From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: front wheel wobble
Date: 12 Nov 1998 18:53:49 GMT

wlim writes anonymously:

>>> I had a rear wheel to which I added approximately three grams of
>>> weight at one location to balance it.  It was noticeably improved
>>> as evidenced by a lot less shaking when spinning the wheel at high
>>> velocity with the bike upside down.

>> Nice experiment but no dice.  We don't ride upside down bicycles.

> This was to illustrate that the addition of the weight reduced the
> imbalance, which can be perceived when spinning the wheel rapidly
> while the bike is upside down.  We do ride bicycles in which wheels
> spin, and this orientation provides a easy way to observe the effect
> of wheel imbalance.

You removed a principal constraint by allowing the wheel to spin
freely.  In reality the wheel is constrained to roll on the ground
with a tire so hard that its imbalance forces are insignificant
to the compliance of the tire, unlike hat of a car tire that has
about the same compliance and about 40 times the mass.  They are
not alike.

>>> Both myself and a friend did blind testing in which the strip of
>>> lead tape that was used was either placed inside the tire under
>>> the tube or not, and we both correctly and easily determined
>>> whether or not the weight was in place by coasting down a freshly
>>> paved hill at 45 MPH.

>> I don't believe a word of it.  Where was the lead strip, between
>> the tire and tube or between the rim and tube?  If it was between
>> the tire and tube (under the tread) you were feeling the lump, not
>> the imbalance.  Beyond that, three grams is about the imbalance of
>> any conventional wheel.  If this were perceptible, do you think
>> professional racing teams would ride unbalanced wheels?

> The lead strip was placed underneath the tube and over the rim
> strip. [...]  Had the lead strip been placed between the tube and
> the tire and caused a lump in the tread, any perceived vibration
> would have been worse, not better.

The reason I asked is that lead between tube and tire a lump of
stiffer tread would be felt and lead between tube and rim would cause
problems in seating the tire.  Both of these conditions have nothing
to do with balance.

> The two riders are 200 and 150 pounds.  The road is freshly paved
> blacktop, about 7%, and we reach speeds between 43 and 48 MPH.

That sounds reasonable except that the 150lb rider would not reach
nearly the speed of the 200lb rider, position and clothing being
equal.  What differences did you observe on these runs?

> As to why it is not done in the professional peleton, you yourself
> have said that asking a technical question to a professional racer,
> who may not have even finished high school, is of dubious value.

I did not say the racers are not pragmatic, only that they don't
necessarily know why some things are done for technical reasons.
Typical of this was the reason for road and track glue for tubulars.

> The fact that they also ride equipment, such as Spinergy wheel,
> which you consider a technically poorly designed or implemented
> product (or both), seems to illustrate a degree of indifference that
> would explain this.

They get paid to ride the stuff and as long as the manufacturer can
make it work so that it doesn't interfere with their success, they
ride it.  The domestiques ride disk wheels and other heavy aero
wheels in hill climbs, and the public eats it up, not knowing that
the ET of these riders does not count at all, so long as they finish
ahead of the broom wagon.  You're grasping at straws.

> In any event, there are other more significant factors:
> professionals regularly go through many tires, and any tire change
> would require a re-balance, which would be very time consuming
> considering the large number of wheels a professional team uses.

You ought to see the preparations of team equipment and realize that
wrapping lead wire around spokes is a common way of balancing spoked
wheels for cars and motorcycles.

> It is also more difficult to place a strip of lead on a tubular,
> unless it were adhered to the inside edge of the rim, assuming it's
> not a V-shaped rim.  It is difficult to spin the front wheel rim
> fast enough to determine the effect of any placement of a balancing
> weight, and there is no current machine that I know of which will
> spin balance a bicycle wheel.

>>> On automobiles wheels, the addition of only marginally greater
>>> weights will remove vibration that is noticeable at speeds
>>> sometimes not much greater than 45 MPH, despite the higher mass of
>>> automobile wheels and the intervening suspension components,
>>> including all sorts of bushings which are designed to isolate the
>>> suspension from the frame.

>> I see you are deducing your results from auto tires that are wholly
>> different from bicycles.  If there weren't this difference, then
>> you would see wheel balancing in the bicycle industry, but you
>> don't.  Your novel discovery of this requirement that apparently no
>> one else has made is highly presumptuous.

> I don't see how balancing a wheel is significantly different in an
> automobile wheel versus a bicycle wheel.  They both spin.

Maybe if you considered a railway wheel you could see the effect.  The
lack of compliance of the tire has a lot to do with it.  You may not
recall bias ply car tires, but they has so much damping that balance
wasn't as important then except that those tires had larger
manufacturing irregularities.  The permissible imbalance weight of
radial car tires shrunk with the advent of radial tires.

> In any event, a several gram weight imbalance on an 18 kg car wheel
> can be felt at speeds in a car that are reachable by a bicycle.  It
> is not difficult to imagine that a three gram weight imbalance on a
> 1 kg wheel can be felt as well.  I'd suggest you or others actually
> try it and see if you can notice it.

How about turning that around and trying to feel that there is an
imbalance in a typical bicycle wheel.  As I said, I coast often on
highways at speeds over 40mph and can detect no ripple.  I am not
convinced of what you seem to feel.

> We can easily perceive this as a significant diminishment in what
> feels like road graininess, similar to the effect of riding on
> concrete versus smooth blacktop.

I don't think so.  One is a random rushing sound, the other a rhythmic
once-around.  I think the difference can easily be distinguished.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: front wheel wobble (long)
Date: 13 Nov 1998 17:38:47 GMT

Wayne Lim writes:

>> You removed a principal constraint by allowing the wheel to spin
>> freely.  In reality the wheel is constrained to roll on the ground
>> with a tire so hard that its imbalance forces are insignificant
>> to the compliance of the tire, unlike hat of a car tire that has
>> about the same compliance and about 40 times the mass.  They are
>> not alike.

> Oh, I now understand.  You are correct - the compliance of the tire
> at the pressures we used, 110-130 PSI, is minimal when compared to
> the 3 grams of wheel imbalance.  I don't know how to explain this.

The point is that car tires bounce completely off the road when used
with imbalance and they do this because they have a low spring rate
compared to their mass.  You can estimate that by the rate at which
the two wheel bounce... like a table tennis ball and a basket ball.
The bicycle tire is more like the table tennis ball

>> The reason I asked is that lead between tube and tire a lump of
>> stiffer tread would be felt and lead between tube and rim would
>> cause problems in seating the tire.  Both of these conditions have
>> nothing to do with balance.

> The lead strip itself is very thin, probably a half mm at most.  The
> strip was about 1 cm wide, and about 2-3 cm long.  I don't know if
> the placement under the tube but over the strip would cause a
> problem, but it might since the Velox is pretty thick as well, but
> as I said, the tire seated easily and evenly.

>>> The fact that they also ride equipment, such as Spinergy wheel,
>>> which you consider a technically poorly designed or implemented
>>> product (or both), seems to illustrate a degree of indifference
>>> that would explain this.

>> They get paid to ride the stuff and as long as the manufacturer can
>> make it work so that it doesn't interfere with their success, they
>> ride it.  The domestiques ride disk wheels and other heavy aero
>> wheels in hill climbs, and the public eats it up, not knowing that
>> the ET of these riders does not count at all, so long as they
>> finish ahead of the broom wagon.  You're grasping at straws.

> But it's not only the domestiques that use this equipment.  The
> contenders do as well, since they are much more often than not the
> subject of photos and live camera shots.  That they risk their
> performance using this equipment is a testament to either the
> monetary pressures of their sponsors, their indifference to riding
> equipment which may or may not help their performance, or their
> belief that the equipment does in fact help.

In a hill climb in stage races, the leaders whose times count, ride
light weight hill climb wheels, not aerodynamic heavy disks, Spinergy,
or others that have no benefit for climbing at the reduced speeds
common when going up hill.  No belief will overcome a heavy bicycles
on a long climb, especially among top riders who know what their
capabilities are.

>>> In any event, there are other more significant factors:
>>> professionals regularly go through many tires, and any tire change
>>> would require a re-balance, which would be very time consuming
>>> considering the large number of wheels a professional team uses.

>> You ought to see the preparations of team equipment and realize that
>> wrapping lead wire around spokes is a common way of balancing spoked
>> wheels for cars and motorcycles.

> I have unfortunately never had the opportunity to view a European
> professional race up close.  It would be a lifelong dream, and would
> perhaps open my eyes to many things which the mainstream press do
> not report on.

My point is that if balance were a real consideration, teams would
balance their wheels even if you think it is tedious.  There are
easy ways to accomplish this such as sticky backed lead tape, that
is not currently available because there is no demand.

>>> It is also more difficult to place a strip of lead on a tubular,
>>> unless it were adhered to the inside edge of the rim, assuming it's
>>> not a V-shaped rim.  It is difficult to spin the front wheel rim
>>> fast enough to determine the effect of any placement of a balancing
>>> weight, and there is no current machine that I know of which will
>>> spin balance a bicycle wheel.

Static balance is all that is needed for a wheel as narrow as that
of a bicyucle and this can be done on a truing stand.  Try it.

>>> I don't see how balancing a wheel is significantly different in an
>>> automobile wheel versus a bicycle wheel.  They both spin.

>> Maybe if you considered a railway wheel you could see the effect.
>> The lack of compliance of the tire has a lot to do with it.  You
>> may not recall bias ply car tires, but they has so much damping
>> that balance wasn't as important then except that those tires had
>> larger manufacturing irregularities.  The permissible imbalance
>> weight of radial car tires shrunk with the advent of radial tires.

> I began driving as bias ply tires were being replaced by radial
> tires, so I have no experience with them, nor would I have had the
> capability to understand the technology at that time in my life
> anyway.  I do understand the need to have compliance in the tire to
> observe small imbalances.

It's the bounce that makes the tire pick up a resonance.  Maybe an
electrical analogy works better for you but an RC circuit with too
much R doesn't resonate.  R resistance is damping and bias ply tires
have plenty of that.  In fact their energy absorbance is why they are
not used today.

>>> In any event, a several gram weight imbalance on an 18 kg car wheel
>>> can be felt at speeds in a car that are reachable by a bicycle.  It
>>> is not difficult to imagine that a three gram weight imbalance on a
>>> 1 kg wheel can be felt as well.  I'd suggest you or others actually
>>> try it and see if you can notice it.

>> How about turning that around and trying to feel that there is an
>> imbalance in a typical bicycle wheel.  As I said, I coast often on
>> highways at speeds over 40mph and can detect no ripple.  I am not
>> convinced of what you seem to feel.

>>> We can easily perceive this as a significant diminishment in what
>>> feels like road graininess, similar to the effect of riding on
>>> concrete versus smooth blacktop.

>> I don't think so.  One is a random rushing sound, the other a rhythmic
>> once-around.  I think the difference can easily be distinguished.

> Considering the compliance of the tire and the amount of imbalanced
> caused by our three gram weight, it is difficult to understand what
> we distinguished.  We each ran the test four times (we got tired
> riding back UP the hill).  One of us would either place or not place
> the strip of lead tape while the other was out of view.  When not
> placed, the lead tape was hidden out of view.  We would fully
> inflate the tire to the other's preferred pressure, and install the
> wheel.  The rider would appear, hop on the bike, and immediately
> head for the hill, about a half mile away.

> We made a chart, and each time after coming back, we would write
> down whether or not we thought the weight was in place.  Being a
> creature of habit, my friend placed the weight two times and did not
> place it two times.  Trying to fool my friend, I placed it three
> times and did not place it once.  He expected two placements and two
> non-placements, and thus doubted himself, but was sure of what he
> felt each time.  We were eight for eight in guessing.

> I can't explain why we felt what we did, but there is a noticeable
> lessening of vibration at speed.  At lower speeds, the effect is not
> noticeable.

That is what I am curious about.  What is it you feel.  My bicycle is
dead solid when coasting downhill on the expressway at 35-40mph on my
daily commute.  Even at much higher speed, no vibration is noticeable.
The effect if any would be a vertical oscillation that would find a
resonance at about 10Hz.  There being no lateral component, no lateral
oscillation would be generated.  So what effect changes and if one can
guess wrong 50% of the time, how sure are you of the results?

> By the way, we had this routine down because of an argument over
> whether or not latex tubes made a difference in feel.  I thought
> they would, my friend did not.  We used the same test protocol for
> tubes (the stems were hidden by the stem extender) except that we
> pumped the tires up to 100 psi, and the rider would appear and then
> pump the tire the remaining way to his desired pressure. We used the
> same hill, the same rear wheel and tire, and the same bikes.  This
> was before we tried balancing the wheels, but we were both unable to
> distinguish between a latex (Vittoria) and butyl (Michelin
> ultralight) tube.

Oh that doesn't count.  You can hear the difference between a
conventional butyl and latex tube when riding.  The latex tube has
less damping of high frequencies.  That's an old test that doesn't
even take much care to see the difference.  How much rolling
resistance changes with the acoustic difference has not been measured.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jobst.brandt@stanfordalumni.org
Subject: Re: Severe speed "wobble"
Newsgroups: rec.bicycles.tech
Message-ID: <4JUa8.20245$TI3.189998@typhoon.sonic.net>
Date: Thu, 14 Feb 2002 20:02:08 GMT

David L. Johnson writes:

>> I suppose the imbalance in car wheels comes from steering wheel
>> input as well.

> What?  No.  But the vast majority of car wheel balance problems come
> from uneven weight distribution radially -- translating into
> up-and-down motion.  It may be possible to balance in the direction
> of the axle, but I've never seen the car wheel that has been
> balanced that way, and never had one that needed it.  And car wheels
> are a lot heavier, and move faster, than bike wheels.  The amount in
> the direction of the axle that a bike wheel could be out-of balance
> is totally insignificant.

I guess it went by too long ago but we had this wheel balancing idea
discussed here at length.

http://yarchive.net/bike/wheel_balancing.html

Subsequently I put a significant wrap of 1/8" thick solder wire around
one spoke at the rim and coasted down a hill no-hands, observing the
incidence and intensity of shimmy.  There was no difference between
balanced and imbalanced wheel. Rather than hypothesize about it, a
test of theory does a lot to put it into perspective.

Also interesting is that the line on the pavement (of a wet tire)
barely shows any deviation from a straight line, the top of the
handlebar stem making the largest excursions.  I find adding weight to
the handlebar more enlightening.  This affects both initiating speed
and amplitude of shimmy.

Jobst Brandt  <jobst.brandt@stanfordalumni.org>  Palo Alto CA