Do Spokes Stretch?

David White said:

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 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.

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.

David White said:

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?

Quoted message said:

Were is the hatrack said:

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.

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.)
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Quoted message said:

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.

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

Quoted message said:

David White said:

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

A Muzi said:

David White said:

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).

A shy person said:

Quoted message said:

Quoted message said:

Here is a photo my buddy has taken of the spokes in question

http://home.comcast.net/~whitedavidp/PC240001.jpg

Quoted message said:

Quoted message said:

Quoted message said:

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.

Quoted message said:

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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

In article <[email hidden]>,

Quoted message said:

Quoted message said:

Here is a photo my buddy has taken of the spokes in question:

http://home.comcast.net/~whitedavidp/PC240001.JPG

Quoted message said:

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.

Quoted message said:

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

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

Jobst Brandt said:

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

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.

========

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

Donald Gillies said:

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>.

Quoted message said:

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.

--
Tom Sherman - Fox River Valley

In article <[email hidden]>,

Someone said:

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.

Zonta ? said:

In article <[email hidden]>,

Someone said:

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.

Quoted message said:

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]

Quoted message said:

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>.

--
Tom Sherman - Fox River Valley

Someone said:

Zonta ? said:

In article <[email hidden]>,

Someone said:

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.

Quoted message said:

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]

Quoted message said:

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>.

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

M-gineering aka Marten Gerritsen said:

DT uses 304 too. But all manufacturers use it in coldworked condition,
so the figures for 304 in annealed state do not apply.

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?

--
Tom Sherman - Fox River Valley

In article <[email hidden]>, M-gineering

Quoted message said:

DT uses 304 too. But all manufacturers use it in coldworked condition,

I stand corrected.