Oddball wheel question

Discussion in 'Cycling Equipment' started by [email protected], Oct 21, 2004.

  1. 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
     
    Tags:


  2. Tim McNamara

    Tim McNamara Guest

    [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.
     
  3. Werehatrack

    Werehatrack Guest

    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.
     
  4. Mark Hickey

    Mark Hickey Guest

    [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
     
  5. 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
     
  6. Leo Lichtman

    Leo Lichtman Guest

    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.
     
  7. 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]
     
  8. 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
     
  9. 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
     
  10. PK

    PK Guest

    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
     
  11. Tim McNamara

    Tim McNamara Guest

    "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.
     
  12. 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]
     
  13. [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
     
  14. ....and one day I'll read the whole thread before replying ;-)
     
  15. PK

    PK Guest

    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
     
  16. almost fast

    almost fast Guest

    [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.
     
  17. 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?
     
  18. Leo Lichtman

    Leo Lichtman Guest

    "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.
     
  19. Tom Sherman

    Tom Sherman Guest

    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
     
  20. "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.
     
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