Why does a spoke break at the head

[Tad Marko]

Howdy!

I broke a spoke the other day and I was wondering why it would have
broken the way it did. Perhaps it is typical, but I've only broken one
other spoke before and that was before I paid much attention to wheels,
so I don't remember where it broke. The spoke broke at the base of the
flare of the spoke head. The bend which passes through the hub was
completely intact. Apparently the head just popped off. What was even
stranger was that the spoke broke several hundred yards AFTER I had
been riding relatively hard. I had slowed down to cross a major road,
and was on the other side gently accelerating again on a sligltly
downhill grade. I do mean gently -- I was pretty tired by then. That
much was the same as last time I had broken a spoke, as I was "just
riding along" then too.

Anyway, I would have thought that particular part of the spoke would be
pretty strong, so I was pretty surprised that it broke there. Can
anyone enlighten me at all?

Thanks,
Tad

 

[jim beam]

Tad Marko wrote:
> Howdy!
>
> I broke a spoke the other day and I was wondering why it would have
> broken the way it did. Perhaps it is typical, but I've only broken one
> other spoke before and that was before I paid much attention to wheels,
> so I don't remember where it broke. The spoke broke at the base of the
> flare of the spoke head. The bend which passes through the hub was
> completely intact. Apparently the head just popped off. What was even
> stranger was that the spoke broke several hundred yards AFTER I had
> been riding relatively hard. I had slowed down to cross a major road,
> and was on the other side gently accelerating again on a sligltly
> downhill grade. I do mean gently -- I was pretty tired by then. That
> much was the same as last time I had broken a spoke, as I was "just
> riding along" then too.
>
> Anyway, I would have thought that particular part of the spoke would be
> pretty strong, so I was pretty surprised that it broke there. Can
> anyone enlighten me at all?
>
> Thanks,
> Tad
>
it's a known failure point. if the flange thickness exceeds that which
is comfortably fitted by the spoke shank, the load on the spoke head is
higher than normal and it fatigues. simply replace and continue riding.
if another goes, consider respoking the whole wheel with good quality
aftermarket spokes. common failure points for otherwise undamaged
spokes are the elbow, the thread and the head. in that order.

 

[Michael Halliwell]

jim beam wrote:

> Tad Marko wrote:
>
>> Howdy!
>>
>> I broke a spoke the other day and I was wondering why it would have
>> broken the way it did. Perhaps it is typical, but I've only broken one
>> other spoke before and that was before I paid much attention to wheels,
>> so I don't remember where it broke. The spoke broke at the base of the
>> flare of the spoke head. The bend which passes through the hub was
>> completely intact. Apparently the head just popped off. What was even
>> stranger was that the spoke broke several hundred yards AFTER I had
>> been riding relatively hard. I had slowed down to cross a major road,
>> and was on the other side gently accelerating again on a sligltly
>> downhill grade. I do mean gently -- I was pretty tired by then. That
>> much was the same as last time I had broken a spoke, as I was "just
>> riding along" then too.
>>
>> Anyway, I would have thought that particular part of the spoke would be
>> pretty strong, so I was pretty surprised that it broke there. Can
>> anyone enlighten me at all?
>>
>> Thanks,
>> Tad
>>
> it's a known failure point. if the flange thickness exceeds that
> which is comfortably fitted by the spoke shank, the load on the spoke
> head is higher than normal and it fatigues. simply replace and
> continue riding. if another goes, consider respoking the whole wheel
> with good quality aftermarket spokes. common failure points for
> otherwise undamaged spokes are the elbow, the thread and the head. in
> that order.

I'll second Jim's comments about the failure locations. I had a bad
batch of spokes in a rear wheel that ended up having about a half dozen
failures (yes, I did get that one torn down and re-laced with different
spokes). In my case, a hard ride, followed by a gentle coast and then
braking on a slight downhill coming off a bridge did about 4 of them in
at once (the other two were singles and I just replaced thembut was
thinking "if one more goes...."). If memory serves, 3 were elbows, 2
were threads and 1 was a head failure.

Michael Halliwell

 

[[email protected]]

Michael Halliwell ha scritto:
> thinking "if one more goes...."). If memory serves, 3 were elbows, 2
> were threads and 1 was a head failure.

My memory serves weel.
I assure you I have never had a spoke break in the 'middle' (so to
speak).

Sergio
Pisa

 

[[email protected]]

forget tom put a tad 'o teflon wax finish line in the holes(both sides
now!) before riding

 

[daveornee]

Howdy!

I broke a spoke the other day and I was wondering why it would have
broken the way it did. Perhaps it is typical, but I've only broken one
other spoke before and that was before I paid much attention to wheels,
so I don't remember where it broke. The spoke broke at the base of the
flare of the spoke head. The bend which passes through the hub was
completely intact. Apparently the head just popped off. What was even
stranger was that the spoke broke several hundred yards AFTER I had
been riding relatively hard. I had slowed down to cross a major road,
and was on the other side gently accelerating again on a sligltly
downhill grade. I do mean gently -- I was pretty tired by then. That
much was the same as last time I had broken a spoke, as I was "just
riding along" then too.

Anyway, I would have thought that particular part of the spoke would be
pretty strong, so I was pretty surprised that it broke there. Can
anyone enlighten me at all?

Thanks,
Tad

What brand spoke?
How were the wheels built? (Machine built, hand built, crossing pattern, radial, etc.)
How do the spokes conform to the hub flange?
How old and how many distance on the wheels?

 

[Tad Marko]

daveornee wrote:
> Tad Marko Wrote:
> > Howdy!
> >
> > I broke a spoke the other day...
> What brand spoke?

DT Swiss

> How were the wheels built? (Machine built, hand built, crossing
> pattern, radial, etc.)

Hand 3x, 32 hole, Chorus hub, Open Pro rim. The spoke that broke was a
drive site puller.

> How do the spokes conform to the hub flange?

They were very snug going into the spoke holes. They are seated
correctly, but it took a lot of pressure to get the J-bend through the
spoke hole.

> How old and how many distance on the wheels?

1 year, about 3,500 km.

 

[daveornee]

daveornee wrote:
> Tad Marko Wrote:
> > Howdy!
> >
> > I broke a spoke the other day...
> What brand spoke?

DT Swiss

> How were the wheels built? (Machine built, hand built, crossing
> pattern, radial, etc.)

Hand 3x, 32 hole, Chorus hub, Open Pro rim. The spoke that broke was a
drive site puller.

> How do the spokes conform to the hub flange?

They were very snug going into the spoke holes. They are seated
correctly, but it took a lot of pressure to get the J-bend through the
spoke hole.

> How old and how many distance on the wheels?

1 year, about 3,500 km.

The spoke head breaks off (this is unusual)
- Bad positioning of the head in the hub (e.g. a slant position puts all the pressure on one side of the bottom of the spoke head. As a result the head snaps off, the so-called "bottle cap effect").
It could have been that while you (or whoever the wheel builder was) were working to get the J-Bend through the tight hole you bent the elbow and this caused a "bad position".

 

[jtaylor]

<[email protected]> wrote in message
news:[email protected]...
>
> Michael Halliwell ha scritto:
> > thinking "if one more goes...."). If memory serves, 3 were elbows, 2
> > were threads and 1 was a head failure.
>
> My memory serves weel.
> I assure you I have never had a spoke break in the 'middle' (so to
> speak).
>

I have - several; all but one were from major trauma to the wheel - the
exception was very rusty and there was a pit at the break.