Carl Fogel said:Maybe a spoke maker could add a final stretching step and simplify
things for us. If the stress-relief theory is correct, then the
pre-stretched spokes would not need to be squeezed in place and
would never break. Both kinds of spokes would get the same
alignment, eliminating that part of the question. Does it speak
volumes that no spoke makers are known to bother with pre-stretching
their final product to relieve stress? They could be cheap [censored]
who don't know or care about the virtues of stretching--or they
could tried it, found no effect, and silently abandoned it, not
wanting to get into a squabble with enthusiasts.)
Not so fast. Outbound spokes are bent into an acute angle when
tensioned and show this, as I pointed out, when a wheel is unspoked.
In and out spokes get different elbow bends when installed. That is
evidence enough for me that the spokes yielded. In that process their
elbows were taken to yield by bending toward the location of the spoke
nipple as they are tensioned. The reason one improves the spoke line
is to make sure that bend is complete and does not teeter on the
flexing edge of yielding with every load cycle. There is a picture of
this in "the Bicycle Wheel" if you recall.
Quoted message said:The absence of real data, as opposed to anecdotes that never even
specify how much squeeze was used, how thick the spokes were, or
even if they were double-butted, speaks volumes about what the faith
is based on--but it doesn't mean that the faith is wrong.
These are not anecdotes to the experienced observer. What we have is
measurable bending, and cold forming of the spoke is visible evidence
that the wire from which the spoke is made was plastically deformed by
exceeding its yield stress. For some folks, only numbers are
evidence, but numbers often obscure what has occurred. I explained
how tensile elongation just beyond the onset of yield straightens a
wire and that this indicates that residual stresses are erased by
yielding of the high stress locations. This does not require an
easily measurable elongation of the spoke, it being in the range of a
tenth of a millimeters.
Just the process of straightening the wire as it comes off the reel is
a process that mystifies many mechanical engineers with whom I have
discussed the process, so it is not odd that non engineers do not
understand this process of stress relieving. Unfortunately the same
method cannot be used on the completed spoke.
Quoted message said:At this point, it seems to be something believed in due to theory
and personal experience. But I know of no actual data that
squeezing has any effect at all that I can present to those
wretchedly skeptical high school physics students, much less any
tests that show how the effect was achieved.
I came on this process by realizing that it had reduced spoke failure
on a wheel that had previously had continuing spoke failures. These
were wheels that had many miles on them. They were not new and the
spokes were clearly sunk into the flanges, which was apparent on spoke
replacements. After the attempt to break spokes by stretching, ones
that had partial failure, two more broke and that was the end of it.
The wheels performed durably for many miles after that.
Quoted message said:Consider that if someone does squeeze spokes that later fail, it is
assumed that either they didn't squeeze hard enough, that the wheel
was built poorly in some other way, or that the spokes must have
been an extraordinarily bad batch.
It was that the spokes were not stretched sufficiently or the high
stress points would have yielded and no longer been at a high enough
stress to cause subsequent fatigue failure. As is apparent, both from
stress relieving and from calculation, spokes are nowhere near their
yield stress in a conventional high performance wheel.
Quoted message said:We often see confident assertions here that squeezed spokes will
never fail, but cannot get even vague predictions on how soon the
same spokes will fail if unsqueezed.
We have seen that by reports of spoke failures on new wheels here
regularly. It seems a consensus that the wheel was improperly built,
considering that it had the best components. So what is it the
builder did wrong? If tension is too low, stress relieving is not
manually possible because that action cannot raise the spoke, even at
residual stress points, to the yield stress and thereby relieve the
stress. If tension is correct, then the spokes were not stress
relieved. These failures are at the threaded end as well as the
elbow, so we don't need to invoke the "bedding in" dodge to avoid the
concept of stress relief by over-stressing.
Quoted message said:I'm willing to believe that the anecdotes will turn out to be true,
but keep this in mind:
Quoted message said:"The fact that decades of anecdotal evidence indicates that
simple ______________ techniques does __________ speaks
volumes."
Quoted message said:What happens if we fill in the blanks with . . .
Quoted message said:"Spoke-tying" and "make wheels stronger"?
I think I addressed that matter adequately in "the Bicycle Wheel".
Quoted message said:Or "chain-cleaning" and "make chains last longer"?
Quoted message said:Or "tread-patterning" and "improve traction"?
Quoted message said:Or "tubular" and "reduce rolling resistance"?
These issues are optional only to those who cannot see the evidence
and the mechanisms that make these phenomena occur. They must live by
faith alone. That's why we have religions. People have lots of faith.
Quoted message said:I'm looking for something that will stand up to something as
practical and skeptical as James Randi's approach to whether dowsing
works.
I am not about to make this my life's work as Randi does. His pursuit
of "magic" is also more important and deserves his attention,
considering the affected audience and their financial and physical
loss.
Quoted message said:The trouble is that bicycle wheel spokes fail take so long to fail
(and involve so many variables) that it's hard to come up with
actual data to see if there really is any effect, much less
demonstrate which variables caused the effect.
Well if you ant to characterize it that way, we can go back to before
"the Bicycle Wheel" and throw salt over our shoulders. Much of what
you think was always known about bicycle wheels was not. That is why
writing the book was important.
Quoted message said:If it were easy, there wouldn't be so much debate.
That is much like smooth tread on bicycle tires. Those who don't
understand it remain in the belief that miniature automotive treads
improve traction on pavement, especially wet pavement. That bicycle
do not hydroplane seems irrelevant to these folks in spite of
traveling on scheduled airliners that travel at least ten times as
fast with slick tires ten times as wide between tread depth
measurement grooves than a bicycle tire... on wet runways.
That's the extent of the understanding of technology amongst many
bicyclists.
Jobst Brandt
[email hidden]
