Oddball wheel question

[[email protected]]

This may be an old chestnut, but I'm curious what people
have to say.

Briefly, Kraig Willett took a 3-spoke rear wheel, cut a
section out of one spoke, rode it around, and asks whether
the wheel stands or hangs from the two remaining spokes:

http://www.biketechreview.com/misc/hangin_hub.htm

My first thought is that it doesn't really address the
question of how a pre-tensioned wheel works, since the two
remaining spokes aren't likely to have any pre-tension and
must be awfully strong and anchored in ways different from
wire-spoke wheels.

(Maybe "struts" would be a better word than "spokes" here?)

I assume that the hub hangs from a very stiff rim when the
struts or spokes are overhead, produces a downward shearing
force when they're off to either side, and stands on the rim
when they're underneath.

If so, when would this maimed wheel be most likely to fail?
With the strut/spokes at the side? Or overhead?

Carl Fogel

 

[Tim McNamara]

[email protected] writes:

> This may be an old chestnut, but I'm curious what people have to
> say.
>
> Briefly, Kraig Willett took a 3-spoke rear wheel, cut a section out
> of one spoke, rode it around, and asks whether the wheel stands or
> hangs from the two remaining spokes:

This is one of those misleading hypothetical questions that almost
seems like it means something, but really doesn't. In a pretensioned
wheel, of course, the wheel would be instantly unrideable when the
spoke is cut. If a Tri-Spoke type wheel, the rim would have to be
incredibly rigid in order for it to be at all rideable.

> If so, when would this maimed wheel be most likely to fail? With
> the strut/spokes at the side? Or overhead?

In my opinion, when the gap is between the hub and the ground. Of
course, that gap covers 240 degrees of the wheel... but I would think
it would collapse as soon as the contact point is equidistant between
the remaining spokes, depending on how close the load is to the
stiffness limits of the rim.

 

[Werehatrack]

On Thu, 21 Oct 2004 21:51:30 -0600, [email protected] wrote:

>This may be an old chestnut, but I'm curious what people
>have to say.
>
>Briefly, Kraig Willett took a 3-spoke rear wheel, cut a
>section out of one spoke, rode it around, and asks whether
>the wheel stands or hangs from the two remaining spokes:
>
>http://www.biketechreview.com/misc/hangin_hub.htm
>
>My first thought is that it doesn't really address the
>question of how a pre-tensioned wheel works, since the two
>remaining spokes aren't likely to have any pre-tension and
>must be awfully strong and anchored in ways different from
>wire-spoke wheels.
>
>(Maybe "struts" would be a better word than "spokes" here?)
>
>I assume that the hub hangs from a very stiff rim when the
>struts or spokes are overhead, produces a downward shearing
>force when they're off to either side, and stands on the rim
>when they're underneath.
>
>If so, when would this maimed wheel be most likely to fail?
>With the strut/spokes at the side? Or overhead?

Rather than going through this Yet Again, might I suggest a bit of
Googling and a trip to whatever library has a copy of Jobst's book?
For a normal spoked bike wheel, if you look at it from a vector force
change standpoint, the answer is that the largest vector change is in
the spoke which most nearly points down, and by a perfectly valid but
counterintuitive engineering principle, this means that the wheel
"stands" on the spoke(s) at the bottom.

In my opinion, your example wheel does not closely model a normal
bicycle wheel since the "spokes" are a part of the rim. Effectively,
this is a disc wheel with holes in it. When a "spoke" is removed, and
the wheel is in the position where there's no downward radial section,
it *appears* that the wheel is "hanging from the spokes", but is it
really? In my opinion, no.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

 

[Mark Hickey]

[email protected] wrote:

>This may be an old chestnut, but I'm curious what people
>have to say.
>
>Briefly, Kraig Willett took a 3-spoke rear wheel, cut a
>section out of one spoke, rode it around, and asks whether
>the wheel stands or hangs from the two remaining spokes:
>
>http://www.biketechreview.com/misc/hangin_hub.htm
>
>My first thought is that it doesn't really address the
>question of how a pre-tensioned wheel works, since the two
>remaining spokes aren't likely to have any pre-tension and
>must be awfully strong and anchored in ways different from
>wire-spoke wheels.
>
>(Maybe "struts" would be a better word than "spokes" here?)

If one were wondering about how wagon wheels work, this would probably
be a good test. If one wonders about how a spoked bicycle wheel
works... try cutting out a 12 adjacent spokes from a 36 spoke wheel
and see how it goes...

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

 

[[email protected]]

On Thu, 21 Oct 2004 21:45:47 -0700, Mark Hickey
<[email protected]> wrote:

>[email protected] wrote:
>
>>This may be an old chestnut, but I'm curious what people
>>have to say.
>>
>>Briefly, Kraig Willett took a 3-spoke rear wheel, cut a
>>section out of one spoke, rode it around, and asks whether
>>the wheel stands or hangs from the two remaining spokes:
>>
>>http://www.biketechreview.com/misc/hangin_hub.htm
>>
>>My first thought is that it doesn't really address the
>>question of how a pre-tensioned wheel works, since the two
>>remaining spokes aren't likely to have any pre-tension and
>>must be awfully strong and anchored in ways different from
>>wire-spoke wheels.
>>
>>(Maybe "struts" would be a better word than "spokes" here?)
>
>If one were wondering about how wagon wheels work, this would probably
>be a good test. If one wonders about how a spoked bicycle wheel
>works... try cutting out a 12 adjacent spokes from a 36 spoke wheel
>and see how it goes...
>
>Mark Hickey
>Habanero Cycles
>http://www.habcycles.com
>Home of the $695 ti frame

Dear Mark,

I don't think that it's even really like a wagon-wheel.

As I understand oldd wooden wheels, the spokes are roughly
wooden dowels driven into holes in the hub and the middle of
each rim section, with a heated iron band shrunk into place
around the wooden rim to give enough compression to hold
things together.

I think that if there were only three such spokes, such a
dowel-style wheel would fall apart after a turn or two if
one spoke were removed, depending on how tightly the two
remaining spokes were shoved into the holes--assuming that
it would even hold its shape long enough to turn.

The Willett wheel strikes more as being the solid disk with
some holes in it suggested by Werehatrack--big holes,
admittedly, but with still enough rigid material left to
make a disk.

I'm still wondering in what position it would be most likely
to fail with the two remaining struts forming a 120-degree
angle.

Carl Fogel

 

[Leo Lichtman]

carlfogel wrote: (clip) I'm still wondering in what position it would be
most likely to fail with the two remaining struts forming a 120-degree
angle.
^^^^^^^^^^^^^^^^
Let's do this thought experiment: Reduce the angle between the remaining
spokes and visualize the behavior of the wheel. In the limit, the angle is
reduced to the point where you have one spoke. So, let's imagine that we
have cut out two spokes, and have one left. Now run the wheel under load,
and increase the load until it starts to fail. Even without a stress
analysis, I think it is obvious that the weakest position is with the spoke
in a horizontal position, so that is where it will fail. I reason that the
two remaining spokes will fail when their axis of symmetry is
horizontal--IOW, when the axis of the missing spoke is horizontal.

As others have pointed out, this bears no relation to wire spokes, which
have no load bearing capacity except in tension.

 

[[email protected]]

Carl Fogel writes:

> This may be an old chestnut, but I'm curious what people have to
> say.

An ancient one.

> Briefly, Kraig Willett took a 3-spoke rear wheel, cut a section out
> of one spoke, rode it around, and asks whether the wheel stands or
> hangs from the two remaining spokes:

http://www.biketechreview.com/misc/hangin_hub.htm

> My first thought is that it doesn't really address the question of
> how a pre-tensioned wheel works, since the two remaining spokes
> aren't likely to have any pre-tension and must be awfully strong and
> anchored in ways different from wire-spoke wheels.

> (Maybe "struts" would be a better word than "spokes" here?)

> I assume that the hub hangs from a very stiff rim when the struts or
> spokes are overhead, produces a downward shearing force when they're
> off to either side, and stands on the rim when they're underneath.

> If so, when would this maimed wheel be most likely to fail? With
> the strut/spokes at the side? Or overhead?

That depends on which is stronger, the spokes or the rim. In either
case, you don't have a complete wheel. If the tri-spoke supports a
rider with only two spokes, then it must be overdesigned. However, I
doubt that anyone would consider riding such a wheel at speed over any
real road. There are also wheels with one spoke much like the old
Girling brake logo with an arm reaching out to grasp a ring shaped
disc brake. These are also used as steering wheels on Citro?n DS's.

http://www.id-ds.com/Pages/Citroen/DS.Barthes.html

So what is it that you are pursuing with this subject? Knowing how
well you search the archives, you must have noticed that this has been
beaten to death for many years. In fact it has been an old chestnut
since "the Bicycle Wheel" reached the bookshelves.

Jobst Brandt
[email protected]

 

[[email protected]]

On Fri, 22 Oct 2004 06:44:22 GMT, "Leo Lichtman"
<[email protected]> wrote:

>
>carlfogel wrote: (clip) I'm still wondering in what position it would be
>most likely to fail with the two remaining struts forming a 120-degree
>angle.
>^^^^^^^^^^^^^^^^
>Let's do this thought experiment: Reduce the angle between the remaining
>spokes and visualize the behavior of the wheel. In the limit, the angle is
>reduced to the point where you have one spoke. So, let's imagine that we
>have cut out two spokes, and have one left. Now run the wheel under load,
>and increase the load until it starts to fail. Even without a stress
>analysis, I think it is obvious that the weakest position is with the spoke
>in a horizontal position, so that is where it will fail. I reason that the
>two remaining spokes will fail when their axis of symmetry is
>horizontal--IOW, when the axis of the missing spoke is horizontal.
>
>As others have pointed out, this bears no relation to wire spokes, which
>have no load bearing capacity except in tension.
>

Dear Leo,


I think that you're right about a single-spoke/strut being
most likely to fail when horizontal--it would bend down.

But I'm wondering about when two spoke/struts 120 degrees
apart will fail.

And with two spoke/struts, both are in kinda-sorta tension
when overhead, each angling down toward the hub at 60
degrees:

\/

When they're on the side, one is in the same kinda-sorta
tension at 60 degrees (I think), but the other has moved to
being in kinda-sorta compression:

\
/

I expect that these spoke-struts are going to be stronger in
compression than in tension, but I'm not sure.

Nor am I all that sure about whether the damned things are
in tension, compression, shear, or what. And how the rim
would distort is another question.

Carl Fogel

 

[[email protected]]

On Fri, 22 Oct 2004 07:12:10 GMT,
[email protected] wrote:

>Carl Fogel writes:
>
>> This may be an old chestnut, but I'm curious what people have to
>> say.
>
>An ancient one.
>
>> Briefly, Kraig Willett took a 3-spoke rear wheel, cut a section out
>> of one spoke, rode it around, and asks whether the wheel stands or
>> hangs from the two remaining spokes:
>
> http://www.biketechreview.com/misc/hangin_hub.htm
>
>> My first thought is that it doesn't really address the question of
>> how a pre-tensioned wheel works, since the two remaining spokes
>> aren't likely to have any pre-tension and must be awfully strong and
>> anchored in ways different from wire-spoke wheels.
>
>> (Maybe "struts" would be a better word than "spokes" here?)
>
>> I assume that the hub hangs from a very stiff rim when the struts or
>> spokes are overhead, produces a downward shearing force when they're
>> off to either side, and stands on the rim when they're underneath.
>
>> If so, when would this maimed wheel be most likely to fail? With
>> the strut/spokes at the side? Or overhead?
>
>That depends on which is stronger, the spokes or the rim. In either
>case, you don't have a complete wheel. If the tri-spoke supports a
>rider with only two spokes, then it must be overdesigned. However, I
>doubt that anyone would consider riding such a wheel at speed over any
>real road. There are also wheels with one spoke much like the old
>Girling brake logo with an arm reaching out to grasp a ring shaped
>disc brake. These are also used as steering wheels on Citro?n DS's.
>
>http://www.id-ds.com/Pages/Citroen/DS.Barthes.html
>
>So what is it that you are pursuing with this subject? Knowing how
>well you search the archives, you must have noticed that this has been
>beaten to death for many years. In fact it has been an old chestnut
>since "the Bicycle Wheel" reached the bookshelves.
>
>Jobst Brandt
>[email protected]

Dear Jobst,

What I was pursuing was whether I understood things
correctly when I thought that Willett was wrong (that's
often why we post questions here) and how the weird-looking
thing would fail.

The Citroen steering wheel is a nice bonus.

So how would it fail if the spokes were stronger than the
rim? When the two spokes were overhead, or to one side? Or
what? And what part would break?

And how would it fail if the rim were stronger than the
spokes? Would the rim break in the middle between the
spokes? Just on either side of one spoke or the other? Way
out opposite the two spokes? Or what?

Carl Fogel

 

[PK]

Werehatrack wrote:

> Rather than going through this Yet Again, might I suggest a bit of
> Googling and a trip to whatever library has a copy of Jobst's book?
> For a normal spoked bike wheel, if you look at it from a vector force
> change standpoint, the answer is that the largest vector change is in
> the spoke which most nearly points down, and by a perfectly valid but
> counterintuitive engineering principle, this means that the wheel
> "stands" on the spoke(s) at the bottom.


what force is exerted by the lower spoke(s) at the point where they are
attached to the hub?

>>

The load is supported by the rim.

The load is transferred to the rim by the spokes.

The rim distortion as it supports the load results in reduced tension in
the lower few spokes.

To ask "hang or stand?" is an irrelvant question as the answer is "neither!"
: THAT is the truly counerintuitive point about the pre-tensioned spoked
wheel!

pk

 

[Tim McNamara]

"PK" <[email protected]> writes:

> To ask "hang or stand?" is an irrelvant question as the answer is
> "neither!" THAT is the truly counerintuitive point about the
> pre-tensioned spoked wheel!

Well, you're making progress as your last round of posts vociferously
argued that the wheel hands from the upper spokes.

 

[[email protected]]

Carl Fogel writes:

> What I was pursuing was whether I understood things correctly when I
> thought that Willett was wrong (that's often why we post questions
> here) and how the weird-looking thing would fail.

> The Citroen steering wheel is a nice bonus.

> So how would it fail if the spokes were stronger than the rim? When
> the two spokes were overhead, or to one side? Or what? And what part
> would break?

The arch of the unsupported rim would fail when the remaining spokes
were at the top. Otherwise the spokes would break in shear when at
the side as someone stated.

Jobst Brandt
[email protected]

 

[Zog The Undeniable]

[email protected] wrote:

> This may be an old chestnut, but I'm curious what people
> have to say.
>
> Briefly, Kraig Willett took a 3-spoke rear wheel, cut a
> section out of one spoke, rode it around, and asks whether
> the wheel stands or hangs from the two remaining spokes:

I'm waiting for the monospoke wheel, like a Citroen steering wheel. I
expect it would be rather heavy and unbalanced, but I'm sure someone
will try it.

http://www.cats-citroen.net/citroen_museum/ami_s_ber_75/amisber75_08.jpg

 

[Zog The Undeniable]

....and one day I'll read the whole thread before replying ;-)

 

[PK]

Tim McNamara wrote:
> "PK" <[email protected]> writes:
>
>> To ask "hang or stand?" is an irrelevant question as the answer is
>> "neither!" THAT is the truly counterintuitive point about the
>> pre-tensioned spoked wheel!
>
> Well, you're making progress as your last round of posts vociferously
> argued that the wheel hands from the upper spokes.

Several rounds ago maybe while I was still distracted by the irrelevant
question.

But if you want to press the point:

Looking at the vector diagram of the loaded hub in equilibrium, the forces
which support the hub come from the upper spokes and the lower spokes are
pulling down. It is therefore a physical and linguistic nonsense to speak of
standing on the lower spokes. it is still wrong, but less so, to speak of
hanging because the supporting forces are coming from above.

But neither is correct and each gives a misleading interpretation of the
complex system.

The load is not standing on the lower spokes because they are pulling down
they do not exert any upward force on the hub

The load is not hanging from the upper spokes as that would imply an
increase in tension in the uppers spokes as the load increases.

The load is carried by the rim and is transferred from the hub to the rim
by the spokes. In carrying the load the rim distorts around the contact
point and the tension in the lower spokes is reduced.

#####

This whole confusion arose from the wrong interpretation of the "ping" test.

The argument went:
It is intuitively obvious that the hub hangs from the upper spokes and the
tension in the upper spokes increases with load.
Ha, said someone, let's ping the upper and lower spokes to check that.
Oh bugger, the ping test shows that the upper spokes show no change but the
lowest few spoke do show a significant change.
Hence the intuition was wrong and it is clear that the hub is actually
standing on the lower spokes.

Good experiment.
Wrong interpretation of the data

The ping test asks the question: Does the hub hang?
It gives the clear answer: No.
But that is where the information from the ping test stops. It does not tell
us how the wheel actually supports the loaded hub.

pk

 

[almost fast]

[email protected] wrote in message news:<[email protected]>...
> On Fri, 22 Oct 2004 07:12:10 GMT,
> [email protected] wrote:
>
> >Carl Fogel writes:
> >
> >> This may be an old chestnut, but I'm curious what people have to
> >> say.
> >
> >An ancient one.
> >
> >> Briefly, Kraig Willett took a 3-spoke rear wheel, cut a section out
> >> of one spoke, rode it around, and asks whether the wheel stands or
> >> hangs from the two remaining spokes:
> >
> > http://www.biketechreview.com/misc/hangin_hub.htm
> >
> >> My first thought is that it doesn't really address the question of
> >> how a pre-tensioned wheel works, since the two remaining spokes
> >> aren't likely to have any pre-tension and must be awfully strong and
> >> anchored in ways different from wire-spoke wheels.
>
> >> (Maybe "struts" would be a better word than "spokes" here?)
>
> >> I assume that the hub hangs from a very stiff rim when the struts or
> >> spokes are overhead, produces a downward shearing force when they're
> >> off to either side, and stands on the rim when they're underneath.
>
> >> If so, when would this maimed wheel be most likely to fail? With
> >> the strut/spokes at the side? Or overhead?
> >
> >That depends on which is stronger, the spokes or the rim. In either
> >case, you don't have a complete wheel. If the tri-spoke supports a
> >rider with only two spokes, then it must be overdesigned. However, I
> >doubt that anyone would consider riding such a wheel at speed over any
> >real road. There are also wheels with one spoke much like the old
> >Girling brake logo with an arm reaching out to grasp a ring shaped
> >disc brake. These are also used as steering wheels on Citro?n DS's.
> >
> >http://www.id-ds.com/Pages/Citroen/DS.Barthes.html
> >
> >So what is it that you are pursuing with this subject? Knowing how
> >well you search the archives, you must have noticed that this has been
> >beaten to death for many years. In fact it has been an old chestnut
> >since "the Bicycle Wheel" reached the bookshelves.
> >
> >Jobst Brandt
> >[email protected]
>
> Dear Jobst,
>
> What I was pursuing was whether I understood things
> correctly when I thought that Willett was wrong (that's
> often why we post questions here) and how the weird-looking
> thing would fail.
>
> The Citroen steering wheel is a nice bonus.
>
> So how would it fail if the spokes were stronger than the
> rim? When the two spokes were overhead, or to one side? Or
> what? And what part would break?
>
> And how would it fail if the rim were stronger than the
> spokes? Would the rim break in the middle between the
> spokes? Just on either side of one spoke or the other? Way
> out opposite the two spokes? Or what?
>
> Carl Fogel

The three-spoke (with one spoke cut out) will fail when some portion
of it's structure is overloaded. Since it's a composite, I don't know
what the allowable loads are at any point, nor how they differe around
the rim+spokes, nor how the aluminum hub is bonded in. So unless you
know that stuff you can't possibly predict how it might fail.

And the second "identical" sawed-out wheel may fail in a different way
as well.

 

[George Herbert Walker]

Werehatrack <[email protected]> wrote in message news:<[email protected]>...

> For a normal spoked bike wheel, if you look at it from a vector force
> change standpoint, the answer is that the largest vector change is in
> the spoke which most nearly points down, and by a perfectly valid but
> counterintuitive engineering principle, this means that the wheel
> "stands" on the spoke(s) at the bottom.

Do you have some engineering textbook that elucidates principles of
"standing" and "hanging"? If so, why did you have to use quote marks?

In fact the name of the principle is "analogy", and contrary to your
statement, it is instead intuitive and not perfect.

For example, whatever the benefical aspects, some may ask: how can a
system be said to stand upon OR hang from a component contained
entirely within it, and which makes no contact with any external
system, e.g. either the ground or an overhead support? For another
example, standing and hanging are at base static or quasi-static
conditions, so why should anybody be considering a vector force change
"stand"point?

 

[Leo Lichtman]

"George Herbert Walker" wrote: (clip) how can a system be said to stand upon
OR hang from a component contained entirely within it, and which makes no
contact with any external system, e.g. either the ground or an overhead
support? (clip)
^^^^^^^^^^^^
Without getting involved in the "standing"/"hanging" question per se, I have
to point out that there IS transfer of load to an external system. The
weight of the bike and rider rests on the hub. The hub is laced to the
spokes, which modify their tension at various points around the
circumference to produce a resultant which equals the hub load. This
resultant is carried by the rim, then the tire, and produces an identical
resultant in the contaqct patch with the ground. QED.

 

[Tom Sherman]

Zog The Undeniable wrote:

> [email protected] wrote:
>
>> This may be an old chestnut, but I'm curious what people
>> have to say.
>> Briefly, Kraig Willett took a 3-spoke rear wheel, cut a
>> section out of one spoke, rode it around, and asks whether
>> the wheel stands or hangs from the two remaining spokes:
>
>
> I'm waiting for the monospoke wheel, like a Citroen steering wheel. I
> expect it would be rather heavy and unbalanced, but I'm sure someone
> will try it.

Sheldon Brown has already done this.
<http://www.sheldonbrown.com/nanodrive/bianchi-quarter.jpg>.

--
Tom Sherman

 

[George Herbert Walker]

"Leo Lichtman" <[email protected]> wrote in message news:<[email protected]>...
> "George Herbert Walker" wrote: (clip) how can a system be said to stand upon
> OR hang from a component contained entirely within it, and which makes no
> contact with any external system, e.g. either the ground or an overhead
> support? (clip)
> ^^^^^^^^^^^^
> Without getting involved in the "standing"/"hanging" question per se, I have
> to point out that there IS transfer of load to an external system.

I said the component in question- the spokes- make no contact with any
external system.