dgk said:Quoted message said:Joseph Santaniello said:If you are breaking non-drive side spokes, this indicates without a
doubt that they are [censored] spokes. (based on info from your previous
posts, that you don't weigh 400lbs,etc)
Even the best spokes fail if they are not formed to the hub and stress
relieved. Don't push it off on the spoke manufacturer when it's the
builder who needs to take measures to make the wheel durable.
Jobst Brandt
Stress relief is just going around the wheel sort of pinching the
spokes?
Dear DGK,
Forgive me, but your innocent response is too good not to cross-post to
rec.bicycles.tech.
While pinching spoke pairs together probably helps to seat the spokes
in the hub and the nipples in the rim, tests showed no further residual
stresses being relieved after ordinary spoke tension, even when tension
was much higher than the typical 60-lb tension increase that other
testing shows can be achieved by pinching.
I pinched spokes together on various wheels with known forces and
measured the tension changes. Despite the impressive bending, the spoke
tension rose only about 55~65 for a 60 lb pinch. (The bending was not
due to the spokes being stretched by tremendous tension increases, but
to the slack gained when the rims bent into faint N or Z shapes.)
I bent new stainless steel spokes into a near-U, tensioned them in a
bench-vise rig up to 394 lbs, and measured how far the spoke ends moved
when the residual stresses in the U-bends were relieved by heating to
glowing orange with a propane torch. As would be expected, the greatest
movement (most residual stress exposed) occurred when the bent spoke
had not been tensioned at all. Modest tension quickly reduced the
amount that the spoke ends would move when the bend was heated,
suggesting that some residual stresses had been relieved by the initial
tension. By the time that tension reached the lowest level of an
ordinary bicycle wheel, scarcely any effect was seen when the bends
were heated.
The most likely explanation for an occasional spoke breaking is
variation in the spoke material. The bending and tensioning and so
forth are quite regular. If pinching the spokes were solving some
residual stress problem, the same problem would be causing all the
other spokes to fail.
There's no question that improvements in spoke material have reduced
spoke failure dramatically. Spokes are still being bent and formed the
same way, but ten years after his book's first edition, Jobst
high-lighted the improvement in spokes in his 3rd edition:
"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
So pinch 'em and expect improved seating, but don't expect miracles in
residual stress relief. That's achieved just by raising the tension to
normal levels.
Cheers,
Carl Fogel
