On Mon, 01 May 2006 19:35:29 -0600,
[email protected] wrote:
>
>[quoting Jobst Brandt]
>"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
>
>Huh?
Possible translation: Older spokes were made from wire which was of
lower quality; as a result, they inherently failed more often than
newer ones which are made with better steel and better forming
techniques. Since they failed more often, the impetus to discover the
cause of the failures, and the drive to find a way to minimize it, was
much stronger than it would have been with a lower failure rate.
Better spokes might have made the issue unworthy of pursuit, but as
better spokes were not what was at hand, the necessity was to find a
way to make do with what was available.
This kind of necessity-driven research is fairly common. In the
search for ways to reduce spoke breakage, a number of techniques were
tried by various people, most of which proved to be fruitless. Tying
and soldering the spokes was one of them. While this procedure did
have the effect of masking many a broken spoke for a while, it
prevented none. Overtightening the nipples and the backing them off
was another; sometimes this may stress-relieve the spoke in the
process, but I'd expect the nipple threads to give out at an annoying
rate if enough tension was really being applied. Many rituals have
been described which have the effect of stress-relieving the spokes
(sitting on a pail inverted on the middle of the spokes of one side of
the wheel while the other side rested flat on a the rim of a
five-gallon bucket was the tactic advocated in one old book I found;
others had equally arcane ceremonies) but in a goodly percentage of
the material I've seen on the subject, it's pretty clear that what was
being described was regarded as Magic, not a well-understood process.
In short, Jobst's description of the process, and his having defined
why and how it works, codified what had been known at an empirical
level for at least forty years that I can verify based on personal
experience. Whether some of the old-time cyclists and bike mechanics
clearly understood the effect that they employed is probably less
important than the fact that they had, by long trial and error, found
that it worked.
>If spoke-squeezing was what made spokes immortal, how could
>spokes become darned near immortal in a few years without
>squeezing? Aren't they still being bent? And if they're
>being bent, aren't the residual stresses still there until
>removed by squeezing two spokes together to raise their
>tension?
Some of the spokes in almost any given wheel will, without having been
overtensioned, achieve a stable existence by luck alone. This should
account for some of your "immortal unrelieved spokes". An additional
number of such "immortal" spokes will result from careless
wheelbuilding in which some of the spokes are overtensioned during
assembly (thereby unintentionally getting stress-relieved to some
degree), and then backed off in truing. Others may simply get the
luck of the stress draw, and never see enough tension to cause them to
fail. And there's also the unknown but possible factor that some
spoke makers may have been stress-relieving their spokes (to some
extent) prior to shipment all along.
>It seems odd that stainless steel spokes of the same shape
>and size had their durability significantly altered in your
>first edition by your spoke-squeezing, but the effect
>somehow became difficult to notice by your third edition.
I've had a chance, over the years, to see some etch testing of alloys
used in machine parts and fasteners. Jobst's assertion that there has
been an improvement in the materials is reflected in the results I
recall. The typical stainless alloy materials provided thirty years
ago had a much less even distribution of alloy fractions than those I
last saw; the etched surfaces of the later alloys were much more
uniform than the earlier ones. Plain steel has also seen considerable
improvement in quality in that time period, with the result that
structural engineering standards have recently been rewritten to
permit the use of lighter materials for a given load on the basis of
the fact that the number of material flaws is now so low that this
measure is safe. (It would always have been safe if the materials had
been as routinely free of defects as they now commonly are.)
>Isn't improvement in the quality of the raw material a
>likely explanation for the improved durability?
Only up to a point. As I understand it, short-service failures are
typical of material defects; long-service failures are indicative of
cyclic overstress or massive single-event overstess. Stress-relieving
the spoke so that the yield point is moved well beyond the expected
level of tension should reduce the overall failure rate both by
inducing at-assembly failure of any defective spokes and by moving the
spoke's yield tension out of the range of operational stresses.
>And all that was 13 years ago. If spoke quality and
>durabilty have continued to improve, it's as if quality made
>more difference than the proposed theory.
And yet unrelieved spokes still break more often than relieved spokes,
in the direct experience of a number of people.
>As always, I'd love to see actual fatigue data showing
>squeezed versus unsqueezed spokes. On Mondays, Wednesdays,
>and Fridays, I tend to believe in spoke squeezing. Tuesdays,
>Thursdays, and Saturdays, it tends to sound like faith-based
>vehemence. On Sundays, I preserve a laudable neutrality.
For best results, I recommend assembling your wheels on M/W/F;
however, it might be more instructive to assemble them on T/T/S. Most
people would, I suspect, favor the M/W/F approach, if for no other
reason than the idea that stress-relief is easy, fast, cheap, and at
the very least harmless. If it does nothing, there's no real loss in
applying it; OTOH, if it really works, you'll never know...because
it's hard to prove that a lack of an event has a cause.
>(It should be added for anyone new to the question that
>serious blind testing of the filthy things is extremely
>tedious and difficult--so difficult that, as I recall, every
>proposed test has been rejected by stress-relief advocates.)
I haven't followed the arguments as closely as you. This, however, I
do know; the very first wheel I built, way back in 1968 when I was
using my bike to run a paper route (remember those?) developed a rusty
rim that kept puncturing the tube. I bought a new rim, and ended up
replacing most of the spokes as well because over half of them had
nipples siezed to the threads. The bike was five or six years old at
that point, and had never broken a spoke. Within a couple of months
after I relaced the wheel, I broke two of the new spokes. None of the
old ones failed. When I went to the bike shop to ask them what was
going on, they explained that the new spokes failed because I didn't
"stretch the spokes into place" when I assembled the wheel. They
demonstrated what to do, I did it...and that same wheel, untouched,
was still serviceable some twenty-five years later when I sold the
bike at a garage sale. Was that an example of Darwinian spoke
selection, or the virtue of stress relief? I can't say for sure; had
I stretched half the new spokes instead of all of them, I might have
some harder data to offer. What I can recall is that the guys at the
bike shop told me that if I didn't stretch them I'd have more spokes
breaking, probably just one at a time, until I took their advice. It
put no money in their pockets to tell me this; they would have sold me
more spokes periodically and I'd have assumed that I had just not
built the wheel properly. And apparently I'd have been right...but
unaware of why or how.
Thirty-five years elapsed between when I built that old wheel and when
I assembled my next wheel, and in the intervening time I had forgotten
the old advice. I'm just glad that Jobst's articles were present here
to tease that memory back to the surface. The wheels in question
haven't given me a minute's spoke trouble, nor do I expect that they
will.
--
Typoes are a feature, not a bug.
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Sometimes I think that some spokes and hub flange combinations just
