonant frequency is the problem but rather that the
imbalance forces are too small to make the tire cushion compress
perceptibly.

Jobst Brandt
[email hidden]

Ken Pisichko said:

Seriously fellas - I don't really understand what all this discussion about
balancing a damned bicycle wheel is all about. I ride wheels that are "true"
in
terms of no lateral wobble on roads that are full of pot-holes, cracks and
uneven slabs of concrete. The wheels are on either 26" MTBs or old 27" road
bikes

Besides watching out for inattentive drivers as I ride during the summer, I'd
be damned if I could ever notice any unbalanced effect on any of my bicycles
(mind you I only ride (so far) cheap Chinese built MTBs and 30 y.o. Peugeots
(10 speed). I never noticed any unbalance on my old CCM single speed with the
big 28 X 1 1/2 tires either.

Should I expect anything different (ie no NOTICEABLE balance shimmy/pulse)
with
my soon to be built touring bicycle with 48 spoked wheels?

As you have surmised, the radial balance of a bike wheel, or the lack of
it, is swamped by the much larger mass of bike and rider.

It has never been an issue for me with any bike, although most bike
wheels have enough unbalance that it is obvious when the bike is
supported without the rider's mass and with the wheels off the ground.

Enjoy your new wheels (and the rest of the bike too). You can put any
concerns about balancing out of your head.

--
Ted Bennett
Portland, OR

On Mon, 28 Feb 2005 06:44:40 GMT,
[email hidden] wrote:

[snip]

Quoted message said:

I regularly see riders spinning downgrade at rates that you cannot
achieve by hand on an upturned bicycle. They do this in 52-13 gears
and the like.

[snip]

Quoted message said:

Jobst Brandt
[email hidden]

Dear Jobst,

What kind of speeds do you have in mind?

I can easily spin the wheel on my upside down bike to
impressive speeds. (It starts hopping, of course.)

You only have to crank a 175 mm pedal on a 53 x 11 like my
touring bike at 6.4 miles per hour to achieve a rear 700c
tire speed of about 60 mph.

I have an upside-down 48 x 12 700c in my basement, an old
Schwinn LeTour triple with a speedometer on its rear wheel
for fooling around with hand-cranked speeds.

I just cranked the 48 x 12 up to 55.0 mph. That happens to
be the same gear ratio as the 52 x 13 that you mention.

Both gearings are lower and slower than the commonly
available 53 x 11, which would produce about 66 mph at the
same cadence of about 174 rpm.

Carl Fogel

<[email hidden]> wrote: I don't believe resonant
frequency is the problem but rather that the imbalance forces are too small
to make the tire cushion compress perceptibly.
^^^^^^^^^^^^^^^^
I think we are both right. What I didn't address, is the fact that the
unbalanced force becomes large at high RPM, while increased the mass, when
the rider is included, results in a vibrating system with a low resonant
frequency. This is essentially the same as what you said: "the imbalance
forces are too small to make the tire compress perceptibly." I suspect that
if the bike could somehow be propelled down a hill at high speed without a
rider, it would hop. This could probably be tested on a stationary
treadmill type machine, but I don't have one.

Quoted message said:

Does the freewheel or cassette float around while the
wheel spins.

That's normal too. Freewheel bearings are assembled to rather poor
tolerances, usually with simple shims to adjust clearance. They don't
have to be very good because they never carry any real load.