Butted vs. straight-gauge spokes



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"Wayne T" <[email protected]> wrote:

>If the straight guage is stronger wouldn't it be more durable than double butted under heavy loads?

Imagine using 500 pound test fishing line with two fishing rods.

One rod is made from a 1/2 inch thick carbon fiber hollow tube all the way to the top.

The other is a "normal fishing pole", tapering from 1/2" at the base to almost nothing at the tip..

"Riding" consists of getting the hook snagged on something solid and whipping the pole back and
forth trying to free it.

The thick rod is the straight 14g spoke, while the thin rod is the butted spoke. It's pretty obvious
the stresses on the pole at the handle will be MUCH higher for the thick non-tapered rod, and it
will be much more likely to break as you pull. The stresses will be distributed along the length of
the thinner fishing rod and it won't break, even though it's "not as strong" as that thick,
non-tapered rod.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
Mark Hickey wrote:

> The thick rod is the straight 14g spoke, while the thin rod is the butted spoke. It's pretty
> obvious the stresses on the pole at the handle will be MUCH higher for the thick non-tapered rod,
> and it will be much more likely to break as you pull. The stresses will be distributed along the
> length of the thinner fishing rod and it won't break, even though it's "not as strong" as that
> thick, non-tapered rod.

Cool analogy, but I don't think it works. I'll switch back to spokes:

Two properly built wheels, one with straight gauge and one with swaged (butted) spokes, will have
the same spoke tension. Regular readers of rbt know that the maximum tension in a spoke is achieved
when the wheel is unused, and the tension only decreases at the contact area. Therefore, the maximum
stress experienced by the spoke heads (site of most failures) is identical for both types of spokes.

The minimum spoke stress will be lower in the straight spokes, because these spokes aren't as
"springy". This might produce a shorter fatigue life, because the material is experiencing a wider
range of stresses. It would be hard to know without testing.
--
terry morse Palo Alto, CA http://www.terrymorse.com/bike/
 
What I'm questioning is how much difference, if any, does it really make? Well built wheels don't
break spokes unless chains get launched into them, big holes/bumps, or accidents. Tensioned
properly, spokes don't pull through the rim. Very large numbers of excellent wheels have been built
with straight guage spokes.

If the spoke makers don't bother to measure, they can say anything they like. I would think that if
there were significant differences they would measure.

On Tue, 11 Feb 2003 02:07:59 GMT, "Wayne T" <[email protected]> wrote:

>
>If I'm reading you right, it sounds like you are questioning the soundness of those posts stating
>that 14/15 double butted spoked wheels are sturdier than straight 14 gauge because there has not
>really been any scientific tests showing it one way or the other.
 
Mark Hickey wrote:

>>The thick rod is the straight 14g spoke, while the thin rod is the butted spoke. It's pretty
>>obvious the stresses on the pole at the handle will be MUCH higher for the thick non-tapered rod,
>>and it will be much more likely to break as you pull. The stresses will be distributed along the
>>length of the thinner fishing rod and it won't break, even though it's "not as strong" as that
>>thick, non-tapered rod.

Terry Morse demurred:

> Cool analogy, but I don't think it works. I'll switch back to spokes:
>
> Two properly built wheels, one with straight gauge and one with swaged (butted) spokes, will have
> the same spoke tension. Regular readers of rbt know that the maximum tension in a spoke is
> achieved when the wheel is unused, and the tension only decreases at the contact area. Therefore,
> the maximum stress experienced by the spoke heads (site of most failures) is identical for both
> types of spokes.

That's true for smooth riding, but not correct when impact loads are considered.

In-line impact loads tend to push the rim inward at the point of impact. This causes a tendency for
the rim to bulge outward in areas immediately adjacent to the impact point. The spokes in the bulge
zones do suffer transient increases in stress.

Lateral stresses also can result in locally increased spoke tension.

Sheldon "Double Bubble" Brown +--------------------------------------------------+
| Conscience is the inner voice which warns us | that someone might be looking. | --H.L. Mencken |
+--------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
 
Terry Morse writes:

> Two properly built wheels, one with straight gauge and one with swaged (butted) spokes, will have
> the same spoke tension. Regular readers of rbt know that the maximum tension in a spoke is
> achieved when the wheel is unused, and the tension only decreases at the contact area. Therefore,
> the maximum stress experienced by the spoke heads (site of most failures) is identical for both
> types of spokes.

> The minimum spoke stress will be lower in the straight spokes, because these spokes aren't as
> "springy". This might produce a shorter fatigue life, because the material is experiencing a wider
> range of stresses. It would be hard to know without testing.

Since spoke failure is a fatigue phenomenon caused by cycle stress, there is no testing required to
determine whether this alters fatigue life. It is as basic a materials problem as there is. With
both spokes at the same peak stress and one with a larger cyclic stress excursion than the other
will statistically fail sooner, assuming there will be a failure.

The same goes for a rim under the choice of the two spokes.

Jobst Brandt [email protected] Palo Alto CA
 
Sheldon Brown wrote:

> Terry Morse demurred:
>
> > Two properly built wheels, one with straight gauge and one with swaged (butted) spokes, will
> > have the same spoke tension. Regular readers of rbt know that the maximum tension in a spoke is
> > achieved when the wheel is unused, and the tension only decreases at the contact area.
> > Therefore, the maximum stress experienced by the spoke heads (site of most failures) is
> > identical for both types of spokes.
>
> That's true for smooth riding, but not correct when impact loads are considered.
>
> In-line impact loads tend to push the rim inward at the point of impact. This causes a tendency
> for the rim to bulge outward in areas immediately adjacent to the impact point. The spokes in the
> bulge zones do suffer transient increases in stress.

I don't see the diffence between smooth loading and in-line impact loading. There's not much mass in
the rim, so the reaction of the rim/spoke system ought to be similar in both cases.
--
terry morse Palo Alto, CA http://www.terrymorse.com/bike/
 
Jobst Brandt wrote:

> Since spoke failure is a fatigue phenomenon caused by cycle stress, there is no testing required
> to determine whether this alters fatigue life. It is as basic a materials problem as there is.
> With both spokes at the same peak stress and one with a larger cyclic stress excursion than the
> other will statistically fail sooner, assuming there will be a failure.

Do you have a reference to demonstrate the "larger cyclic stress" behavior? The material fatigue
tests I remember lowered the stress down to zero on every cycle.
--
terry morse Palo Alto, CA http://www.terrymorse.com/bike/
 
>> That's true for smooth riding, but not correct when impact loads are considered.

>> In-line impact loads tend to push the rim inward at the point of impact. This causes a tendency
>> for the rim to bulge outward in areas immediately adjacent to the impact point. The spokes in the
>> bulge zones do suffer transient increases in stress.

> I don't see the difference between smooth loading and in-line impact loading. There's not much
> mass in the rim, so the reaction of the rim/spoke system ought to be similar in both cases.

That is correct. There is no dynamic here, the response of the wheel being so fast that its
deflection is the same as static. The magnitude of the outward bulge adjacent to the inward
deflected rim section is so small that the general statement that spoke tension is greatest on an
unloaded wheel is true for practical purposes.

Jobst Brandt [email protected] Palo Alto CA
 
Terry Morse writes:

>> Since spoke failure is a fatigue phenomenon caused by cycle stress, there is no testing required
>> to determine whether this alters fatigue life. It is as basic a materials problem as there is.
>> With both spokes at the same peak stress and one with a larger cyclic stress excursion than the
>> other will statistically fail sooner, assuming there will be a failure.

> Do you have a reference to demonstrate the "larger cyclic stress" behavior? The material fatigue
> tests I remember lowered the stress down to zero on every cycle.

Some materials suffer more from stress reversals but steel is interested in the stress change and
the peak stress. I show a simple diagram in "the Bicycle Wheel" what these effects are. See also:

http://www.efunda.com/DesignStandards/springs/calc_comp_fatigue_eqn.cfm
http://www.grc.nasa.gov/WWW/RT1996/5000/5220l.htm

Jobst Brandt [email protected] Palo Alto CA
 
Terry Morse <[email protected]> wrote:

> Mark Hickey wrote:
>
>> The thick rod is the straight 14g spoke, while the thin rod is the butted spoke. It's pretty
>> obvious the stresses on the pole at the handle will be MUCH higher for the thick non-tapered rod,
>> and it will be much more likely to break as you pull. The stresses will be distributed along the
>> length of the thinner fishing rod and it won't break, even though it's "not as strong" as that
>> thick, non-tapered rod.
>
>Cool analogy, but I don't think it works.

I think it gets to the heart of the matter. What I probably didn't make clear enough is that the
expected "breaking point" for either the thick, non-tapered stiff pole and the tapered pole would be
at the point where the carbon fiber fishing pole joined the handle. Imagine whip-sawing the pole
back and forth and it's easy to see that the stresses are distributed along the tapered pole, but
concentrated at the handle-pole junction of the straight fishing rod.

As you said, the point of maximum and minimum tension are reversed, but that doesn't really change
the model in terms of distributing the changes in stress vs. concentrating it at the handle (or
elbow or thread).

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
<[email protected]> wrote in message news:[email protected]...
> "Wayne T" <[email protected]> wrote:
>
> > > Weight savings is an extra bonus. The real reason is that a wheel
with
> > > DB spokes will be more durable, not necessarily stronger.
> >
> > If the straight guage is stronger wouldn't it be more durable than
double
> > butted under heavy loads?
>
>
> No, because spokes don't break from overload, they break from fatigue. Double butted, or swaged,
> spokes fatigue more slowly.

I guess it is hard for me to understand how something thinner could fatigue faster than
something thicker.

>
> --
> Ted Bennett Portland OR
 
On Tue, 11 Feb 2003 18:28:13 +0000, Paul Kopit wrote:

> What I'm questioning is how much difference, if any, does it really make? Well built wheels don't
> break spokes unless chains get launched into them, big holes/bumps, or accidents. Tensioned
> properly, spokes don't pull through the rim. Very large numbers of excellent wheels have been
> built with straight guage spokes.

I'm with you. I think the difference is in the noise level. I've had butted spokes break as well as
straight gage. In the absence of test data, I'll save a bit of money and make wheel building a
little easier by using straight gage.
 
<[email protected]> wrote in message news:[email protected]...
> Wayne T Dunlap writes:
>
> >>> I've always used 14 gauge straight gauge 36 spoke wheels on my touring bike because I was told
> >>> that these spokes are more dependable under touring loads. Now it sounds like most posters
> >>> here feel that double butted wheels are at least as strong or maybe stronger. My builder who
> >>> is converting my bike to cassette and will be rebuilding my rear wheel, feels that I should go
> >>> with double butted. I weigh a little under 180. Used to go up to 195, but no more. Since the
> >>> front wheel doesn't need to be rebuilt, it will remain 14 gauge straight gauge 36 spoked
> >>> wheel. What is the primary reason for double butted wheels? I would think weight savings. How
> >>> much savings would that be?
>
> >> Weight savings is an extra bonus. The real reason is that a wheel with DB spokes will be more
> >> durable, not necessarily stronger.
>
> > If the straight gauge is stronger wouldn't it be more durable than double butted under heavy
> > loads?
>
> If... but they are not, because their ends, where they fail, are identical for both types of
> spoke, having the same cross section. The swaged spoke having been made from a straight gauge
> spoke blank.
>
> Fatigue is a process by which a metal is torn apart by repeated loading much lower than that
> needed to forcefully break the part. Therefore, it is not rupture strength but rather stress
> levels under cyclic loading that cause spokes to fail. That is why stress relieving is highly
> important in building durable wheels.

so, essentially what you are saying is that the fact that the middle of a double butted spoke is
thinner, it allows it to flex and take the stress off the ends of the spoke where most spoke tend to
break. But wouldn't the fact that the middle of a double butted spoke flexes more than a straight
gauge, cause the middle section to fatique more and, therefore, cause more mid section breakage?
>
> Jobst Brandt [email protected] Palo Alto CA
 
"Mark Hickey" <[email protected]> wrote in message
news:[email protected]...
> "Wayne T" <[email protected]> wrote:
>
> >If the straight guage is stronger wouldn't it be more durable than double butted under
> >heavy loads?
>
> Imagine using 500 pound test fishing line with two fishing rods.
>
> One rod is made from a 1/2 inch thick carbon fiber hollow tube all the way to the top.
>
> The other is a "normal fishing pole", tapering from 1/2" at the base to almost nothing at
> the tip..
>
> "Riding" consists of getting the hook snagged on something solid and whipping the pole back and
> forth trying to free it.
>
> The thick rod is the straight 14g spoke, while the thin rod is the butted spoke. It's pretty
> obvious the stresses on the pole at the handle will be MUCH higher for the thick non-tapered rod,
> and it will be much more likely to break as you pull. The stresses will be distributed along the
> length of the thinner fishing rod and it won't break, even though it's "not as strong" as that
> thick, non-tapered rod.
Wayne writes: Interesting analogy. It makes sense. Thanks.
>
> Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
> > Wayne T Dunlap writes:
> > >>> I've always used 14 gauge straight gauge 36 spoke wheels on my touring bike because I was
> > >>> told that these spokes are more dependable under touring loads. Now it sounds like most
> > >>> posters here feel that double butted wheels are at least as strong or maybe stronger. My
> > >>> builder who is converting my bike to cassette and will be rebuilding my rear wheel, feels
> > >>> that I should go with double butted. I weigh a little under 180. Used to go up to 195, but
> > >>> no more. Since the front wheel doesn't need to be rebuilt, it will remain 14 gauge straight
> > >>> gauge 36 spoked wheel. What is the primary reason for double butted wheels? I would think
> > >>> weight savings. How much savings would that be?
> >
> > >> Weight savings is an extra bonus. The real reason is that a wheel with DB spokes will be more
> > >> durable, not necessarily stronger.
> >
> > > If the straight gauge is stronger wouldn't it be more durable than double butted under heavy
> > > loads?

> <[email protected]> wrote in message
> news:[email protected]...
> > If... but they are not, because their ends, where they fail, are identical for both types of
> > spoke, having the same cross section. The swaged spoke having been made from a straight gauge
> > spoke blank.
> >
> > Fatigue is a process by which a metal is torn apart by repeated loading much lower than that
> > needed to forcefully break the part. Therefore, it is not rupture strength but rather stress
> > levels under cyclic loading that cause spokes to fail. That is why stress relieving is highly
> > important in building durable wheels.

"Wayne T" <[email protected]> wrote in message
news:[email protected]...
> so, essentially what you are saying is that the fact that the middle of a double butted spoke is
> thinner, it allows it to flex and take the stress
off
> the ends of the spoke where most spoke tend to break. But wouldn't the
fact
> that the middle of a double butted spoke flexes more than a straight
gauge,
> cause the middle section to fatique more and, therefore, cause more mid section breakage?
> >
> > Jobst Brandt [email protected] Palo Alto CA
>
>

Spokes almost never break anywhere but the head. "Midsection breakage" is all but unknown.
--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
 
"Sheldon Brown" <[email protected]> wrote in message
news:[email protected]...
> Mark Hickey wrote:
>
> >>The thick rod is the straight 14g spoke, while the thin rod is the butted spoke. It's pretty
> >>obvious the stresses on the pole at the handle will be MUCH higher for the thick non-tapered
> >>rod, and it will be much more likely to break as you pull. The stresses will be distributed
> >>along the length of the thinner fishing rod and it won't break, even though it's "not as strong"
> >>as that thick, non-tapered rod.
>
> Terry Morse demurred:
>
> > Cool analogy, but I don't think it works. I'll switch back to spokes:
> >
> > Two properly built wheels, one with straight gauge and one with swaged (butted) spokes, will
> > have the same spoke tension. Regular readers of rbt know that the maximum tension in a spoke is
> > achieved when the wheel is unused, and the tension only decreases at the contact area.
> > Therefore, the maximum stress experienced by the spoke heads (site of most failures) is
> > identical for both types of spokes.
>
> That's true for smooth riding, but not correct when impact loads are considered.
>
> In-line impact loads tend to push the rim inward at the point of impact. This causes a tendency
> for the rim to bulge outward in areas immediately adjacent to the impact point. The spokes in the
> bulge zones do suffer transient increases in stress.

So which would handle this stress better? 14 straight gauge or double butted?
>
> Lateral stresses also can result in locally increased spoke tension.
>
> Sheldon "Double Bubble" Brown +--------------------------------------------------+
> | Conscience is the inner voice which warns us | that someone might be looking. | --H.L.
> | Mencken |
> +--------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts
> Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
> http://captainbike.com http://sheldonbrown.com
 
"Paul Kopit" <[email protected]> wrote in message
news:[email protected]...
> What I'm questioning is how much difference, if any, does it really make? Well built wheels don't
> break spokes unless chains get launched into them, big holes/bumps, or accidents.

The question then is when you hit a big hole or bump under heavy load, which would hold up better?
14 straight gauge or 14/15 double butted? I know of a 250 pounder that kept breaking 14 gauge
spokes. He had to go to a 12 gauge.

\ Tensioned properly, spokes
> don't pull through the rim. Very large numbers of excellent wheels have been built with straight
> guage spokes.
>
> If the spoke makers don't bother to measure, they can say anything they like. I would think that
> if there were significant differences they would measure.
>
> On Tue, 11 Feb 2003 02:07:59 GMT, "Wayne T" <[email protected]> wrote:
>
> >
> >If I'm reading you right, it sounds like you are questioning the
soundness
> >of those posts stating that 14/15 double butted spoked wheels are
sturdier
> >than straight 14 gauge because there has not really been any scientific tests showing it one way
> >or the other.
 
"Wayne T" <[email protected]> wrote:

> > > If the straight guage is stronger wouldn't it be more durable than
> double
> > > butted under heavy loads?
> >
> >
> > No, because spokes don't break from overload, they break from fatigue. Double butted, or swaged,
> > spokes fatigue more slowly.
>
>
> I guess it is hard for me to understand how something thinner could fatigue faster than something
> thicker.

It is true that thinner metal, given equal stress cycles, will break sooner than thicker metal. But
in the case of spokes, as A. Muzi and others have pointed out, spokes almost always break at the
head, where the metal is the same thickness for swaged or for straight gauge spokes.

Fatiguing of the thinner portion of the spoke isn't the problem. The thinner portion of the spoke
helps to reduce the stress cycle on the head and elbow.

--
Ted Bennett Portland OR
 
May I put it differently? Suppose you have a bad back that gets sore when riding over rough terrain.
Don't you profit by not sitting hard on the saddle and prefer instead to absorb shocks with your
knees and legs? The comparison goes only as far as your knees don't fatigue. As if it were ... .

Sergio Pisa
 
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