Spoke Breakage

david said:

Just wondering and Jobst... yeah yeah I'm a moron- I'm not a mechanical
engineer, just a lowly biomedical engineering student.

Beautiful attempt at a preemptive strike. I'll be interested to see
how effective it is!

david said:

Sorry if this has been already discussed.

But I am somewhat interested in why spokes are not hollow? Is it the
bending moment that breaks the spokes most often (J bend region) and
if so a larger diameter hollow spoke would increased polar moment of
inertia considerably without any increased weight. However if it is
fatigue related what type of implications would a hollow spoke have
with the same cross sectional area, but with a hollow center and a
larger diameter? Would this greatly reduce aerodynamics of the wheel?

Just wondering and Jobst... yeah yeah I'm a moron- I'm not a
mechanical engineer, just a lowly biomedical engineering student.

Hey, if someone crashes badly you could remove a spoke and use it as a stent
for a stint!

(Or a /catheter/...)

Shudder Bill

good work. That's beautiful.

david

david said:

Sorry if this has been already discussed.

But I am somewhat interested in why spokes are not hollow? Is it the bending
moment that breaks the spokes most often (J bend region) and if so a larger
diameter hollow spoke would increased polar moment of inertia considerably
without any increased weight. However if it is fatigue related what type of
implications would a hollow spoke have with the same cross sectional area,
but with a hollow center and a larger diameter? Would this greatly reduce
aerodynamics of the wheel?

Just wondering and Jobst... yeah yeah I'm a moron- I'm not a mechanical
engineer, just a lowly biomedical engineering student.

Thanks for your time-

David

Dear David,

A) That idea is for the birds, bonehead.

B) Or maybe featherbrain?

C) Sorry, but those two puns were irresistible, even if they
shaft an innocent inquiry.

D) The previous answer sounded hollow. The next answer is
forced.

E) Spokes are cheaply and easily made by drawing wire
through smaller and smaller holes. The sides of hollow wire
would squish together, defeating the purpose.

F) Running stainless steel tubes through the process above
would deplete our precious stocks of frame tubing.

G) No, that was no joke, it Raleigh would! The 531 tubing is
now available only by special order:

https://vault2.secured-url.com/reynolds/steel531.html

H) The greatest stress is on the outside of the shaft as it
bends into a J, so removing the interior wouldn't address
that concern. (The inner curve compresses, the outer curve
stretches, and the center changes least of all. Look at your
forefinger from the side and curve it--the big skin fold on
the inside allows compression, the wrinkly knuckle allows
stretching, and the skin is almost smooth in the middle of
the side of the joint, where little happens.)

I) Fatter spokes would increase drag a bit, but the
interesting question would be whether to replace hollow
nipples with tiny bolts.

J) Here's a brief account of how actual seamed and seamless
tubing is made:

https://vault2.secured-url.com/reynolds/buttedtubing.html

This would be rather more expensive than drawn wire spokes,
most of which actually work just fine and last a long time
outside the hypercritical atmosphere of rec.bicycles.tech

Carl Fogel

david said:

Sorry if this has been already discussed.

But I am somewhat interested in why spokes are not hollow?

To maintain strength and make manufacture possible you'd need a pretty
big spoke diameter. For many riders aerodynamics are more important
than mass when it comes to wheels, and big fat spokes would be really
bad in this context. You could make long chord aero versions but then
you'd need a fancy way of attaching them to the hub and the rim.

Anyway, your average trispoke or pentaspoke carbon aero wheel does have
hollow (foam-filled) spokes; it's just that they work like cartwheels
rather than tension-spoked wheels and they are not very efficient in
terms of weight. Good for time trialling or pursuiting though.

Tubing in tension has no more strength than solid rod. The best way to
eliminate the bending stresses at the hub end of the spoke would be to make
them "straight pull" by redesigning the hub. I think it has been done on
wheelchairs, but why isn't it done on bikes?

Leo Lichtman said:

Tubing in tension has no more strength than solid rod.

Less strength, surely? Tubing is more efficient when you have bending
or torsional stresses; there should be no significant torsional stresses
in a spoke once the wheel is built, so that just leaves bending.

The best way to

Quoted message said:

eliminate the bending stresses at the hub end of the spoke would be to make
them "straight pull" by redesigning the hub. I think it has been done on
wheelchairs, but why isn't it done on bikes?

And therefore this is the real point. Most spokes break at the elbow.
However, straight-pull spokes (it *has* been done for bikes) have a few
problems:

1) they create a new standard for spokes, and new standards are resisted
by the industry

2) the hub will probably be heavier; the parts of the flange where the
spoke attached had better be strong, otherwise you have the radial wheel
issue where spokes can rip straight out. With a conventional flange and
tangential spoking, the spoke has around half an inch of metal between
it and freedom.

3) straight-pull spokes rotate when you're trying to tighten them. Not
helpful.

Leo Lichtman said:

Tubing in tension has no more strength than solid rod. The best way to
eliminate the bending stresses at the hub end of the spoke would be to make
them "straight pull" by redesigning the hub. I think it has been done on
wheelchairs, but why isn't it done on bikes?

Dear Leo,

Some bicycles do use straight-pull spokes, and so do many
motorcycles.

In all likelihood, the manufacturers see no reason to change
the J-bend spoke design that's cheap, simple, easy to work
with, and incredibly reliable, despite our fuss here on
rec.bicycles.tech.

For example, it took years for the old motorycle frame
design with twin exposed rear suspension units to be
replaced by the modern monoshock tucked inside the frame.
Bicycles came to rear suspension late, so they pretty much
started out with modern rear monoshocks.

Carl Fogel

On Tue, 1 Mar 2005 13:46:33 -0500, "david" <[email hidden]>

may have said:

Sorry if this has been already discussed.

But I am somewhat interested in why spokes are not hollow?

A tubular spoke with the same tensile strength as the ordinary solid
ones would have a much larger diameter, and thereby higher wind
resistance. This would be viewed as a Bad Thing.

Quoted message said:

Is it the bending
moment that breaks the spokes most often (J bend region)

That's just one place where they break, and the problem is commonly
addressed by appropriate stress-relief procedures during wheel prep.

Quoted message said:

and if so a larger
diameter hollow spoke would increased polar moment of inertia considerably
without any increased weight. However if it is fatigue related what type of
implications would a hollow spoke have with the same cross sectional area,
but with a hollow center and a larger diameter?

It would need to have a solid end for the J; a tube would simply
deform at the bend unless some fairly fragile manufacturing techniques
were used, and even then, the larger-OD spoke would mandate a larger
flange diameter...no, this would not be a good thing.

Quoted message said:

Would this greatly reduce
aerodynamics of the wheel?

The perception would be that it would impact wheel aerodynamics,
whether that was a significant factor or not.

Tubes are good for resisting twist and bend forces, but a spoke's load
is almost purely tensile; there is no advantage in using a tube.

Quoted message said:

Just wondering and Jobst... yeah yeah I'm a moron- I'm not a mechanical
engineer, just a lowly biomedical engineering student.

I'm not an engineer either, but this one's not rocket science. (Or
brain surgery, if you prefer.)

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

David G said:

But I am somewhat interested in why spokes are not hollow? Is it
the bending moment that breaks the spokes most often (J bend region)
and if so a larger diameter hollow spoke would increased polar
moment of inertia considerably without any increased weight.
However if it is fatigue related what type of implications would a
hollow spoke have with the same cross sectional area, but with a
hollow center and a larger diameter? Would this greatly reduce
aerodynamics of the wheel?

Structural elements are made hollow to improve resistance to bending
and torsion without adding material, both of which is not a desirable
feature for spokes. Spoke failures are caused by localized peak
stresses caused by spoke forming and by bending them into position at
the hub flange. Such stresses would increase if the cross section
were greater (hollow).

Subsequent tensioning guarantees that peak forming stresses remain if
no effort is is made to relieve them. Stress relief can be achieved
by over-tensioning spokes, causing yield at these peak stress
locations, so that when tension is relaxed to normal, peak stress is
also commensurately lower.

Jobst Brandt
[email hidden]

Quoted message said:

David G said:

But I am somewhat interested in why spokes are not hollow? Is it
the bending moment that breaks the spokes most often (J bend region)
and if so a larger diameter hollow spoke would increased polar
moment of inertia considerably without any increased weight.
However if it is fatigue related what type of implications would a
hollow spoke have with the same cross sectional area, but with a
hollow center and a larger diameter? Would this greatly reduce
aerodynamics of the wheel?

Structural elements are made hollow to improve resistance to bending
and torsion without adding material, both of which is not a desirable
feature for spokes. Spoke failures are caused by localized peak
stresses caused by spoke forming

no, failures are caused by the bending cycles that occur due to
non-axial loading - a problem solved by straight pull spokes.

Quoted message said:

and by bending them into position at
the hub flange.

a practice you endorse but which manufacturers specifically recommend
against. do the math for a 2.4mm hub hole, 2.0mm spoke & canted flange.
and don't forget local deformation of the hole either. bending is
unnecessary.

Quoted message said:

Such stresses would increase if the cross section
were greater (hollow).

no, that depends on the form.

Quoted message said:

Subsequent tensioning guarantees that peak forming stresses remain if
no effort is is made to relieve them. Stress relief can be achieved
by over-tensioning spokes, causing yield at these peak stress
locations, so that when tension is relaxed to normal, peak stress is
also commensurately lower.

coming from a guy that's yet to demonstrate any grasp of deformation
theory, that statement is indeed a "stretch".

Quoted message said:

Jobst Brandt
[email hidden]

On Wed, 02 Mar 2005 06:25:34 -0800, jim beam <[email hidden]>

Quoted message said:

Quoted message said:

Structural elements are made hollow to improve resistance to bending
and torsion without adding material, both of which is not a desirable
feature for spokes. Spoke failures are caused by localized peak
stresses caused by spoke forming

no, failures are caused by the bending cycles that occur due to
non-axial loading - a problem solved by straight pull spokes.

Quoted message said:

and by bending them into position at
the hub flange.

a practice you endorse but which manufacturers specifically recommend
against. do the math for a 2.4mm hub hole, 2.0mm spoke & canted flange.
and don't forget local deformation of the hole either. bending is
unnecessary.

You seem to think that reshaping spoke elbows is actually an option.
Please advise how one would get the heads-in spokes in the photo below
to take the proper line to the rim without any bending.

http://www.businesscycles.com/graphics/spokelinebouquet.jpg (~73k
file).

-------------------------------
John Dacey
Business Cycles, Miami, Florida
Since 1983
Comprehensive catalogue of track equipment: online since 1996.
http://www.businesscycles.com

On Wed, 02 Mar 2005 10:45:37 -0500, John Dacey

may have said:

You seem to think that reshaping spoke elbows is actually an option.

Having done a little before-and-after comparison with a magnifier, I
have to say that what you feel that Jobst has implied is in fact what
I have observed; the elbows changed shape after stress-relief.

Quoted message said:

Please advise how one would get the heads-in spokes in the photo below
to take the proper line to the rim without any bending.

http://www.businesscycles.com/graphics/spokelinebouquet.jpg

More importantly, how the hell would a rim that wide fit between the
stays? Or is this a custom dual-rim setup for snuff-toting,
boot-wearing afficionadoes of ultra-macho pickup trucks, using a pair
of the wide rear rims from a Schwinn Stingray laced to one hub? And
if so, why is a DA hub involved? Those guys would want chrome-plated
beefy steel parts, not wimpy-assed aluminum [censored]. (Except for the
rims, where *polished* aluminum might be accepted.)

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

In article <1109773535.e2bf691a044f6808ede5af65a55ae07e@teranews>,

jim beam said:

Quoted message said:

Structural elements are made hollow to improve resistance to bending
and torsion without adding material, both of which is not a desirable
feature for spokes. Spoke failures are caused by localized peak
stresses caused by spoke forming

no, failures are caused by the bending cycles that occur due to
non-axial loading - a problem solved by straight pull spokes.

That makes no sense. Spokes break in the threads too and the load is
axial.

I'd like to see a spoke cut and sectioned at the threads. I'm betting
there are cracks at the root of the threads. That would explain some
early life failures.

--
Mike DeMicco <[email hidden]>

Werehatrack said:

On Wed, 02 Mar 2005 10:45:37 -0500, John Dacey

may have said:

You seem to think that reshaping spoke elbows is actually an option.

Having done a little before-and-after comparison with a magnifier, I
have to say that what you feel that Jobst has implied is in fact what
I have observed; the elbows changed shape after stress-relief.

Quoted message said:

Please advise how one would get the heads-in spokes in the photo below
to take the proper line to the rim without any bending.

http://www.businesscycles.com/graphics/spokelinebouquet.jpg

More importantly, how the hell would a rim that wide fit between the
stays? Or is this a custom dual-rim setup for snuff-toting,
boot-wearing afficionadoes of ultra-macho pickup trucks, using a pair
of the wide rear rims from a Schwinn Stingray laced to one hub? And
if so, why is a DA hub involved? Those guys would want chrome-plated
beefy steel parts, not wimpy-assed aluminum [censored]. (Except for the
rims, where *polished* aluminum might be accepted.)

Maybe I just need another treatment for my chronic humor-impairment,
but to the extent that it wasn't obvious in the photo above, the
spokes lie oriented in the hub _before_ trying to lace them to the
rim. If you've got the bandwidth, here it is from a more distant
perspective:
http://www.businesscycles.com/graphics/spokelinebouquet2.jpg (~128k)

In deference to Peter C's return to rbt, it's a Chorus hub.
-------------------------------
John Dacey
Business Cycles, Miami, Florida
Since 1983
Comprehensive catalogue of track equipment: online since 1996.
http://www.businesscycles.com

Werehatrack said:

Having done a little before-and-after comparison with a magnifier, I
have to say that what you feel that Jobst has implied is in fact what
I have observed; the elbows changed shape after stress-relief.

Well, they bend to an acute or obtuse angle depending on whether they're
wrapped around the flange (heads in) or hanging off it (heads out). You
can separate inside/outside spokes from a dismantled wheel just by
looking at them. I'm not sure whether anything is happening at the
metallurgical level, but it makes sense to me that this bending should
happen during building rather than when riding.

Quoted message said:

Quoted message said:

Please advise how one would get the heads-in spokes in the photo below
to take the proper line to the rim without any bending.

http://www.businesscycles.com/graphics/spokelinebouquet.jpg

More importantly, how the hell would a rim that wide fit between the
stays? Or is this a custom dual-rim setup for snuff-toting,
boot-wearing afficionadoes of ultra-macho pickup trucks, using a pair
of the wide rear rims from a Schwinn Stingray laced to one hub? And
if so, why is a DA hub involved? Those guys would want chrome-plated
beefy steel parts, not wimpy-assed aluminum [censored]. (Except for the
rims, where *polished* aluminum might be accepted.)

Hehe.

On Wed, 02 Mar 2005 12:27:26 -0500, John Dacey

may have said:

Werehatrack said:

On Wed, 02 Mar 2005 10:45:37 -0500, John Dacey

may have said:

You seem to think that reshaping spoke elbows is actually an option.

Having done a little before-and-after comparison with a magnifier, I
have to say that what you feel that Jobst has implied is in fact what
I have observed; the elbows changed shape after stress-relief.

Quoted message said:

Please advise how one would get the heads-in spokes in the photo below
to take the proper line to the rim without any bending.

http://www.businesscycles.com/graphics/spokelinebouquet.jpg

More importantly, how the hell would a rim that wide fit between the
stays? Or is this a custom dual-rim setup for snuff-toting,
boot-wearing afficionadoes of ultra-macho pickup trucks, using a pair
of the wide rear rims from a Schwinn Stingray laced to one hub? And
if so, why is a DA hub involved? Those guys would want chrome-plated
beefy steel parts, not wimpy-assed aluminum [censored]. (Except for the
rims, where *polished* aluminum might be accepted.)

Maybe I just need another treatment for my chronic humor-impairment,
but to the extent that it wasn't obvious in the photo above, the
spokes lie oriented in the hub _before_ trying to lace them to the
rim.

Yeah, but I couldn't resist the opportunity presented.

Quoted message said:

If you've got the bandwidth, here it is from a more distant
perspective:
http://www.businesscycles.com/graphics/spokelinebouquet2.jpg (~128k)

In deference to Peter C's return to rbt, it's a Chorus hub.

Both Chorus and DA are out of band for my budget, but I could see that
the splines for the cassette were taller than the ones on any I had,
and I knew that the DA had that feature. Now I know that Chorus does
as well...but, of course, *differently* since it's Campy.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

John Dacey said:

On Wed, 02 Mar 2005 06:25:34 -0800, jim beam <[email hidden]>

Quoted message said:

Quoted message said:

Structural elements are made hollow to improve resistance to bending
and torsion without adding material, both of which is not a desirable
feature for spokes. Spoke failures are caused by localized peak
stresses caused by spoke forming

no, failures are caused by the bending cycles that occur due to
non-axial loading - a problem solved by straight pull spokes.

Quoted message said:

and by bending them into position at
the hub flange.

a practice you endorse but which manufacturers specifically recommend
against. do the math for a 2.4mm hub hole, 2.0mm spoke & canted flange.
and don't forget local deformation of the hole either. bending is
unnecessary.

You seem to think that reshaping spoke elbows is actually an option.
Please advise how one would get the heads-in spokes in the photo below
to take the proper line to the rim without any bending.

http://www.businesscycles.com/graphics/spokelinebouquet.jpg (~73k
file).

you elastically position the spoke in the rim as per normal, then
tighten as per normal. as you know, tension of the steel spoke in thw
alloy hub deforms the spoke holes, so by the time that's happened, and
you've allowed for the slant of the 2.0mm spoke in the 2.4mm hole with a
3.2 flange, you should end up with an obtuse angle on the elbow, not
acute. if it /is/ acute, it was bent in lacing and is not seated
properly in the hub hole. as is often evident by the way the heads sit
- no need to disassemble to see that.

Quoted message said:

-------------------------------
John Dacey
Business Cycles, Miami, Florida
Since 1983
Comprehensive catalogue of track equipment: online since 1996.
http://www.businesscycles.com

John Dacey said:

...
Maybe I just need another treatment for my chronic humor-impairment,
but to the extent that it wasn't obvious in the photo above, the
spokes lie oriented in the hub _before_ trying to lace them to the
rim. If you've got the bandwidth, here it is from a more distant
perspective:
http://www.businesscycles.com/graphics/spokelinebouquet2.jpg (~128k)...

Now that is what I call a lightweight rim! 😉

--
Tom Sherman - Earth