Spoke breakage problem?

I experienced an interesting problem this weekend. After completing a
long ride on Saturday, a rear drive side spoke broke (at the nipple) in
the back of the van while driving home.

I built the wheels a few years ago; 32 hole small flange Campy Record
freewheel hubs, Campy Victory Strada tubulars, w/ DT 14 g butted spokes,
3X on the drive side, radial on the non-drive side.

I don't recall ever seeing a spoke break at the nipple before, and that
it popped two hours after riding has me looking for help w/ an explanation?

Thanks, MW

I experienced an interesting problem this weekend. After completing a
long ride on Saturday, a rear drive side spoke broke (at the nipple) in
the back of the van while driving home.

I built the wheels a few years ago; 32 hole small flange Campy Record
freewheel hubs, Campy Victory Strada tubulars, w/ DT 14 g butted spokes,
3X on the drive side, radial on the non-drive side.

I don't recall ever seeing a spoke break at the nipple before, and that
it popped two hours after riding has me looking for help w/ an
explanation?

Spokes do sometimes break at the nipple, typically right where the threads
end. That's obviously a weak spot in the spoke, but under normal conditions
it doesn't cause a problem. Is it possible that the spokes suffered quite a
bit of twisting during the assembly process? That's more often the case on
the drive side, due to the increased tension.

The fact that it popped two hours after riding probably isn't any more
significant than a tube that suddenly decides it doesn't want to hold air as
your bike's just sitting there. I'm sure that, had you ridden for two hours
and five minutes (instead of just two hours) it may have broken on you while
riding.

--Mike-- Chain Reaction Bicycles
http://www.ChainReactionBicycles.com

To me, a classic symptom of a wheel that needs to be stress relieved
(pulling spoke, I would assume). Radial NDS spoking didn't help things,
either. If you need further info on this try a google groups for "stress
relieving" or get "The Bicycle Wheel" by Jobst Brandt.

"Mark Wolff" wrote in message
...
I experienced an interesting problem this weekend. After completing a
long ride on Saturday, a rear drive side spoke broke (at the nipple) in
the back of the van while driving home.

I built the wheels a few years ago; 32 hole small flange Campy Record
freewheel hubs, Campy Victory Strada tubulars, w/ DT 14 g butted spokes,
3X on the drive side, radial on the non-drive side.

I don't recall ever seeing a spoke break at the nipple before, and that
it popped two hours after riding has me looking for help w/ an
explanation?

Thanks, MW

it's fatigue. it happens for a variety of reasons, none of which are
significantly preventable at the user level. just replace the spoke.

jb

Mark Wolff wrote:
I experienced an interesting problem this weekend. After completing a
long ride on Saturday, a rear drive side spoke broke (at the nipple) in
the back of the van while driving home.

I built the wheels a few years ago; 32 hole small flange Campy Record
freewheel hubs, Campy Victory Strada tubulars, w/ DT 14 g butted spokes,
3X on the drive side, radial on the non-drive side.

I don't recall ever seeing a spoke break at the nipple before, and that
it popped two hours after riding has me looking for help w/ an explanation?

Thanks, MW

Mark Wolff wrote:

I experienced an interesting problem this weekend. After completing a
long ride on Saturday, a rear drive side spoke broke (at the nipple) in
the back of the van while driving home.

I built the wheels a few years ago; 32 hole small flange Campy Record
freewheel hubs, Campy Victory Strada tubulars, w/ DT 14 g butted spokes,
3X on the drive side, radial on the non-drive side.

I don't recall ever seeing a spoke break at the nipple before, and that
it popped two hours after riding has me looking for help w/ an explanation?

I think its time was just up. The only spoke I've ever broken was 50
miles into a 60 miles ride, and it was a couple of years old too (the
wheels were rather nasty machine-built ones with "rustless" spokes).
It's annoying how they always go on the rear drive side though.

Mark Wolff writes:

I experienced an interesting problem this weekend. After completing
a long ride on Saturday, a rear drive side spoke broke (at the
nipple) in the back of the van while driving home.

I built the wheels a few years ago; 32 hole small flange Campy
Record freewheel hubs, Campy Victory Strada tubulars, w/ DT 14 g
butted spokes, 3X on the drive side, radial on the non-drive side.

I don't recall ever seeing a spoke break at the nipple before, and
that it popped two hours after riding has me looking for help w/ an
explanation?

Spokes break equally well at either end for the same reason, fatigue.
These are fatigue failures or the spoke would have broken at the first
hard jolt from a bump in the road at speed. Spokes generally break at
the elbow or at the thread because the elbow can easily be at its
yield stress (the stress that causes permanent deformation) from being
bent around the flange to reach the rim. In the threads, the reduced
cross section also increases stress and if the entry into the nipple
isn't straight, it will also be near its yield stress.

Every wheel rotation causes each spoke to go through one major stress
change as it passes the ground contact of the wheel. About 768 cycles
per mile and about 800 miles for one million cycles, a number often
used in fatigue characterization. Steel does not last long if stress
cycled near its yield point, so reducing stress or stress relieving
after wheel building is the single most important step in building
durable wheels.

Your wheel would surely have broken its spoke in the next quarter mile
had you continued because it was already cracked so far through that
it was like a piece of soft material stretching the last strand still
connected so it could snap.

http://draco.acs.uci.edu/rbfaq/FAQ/8c.1.html

There's more about this in "the Bicycle Wheel".

Jobst Brandt

wrote in message ...
Mark Wolff writes:

I experienced an interesting problem this weekend. After completing
a long ride on Saturday, a rear drive side spoke broke (at the
nipple) in the back of the van while driving home.

I built the wheels a few years ago; 32 hole small flange Campy
Record freewheel hubs, Campy Victory Strada tubulars, w/ DT 14 g
butted spokes, 3X on the drive side, radial on the non-drive side.

I don't recall ever seeing a spoke break at the nipple before, and
that it popped two hours after riding has me looking for help w/ an
explanation?

Spokes break equally well at either end for the same reason, fatigue.
These are fatigue failures or the spoke would have broken at the first
hard jolt from a bump in the road at speed. Spokes generally break at
the elbow or at the thread because the elbow can easily be at its
yield stress (the stress that causes permanent deformation) from being
bent around the flange to reach the rim. In the threads, the reduced
cross section also increases stress and if the entry into the nipple
isn't straight, it will also be near its yield stress.

Every wheel rotation causes each spoke to go through one major stress
change as it passes the ground contact of the wheel. About 768 cycles
per mile and about 800 miles for one million cycles, a number often
used in fatigue characterization. Steel does not last long if stress
cycled near its yield point, so reducing stress or stress relieving
after wheel building is the single most important step in building
durable wheels.

Your wheel would surely have broken its spoke in the next quarter mile
had you continued because it was already cracked so far through that
it was like a piece of soft material stretching the last strand still
connected so it could snap.

http://draco.acs.uci.edu/rbfaq/FAQ/8c.1.html

There's more about this in "the Bicycle Wheel".

Jobst Brandt



Dear Jobst

Do elbow-spokes really break equally well at
either end?

If so, are there bad practices that might favor
breaking far more spokes at the hub?

I ask because my spokes have always broken at
the hub, never at the nipple. They're almost
always the rear drive-side spokes with more
tension, just as you predict, but even my
rare front spoke breaks at the hub, not the
nipple.

I have an embarrassing suspcion that a really
badly matched derailleur sometimes rattled
against the rear drive-side spokes, closer
to the hub than the rim.

Incidentally, where exactly would you expect
spokes to break at the hub? Out in the open
and across the main shaft? At 45 degrees
in the elbow? Or all the way around the bend,
just short of the flared spoke-end?

I have a vague notion that my spokes usually
crack just before the flared end, leaving a
spoke with a jagged elbow and a button still
sitting flush in the hub-hole that I have to
knock out.

Carl Fogel

Thanks to all the info. I've broken spokes before, but always at the
elbow, and most always non-drive side ones.

I've read the book and refer to it before each try at wheel building.
These were indeed "stress relieved" as described in the book when built.
Given that the drive side spokes were all fairly equally tensioned
originally, but fairly high to try and achieve reasonable tension on the
non-drive side, should I assume the remaining drive side ones are ready
to fail and replace them all?

MW

Carl Fogel writes:

Your wheel would surely have broken its spoke in the next quarter
mile had you continued because it was already cracked so far
through that it was like a piece of soft material stretching the
last strand still connected so it could snap.

http://draco.acs.uci.edu/rbfaq/FAQ/8c.1.html

There's more about this in "the Bicycle Wheel".

Do elbow-spokes really break equally well at either end?

If so, are there bad practices that might favor breaking far more
spokes at the hub?

That depends more on the flange size, spoke pattern and skill of the
wheel builder. The point is that a spoke nipple not entirely in-line
with the spoke line causes a bend and this bend is concentrated in the
first thread. Without a hefty stress reliving stretch, this will be a
high stress point. If the wheel is loosely built, it may not causer a
break. The reason for carrying spare spokes when touring WITH nipples
threaded on is that when a spoke breaks off in the thread the nipple
is usually useless.

I ask because my spokes have always broken at the hub, never at the
nipple. They're almost always the rear drive-side spokes with more
tension, just as you predict, but even my rare front spoke breaks at
the hub, not the nipple.

That's usually for lack of "improving the spoke line" and insufficient
stress relief.

I have an embarrassing suspicion that a really badly matched
derailleur sometimes rattled against the rear drive-side spokes,
closer to the hub than the rim.

These are fatigue failures unless you can see cuts in the spoke. I
can't imagine an aluminum derailleur cutting a spoke.

Incidentally, where exactly would you expect spokes to break at the
hub? Out in the open and across the main shaft? At 45 degrees in
the elbow? Or all the way around the bend, just short of the flared
spoke-end?

Most often right in the bend, but then I have seen them break
elsewhere, usually from having been bent by some external force.
Gouged spokes from a dropped chain often last a long time even with
gouges in them if they weren't bent. This shows that it is not
tension that causes failures, but bending (forming) stresses.

I have a vague notion that my spokes usually crack just before the
flared end, leaving a spoke with a jagged elbow and a button still
sitting flush in the hub-hole that I have to knock out.

You should get over that syndrome. Build some good wheels with good
components with 36 spokes. Mine have lasted about 25 years with rim
replacements now and then.

Jobst Brandt

Mark Wolff writes:

Thanks to all the info. I've broken spokes before, but always at
the elbow, and most always non-drive side ones.

I've read the book and refer to it before each try at wheel
building. These were indeed "stress relieved" as described in the
book when built.

Given that the drive side spokes were all fairly equally tensioned
originally, but fairly high to try and achieve reasonable tension on
the non-drive side, should I assume the remaining drive side ones
are ready to fail and replace them all?

No! Save those spokes. The ones that didn't break and don't break on
the next build with stress relieving are probably lifers, well set in
their places. Next time work on the spoke alignment after initial
tensioning. Push those outbound spokes down against the flange.

Jobst Brandt