Do Spokes Stretch?
David White
is in use. But my question is: can a normal human, using normal pressure on a
normal spoke wrench cause a spoke's measurable length to increase permanently
on the order of .2"?
I have a friend who rides American Classic 420 wheels on most of his bikes.
They employ a DT stainless spoke which is 1.5mm in the center (double butted).
He has had several cases where he could not get a spoke to tighten-up while
performing maintenance and he has had to replaced the spoke (with the proper
replacement).
He holds that the problem is that the spoke is stretching (I suppose like
taffy). I have only used heavier guage spokes. So it seems unlikely to me that
this could be the cause of his problems. Jobst or anyone else out there have
any position on this?
Thanks.
russell...@yahoo.com
I'm convinced spokes can stretch. I had 15/16 double butted spokes on
a set of wheels once. Front and back. I kept having to tighten them.
Eventually replaced them with 14/15 and no more problems.
jobst....@stanfordalumni.org
> I understand that spokes can (and should) "stretch" temporarily
> while a wheel is in use. But my question is: can a normal human,
> using normal pressure on a normal spoke wrench cause a spoke's
> measurable length to increase permanently on the order of .2"?
No, you cannot stretch a spoke by tensioning it with a spoke nipple
and because tension does not increase significantly from there in a
wheel in use and because in its tensioned stress in a wheel the spoke
is at about 1/3 its yield stress, it will not stretch. If it were to
reach yield stress in use, it would break soon because it gets a
million stress cycles in about 2100km of riding (1300mi).
> I have a friend who rides American Classic 420 wheels on most of his
> bikes. They employ a DT stainless spoke which is 1.5mm in the
> center (double butted). He has had several cases where he could not
> get a spoke to tighten-up while performing maintenance and he has
> had to replaced the spoke (with the proper replacement).
Could you expand on that. Why could he not tighten the spoke? You
should know that properly tightening DT Revolution spokes is a
difficult task anyway because they are torsionally so weak that they
rather twist than tighten, especially with a large diameter thread
that they have.
> He holds that the problem is that the spoke is stretching (I suppose
> like taffy). I have only used heavier gauge spokes. So it seems
> unlikely to me that this could be the cause of his problems. Jobst
> or anyone else out there have any position on this?
I don't understand the circumstances well enough to say more.
Jobst Brandt
David White
here is what I know and have seen...
The problem seems to occur only on the radially laced, front AmerClassic 420
wheel. The ones in question have DT Revolution spokes that have very short, 2mm
butted ends and are 1.5mm in the center.
My buddy have purchased several sets of these used and occasionally, they
require some truing and tensioning upon arrival. He tests for even tension by
plucking the spokes like a harp string and listening to hear that spokes make
the same sound (which I think they should on a radially spoke front wheel).
Sometimes, one or two spoke require more tension and he uses a normal spoke
wrench to tighen them up. He works slowly but finds that sometimes the spokes
seem to never reach tension even with lots of turns. Since he has seen this
before, he first assumes the alloy nipple is hosed and replaces it with a brass
one. But this does not help. He gets the same result.
Sometimes he gets to a point where there is .2" of threaded spoke above the end
of the nipple and it seems that the threaded portion of the nipple is down the
spoke far enough to be off the threads. At this point, turning the spoke does
nothing and generally backing it off does nothing. At such a point, he has no
choice but to cut the spoke and replace it.
He has a stash of the proper spokes so he replaces them with new and generally
the problem does not reappear. He has no problems with spoke breakage nor does
he need to perform lots of on-going maintenance.
I find it near impossible to believe that normal spoke wrench work could
stretch a spoke (even of this thin diameter) by nearly 1/4". Maybe if one
placed the spoke into a special test rig built to try and stretch a spoke, but
not using anything like normal force via a spoke wrench. I'd think that the
spoke thread would strip or the nipple would round-over before the spoke wire
would stretch.
However, I assume that there is a point which, when overcome, the metal will
fatigue and once this starts on-going force will cause it to continue. I have
no idea how much force would be required to overcome this point but since the
spokes are stainless steel I would think it is a fairly high value.
My best guess is that somehow spokes that are too long have been installed
somewhere along the way and that this has simply been missed in production. My
buddy believes these are machine assembled since some many are made and given
that they are radially laced front wheels it is unlikely that someone would
drop some incorrect sized spokes into the machine hopper. We'll likely never
know. But it would seem that someone up on material science/mechanical
engineering should be able to help us determine if physical stretch is at work
here.
Hope this helps. Thanks for your input.
jobst....@stanfordalumni.org
> My buddy have purchased several sets of these used and occasionally,
> they require some truing and tensioning upon arrival. He tests for
> even tension by plucking the spokes like a harp string and listening
> to hear that spokes make the same sound (which I think they should
> on a radially spoke front wheel).
> Sometimes, one or two spoke require more tension and he uses a
> normal spoke wrench to tighten them up. He works slowly but finds
> that sometimes the spokes seem to never reach tension even with lots
> of turns. Since he has seen this before, he first assumes the alloy
> nipple is hosed and replaces it with a brass one. But this does not
> help. He gets the same result.
> Sometimes he gets to a point where there is .2" of threaded spoke
> above the end of the nipple and it seems that the threaded portion
> of the nipple is down the spoke far enough to be off the threads.
> At this point, turning the spoke does nothing and generally backing
> it off does nothing. At such a point, he has no choice but to cut
> the spoke and replace it.
As I mentioned on this subject in the past, 1.5mm diameter spokes have
so little twist resistance that they do that rather than allow the
spoke nipple to be screwed on tighter. In spokes of the past, they
usually snapped at that point, because they were already reasonably
tight and taking them beyond yield in twist made them fracture.
As is evident from the stress-strain curves in "the Bicycle Wheel", DT
spokes can withstand going beyond yield for an amazing amount. I
believe the spokes in question cannot be readily tightened because
they need to be slacker to allow thread movement. The spokes are
probably only twisting when the nipple is turned and not advancing in
the thread.
To get around this problem, spokes must momentarily be slackened by
pulling the rim sideways toward the flange of that spoke. This is a
tedious process but it works. You must become sensitive to the
difference between thread motion and spoke twist, or the whole process
gets confused (as it has).
In the future, don't use spokes thinner than 1.6mm. I haven't used
any in many years for that reason.
Jobst Brandt
David White
<http://home.comcast.net/~whitedavidp/PC240001.JPG>. The ones with nipples
bottomed-out have been cut out of wheels. When I look at it, I am amazed to
believe that these all were supposed to have started out as the same length.
Jobst, if I understand your responses, you suggest that the spoke is twisting
in place when the nipple is tightened instead of the nipple proceeding down the
spoke as anticipated. But the nipple has move down the spoke to the point where
it has bottomed-out. If there is an application of torsional stress to the
spoke how could this account for the greatly increased length of the spokes in
the photo?
Thanks
Zonta
<white...@comcast.net> wrote:
Metal under tension elongates, first they go through a phase where
elastic elongation dominates, when tension is removed, they spring back
to almost original length, but when tension is applied strong enough,
plastic elongation effect will become noticeable, and the extensions in
the metal stays, they will remain as strong though and sometimes even
stronger.
If (I am only making a suggestion here as I have no knowledge of the
actual application) the wheels in question have a faulty design, that
the spokes are not strong enough to carry the force of impact from the
bike and the rider together in motion, or that the previous owners of
those wheel had operated their bikes beyond their design limit, the
spokes may experience tension exceeding their elastic limit and will
suffer permanent elongation. If you really want to prove it, you can
remove some of the spokes and measure their actual length against each
other.
You've mentioned that your friend does not have to perform "ongoing
maintenance" on the corrected spokes, it could be that your friend is a
more gentle rider.
Werehatrack
<white...@comcast.net> wrote:
>My buddy have purchased several sets of these used and occasionally, they
>require some truing and tensioning upon arrival. He tests for even tension by
>plucking the spokes like a harp string and listening to hear that spokes make
>the same sound (which I think they should on a radially spoke front wheel).
This isn't an accurate measure of tension, however. It's a useful
quick check, but not an accurate measure.
>Sometimes, one or two spoke require more tension and he uses a normal spoke
>wrench to tighen them up.
Two tools are needed. The other is a pair of vice-grips (with
something to provide "soft jaws" such as a piece of brass scrap in a
V-shape) clamped just below the nipple to keep the spoke from simply
winding up like a long torsion bar spring.
>He works slowly but finds that sometimes the spokes
>seem to never reach tension even with lots of turns. Since he has seen this
>before, he first assumes the alloy nipple is hosed and replaces it with a brass
>one. But this does not help. He gets the same result.
Were it not for the next paragraph, I'd be expecting wind-up to be the
whole issue.
>Sometimes he gets to a point where there is .2" of threaded spoke above the end
>of the nipple and it seems that the threaded portion of the nipple is down the
>spoke far enough to be off the threads. At this point, turning the spoke does
>nothing and generally backing it off does nothing. At such a point, he has no
>choice but to cut the spoke and replace it.
And at that point, I think it's probably the proper thing to do
anyway. Has he had this problem with any of the replacement spokes?
>He has a stash of the proper spokes so he replaces them with new and generally
>the problem does not reappear. He has no problems with spoke breakage nor does
>he need to perform lots of on-going maintenance.
>
>I find it near impossible to believe that normal spoke wrench work could
>stretch a spoke (even of this thin diameter) by nearly 1/4". Maybe if one
>placed the spoke into a special test rig built to try and stretch a spoke, but
>not using anything like normal force via a spoke wrench. I'd think that the
>spoke thread would strip or the nipple would round-over before the spoke wire
>would stretch.
I tend to agree, but then again, the small experience that I've had
with the DT butted spokes left me with the impression that I'd rather
use anything else. Jobst Brandt's opinion is that the cited amount of
elongation is impossible. Absent a different explanation for the
observed behavior, however, I have no alternative view to offer
besides your surmise that elongation must be taking place. Has any
attempt been made to see if the spoke is still elongated after it's
been cut and removed?
>However, I assume that there is a point which, when overcome, the metal will
>fatigue and once this starts on-going force will cause it to continue. I have
>no idea how much force would be required to overcome this point but since the
>spokes are stainless steel I would think it is a fairly high value.
The specs say it should be beyond the limits of the threads.
>My best guess is that somehow spokes that are too long have been installed
>somewhere along the way and that this has simply been missed in production. My
>buddy believes these are machine assembled since some many are made and given
>that they are radially laced front wheels it is unlikely that someone would
>drop some incorrect sized spokes into the machine hopper. We'll likely never
>know. But it would seem that someone up on material science/mechanical
>engineering should be able to help us determine if physical stretch is at work
>here.
That the incorrect length spokes should not be present in a
machine-assembled wheel is a contention I would agree with,
particularly scattered across samples obtained from various sources.
It seems just as unlikely that the same error in replacement selection
would have been present across various wheels as well. It is,
however, not impossible that this is the case. Holmes' Maxim holds
that the wrong spokes must be present...but Holmes was only a
fictional detective. I believe that the next such wheel should be
carefully inspected for overlength spokes *before* tensioning is
attempted; this might save the trouble of having to cut them out if
they're discovered before the point of full thread overrun is reached.
If it can be observed that a spoke which had *some* tension became
stretched to the point you describe during the tensioning process,
that would prove that some other factor is operating to override the
theoretical prediction.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
Werehatrack
<white...@comcast.net> wrote:
>Here is a photo my buddy has taken of the spokes in question
><http://home.comcast.net/~whitedavidp/PC240001.JPG>. The ones with nipples
>bottomed-out have been cut out of wheels. When I look at it, I am amazed to
>believe that these all were supposed to have started out as the same length.
I does seem to be an improbable situation. Is it known that they
were, in fact, the same length to begin with? Was this checked?
Ernie Willson
> I understand that spokes can (and should) "stretch" temporarily while a
> wheel is in use. But my question is: can a normal human, using normal
> pressure on a normal spoke wrench cause a spoke's measurable length to
> increase permanently on the order of .2"?
>
> I have a friend who rides American Classic 420 wheels on most of his
> bikes. They employ a DT stainless spoke which is 1.5mm in the center
That .2 inch stretch would be about 5mm on a spoke about (say) 230 mm,
or about 2% strain (stretch). There are not many high strength steels
that can do this without breaking. ISTM that your friend may have a
wheel with a flat spot, which is causing his problem. The symptons would
be about the same a you describe. YMMV.
HTH,
EJ in NJ
A Muzi
> Here is a photo my buddy has taken of the spokes in question
> <http://home.comcast.net/~whitedavidp/PC240001.JPG>. The ones with
> nipples bottomed-out have been cut out of wheels. When I look at it, I
> am amazed to believe that these all were supposed to have started out as
> the same length.
Yes.
I have experienced a few times a very tight new wheel in
which, to get out a high spot at the seam, I tightened one
new lubricated spoke/nipple until several millimeters stuck
out the back. Without moving the rim at all. Clearly a case
of spoke stretch.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
Zonta
<white...@comcast.net> wrote:
> Here is a photo my buddy has taken of the spokes in question
> <http://home.comcast.net/~whitedavidp/PC240001.JPG>. The ones with nipples
> bottomed-out have been cut out of wheels. When I look at it, I am amazed to
> believe that these all were supposed to have started out as the same length.
It is really surprising to see such big difference in length, but you
can easily check if the spokes were different in length to start with,
or it was really tension stretching by sliding a caliper (a micrometer
is better if you have one) along the whole length of the "stretched"
spokes, what you will be looking for is change in diameter.
Typically spokes are roll formed therefore should have very uniform
cross sectional diameter, if you notice any change in diameter (unless
they are not stainless steel and have rusted), the spoke has suffered
elongation or begin stretched.
daveornee
spokes with overly long spokes. Many of the samples I saw and measured
had spokes that were 4 - 5 mm too long.
DT Revolution spokes have a little more elasticity than DT Competition
spokes, but nothing in the range that would cause the problems
described. From the picture, it sure looks like the spokes were just
too long to start with.
--
daveornee
Phil, Squid-in-Training
> David White writes:
>
>> My buddy have purchased several sets of these used and occasionally,
>> they require some truing and tensioning upon arrival. He tests for
>> even tension by plucking the spokes like a harp string and listening
>> to hear that spokes make the same sound (which I think they should
>> on a radially spoke front wheel).
>
>> Sometimes, one or two spoke require more tension and he uses a
>> normal spoke wrench to tighten them up. He works slowly but finds
>> that sometimes the spokes seem to never reach tension even with lots
>> of turns. Since he has seen this before, he first assumes the alloy
>> nipple is hosed and replaces it with a brass one. But this does not
>> help. He gets the same result.
>
>> Sometimes he gets to a point where there is .2" of threaded spoke
>> above the end of the nipple and it seems that the threaded portion
>> of the nipple is down the spoke far enough to be off the threads.
>> At this point, turning the spoke does nothing and generally backing
>> it off does nothing. At such a point, he has no choice but to cut
>> the spoke and replace it.
At first, creep came into my mind, but after reviewing the concept, it
appears that it manifests in SS at temperatures above 1000F.
> As I mentioned on this subject in the past, 1.5mm diameter spokes have
> so little twist resistance that they do that rather than allow the
> spoke nipple to be screwed on tighter. In spokes of the past, they
> usually snapped at that point, because they were already reasonably
> tight and taking them beyond yield in twist made them fracture.
>
> As is evident from the stress-strain curves in "the Bicycle Wheel", DT
> spokes can withstand going beyond yield for an amazing amount. I
> believe the spokes in question cannot be readily tightened because
> they need to be slacker to allow thread movement. The spokes are
> probably only twisting when the nipple is turned and not advancing in
> the thread.
>
> To get around this problem, spokes must momentarily be slackened by
> pulling the rim sideways toward the flange of that spoke. This is a
> tedious process but it works. You must become sensitive to the
> difference between thread motion and spoke twist, or the whole process
> gets confused (as it has).
Usually at the correct tensions, even lubed spokes and nipples will undergo
a static/kinetic friction cycling as the spoke is tensioned. One can feel
it as the nipple and spoke turn together, then they slip and the spoke
attains higher tension. With a wheelbuilder paying even cursory attention,
excessive spoke windup can be avoided. Not only that, but black DT spokes
have a textured, characteristically brown surface that is rough enough for
anyone to see if the spoke is turning.
I built my race wheels with AC hubs and DT Revolutions in these same butted
diameters. There was only a little spoke windup, and using JB's slackening
method above, very even tension was achieved. They keep oh-so-true and the
wheels are about the same weight as AC's Sprint 350 wheelset but at 1/4 of
the price and 1/4 more spokes! AC's superlight rear left flange is so far
inward that an offset rim puts slightly *more* tension on the left side than
the right side.
--
Phil, Squid-in-Training
jobst....@stanfordalumni.org
>> I understand that spokes can (and should) "stretch" temporarily
>> while a wheel is in use. But my question is: can a normal human,
>> using normal pressure on a normal spoke wrench cause a spoke's
>> measurable length to increase permanently on the order of .2"?
>> I have a friend who rides American Classic 420 wheels on most of
>> his bikes. They employ a DT stainless spoke which is 1.5mm in the
>> center (double butted). He has had several cases where he could
>> not get a spoke to tighten-up while performing maintenance and he
>> has had to replaced the spoke (with the proper replacement).
>> He holds that the problem is that the spoke is stretching (I
>> suppose like taffy). I have only used heavier gauge spokes. So it
>> seems unlikely to me that this could be the cause of his problems.
>> Jobst or anyone else out there have any position on this?
> Here is a photo my buddy has taken of the spokes in question:
http://home.comcast.net/~whitedavidp/PC240001.JPG
> The ones with nipples bottomed-out have been cut out of wheels. When
> I look at it, I am amazed to believe that these all were supposed to
> have started out as the same length.
From the picture it seems the broken spokes are twisted and show a
helical pattern on them. That follows the scenario I mentioned. The
nipple does not turn on the spoke but takes it along as it turns and
goes beyond yield. When a material yields, it does so in the
direction of force, which in this case is both tensile and torsional
(what normally causes fracture) but because the DT spoke material has
both a high yield strength AND ductility, it permanently twists and
elongates simultaneously.
> Jobst, if I understand your responses, you suggest that the spoke is
> twisting in place when the nipple is tightened instead of the nipple
> proceeding down the spoke as anticipated. But the nipple has move
> down the spoke to the point where it has bottomed-out. If there is
> an application of torsional stress to the spoke how could this
> account for the greatly increased length of the spokes in the photo?
The spoke is twisting and stretching at the same time but the nipple
must also be advancing a little bit at a time as the spoke work
hardens allowing for some thread movement. I have not seen such a
spoke failure but I think if you look carefully, you'll see that the
spoke is twisted... permanently. As I said, you need to look for
spoke twist as you do this. That can be done with a swipe with a
Sharpie down one side of the spoke, or more dramatically by a small
tape flag stuck on the spoke.
Jobst Brandt
jobst....@stanfordalumni.org
> Metal under tension elongates, first they go through a phase where
> elastic elongation dominates, when tension is removed, they spring
> back to almost original length, but when tension is applied strong
> enough, plastic elongation effect will become noticeable, and the
> extensions in the metal stays, they will remain as strong though and
> sometimes even stronger.
> If (I am only making a suggestion here as I have no knowledge of the
> actual application) the wheels in question have a faulty design,
> that the spokes are not strong enough to carry the force of impact
> from the bike and the rider together in motion, or that the previous
> owners of those wheel had operated their bikes beyond their design
> limit, the spokes may experience tension exceeding their elastic
> limit and will suffer permanent elongation. If you really want to
> prove it, you can remove some of the spokes and measure their actual
> length against each other.
I think you'll find that riding the bicycle primarily slackens spokes
when loads are carried by a wheel. The greatest stresses the spokes
receive are during truing. Therefore, the above assessment should be
revised.
> You've mentioned that your friend does not have to perform "ongoing
> maintenance" on the corrected spokes, it could be that your friend
> is a more gentle rider.
You might explain what that does for spokes. I doubt that that is the
case.
Jobst Brandt
jobst....@stanfordalumni.org
>> My buddy have purchased several sets of these used and
>> occasionally, they require some truing and tensioning upon
>> arrival. He tests for even tension by plucking the spokes like a
>> harp string and listening to hear that spokes make the same sound
>> (which I think they should on a radially spoke front wheel).
> This isn't an accurate measure of tension, however. It's a useful
> quick check, but not an accurate measure.
>> Sometimes, one or two spoke require more tension and he uses a
>> normal spoke wrench to tighten them up.
> Two tools are needed. The other is a pair of vice-grips (with
> something to provide "soft jaws" such as a piece of brass scrap in a
> V-shape) clamped just below the nipple to keep the spoke from simply
> winding up like a long torsion bar spring.
I doubt that you can actually do that because if you try, you'll see
that you cannot hold a spoke without biting into it with saw-tooth
plier faces. This is often suggested and each time I wonder whether
the advice comes from experience or is merely hypothetical. Long ago,
I tried it and found the only way to overcome thread friction was to
unload the spoke by pulling the rim toward the home flange of the
spoke to be adjusted.
Jobst Brandt
jobst....@stanfordalumni.org
>> I understand that spokes can (and should) "stretch" temporarily
>> while a wheel is in use. But my question is: can a normal human,
>> using normal pressure on a normal spoke wrench cause a spoke's
>> measurable length to increase permanently on the order of .2"?
>> I have a friend who rides American Classic 420 wheels on most of
>> his bikes. They employ a DT stainless spoke which is 1.5mm in the
>> center
> I doubt seriously that your friends spokes are stretching that much.
> That .2 inch stretch would be about 5mm on a spoke about (say) 230
> mm, or about 2% strain (stretch). There are not many high strength
> steels that can do this without breaking. ISTM that your friend may
> have a wheel with a flat spot, which is causing his problem. The
> symptoms would be about the same a you describe. YMMV.
As I mentioned, the stress/strain curves in "the Bicycle Wheel" show
that DT spokes have such a long ductile strain that the spokes tested
did not break but elongated like so much rubber within the stroke of
the testing machine. It is an unusual alloy, ideal for the purpose.
Look at the charts!
Jobst Brandt
jobst....@stanfordalumni.org
> It is really surprising to see such big difference in length, but
> you can easily check if the spokes were different in length to start
> with, or it was really tension stretching by sliding a caliper (a
> micrometer is better if you have one) along the whole length of the
> "stretched" spokes, what you will be looking for is change in
> diameter.
> Typically spokes are roll formed therefore should have very uniform
> cross sectional diameter, if you notice any change in diameter
> (unless they are not stainless steel and have rusted), the spoke has
> suffered elongation or begin stretched.
DT swaged spokes are hammer swaged in a machine of great precision
that can reliably make a desired spoke diameter of previously work
hardened wire. Their spokes are made of the same stock whether 2.0mm
straight gauge or 1.5 diameter swaged spokes with a 2.0mm threaded
end. The material ductility apparently does not change much over that
working range or it would fail in manufacture.
Jobst Brandt
Trent Piepho
<jobst....@stanfordalumni.org> wrote:
>I doubt that you can actually do that because if you try, you'll see
>that you cannot hold a spoke without biting into it with saw-tooth
>plier faces. This is often suggested and each time I wonder whether
>the advice comes from experience or is merely hypothetical. Long ago,
I've done this with ovalized spokes. I padded the jaws with paper folded over
many times. Using two vice grips, I was able to un-twist a spoke that had
taken a permanent 90 degree twist (loosening the nipple didn't further
un-twist the spoke).
Qui si parla Campagnolo
We have a bundle of about a dozen wheelsmith spokes, thin center
section, that 'gave up' their integrity...so turning the nipple makes
the rim move away instead of toward the tightened spoke. Essentially,
the spoke failed and is getting longer and longer. The only thing to do
is replace it.
Tim McNamara
> Here is a photo my buddy has taken of the spokes in question
> <http://home.comcast.net/~whitedavidp/PC240001.JPG>. The ones with
> nipples bottomed-out have been cut out of wheels. When I look at it,
> I am amazed to believe that these all were supposed to have started
> out as the same length.
Which is the question I have about the situation- were there possibly
some spokes that were just too long? Alternatively, was there a low
spot in the rim at that point?
Werehatrack
I've had slightly mixed results with it; sometimes, as you've
experienced, the only way to immobilize the shaft is by gripping it
directly. I have, however, had overall good results using a folded
piece of brass stock which I've kept in my toolbox for other purposes
for many years. I have also noticed on a couple of occasions that a
highly tensioned spoke would begin to twist between the nipple and the
vice-grip; in that instance, only your technique will allow any
progress. There's apparently a range of friction/torque combinations
for which the soft jaws are adequate, and another for which the spoke
simply must be unloaded, and between those two the vice-grip needs to
get a direct bite. At least, that's how it seems to me. (It may also
be a function of the brass alloy used. Some make good bearings while
others don't; I may have just fortuitously employed a lousy bearing
material.)
Mike Jacoubowsky
> I have experienced a few times a very tight new wheel in which, to get out
> a high spot at the seam, I tightened one new lubricated spoke/nipple until
> several millimeters stuck out the back. Without moving the rim at all.
> Clearly a case of spoke stretch.
I vote for rim deformation (at the nipple/rim interface) before believing
that the spoke is actually stretching. Such a deformation would be local and
not make a difference in the perceived trueness of the wheel.
--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com
"A Muzi" <a...@yellowjersey.org> wrote in message
news:11qs4le...@corp.supernews.com...
b...@mambo.ucolick.org
> David White wrote:
> > Here is a photo my buddy has taken of the spokes in question
> > <http://home.comcast.net/~whitedavidp/PC240001.JPG>. The ones with
> > nipples bottomed-out have been cut out of wheels. When I look at it, I
> > am amazed to believe that these all were supposed to have started out as
> > the same length.
>
> Yes.
> I have experienced a few times a very tight new wheel in
> which, to get out a high spot at the seam, I tightened one
> new lubricated spoke/nipple until several millimeters stuck
> out the back. Without moving the rim at all. Clearly a case
> of spoke stretch.
There's no question that spokes stretch when tension
is applied. Better spoke calculators take this effect into
account. The question here is whether the stretch ever
causes the spokes to be permanently elongated even
after the tension is taken away. That is, most of the time,
the tension applied to spokes is in the elastic deformation
regime, so on de-tensioning the spokes return to their
original length. If the tension were increased past the
yield strength, the spokes would plastically deform and
take a permanent set.
For modern stainless spokes, I would guess that increasing
the tension that high would deform the rim first. Jobst says
spokes in a highly tensioned wheel are at only about 1/3rd
of their yield (is that for 1.8mm spokes? I don't have the book
around to check against).
jobst....@stanfordalumni.org
>>> Here is a photo my buddy has taken of the spokes in question
http://home.comcast.net/~whitedavidp/PC240001.jpg
>>> The ones with nipples bottomed-out have been cut out of
>>> wheels. When I look at it, I am amazed to believe that these all
>>> were supposed to have started out as the same length.
>> Yes. I have experienced a few times a very tight new wheel in
>> which, to get out a high spot at the seam, I tightened one new
>> lubricated spoke/nipple until several millimeters stuck out the
>> back. Without moving the rim at all. Clearly a case of spoke
>> stretch.
> There's no question that spokes stretch when tension is applied.
> Better spoke calculators take this effect into account. The
> question here is whether the stretch ever causes the spokes to be
> permanently elongated even after the tension is taken away.
That implies that spoke tension exceeded the yield stress of the spoke
and that it remained that way. In use that would not survive for any
useful time before such a spoke broke, being stress cycled at its
yield stress. I don't believe this is the case or the wheel would not
survive long anyway.
> That is, most of the time, the tension applied to spokes is in the
> elastic deformation regime, so on de-tensioning the spokes return to
> their original length. If the tension were increased past the yield
> strength, the spokes would plastically deform and take a permanent
> set.
The value that spoke calculators include is elastic elongation, not
plastic, which cannot be accounted for because it is an unknown and
indeterminable dimension arising from failure.
> For modern stainless spokes, I would guess that increasing the
> tension that high would deform the rim first. Jobst says spokes in
> a highly tensioned wheel are at only about 1/3rd of their yield (is
> that for 1.8mm spokes? I don't have the book around to check
> against).
I don't know where low spoke count wheels operate but it probably
isn't much higher because torsion must be a consideration for wheel
building and truing and if spokes are at higher tensile stress,
torsion will be a killer... in wheel building and even more so in
subsequent use.
So why are people so intent on building unsound wheels that cannot be
machine built these days. It seems like a death wish.
Jobst Brandt
Luke
<jobst....@stanfordalumni.org> wrote:
From the photos it appears as if you're left with 3 lengths: the two
upper (intact) spokes being the shortest, the third from the top,
middling; and the bottom, seemingly the longest. Further, it seems that
amount of (threaded) spoke protruding from nipple is equal - i.e., the
nipples have bottomed out on the threads on the two cut spokes.
Perhaps the positioning of the broken spokes in the photo is skewing
the differences in length, but, assuming that spokes 3 and 4 were of
equal length to begin with and their nipples both ran out of thread,
shouldn't they, post elongation, be roughly the same length?
Luke
Someone
Jobst Brandt <jobst....@stanfordalumni.org> wrote:
>
> As I mentioned, the stress/strain curves in "the Bicycle Wheel" show
> that DT spokes have such a long ductile strain that the spokes tested
> did not break but elongated like so much rubber within the stroke of
> the testing machine. It is an unusual alloy, ideal for the purpose.
> Look at the charts!
Is 304 stainless steel an unusual alloy? This table [1] lists 55%
elongation, which matches well with the tests I have observed.
[1]
<http://www.matweb.com/search/SpecificMaterial.asp?bassnum=NAKS107>.
--
Tom Sherman - Fox River Valley
Donald Gillies
Disclaimer : I'm no metallurgist at all, please take with a grain of
salt.
Metals have two limits, the yield tensile strength and then ultimate
tensile strength. below the yield strength, it flexes and returns,
above the yield strength, it bends permanently, and at the ultimate
strength the metal tears / breaks.
http://www.answers.com/topic/tensile-strength#h_ads2
For example, when you think about cold-setting a rear triangle, you
are talking about taking a 120 mm pair of tubes and you can actually
"stretch" the tubes out to 126 mm and they will pop back to 120 mm -
the yield strength is more than 6% elongation for this steel tube. To
cold set the frame you must take it out to 130 mm or something, and
then it pops back to 126mm. So the yield strength is something like
8-10%, for a hollow steel tube and lateral deflection.
========
so I'm thinking that a spoke will stretch a little when tightened -
maybe a quarter or half a millimeter out of 250 mm, but it's probably
not getting beyond its yield tensile strength. A spoke that "can no
longer be tightened" is probably occurring because of a flat spot or
out-of-round wheel, like others have suggested.
- Don Gillies
San Diego, CA
Someone
Donald Gillies wrote:
> Re: Do spokes stretch
>
> Disclaimer : I'm no metallurgist at all, please take with a grain of
> salt.
>
> Metals have two limits, the yield tensile strength and then ultimate
> tensile strength. below the yield strength, it flexes and returns,
> above the yield strength, it bends permanently, and at the ultimate
> strength the metal tears / breaks.
>
> http://www.answers.com/topic/tensile-strength#h_ads2
>
> For example, when you think about cold-setting a rear triangle, you
> are talking about taking a 120 mm pair of tubes and you can actually
> "stretch" the tubes out to 126 mm and they will pop back to 120 mm -
> the yield strength is more than 6% elongation for this steel tube. To
> cold set the frame you must take it out to 130 mm or something, and
> then it pops back to 126mm. So the yield strength is something like
> 8-10%, for a hollow steel tube and lateral deflection.
I believe you are confused about what is being done when changing
dropout spacing. The chain and seat stays are not being elongated.
Sheldon "Cold Set" Brown has an illustrative web page:
<http://sheldonbrown.com/frame-spacing.html>.
> so I'm thinking that a spoke will stretch a little when tightened -
> maybe a quarter or half a millimeter out of 250 mm, but it's probably
> not getting beyond its yield tensile strength. A spoke that "can no
> longer be tightened" is probably occurring because of a flat spot or
> out-of-round wheel, like others have suggested.
Wheelsmith uses 304 stainless steel and Sapim uses 18-8 (which is
generally 304) for their spokes according to the websites (I did not
see exact composition mentioned on the DT Swiss website, but it is
likely a similar material). In general, 304 has more than 50%
elongation before ductile fracture, which is why it is favored in
applications that require high formability and corrosion resistance.
Zonta
Someone <sunset...@yahoo.com> wrote:
> Is 304 stainless steel an unusual alloy? This table [1] lists 55%
> elongation, which matches well with the tests I have observed.
Yes, 304 is an unusual alloy for spokes!
304 is found most where durability is not of great concern but
corrosion resisitance is, because it is very soft, very ductile, very
easy to work with, typically cheaper SS watch bands are all made with
304. To give an idea, 304 is not even tough enough for cookery
utensils, and if they are used, you will find manufacturers' warnings
accompanying them.
Someone
>From the Wheelsmith website; "All Wheelsmith spokes are produced from a
specially drawn 304 stainless steel using a variety of cold forging
techniques, some proprietary." [1]
>From the Sapim website; "Intended for every day use, these spokes are
produced using top quality materials. Made from high-tensile,
fatigue-resistant 18/8 stainless steel..." [2]
AISI 304 Cr-Ni stainless steel has a minimum of 18% chromium and 8%
nickel, so my understanding is that Sapim is using a very similar
material to 304 (or that could be classified as 304).
While basic 304 has a rather low yield strength (215 MPa / 31 ksi)
along with exceptional ductility (70% elongation at ductile fracture),
the high nitrogen 304 has nearly twice the yield strength (415 MPa / 60
ksi) while retaining a high ductility of 50% elongation at ductile
fracture.
Based on the Wheelsmith and Sapim websites, it appears that 304 Cr-Ni
stainless steel is a USUAL material for spokes. Unfortunately, the DT
Swiss website does not state the material used for their spokes.
[1] <http://www.wheelsmith.com/index_files/wsspokes.htm>.
[2]
<http://www.sapim.be/index.php?st=products&sub=spokes&detail=basic&category=3961>.
M-gineering
DT uses 304 too. But all manufacturers use it in coldworked condition,
so the figures for 304 in annealed state do not apply
--
---
Marten Gerritsen
INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl
Someone
M-gineering aka Marten Gerritsen wrote:
>
> DT uses 304 too. But all manufacturers use it in coldworked condition,
If DT Swiss, Sapim and Wheelsmith use 304 Cr-Ni stainless steel for
spokes, it would seem to be a usual material for QUAILTY spokes (pace
Trevor Jeffrey).
I suspect the most USUAL spoke material would that used for Flying
Pigeon bicycles.
Does anyone know what the typical yield strength and percent elongation
would be for wheel spokes from the aforementioned manufacturers?
Zonta
<ikmotg...@m-gineering.nl> wrote:
> DT uses 304 too. But all manufacturers use it in coldworked condition,
I stand corrected.