Yet another broken spoke

[[email protected]]

On Tue, 04 Sep 2007 21:49:01 -0600, [email protected] wrote:

>On Wed, 05 Sep 2007 03:02:33 GMT, "Mike Kruger"
><[email protected]> wrote:
>
>>[email protected] wrote:
>>>
>>> My experience agrees with Jobst's experience, with Professor Gavin's
>>> strain gauge measurements, and with Ian's theoretical calculations.
>>>
>>> The spokes lose huge amounts of pre-tension as they roll under the
>>> wheel. The individual the spokes all the way around the wheel show an
>>> increase of only up to 10% in tension, compared to the spoke directly
>>> under the axle's loss of tension.
>>>
>>So, this means those Kevlar "emergency" spokes I've carried with me on tours
>>are basicallly useless?
>>
>>You can't "pull" them because the cord is strong, but you can "push" them
>>like cooked spaghetti.
>>
>>Here's the product I'm referring to:
>>http://www.yellowjersey.org/fiberfix.html
>
>Dear Mark,
>
>Sorry, but you're still misunderstanding how pre-tension works. (Don't
>feel bad--it's a common mistake.)
>
>The Kevlar spokes work just like wire spokes.
>
>You pre-tension the Kevlar spoke to 200 pounds.
>
>As it rolls under the wheel, it loses considerable tension.
>
>You can see how this works with a brick, a hefty weight, and a
>bathroom scale.
>
>Put the weight on the scale and note what the scale says, say 10
>pounds.
>
>Now tie the rubber band to the weight and pull up, putting tension on
>the rubber "spoke" as if it were a wire or kevlar spoke. Rubber
>stretches much more visibly than steel or kevlar, so you can see that
>tension means elongation.
>
>Note that the scale now reads less, say 5 pounds.
>
>To push down with the pre-tensioned rubber "spoke", just relax your
>hand a little. The rubber "spoke" visibly shortens (compression) and
>the scale gains what the pre-tensioned rubber band loses.
>
>Once you lose _all_ the pre-tension, the spoke becomes literally loose
>and rattles or flops uselessly, whether it's steel wire, kevlar cord,
>or rubber band.
>
>Until you work your way through how pre-tension actually works, it
>will seem absolutely ridiculous.
>
>And yes, I carry a spare Kevlar spoke, whose pre-tensioned physics
>have been repeatedly discussed on RBT. Again, don't feel bad about the
>misunderstanding--I've been in your position, and so have most people
>who glance at a wheel and mistakenly assume that the load must hang
>from the upper spokes because it seems so damned obvious and logical.
>
>The trouble is, engineering theory predicts and strain gauge
>measurements confirm that the stupid wheel works almost exactly the
>opposite of what we expect. Work your way through those links,
>remember that Kevlar stretches and pre-tensions much like steel (an
>amount invisible to the naked eye), and you'll see why the tension
>drops dramatically for the spokes _under_ the axle, but scarcely rises
>at all for _all_ the other spokes, including the ones pulling sideways
>and downward.
>
>Cheers,
>
>Carl Fogel

Dear Mike,

Aaaargh!

Sorry about getting your name wrong!

Sadly, you're not my first innocent victim.

Cheers,

Charles Vogel

 

[Ben C]

On 2007-09-04, [email protected] <[email protected]> wrote:
> On Tue, 04 Sep 2007 15:35:56 -0500, Ben C <[email protected]> wrote:
>
>>On 2007-09-04, [email protected] <[email protected]> wrote:
>>[...]
>>> With a tighter spoke the stress variation can have a larger excursion
>>> than that of a looser spoke.
>>
>>Why?
>>
>>Just to clarify: suppose I plot a graph of stress against time for a
>>spoke on a wheel on a bicycle that's being ridden down the road. I
>>expect the graph would be some kind of wave, going up and down as the
>>spoke passes over the contact patch.
>>
>>By "larger excursion" do you mean that this wave would have a greater
>>amplitude?
>>
>>Perhaps I'm being stupid but I don't see why you would get a larger
>>amplitude for a tighter spoke.
>
> Dear Ben,
>
> A spoke cannot lose more than its pre-tension, so the pre-tension is
> the limit of how much its tension can vary. The higher the initial
> tension, the greater the possible range of tension change.
>
> First, consider two spokes, one tensioned to 200 pounds, one to only
> 100 pounds, on a bicycle where rolling under the axle causes a maxium
> loss of 50 pounds of tension.
>
> The excursion, or tension loss, will be the same, with one varying
> from 200 down to 150 pounds, the other from 100 down to 50 pounds.
>
> Technically, neither spoke is ever loose--both spokes are always under
> tension, so both experience the same 50 pound tension change.
>
> But now let the bike hit some bumps at speed, hard enough to cause a
> maximum 120 pound loss of tension.
>
> The first spoke, pre-tensioned to 200 pounds, can still lose 120
> pounds of pre-tension, dropping from 200 down to 80.
>
> But the other spoke can only drop from 100 pounds of pre-tension down
> to 0. After it loses only 100 pounds of tension, it just rattles.

I get it! Thanks.

Of course whether it does rattle harmlessly or flex horribly, rapidly
fatiguing itself to death, is another matter.

 

[Ben C]

On 2007-09-05, clare at snyder.on.ca <> wrote:
[...]
> Loose spokes also wear the holes in the hubs - and wear the spokes
> where they go through the hub.

I hadn't thought of that. That would explain the phenomenon (loose
spokes breaking) in a way that's consistent with my understanding of
Jobst's earlier suggestion that there is a bit of clearance down there.

I thought the reasoning was: the spoke can't easily be bent since it
isn't firmly held in the hub hole but free to wobble a bit. But if it's
wobbling up and down it can wear and that can initiate fatigue.

> I've replaced numerous spokes that were worn half way through before
> breaking (and some that had not yet broken)

Maybe this is something datakoll's practice of putting Teflon wax in the
hub holes before you put the spokes in could help with.

 

[Ben C]

On 2007-09-05, [email protected] <[email protected]> wrote:
> Ben C? writes surreptitiously:
>
>>> With a tighter spoke the stress variation can have a larger excursion
>>> than that of a looser spoke.
>
>> Why?
>
> Because the loose spoke can only go from its insufficient tension to
> zero while the more highly tensioned one can vary from its full
> tension to the reduction caused by the load. This is greater than the
> loose spoke stress cycle and at a higher average stress.

Thanks. That is also how Carl explained it.

 

[jim beam]

Ben C wrote:
> On 2007-09-05, [email protected] <[email protected]> wrote:
>> Ben C? writes surreptitiously:
>>
>>>> With a tighter spoke the stress variation can have a larger excursion
>>>> than that of a looser spoke.
>>> Why?
>> Because the loose spoke can only go from its insufficient tension to
>> zero while the more highly tensioned one can vary from its full
>> tension to the reduction caused by the load. This is greater than the
>> loose spoke stress cycle and at a higher average stress.
>
> Thanks. That is also how Carl explained it.

shame that doesn't account for the full bending cycle though...

 

[jim beam]

Ben C wrote:
> On 2007-09-05, clare at snyder.on.ca <> wrote:
> [...]
>> Loose spokes also wear the holes in the hubs - and wear the spokes
>> where they go through the hub.
>
> I hadn't thought of that. That would explain the phenomenon (loose
> spokes breaking) in a way that's consistent with my understanding of
> Jobst's earlier suggestion that there is a bit of clearance down there.
>
> I thought the reasoning was: the spoke can't easily be bent since it
> isn't firmly held in the hub hole but free to wobble a bit. But if it's
> wobbling up and down it can wear and that can initiate fatigue.
>
>> I've replaced numerous spokes that were worn half way through before
>> breaking (and some that had not yet broken)
>
> Maybe this is something datakoll's practice of putting Teflon wax in the
> hub holes before you put the spokes in could help with.

he lives in a hot salty climate, so in his case, it's more likely that
it mitigates corrosion or stress corrosion. sticky **** that retains
grit sure isn't going to do a thing to mitigate wear.

 

[Peter Cole]

jim beam wrote:
> [email protected] wrote:

>> What is bending the elbow in your perception?
>
> simple loading!!! the spoke elbow is offset from the spoke axis, thus
> is it subject to bending - by definition!!!

If the spoke elbow is fully supported on its inside radius it can't
bend. By definition!!!!!!!!


> except that it /is/ being bent back and forth more, simply because it's
> interleaved.

Do the math. How much force (tension) does it take to fully straighten a
clothesline with a 5lb weight in the center?

 

[Ben C]

On 2007-09-05, jim beam <[email protected]> wrote:
> Ben C wrote:
>> On 2007-09-05, clare at snyder.on.ca <> wrote:
>> [...]
>>> Loose spokes also wear the holes in the hubs - and wear the spokes
>>> where they go through the hub.
>>
>> I hadn't thought of that. That would explain the phenomenon (loose
>> spokes breaking) in a way that's consistent with my understanding of
>> Jobst's earlier suggestion that there is a bit of clearance down there.
>>
>> I thought the reasoning was: the spoke can't easily be bent since it
>> isn't firmly held in the hub hole but free to wobble a bit. But if it's
>> wobbling up and down it can wear and that can initiate fatigue.
>>
>>> I've replaced numerous spokes that were worn half way through before
>>> breaking (and some that had not yet broken)
>>
>> Maybe this is something datakoll's practice of putting Teflon wax in the
>> hub holes before you put the spokes in could help with.
>
> he lives in a hot salty climate, so in his case, it's more likely that
> it mitigates corrosion or stress corrosion. sticky **** that retains
> grit sure isn't going to do a thing to mitigate wear.

Good point. IIRC he may also have reported this was a way to get more
life out of generic spokes. I don't know if those are the galvanized
kind, but also some kinds of Chinese "stainless" steel do rust in little
spots. I know because I've seen it happen to teaspoons.

 

[Peter Cole]

Ben C wrote:
> On 2007-09-04, [email protected] <[email protected]> wrote:

>> But the other spoke can only drop from 100 pounds of pre-tension down
>> to 0. After it loses only 100 pounds of tension, it just rattles.
>
> I get it! Thanks.
>
> Of course whether it does rattle harmlessly or flex horribly, rapidly
> fatiguing itself to death, is another matter.

It could only "flex horribly" (or at all) if the spoke was bowed. Even
in that case, you'd have to consider where the flex occurred vs where
the spokes broke. The "flexing horribly" speculation also needs to
consider the actual amount of rim deflection which bounds the degree of
"horribleness".

A worst case scenario would be where the spoke elbow angle did not match
the angle of the spoke hole to flange. In that case, fluctuations in
tension could cause elbow bending when the overall tension wasn't high
enough to keep the spoke fully supported. To have that happen the
angular mismatch would have had to survived the initial wheel tensioning
and stress relief. If a wheel was built with low tension and not stress
relieved, and a spoke subsequently became loose enough to lose support
at the elbow, it might bend enough to fatigue rapidly, but I would
consider this to be the consequence of a bad initial build rather than a
loose spoke per se.

 

[jim beam]

Peter Cole wrote:
> jim beam wrote:
>> [email protected] wrote:
>
>>> What is bending the elbow in your perception?
>>
>> simple loading!!! the spoke elbow is offset from the spoke axis, thus
>> is it subject to bending - by definition!!!
>
> If

"if"??

> the spoke elbow is fully supported on its inside radius it can't
> bend. By definition!!!!!!!!

but it's not. so you're bullshitting.


>
>
>> except that it /is/ being bent back and forth more, simply because
>> it's interleaved.
>
> Do the math. How much force (tension) does it take to fully straighten a
> clothesline with a 5lb weight in the center?
>

false example - the usual peter cole deceit.

 

[jim beam]

Peter Cole wrote:
> Ben C wrote:
>> On 2007-09-04, [email protected] <[email protected]> wrote:
>
>>> But the other spoke can only drop from 100 pounds of pre-tension down
>>> to 0. After it loses only 100 pounds of tension, it just rattles.
>>
>> I get it! Thanks.
>>
>> Of course whether it does rattle harmlessly or flex horribly, rapidly
>> fatiguing itself to death, is another matter.
>
> It could only "flex horribly" (or at all) if the spoke was bowed. Even
> in that case, you'd have to consider where the flex occurred vs where
> the spokes broke. The "flexing horribly" speculation also needs to
> consider the actual amount of rim deflection which bounds the degree of
> "horribleness".
>
> A worst case scenario would be where the spoke elbow angle did not match
> the angle of the spoke hole to flange. In that case, fluctuations in
> tension could cause elbow bending when the overall tension wasn't high
> enough to keep the spoke fully supported. To have that happen the
> angular mismatch would have had to survived the initial wheel tensioning
> and stress relief. If a wheel was built with low tension and not stress
> relieved, and a spoke subsequently became loose enough to lose support
> at the elbow, it might bend enough to fatigue rapidly, but I would
> consider this to be the consequence of a bad initial build rather than a
> loose spoke per se.

wow! how to admit something you've previously denied, while phrasing it
as further denial!!! quite masterful.

 

[Peter Cole]

jim beam wrote:
> Peter Cole wrote:
>> jim beam wrote:
>>> [email protected] wrote:
>>
>>>> What is bending the elbow in your perception?
>>>
>>> simple loading!!! the spoke elbow is offset from the spoke axis,
>>> thus is it subject to bending - by definition!!!
>>
>> If
>
> "if"??
>
>> the spoke elbow is fully supported on its inside radius it can't bend.
>> By definition!!!!!!!!
>
> but it's not. so you're bullshitting.

It is if you've built your wheel right.


>>> except that it /is/ being bent back and forth more, simply because
>>> it's interleaved.
>>
>> Do the math. How much force (tension) does it take to fully straighten
>> a clothesline with a 5lb weight in the center?
>>
>
> false example - the usual peter cole deceit.

No, the interleaving force is in the middle of the spoke, like the
clothesline. Consider the vectors.

 

[Peter Cole]

jim beam wrote:
> Peter Cole wrote:
>> Ben C wrote:
>>> On 2007-09-04, [email protected] <[email protected]> wrote:
>>
>>>> But the other spoke can only drop from 100 pounds of pre-tension down
>>>> to 0. After it loses only 100 pounds of tension, it just rattles.
>>>
>>> I get it! Thanks.
>>>
>>> Of course whether it does rattle harmlessly or flex horribly, rapidly
>>> fatiguing itself to death, is another matter.
>>
>> It could only "flex horribly" (or at all) if the spoke was bowed. Even
>> in that case, you'd have to consider where the flex occurred vs where
>> the spokes broke. The "flexing horribly" speculation also needs to
>> consider the actual amount of rim deflection which bounds the degree
>> of "horribleness".
>>
>> A worst case scenario would be where the spoke elbow angle did not
>> match the angle of the spoke hole to flange. In that case,
>> fluctuations in tension could cause elbow bending when the overall
>> tension wasn't high enough to keep the spoke fully supported. To have
>> that happen the angular mismatch would have had to survived the
>> initial wheel tensioning and stress relief. If a wheel was built with
>> low tension and not stress relieved, and a spoke subsequently became
>> loose enough to lose support at the elbow, it might bend enough to
>> fatigue rapidly, but I would consider this to be the consequence of a
>> bad initial build rather than a loose spoke per se.
>
> wow! how to admit something you've previously denied, while phrasing it
> as further denial!!! quite masterful.

Only in your world. In the first paragraph, I was referring to the spoke
bending along its whole length, the second only at the elbow -- in case
that wasn't clear.

I think the burden is on you to explain how the spoke elbow is
unsupported (or how it can bend if it isn't).

 

[[email protected]]

Ben C? writes:

>> [...]
>> Loose spokes also wear the holes in the hubs - and wear the spokes
>> where they go through the hub.

> I hadn't thought of that. That would explain the phenomenon (loose
> spokes breaking) in a way that's consistent with my understanding of
> Jobst's earlier suggestion that there is a bit of clearance down
> there.

You'll have to show some evidence of loose spokes wearing thin at the
elbow. That has not been observed by anyone building wheels around
here and I've been watching this sort of thing for more years than
most. Spoke failures are from residual stress and stress
concentrations, not loose spokes or flexing from interleaving.

Flexing from interleaving (assuming the wheel was reasonably true) is
no greater with loose spokes than with tight ones, and probably less,
there being less force involved. Besides, if that were the source of
failure, then non-interleaved or radial spokes would be more durable,
as would tangential spoking, where spoke crossings are father from the
flange and have a minuscule angle.

> I thought the reasoning was: the spoke can't easily be bent since it
> isn't firmly held in the hub hole but free to wobble a bit. But if
> it's wobbling up and down it can wear and that can initiate fatigue.

But it doesn't because even becoming slack does not cause the contact
area to wear, there being no contact.

>> I've replaced numerous spokes that were worn half way through before
>> breaking (and some that had not yet broken)

That is pure imagination to put it mildly. Where are the readers
who detest exaggeration now?

> Maybe this is something datakoll's practice of putting Teflon wax in the
> hub holes before you put the spokes in could help with.

Bicycling is full of snake oil. Remember how a while back it was the
stem jam nut that caused stem separations from inner tubes? Well that
manufacturing run is gone now and we don't hear of it any more, but
there were many who believed the jam nut fable religiously in spite of
proof to the contrary (a manually tightened jam nut becomes loose when
the tire is inflated, showing that separation force is inflation
pressure, not the nut.) Now its spoke wear that causes loose spokes
to fail!

Jobst Brandt

 

[[email protected]]

Ben C? writes:

>>>> Loose spokes also wear the holes in the hubs - and wear the
>>>> spokes where they go through the hub.

>>> I hadn't thought of that. That would explain the phenomenon
>>> (loose spokes breaking) in a way that's consistent with my
>>> understanding of Jobst's earlier suggestion that there is a bit of
>>> clearance down there.

>>> I thought the reasoning was: the spoke can't easily be bent since
>>> it isn't firmly held in the hub hole but free to wobble a bit.
>>> But if it's wobbling up and down it can wear and that can initiate
>>> fatigue.

>>>> I've replaced numerous spokes that were worn half way through
>>>> before breaking (and some that had not yet broken)

>>> Maybe this is something datakoll's practice of putting Teflon wax
>>> in the hub holes before you put the spokes in could help with.

>> he lives in a hot salty climate, so in his case, it's more likely
>> that it mitigates corrosion or stress corrosion. sticky **** that
>> retains grit sure isn't going to do a thing to mitigate wear.

> Good point. IIRC he may also have reported this was a way to get
> more life out of generic spokes. I don't know if those are the
> galvanized kind, but also some kinds of Chinese "stainless" steel do
> rust in little spots. I know because I've seen it happen to
> teaspoons.

You needn't fly your kite on every breeze that comes along. Remember,
it's the jam nut on valve stems that caused stem separations about a
year ago, information that was brought to this newsgroup by the same
folks who say spokes break from low tension.

Jobst Brandt

 

[Ben C]

On 2007-09-05, [email protected] <[email protected]> wrote:
> Ben C? writes:
>
>>> [...]
>>> Loose spokes also wear the holes in the hubs - and wear the spokes
>>> where they go through the hub.
>
>> I hadn't thought of that. That would explain the phenomenon (loose
>> spokes breaking) in a way that's consistent with my understanding of
>> Jobst's earlier suggestion that there is a bit of clearance down
>> there.
>
> You'll have to show some evidence of loose spokes wearing thin at the
> elbow. That has not been observed by anyone building wheels around
> here

Do people build with the spokes too loose around there?

> and I've been watching this sort of thing for more years than most.
> Spoke failures are from residual stress and stress concentrations, not
> loose spokes or flexing from interleaving.

I believe those are possible causes. But I am not as sure as you that
they are the main or only causes.

> Flexing from interleaving (assuming the wheel was reasonably true) is
> no greater with loose spokes than with tight ones, and probably less,
> there being less force involved. Besides, if that were the source of
> failure, then non-interleaved or radial spokes would be more durable,
> as would tangential spoking, where spoke crossings are father from the
> flange and have a minuscule angle.
>
>> I thought the reasoning was: the spoke can't easily be bent since it
>> isn't firmly held in the hub hole but free to wobble a bit. But if
>> it's wobbling up and down it can wear and that can initiate fatigue.
>
> But it doesn't because even becoming slack does not cause the contact
> area to wear, there being no contact.
>
>>> I've replaced numerous spokes that were worn half way through before
>>> breaking (and some that had not yet broken)
>
> That is pure imagination to put it mildly.

How are you so sure that what Clare is describing cannot possibly have
occurred? I see no particular reason to doubt the report.

> Where are the readers who detest exaggeration now?
>
>> Maybe this is something datakoll's practice of putting Teflon wax in the
>> hub holes before you put the spokes in could help with.
>
> Bicycling is full of snake oil.

Ain't that the truth.

> Remember how a while back it was the stem jam nut that caused stem
> separations from inner tubes? Well that manufacturing run is gone now
> and we don't hear of it any more, but there were many who believed the
> jam nut fable religiously in spite of proof to the contrary (a
> manually tightened jam nut becomes loose when the tire is inflated,
> showing that separation force is inflation pressure, not the nut.)
> Now its spoke wear that causes loose spokes to fail!

There's no law that says all spokes have to fail for the same reason.

Here are a variety of possible reasons I can remember from RBT, in no
particular order, any accumulation of which any individual spoke might
suffer from:

1. Residual stress from manufacture
2. Retained stress in elbow from the build
3. Shank too long/bad spoke line
4. Surface finish of spokes poor (**** spokes)
5. Corrosion
6. Stress corrosion
7. Not enough tension, so spokes go slack
8. Rim flat spot causing slack spokes at the flat spot
9. Riding with too much weight on the bike so spokes go slack
10. Wear at the elbow

They all have varying degrees of supporting evidence, mostly indirect,
and of theoretical plausibility.

I have not seen anyone provide any convincing evidence that (1) and (2)
are the dominant factors to the total exclusion of all the others.
Personally I suspect (4), (7) and (9) are also quite a big part of the
picture.

 

[[email protected]]

Ben C? writes:

>>>> Loose spokes also wear the holes in the hubs - and wear the
>>>> spokes where they go through the hub.

>>> I hadn't thought of that. That would explain the phenomenon
>>> (loose spokes breaking) in a way that's consistent with my
>>> understanding of Jobst's earlier suggestion that there is a bit of
>>> clearance down there.

>> You'll have to show some evidence of loose spokes wearing thin at
>> the elbow. That has not been observed by anyone building wheels
>> around here

> Do people build with the spokes too loose around there?

Wheelsmith was the first, when they started using their Holland
Mechanics robot to build wheels. It was their bad experience with
wheels losing alignment that introduced SpokePrep, a glue to hide
loose spoking and imitated world wide by machine builders because the
machines could not distinguish spoke twist from spoke nipple rotating
(adjustment) causing an infinite loop of (non) corrections when wheels
got reasonably tight. Holland Mechanics said last year that they were
addressing this issue, one that is easily solved by a radial pneumatic
piston that unloads the spoke to be adjusted.

>> and I've been watching this sort of thing for more years than most.
>> Spoke failures are from residual stress and stress concentrations, not
>> loose spokes or flexing from interleaving.

> I believe those are possible causes. But I am not as sure as you that
> they are the main or only causes.

Yes, lets hear what you believe are the main causes.

>> Flexing from interleaving (assuming the wheel was reasonably true)
>> is no greater with loose spokes than with tight ones, and probably
>> less, there being less force involved. Besides, if that were the
>> source of failure, then non-interleaved or radial spokes would be
>> more durable, as would tangential spoking, where spoke crossings
>> are father from the flange and have a minuscule angle.

>>> I thought the reasoning was: the spoke can't easily be bent since
>>> it isn't firmly held in the hub hole but free to wobble a bit.
>>> But if it's wobbling up and down it can wear and that can initiate
>>> fatigue.

Only if you believe it is making solid contact, has grit between it
and the flange hole and doesn't slacken that force when wobbling,
wobbling caused by slackening. This scenario doesn't make sense.

>> But it doesn't because even becoming slack does not cause the
>> contact area to wear, there being no contact.

>>>> I've replaced numerous spokes that were worn half way through before
>>>> breaking (and some that had not yet broken)

>> That is pure imagination to put it mildly.

> How are you so sure that what Clare is describing cannot possibly have
> occurred? I see no particular reason to doubt the report.

As I mentioned, in theory it is not possible and in practice I have
never seen wear inside the spoke elbow in all the years I have been
involved with bicycles. I think if you read "the Bicycle Wheel" you
should be aware how thoroughly I have considered these effects.

>> Where are the readers who detest exaggeration now?

>>> Maybe this is something datakoll's practice of putting Teflon wax in the
>>> hub holes before you put the spokes in could help with.

>> Bicycling is full of snake oil.

> Ain't that the truth.

>> Remember how a while back it was the stem jam nut that caused stem
>> separations from inner tubes? Well that manufacturing run is gone now
>> and we don't hear of it any more, but there were many who believed the
>> jam nut fable religiously in spite of proof to the contrary (a
>> manually tightened jam nut becomes loose when the tire is inflated,
>> showing that separation force is inflation pressure, not the nut.)
>> Now its spoke wear that causes loose spokes to fail!

> There's no law that says all spokes have to fail for the same reason.

Oh, so what is the reason? I'll stick with residual stress as cause,
the explanation for which is explained in "the Bicycle Wheel".

> Here are a variety of possible reasons I can remember from RBT, in no
> particular order, any accumulation of which any individual spoke might
> suffer from:

> 1. Residual stress from manufacture
> 2. Retained stress in elbow from the build
> 3. Shank too long/bad spoke line
> 4. Surface finish of spokes poor (**** spokes)
> 5. Corrosion
> 6. Stress corrosion

> 8. Rim flat spot causing slack spokes at the flat spot
> 9. Riding with too much weight on the bike so spokes go slack
> 10. Wear at the elbow
> 7. Not enough tension, so spokes go slack

These are all the same issue and you slipped them in with valid
causes. However, that is what we are pursuing in this thread. How
does low tension cause spoke failure?

> They all have varying degrees of supporting evidence, mostly indirect,
> and of theoretical plausibility.

The first three have direct theoretical and practical evidence and
were resolved with the solutions I proposed. You can skip 4 through 5
for the spokes most of us use. As I have often mentioned, I have
wheels that went 300,000 miles with the same spokes (replacing rims)
when they wore out and no failures on the front wheel and outbound
right side spokes that got damaged by the chain.

> I have not seen anyone provide any convincing evidence that (1) and (2)
> are the dominant factors to the total exclusion of all the others.
> Personally I suspect (4), (7) and (9) are also quite a big part of the
> picture.

Basic material science spends great effort to make them credible,
through theory and lab testing. I think we have discussed this at
great length with only a "former metallurgist" claiming that new
materials resolved those causes rather than going back to short elbows
(that DT did) and to properly shape spokes and stress relieve after
building

Jobst Brandt

 

[clare at snyder.on.ca]

On 05 Sep 2007 21:13:42 GMT, [email protected] wrote:

>Ben C? writes:
>
>>> [...]
>>> Loose spokes also wear the holes in the hubs - and wear the spokes
>>> where they go through the hub.
>
>> I hadn't thought of that. That would explain the phenomenon (loose
>> spokes breaking) in a way that's consistent with my understanding of
>> Jobst's earlier suggestion that there is a bit of clearance down
>> there.
>
>You'll have to show some evidence of loose spokes wearing thin at the
>elbow. That has not been observed by anyone building wheels around
>here and I've been watching this sort of thing for more years than
>most. Spoke failures are from residual stress and stress
>concentrations, not loose spokes or flexing from interleaving.

I just threw out a couple spokes I pulled from a 1970 CCM that were
worn noticeably - and ONE of them was broken.Same on a 1963 Schwinn
American that had sat for about 15 years. Replaced 6 spokes on that
one.Only one was initially broken.
All the spokes were loose on all 4 wheels.


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[[email protected]]

clare who? writes:

>>>> Loose spokes also wear the holes in the hubs - and wear the
>>>> spokes where they go through the hub.

>>> I hadn't thought of that. That would explain the phenomenon
>>> (loose spokes breaking) in a way that's consistent with my
>>> understanding of Jobst's earlier suggestion that there is a bit of
>>> clearance down there.

>> You'll have to show some evidence of loose spokes wearing thin at
>> the elbow. That has not been observed by anyone building wheels
>> around here and I've been watching this sort of thing for more
>> years than most. Spoke failures are from residual stress and
>> stress concentrations, not loose spokes or flexing from
>> interleaving.

> I just threw out a couple spokes I pulled from a 1970 CCM that were
> worn noticeably - and ONE of them was broken.Same on a 1963 Schwinn
> American that had sat for about 15 years. Replaced 6 spokes on that
> one.Only one was initially broken.

You say "noticeably". What did you notice other than a clean area
where the spokes contacted the flange?

> All the spokes were loose on all 4 wheels.

Your experience being different from the norm, how about some pictures
of these worn spokes? How much wear did they have? How much was the
spoke cross section reduced from the original? As I said, no one I
know in the wheel building business has observed such wear, so it
makes your findings unusual enough to be questioned. Something that
could be resolved with some photos of the worn spokes.

Jobst Brandt

 

[clare at snyder.on.ca]

On 06 Sep 2007 02:32:56 GMT, [email protected] wrote:

>clare who? writes:
>
>>>>> Loose spokes also wear the holes in the hubs - and wear the
>>>>> spokes where they go through the hub.
>
>>>> I hadn't thought of that. That would explain the phenomenon
>>>> (loose spokes breaking) in a way that's consistent with my
>>>> understanding of Jobst's earlier suggestion that there is a bit of
>>>> clearance down there.
>
>>> You'll have to show some evidence of loose spokes wearing thin at
>>> the elbow. That has not been observed by anyone building wheels
>>> around here and I've been watching this sort of thing for more
>>> years than most. Spoke failures are from residual stress and
>>> stress concentrations, not loose spokes or flexing from
>>> interleaving.
>
>> I just threw out a couple spokes I pulled from a 1970 CCM that were
>> worn noticeably - and ONE of them was broken.Same on a 1963 Schwinn
>> American that had sat for about 15 years. Replaced 6 spokes on that
>> one.Only one was initially broken.
>
>You say "noticeably". What did you notice other than a clean area
>where the spokes contacted the flange?
The elbow was worn on the inside -had a sharp edge showing. Was also
showing rust at the wear point while the rest of the spokes still had
zinc/tin/whatever preventing rust.
>
>> All the spokes were loose on all 4 wheels.
>
>Your experience being different from the norm, how about some pictures
>of these worn spokes? How much wear did they have? How much was the
>spoke cross section reduced from the original? As I said, no one I
>know in the wheel building business has observed such wear, so it
>makes your findings unusual enough to be questioned. Something that
>could be resolved with some photos of the worn spokes.
>
>Jobst Brandt

I threw them out -the garbage went at about 07:30 last thursday so I
can't get THOSE back - but I'll definitely shoot the next ones I find
(which could be a while - I've got all the "old stuff" fixed up for
now. I'd say they were worn better than 10% and less than 25%, but had
a sharp edge to the wear, which would act as a stress rizer - allowing
even minor stress reversals to break the spokes. I will check my
"stash" to see if I have any worn ones left floating around.

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