Spoke Fatigue Study

In said:

I just stumbled across this pdf, which seems to be a
mechanical engineering course project about spoke fatigue
from last Christmas:

Quoted message said:

http://www-personal.umich.edu/~jtalliso/Research/SpokeLife.pdf

Quoted message said:

Some of their comments may be of interest.

These guys start with the hypothesis that the hub is
supported by the upper spokes. This is wrong even using the
traditional mechanical engineering explanation of how a
wheel works, which assumes the rim is rigid so that half of
the load is supported by increased tension in the upper
spokes and the other half by reduced compression in the
lower.

Jobst states that most of the support actually comes from
the lower spokes, which seems to imply some bending loads on
the rim so that it doesn't transmit load to the upper spokes
as in the rigid-rim hypothesis, though I have never seen him
say this outright. Either way, if the students who wrote
that report truly believe the upper spokes are supporting
the rim load, everything else in the report is suspect.

Mike

Michael Wileman said:

In said:

I just stumbled across this pdf, which seems to be a
mechanical engineering course project about spoke fatigue
from last Christmas:

Quoted message said:

http://www-personal.umich.edu/~jtalliso/Research/SpokeLife.pdf

Quoted message said:

Some of their comments may be of interest.

These guys start with the hypothesis that the hub is
supported by the upper spokes. This is wrong even using the
traditional mechanical engineering explanation of how a
wheel works, which assumes the rim is rigid so that half of
the load is supported by increased tension in the upper
spokes and the other half by reduced compression in the
lower.

Jobst states that most of the support actually comes from
the lower spokes, which seems to imply some bending loads on
the rim so that it doesn't transmit load to the upper spokes
as in the rigid-rim hypothesis, though I have never seen him
say this outright. Either way, if the students who wrote
that report truly believe the upper spokes are supporting
the rim load, everything else in the report is suspect.

Mike

Dear Mike,

That's what it looked like to me, too--I think that they're
mistakenly hanging the hub from the upper spoke. (I think
that they're also mistakenly talking about "repairing"
spokes, as if the spokes stretched, but I'm not sure.)

But I'm wondering whether that affects the rest of their
notions.

For example, they seem to have tested the spokes (according
to their theories) and found them failing at about 625~650
pounds of tension.

I think that this is roughly what Jobst found in the 2nd
edition of "The Bicycle Wheel" in the "Spoke Strength"
appendix, where he just pulled spokes apart. Jobst's tests
showed that unbutted spokes "failed at their elbows"--and
that's what the picture in the pdf seems to show, unbutted
spokes busted at the elbows (they're a bit odd-looking).
It's nice to have some pictures of what the broken ends look
like, and it's nice to see confirmation of Jobst's point.

Despite their idea of hubs hanging from the top of the
wheel, is their pretty colored picture a good FEA of where
the stress is on a spoke under tension?

Does doubling spoke pretension from 200 to 400 pounds affect
fatigue life? They're assuming that impacts increase spoke
tension beyond this (I think), while most of us here believe
that Jobst's loss of pretension on the bottom spoke is what
actually happens, but is their notion of increased spoke
tension affecting fatigue correct, or is it just a mistaken
consequence of their initial assumption of hanging?

Is their cold-working stuff just goofy, or are they saying
something of interest?

Carl Fogel

Quoted message said:

Carl Fogel said:

Quoted message said:

> I just stumbled across this pdf, which seems to be a mechanical
> engineering course project about spoke fatigue from last Christmas:

http://www-personal.umich.edu/~jtalliso/Research/SpokeLife.pdf

[snip]

Quoted message said:

Quoted message said:

Er, what support do we have for the popular theory of spoke
stress-relief? Where can I find the data (other than anecdotal)
that supports the claims for squeezing spokes together to stretch
them in "The Bicycle Wheel"?

That has been explained here in detail and you know it.

[snip]

Quoted message said:

Quoted message said:

It is odd that in your third edition you added that disclaimer that
within a decade the improved spokes would somehow have made the
effect almost invisible.

Those are not the words. I said that the statistical indicators would
not have jumped out at me as they did with the poor spokes of the
1950's and 1960's. I am riding on spokes of that era today.

Dear Jobst,

First, you keep saying that it has been explained, but I
keep hoping to see data and testing to confirm or refute the
theory.

Every test that I've heard proposed has been dismissed in
advance as inadequate.

Second, here's the disclaimer that we seem to disagree
about:

"It appears that the better spokes now available would have
made the discovery of many of the concepts of this book more
difficult for lack of failure data. I am grateful in
retrospect for the poor durability of earlier spokes. They
operated so near their limits that durability was
significantly altered by the techniques that I have
outlined."

--Jobst Brandt, "The Bicycle Wheel," 3rd Edition, 1993,
p.124

What caused the earlier spokes to fail so often and the 1993
spokes to be so much more durable?

They were the same gauge and general shape.

Did the manufacturers eliminate the residual stresses by
changing the shape subtly or using a different bending
process?

Or did the same stresses just lose their importance because
they no longer had much effect on better quality metal?

Incidentally, even the disclaimer seems a bit odd now that I
look at it.

What "failure data" were you writing about in 1993? Does it
appear in "The Bicycle Wheel"? Was it just a general
impression?

Do we agree that a "lack of failure data" might make not
just "the discovery," but the confirmation "of many of the
concepts of this book more difficult"?

Carl Fogel

In Michael Wileman said:

In <[email hidden]> [email hidden] writes:

Quoted message said:

Quoted message said:

I just stumbled across this pdf, which seems to be a
mechanical engineering course project about spoke fatigue
from last Christmas:

Quoted message said:

Quoted message said:

http://www-personal.umich.edu/~jtalliso/Research/SpokeLife.pdf

Quoted message said:

Quoted message said:

Some of their comments may be of interest.

Quoted message said:

These guys start with the hypothesis that the hub is
supported by the upper spokes. This is wrong even using the
traditional mechanical engineering explanation of how a
wheel works, which assumes the rim is rigid so that half of
the load is supported by increased tension in the upper
spokes and the other half by reduced compression in the
lower.

Oops, obviously I meant reduced tension in the lower spokes.

Mike

Quoted message said:

Er, what support do we have for the popular theory of spoke
stress-relief? Where can I find the data (other than
anecdotal) that supports the claims for squeezing spokes
together to stretch them in "The Bicycle Wheel"?

One thing that escapes me about stress-relief of spokes is that it's
often done before winding the spokes up to full tension (presumably
because it must necessarily leave the spokes with lower tension, having
stretched them plastically). Surely then going on to put full tension
into the spokes leaves them in a dangerous state of stress in the
finished wheel, so nothing has been achieved?

Now I do stress-relieve my spokes and have never had one of my own
wheels break a spoke, but I'm not sure it isn't really about forming the
bend around the hub flange and straightening the spokes where they cross.

"Zog The Undeniable" <[email hidden]> wrote in message
news:42b52887.0@entanet...

Quoted message said:

Quoted message said:

Er, what support do we have for the popular theory of spoke
stress-relief? Where can I find the data (other than
anecdotal) that supports the claims for squeezing spokes
together to stretch them in "The Bicycle Wheel"?

One thing that escapes me about stress-relief of spokes is that it's often
done before winding the spokes up to full tension (presumably because it
must necessarily leave the spokes with lower tension, having stretched
them plastically). Surely then going on to put full tension into the
spokes leaves them in a dangerous state of stress in the finished wheel,
so nothing has been achieved?

Now I do stress-relieve my spokes and have never had one of my own wheels
break a spoke, but I'm not sure it isn't really about forming the bend
around the hub flange and straightening the spokes where they cross.

I'm really curious. Are you "stress-relieving" you spokes, or are you
de-tensioning them, or aligning them, or untwisting them, or just plain
squeezing them. The reason I ask, is that I have not really seen anything
that demonstrates that the specific stresses existing in a just-built wheel
are specifically eliminated, when you squeeze them. Could someone point me
in the direction of a test/experiment/study which answers this particular
question to the point ? Anecodtal evidence is OK, as it is still
information ; statistics of a broad range of results would be good, too ;
and laboratory measurements of this precise phenomenon would be super.

Maybe it's just not technical enough to say "squeezing". Sounds too homey
or sensual ?
--
Bonne route !

Sandy
Verneuil-sur-seine FR

Zog The Undeniable said:

Quoted message said:

Er, what support do we have for the popular theory of spoke
stress-relief? Where can I find the data (other than
anecdotal) that supports the claims for squeezing spokes
together to stretch them in "The Bicycle Wheel"?

One thing that escapes me about stress-relief of spokes is that it's
often done before winding the spokes up to full tension (presumably
because it must necessarily leave the spokes with lower tension, having
stretched them plastically). Surely then going on to put full tension
into the spokes leaves them in a dangerous state of stress in the
finished wheel, so nothing has been achieved?

Now I do stress-relieve my spokes and have never had one of my own
wheels break a spoke, but I'm not sure it isn't really about forming the
bend around the hub flange and straightening the spokes where they cross.

Mechanical stress relief is a well known technique for lowering residual
manufacturing stresses. Since the applied stress is below yield for the
bulk material, the spokes don't stretch.

Zog The Undeniable said:

One thing that escapes me about stress-relief of spokes is that it's
often done before winding the spokes up to full tension (presumably
because it must necessarily leave the spokes with lower tension, having
stretched them plastically). Surely then going on to put full tension
into the spokes leaves them in a dangerous state of stress in the
finished wheel, so nothing has been achieved?

FWIW, I stress-relieve spokes several times during a wheel build.
First time is when I'm getting the wheel close to full tension and
close to completely true. I usually support the axle against the
workbench and give a hard lateral load on the rim, doing this in
several places and both directions. I've been doing this since before
reading Jobst's book.

The last pass with the spoke wrench is just a fine adjustment. I doubt
it adds much tension.

- Frank Krygowski

jim beam said:

Peter Cole said:

Mechanical stress relief is a well known technique for lowering residual
manufacturing stresses. Since the applied stress is below yield for the
bulk material, the spokes don't stretch.

mechanical yielding /is/ a well known technique for lowering residual
stress, but you /do/ need to yield the bulk material. for hard drawn
wire, [like a spoke] the typical additional yield necessary is 1% - 2%.
springs that are mechanically relieved take a permanent set from the
process.

but again, this is all based on the /assumption/ that spokes are
delivered from factory with residual stress.

What difference does it make if the spokes come from the factory with
residual stress or not? As soon as you tension the spoke in the wheel, the
spoke elbow changes shape.

--
Benjamin Lewis

Seeing is deceiving. It's eating that's believing.
-- James Thurber

Quoted message said:

Er, what support do we have for the popular theory of spoke
stress-relief? Where can I find the data (other than
anecdotal) that supports the claims for squeezing spokes
together to stretch them in "The Bicycle Wheel"?

Er, there is some real confusion here over the meaning of "anecdotal".
JB's reports are not anecdotal. In the scientific context, anecdotal
means that one cannot trace down or verify the facts of the report,
because they have been reported haphazardly, second or third hand, via
rumor or some such. From the Greek "anekdota", things not published.

JB's reports are systematic, well documented, and as you yourself note,
published. They are no more anecdotal than that undergraduate homework
assignment you cite. He noted his rate of spoke breakage before his use
of the stress relief technique he advises, and after: from frequent
(every few thousand miles, consistent with the experiences of others of
the era) to about one every 3-5 years or 30-50,000 miles (about 5-10
out of 72, I believe the total is at now), each one from an identified
sudden mechanical trauma (chain hang up, stick, baggage smasher, etc.)
Furthermore, just as JB keeps the stack of worn rims and busted parts
in his basement, I presume he has most of his busted spokes too, if you
care to look. No anecdotes here.

As he has noted before, such stress relief is now even used in the
industrial fabrication of wheels (Trek, if not others). It is not
controversial- amongst people who know what they are talking about.

Quoted message said:

Jim Beam are trying to describe in

Uh, if you want to know about anecdotal, try his posts. Unlike JB he
has published no reports of his own to back up his claims. "Trying to
describe"? More like trying exorcise some weird personal demon, to
which he has associated the name JB.

Quoted message said:

These college guys, who seem wrong about where the spoke
hangs, nevertheless duplicated your pull-apart test and
added pictures, which I thought might please you.

No they did not duplicate his tests, as in JB's they failed at the
midsections, not at the elbows. This suggests the undergraduate
homework assignment used a fixture which did not support the elbows in
the way found in an actual bicycle hub.(

In said:

On Sun, 19 Jun 2005 18:43:14 +0000 (UTC), Michael Wileman
<[email hidden]> wrote:

Quoted message said:

Quoted message said:

Is the stress relieving Jobst is talking about relieving
residual stresses from the wire drawing, or residual
stresses from forming and bending the ends, or stresses
resulting from stress concentration at the rim and hub
holes.

I'm betting the stress relief occurs only at the points on
the spoke with high stress concentration (and, therefore,
the points where they are most likely to fail in fatigue),
without no yielding at all occuring in the straight
portion of the spoke.

Quoted message said:

To my surprise, I found no mention whatsover of
manufacturing stresses being relieved in the 2nd edition.

Quoted message said:

I began looking at "Metals and Stress" on pages 31-35 of
the 2nd edition and found nothing about residual stresses
from the manufacturer bending the straight wire or the
wheel builder bending it a little further to correct the
spoke line. The text seems to refer to fatigue cycles that
cause failure where the ordinary spoke tension concentrates
stress at the elbows and threads.

This is basically what I said in my post. Manufacturing the
spokes is done by yielding the material, so the residual
stresses, if any, are small compared to stresses at points
of stress concentration after the spoke is installed in the
rim.

Quoted message said:

Then I looked at "Spokes" on pages 48-53 of the 2nd
edition. Again, I found nothing about residual stresses.

Quoted message said:

in "Stress-Relieving" on pages 79-80, what appear to be
residual stresses are mentioned, but they are from the
being bent into place for a correct spoke line, not from
the manufacturing process--only some of the spokes have
these stresses:

[snip]

Quoted message said:

Reading this again, I'm struck by how the text seems to be
saying that stress relief by squeezing pairs of spokes is
relieving the stress from the very faint bending at the
elbow and perhaps threaded end for getting a correct spoke
line--there is no mention of the massive elbow angle bend
of the spoke during manufacture.

Quoted message said:

It's possible that I've simply misunderstood things badly
all along and that squeezing pairs of spokes is intended
solely to deal with the faint bends on some spokes that
have had their spoke line corrected, but my overwhelming
impression was that the major bend at the factory was what
people thought they were discussing when they spoke of
residual stresses.

I think people often use the term "residual stresses" way
too loosely. Residual stresses are stresses that remain in
the material once the load has been reduced, and they only
occur in cases where the loading produces a combination of
elastic and plastic deformation, as in manufacturing.

The local yielding that relieves the stress concentrations
in installed spokes is unrelated to the global yielding that
occurs when drawing the wire.

Quoted message said:

"Torque required to turn spoke nipples increases with
tension, and if the nipples are not well-lubricated, the
combined stress of tension and twist can cause spoke
failure. The combined stress has a greater effect than the
sum of the individual stresses." --p.76, 2nd edition

There's no doubt that a triaxial stress state increases the
probability of failure if the tension is the same.

Quoted message said:

While I recall lots posts about overshooting and backing
off for tightening spokes to eliminate spoke windup, I
don't recall any that mentioned that the slight barber-pole
twisting of the spoke, which is practically invisible,
could cause spoke failure. Now I'm wondering how many
broken spokes failed because of the extra stress of simple
torsion. It's easy to believe that a wheelbuilder could
leave one spoke out of 72 twisted more than he thought.

That's a complicated question and the study of fatigue in
triaxial stress states is still relatively young. However,
the failure is still going to occur at the stress
concentrations, so stress relieving ought to help. I always
thought the main reason for eliminating the spoke windup is
to keep the spokes from loosening in use. I think you'd have
to wind the spoke a whole lot for that component of the
stress to make a big difference. But my opinion here is
worth what everyone else's is. You builds your wheels, and
you takes your chances.

Mike (steel riding on my steel wheels with galvanized
spokes)

41 said:

They are no more anecdotal than that undergraduate homework
assignment you cite.

It would be comforting if that paper was undergraduate homework, but
the guy who is hosting it, and whose name appears as one of the
authors, is a Ph.D. student who apparantly already had an MS in
engineering when the paper was written. Ouch. And it's from
University of Michigan too, which is supposedly a good school.

Well, at least is serves to illustrate why papers for publication in
scientific journals are peer reviewed.

On 19 Jun 2005 13:48:40 -0700, "41" <[email hidden]>
wrote:
[snip]

Quoted message said:

Quoted message said:

These college guys, who seem wrong about where the spoke
hangs, nevertheless duplicated your pull-apart test and
added pictures, which I thought might please you.

No they did not duplicate his tests, as in JB's they failed at the
midsections, not at the elbows.

[snip]

Dear 41,

Your disagreement is understandable.

You're probably reading the text of "The Bicycle Wheel,"
which does indeed claim that all spokes, butted and
straight, fail at the midsection when pulled apart, exactly
as you say.

But the actual tests in the appendix at the end of the book
contradict this statement. They state that the straight
spokes pulled apart at the elbow, not the midsection, in
both the 2nd and the 3rd edition.

It's easy to be confused by this, since the contradictory
statements appear at either end of the book--I'd never
noticed them before.

I point this out elsewhere in this thread in some detail.
The book simply contains a contradiction, but it should be
easy to clear up.

I think that the college tests and Jobst's tests showed that
straight spokes pulled apart at the elbow, just as Jobst
explicitly says at the end of his book.

I'm just assuming that the college spokes were straight
spokes--the picture doesn't show whole spokes or say whether
they were butted or straight.

It seems quite reasonable that a straight spoke would fail
at the elbow because of the extra stress, while a butted
spoke would fail at the midsection because it was so much
thinner.

Many of us refer to "The Bicycle Wheel" as "the book" or
even "Bible," but a surprising number of us haven't got a
copy of any edition and haven't hopped back and forth
through the text and appendixes enough to follow all this,
so either browse my other posts in this thread for page
numbers and quotes, ask for more details, or send your box
tops to Battle Creek, Mich--

Er, to Sheldon Brown for a 3rd edition:

http://www.sheldonbrown.com/harris/books.html

Carl Fogel

41 said:

Quoted message said:

Er, what support do we have for the popular theory of spoke
stress-relief? Where can I find the data (other than
anecdotal) that supports the claims for squeezing spokes
together to stretch them in "The Bicycle Wheel"?

Er, there is some real confusion here over the meaning of "anecdotal".
JB's reports are not anecdotal. In the scientific context, anecdotal
means that one cannot trace down or verify the facts of the report,
because they have been reported haphazardly, second or third hand, via
rumor or some such. From the Greek "anekdota", things not published.

JB's reports are systematic, well documented, and as you yourself note,
published. They are no more anecdotal than that undergraduate homework
assignment you cite. He noted his rate of spoke breakage before his use
of the stress relief technique he advises, and after: from frequent
(every few thousand miles, consistent with the experiences of others of
the era) to about one every 3-5 years or 30-50,000 miles (about 5-10
out of 72, I believe the total is at now), each one from an identified
sudden mechanical trauma (chain hang up, stick, baggage smasher, etc.)
Furthermore, just as JB keeps the stack of worn rims and busted parts
in his basement, I presume he has most of his busted spokes too, if you
care to look. No anecdotes here.

Your highness, I think you are confused about the meaning of
"anecdotal." It is entirely possible to have well documented
verifiable anecdotal evidence. The question is one of weather or not
it is possible to generalize the results, and whether or not the data
was collected systematicaly. It also happens to be quite common in
some fields to publish anecdotal evidence, which is fine as long as
everyone recognizes it as anecdotal evidence and doesn't try to
generalize or draw conclusions.

The sort of evidence one could use to make broader statements would
come from, say, building wheels identical except for "stress relief"
and comparing the lives of their spokes. The theory on how to do
this, how many wheels need to be built, etc. is well established. As
far as I know, no one has done this.

Also, even if one establishes by this method that stress relieved
spokes last longer, one has learned nothing about WHY they last
longer. Other experiments would need to be devised to check any
proposed mechanism.

I also hope that you understand that the fact the Jobst Brandt
published a book in no way affects the credibility or generalizability
of his evidence.

You may be thinking of papers published in peer reviewed journals,
which are something else entirely. The idea there is that several
people knowledgeable in the field will look over the paper to help
ensure that blatant nonsense does not make it through. The glaring
errors of the homework paper, for example, would be caught
immediately. Jobst's book was not subjected to any such sort of
review process.

Quoted message said:

Quoted message said:

Carl Fogel said:

>> I just stumbled across this pdf, which seems to be a mechanical
>> engineering course project about spoke fatigue from last Christmas:

http://www-personal.umich.edu/~jtalliso/Research/SpokeLife.pdf

Quoted message said:

>> Some of their comments may be of interest.

Quoted message said:

Quoted message said:

Quoted message said:

> Come on now Carl. This is a troll isn't it.

-snip-

Quoted message said:

Quoted message said:

Spokes are not bent around a mandrel.

jim beam said:

now that jobst, is a real peach. so here i am, sitting with a box of
nice new d.t. competition's on my desk as i write, and guess what? every
single one of them has bending mandrel marks on them!

I just happen to have an old box of DT Competition (odd
length). Here's as good a photo as I could manage in direct
sunlight. What the heck do you see there that I don't? The
elbows are no different from any other premium spoke.

http://www.yellowjersey.org/photosfromthepast/DTCOMPHD.JPG

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

The Indecipherable said:

Quoted message said:

Er, what support do we have for the popular theory of spoke
stress-relief? Where can I find the data (other than anecdotal)
that supports the claims for squeezing spokes together to stretch
them in "The Bicycle Wheel"?

Quoted message said:

One thing that escapes me about stress-relief of spokes is that it's
often done before winding the spokes up to full tension (presumably
because it must necessarily leave the spokes with lower tension, having
stretched them plastically). Surely then going on to put full tension
into the spokes leaves them in a dangerous state of stress in the
finished wheel, so nothing has been achieved?

Stress reliving only stretches beyond yield, those locations in spokes
that have high stress, such as the outside of a spoke elbow that was
changed from an acute angle to an obtuse angle in lacing and
tensioning. It cannot materially affect the length of a spoke and
isn't intended to do so. Stress relieving should be done at full
tension or it won't achieve it's goal, that of causing yield at the
locations of high residual stress.

Quoted message said:

Now I do stress-relieve my spokes and have never had one of my own
wheels break a spoke, but I'm not sure it isn't really about forming the
bend around the hub flange and straightening the spokes where they cross.

It isn't that, and your initial perception is correct. However, that
spokes break is not disputed. Just because some folks haven't had a
spoke failure doesn't mean spokes do not fail.

[email hidden]

Frank Krygowski said:

Quoted message said:

One thing that escapes me about stress-relief of spokes is that
it's often done before winding the spokes up to full tension
(presumably because it must necessarily leave the spokes with lower
tension, having stretched them plastically). Surely then going on
to put full tension into the spokes leaves them in a dangerous
state of stress in the finished wheel, so nothing has been
achieved?

Quoted message said:

FWIW, I stress-relieve spokes several times during a wheel build.
First time is when I'm getting the wheel close to full tension and
close to completely true. I usually support the axle against the
workbench and give a hard lateral load on the rim, doing this in
several places and both directions. I've been doing this since
before reading Jobst's book.

That will not stress relieve a spoke, it will only allow twisted
spokes to untwist, giving the classic click of an untwisting spoke.
This method was long used by people who believed the clicking sounds
were proof of some unexplained improvement in the wheel, while in fact
it was misaligning the wheel as spokes advanced or receded in their
threads, the nipple having a far high friction with the rim than the
small diameter thread with the nipple. This requires a follow-up
truing as you mentioned for your wheels:

Quoted message said:

The last pass with the spoke wrench is just a fine adjustment. I

doubt it adds much tension.

I have gone over this many time on this newsgroup in the last 20
years.

[email hidden]

A Muzi said:

Quoted message said:

Quoted message said:

Carl Fogel writes:
>>> I just stumbled across this pdf, which seems to be a mechanical
>>> engineering course project about spoke fatigue from last Christmas:
http://www-personal.umich.edu/~jtalliso/Research/SpokeLife.pdf
>>> Some of their comments may be of interest.

Quoted message said:

Quoted message said:

>> Come on now Carl. This is a troll isn't it.

-snip-

Quoted message said:

Quoted message said:

Spokes are not bent around a mandrel.

jim beam said:

now that jobst, is a real peach. so here i am, sitting with a box of
nice new d.t. competition's on my desk as i write, and guess what? every
single one of them has bending mandrel marks on them!

I just happen to have an old box of DT Competition (odd
length). Here's as good a photo as I could manage in direct
sunlight. What the heck do you see there that I don't? The
elbows are no different from any other premium spoke.

http://www.yellowjersey.org/photosfromthepast/DTCOMPHD.JPG

Dear Andrew,

Your post prompted me to look at a new Sapim straight 14
gauge spoke's inside elbow (possibly different from DT
Competition).

My $15 USB camera and magnifying glass aren't up to showing
the tiny detail, but the inside curve of the spoke elbow has
a clear, smooth, flattened stripe, presumably where it was
pressed against a mandrel.

The stripe goes about half-way toward the flared end and
terminates fairly bluntly in that direction, while it seems
to go further out onto the straight shaft and dwindles to a
point.

The outside of the curve, again under a magnifying glass,
shows the orange-peel surface (pebbling) that I seem to
recall has been mentioned elsewhere.

Instead of being a smooth flaring bell, the flared end shows
two ridges and two dimples. If you think of the spoke as a
submarine periscope, viewed the back of the submarine, the
two ridges go out to the left and right, while the two
dimples are close together on the back of the top. Sorry,
but this isn't much easier to describe than it is to
photograph.

two side-by-side dimples on back of top of flare
\
\ /|
orange / |
peel________/ |
/ ---| ridges on either side of flare
/ _____ |
| / \ |
| |\ \ |
| | \ \|
| | \
| | \ flattened stripe along inside of curve,
| | presumably where mandrel was?

Even to the naked eye, the two ridges are slightly askew,
meaning not level in the diagram above.

Again, this is a Sapim spoke, not the old or new DT that you
and Jim are discussing. At the same level of magnification
in your picture and with the same lighting, I doubt that I
could see these features on my spokes, except maybe the two
ridges.

Carl Fogel

Carl Fogel said:

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Quoted message said:

These college guys, who seem wrong about where the spoke hangs,
nevertheless duplicated your pull-apart test and added pictures,
which I thought might please you.

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No they did not duplicate his tests, as in JB's they failed at the
midsections, not at the elbows.

Quoted message said:

Your disagreement is understandable.

Quoted message said:

You're probably reading the text of "The Bicycle Wheel," which does
indeed claim that all spokes, butted and straight, fail at the
midsection when pulled apart, exactly as you say.

Quoted message said:

But the actual tests in the appendix at the end of the book
contradict this statement. They state that the straight spokes
pulled apart at the elbow, not the midsection, in both the 2nd and
the 3rd edition.

You are trying hard but no cigar. The spokes all broke in the straight
runs while the straight gauge ones failed near one end instead of
midspan, near the elbow. Nowhere did it state that the elbow failed,
which is what you seem to be pursuing.

Quoted message said:

It's easy to be confused by this, since the contradictory
statements appear at either end of the book--I'd never
noticed them before.

You are willfully deceiving yourself and trying to pass this on to
people who did not read the book. Just let up for a moment.

Quoted message said:

I point this out elsewhere in this thread in some detail.
The book simply contains a contradiction, but it should be
easy to clear up.

You wouldn't use the term "simply" if it was simple and a true
contradiction as you wish it to be.

Quoted message said:

I think that the college tests and Jobst's tests showed that
straight spokes pulled apart at the elbow, just as Jobst
explicitly says at the end of his book.

That is untrue. They showed failed elbows that failed under forced
rupture rather than fatigue. As I said, back off a bit and review
your position before attacking further.

Quoted message said:

I'm just assuming that the college spokes were straight spokes--the
picture doesn't show whole spokes or say whether they were butted or
straight.

Quoted message said:

It seems quite reasonable that a straight spoke would fail at the
elbow because of the extra stress, while a butted spoke would fail
at the midsection because it was so much thinner.

I just explained why spokes do not break in the elbows under tensile
testing and that they did not fail when I ruptured spokes. In fact I
tested DT spokes that did not rupture but yielded extensively.

Quoted message said:

Many of us refer to "The Bicycle Wheel" as "the book" or even
"Bible," but a surprising number of us haven't got a copy of any
edition and haven't hopped back and forth through the text and
appendixes enough to follow all this, so either browse my other
posts in this thread for page numbers and quotes, ask for more
details, or send your box tops to Battle Creek, Mich--

Quoted message said:

Er, to Sheldon Brown for a 3rd edition:

Quoted message said:

http://www.sheldonbrown.com/harris/books.html

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