Wheelbuilding wisdom for the novice

Discussion in 'Road Cycling' started by Mrbubl, Jun 20, 2003.

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  1. Mrbubl

    Mrbubl Guest

    My personal experience to date is a whopping 4 wheels, all road, all 3 cross, all clinchers. I have
    invested in the printed wisdom of Guru Jobst and the electronic wisdom of Gurus Art, Sheldon, Peter
    et al.......

    My query is when a wheel is round and true and without the benefit of a tensionmeter, how tight is
    TOO TIGHT on the spokes?

    I have done the requisite stress reliefs as recommended but it would appear after a hundred miles or
    so the wheel still needs (and benenfits from) a "touch up" with the spoke wrench. Is the "normal" or
    am I not doing something right?

    Is this just a right of passage of wheelbuilding and one of the skills that gets better with age
    and trial?

    michael
     
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  2. Harris

    Harris Guest

    "mrbubl" wrote:
    > My query is when a wheel is round and true and without the benefit of a tensionmeter, how tight is
    > TOO TIGHT on the spokes?

    > I have done the requisite stress reliefs as recommended but it would
    appear
    > after a hundred miles or so the wheel still needs (and benenfits from) a "touch up" with the spoke
    > wrench. Is the "normal" or am I not doing something right?

    The most common reasons for a wheel going out of true are:

    1) Spokes too loose or uneven tension
    2) Spoke windup coming unwound
    3) Damage to rim from hitting a pot hole, etc.

    As described in "The Bicycle Wheel," the test for tightness is to stress relieve and when the wheel
    deveops waves afterward, it's too tight. Back off
    4/4 to 1/2 turn all around and try again.

    Art Harris
     
  3. In article <[email protected]>, [email protected] says...

    >My personal experience to date is a whopping 4 wheels, all road, all 3 cross, all clinchers. I have
    >invested in the printed wisdom of Guru Jobst and the electronic wisdom of Gurus Art, Sheldon, Peter
    >et al....... My query is when a wheel is round and true and without the benefit of a tensionmeter,
    >how tight is TOO TIGHT on the spokes?

    This is covered in Jobst' book. Too tight is when the wheel taco's when you stress relieve it.

    >I have done the requisite stress reliefs as recommended but it would appear after a hundred miles
    >or so the wheel still needs (and benenfits from) a "touch up" with the spoke wrench. Is the
    >"normal" or am I not doing something right?

    If you are getting spoke wind up, that can cause your wheel to go untrue after riding it. Too low a
    tension will also cause the problem you are having.

    >Is this just a right of passage of wheelbuilding and one of the skills that gets better with age
    >and trial?

    With more practice, you get faster, not necessarily better.
    -----------------
    Alex __O _-\<,_ (_)/ (_)
     
  4. I haven't read the book, this might be covered there. A trick learned from a motorcycle wheel
    builder. Spokes "settle" at the bend were the go through the hub. First build and tension wheel as
    normal. Then to encourage the correct spoke bend take an aluminum punch and hammer the spoke, force
    it into the flange at the hub. Outside spokes only. Check tension again Most wheels take another 1/2
    to 1 full turn on the threads Install the tire to proper pressure. Check tension again Most wheels
    take another 1/2 to 1 full turn at the threads Speedy

    mrbubl wrote:

    > My personal experience to date is a whopping 4 wheels, all road, all 3 cross, all clinchers. I
    > have invested in the printed wisdom of Guru Jobst and the electronic wisdom of Gurus Art, Sheldon,
    > Peter et al.......
    >
    > My query is when a wheel is round and true and without the benefit of a tensionmeter, how tight is
    > TOO TIGHT on the spokes?
    >
    > I have done the requisite stress reliefs as recommended but it would appear after a hundred miles
    > or so the wheel still needs (and benenfits from) a "touch up" with the spoke wrench. Is the
    > "normal" or am I not doing something right?
    >
    > Is this just a right of passage of wheelbuilding and one of the skills that gets better with age
    > and trial?
    >
    > michael

    -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1
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  5. Amit

    Amit Guest

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

    > My personal experience to date is a whopping 4 wheels, all road, all 3 cross, all clinchers. I
    > have invested in the printed wisdom of Guru Jobst and the electronic wisdom of Gurus Art, Sheldon,
    > Peter et al.......
    >
    > My query is when a wheel is round and true and without the benefit of a tensionmeter, how tight is
    > TOO TIGHT on the spokes?
    >

    If you did read JB's book you wouldn't ask this question.

    > I have done the requisite stress reliefs as recommended but it would appear after a hundred miles
    > or so the wheel still needs (and benenfits from) a "touch up" with the spoke wrench. Is the
    > "normal" or am I not doing something right?
    >

    This seems to indicate the spokes are too loose.

    -Amit
     
  6. On Fri, 20 Jun 2003 10:52:00 +0000, mrbubl wrote:

    > My query is when a wheel is round and true and without the benefit of a tensionmeter, how tight is
    > TOO TIGHT on the spokes?

    As someone else said, it'll taco when you try to stress-relieve. Startling thing to happen, but
    salvagable.
    >
    > I have done the requisite stress reliefs as recommended but it would appear after a hundred miles
    > or so the wheel still needs (and benenfits from) a "touch up" with the spoke wrench. Is the
    > "normal" or am I not doing something right?

    Something is not right. Spend more time making sure tension is even before worrying about
    true. A wheel can look true on the stand with a sequence of spokes too loose then too tight.
    This is especially true with stronger rims that average out the unevenness. But it will go out
    of true with use.

    --

    David L. Johnson

    __o | "What am I on? I'm on my bike, six hours a day, busting my ass. _`\(,_ | What are you on?"
    --Lance Armstrong (_)/ (_) |
     
  7. "mrbubl" <[email protected]> wrote in message news:kHBIa.56202>

    > Is this just a right of passage of wheelbuilding and one of the skills that gets better with age
    > and trial?

    This is right out of the 1980's, we haven't competed on those things in decades!

    Get yourself three or four sets of something like Mavic Cosmic Carbone SSC or Spinergy Tilium
    Carbons and you are set for the whole season.
     
  8. Jobst Brandt

    Jobst Brandt Guest

    Michael Bubl? writes:

    > My personal experience to date is a whopping 4 wheels, all road, all 3 cross, all clinchers. I
    > have invested in the printed wisdom of Guru Jobst and the electronic wisdom of Gurus Art, Sheldon,
    > Peter et al.......

    > My query is when a wheel is round and true and without the benefit of a tensionmeter, how tight is
    > TOO TIGHT on the spokes?

    "tensiometer"

    I see you didn't get the book or at least read it. There are probably few technical questions you
    could devise that are not addressed there besides the explanation of what a tensiometer is and
    how it works.

    > I have done the requisite stress reliefs as recommended but it would appear after a hundred miles
    > or so the wheel still needs (and benefits from) a "touch up" with the spoke wrench. Is the
    > "normal" or am I not doing something right?

    Your wheel is too loose. Read the book!

    > Is this just a right of passage of wheelbuilding and one of the skills that gets better with age
    > and trial?

    You can do it right the first time. Many people have.

    Jobst Brandt [email protected] Palo Alto CA
     
  9. Jobst Brandt

    Jobst Brandt Guest

    S? Delaire writes:

    > I haven't read the book, this might be covered there. A trick learned from a motorcycle wheel
    > builder. Spokes "settle" at the bend were the go through the hub. First build and tension wheel
    > as normal.

    They do that from tension all by themselves, the highest tension a spoke carries is when the wheel
    is unloaded. Therefore you needn't worry about seating, especially after stress relieving, probably
    the most important part of wheel building.

    > Then to encourage the correct spoke bend take an aluminum punch and hammer the spoke, force it
    > into the flange at the hub. Outside spokes only.

    Don't do this! It damages trueness and integrity of hub flanges.

    > Check tension again Most wheels take another 1/2 to 1 full turn on the threads Install the tire to
    > proper pressure.

    > Check tension again Most wheels take another 1/2 to 1 full turn at the threads.

    This may apply to your M/C but not to bicycle wheels.

    Jobst Brandt [email protected] Palo Alto CA
     
  10. David Kunz

    David Kunz Guest

    S. Delaire "Rotatorrecumbent" wrote:
    > I haven't read the book, this might be covered there. A trick learned from a motorcycle wheel
    > builder. Spokes "settle" at the bend were the go through the hub. First build and tension wheel as
    > normal. Then to encourage the correct spoke bend take an aluminum punch and hammer the spoke,
    > force it into the flange at the hub. Outside spokes only.

    I wouldn't do this. If you stress relieve using a screw driver handle or something similar, it'll
    seat the spokes. We're not talking big motorcycle spokes and rims here!

    > Check tension again Most wheels take another 1/2 to 1 full turn on the threads Install the tire
    > to proper pressure. Check tension again Most wheels take another 1/2 to 1 full turn at the
    > threads Speedy
    >
    >
    >
    >
    > mrbubl wrote:
    >
    >
    >>My personal experience to date is a whopping 4 wheels, all road, all 3 cross, all clinchers. I
    >>have invested in the printed wisdom of Guru Jobst and the electronic wisdom of Gurus Art, Sheldon,
    >>Peter et al.......
    >>
    >>My query is when a wheel is round and true and without the benefit of a tensionmeter, how tight is
    >>TOO TIGHT on the spokes?
    >>
    >>I have done the requisite stress reliefs as recommended but it would appear after a hundred miles
    >>or so the wheel still needs (and benenfits from) a "touch up" with the spoke wrench. Is the
    >>"normal" or am I not doing something right?
    >>
    >>Is this just a right of passage of wheelbuilding and one of the skills that gets better with age
    >>and trial?
    >>
    >>michael
     
  11. David Kerber

    David Kerber Guest

    In article <XNPIa.4217$%[email protected]>, [email protected] says...
    > S? Delaire writes:
    >
    > > I haven't read the book, this might be covered there. A trick learned from a motorcycle wheel
    > > builder. Spokes "settle" at the bend were the go through the hub. First build and tension wheel
    > > as normal.
    >
    > They do that from tension all by themselves, the highest tension a spoke carries is when the wheel
    > is unloaded.

    Huh? I would think the spokes at the top of the wheel rotation would have higher tension when loaded
    than they do unloaded. I can see why the bottoms might not carry any less load than their pre-load
    (assuming no elongation of the uppers), but the uppers would have to carry more. If they don't, then
    what is supporting the additional axle weight?

    --
    Dave Kerber Fight spam: remove the ns_ from the return address before replying!

    REAL programmers write self-modifying code.
     
  12. Jobst Brandt

    Jobst Brandt Guest

    David Kerber writes:

    >>> I haven't read the book, this might be covered there. A trick learned from a motorcycle wheel
    >>> builder. Spokes "settle" at the bend were the go through the hub. First build and tension wheel
    >>> as normal.

    >> They do that from tension all by themselves, the highest tension a spoke carries is when the
    >> wheel is unloaded.

    > Huh? I would think the spokes at the top of the wheel rotation would have higher tension when
    > loaded than they do unloaded. I can see why the bottoms might not carry any less load than their
    > pre-load (assuming no elongation of the uppers), but the uppers would have to carry more. If they
    > don't, then what is supporting the additional axle weight?

    Wire spoked wheels do not work the way we were led to believe for the past century although I'm sure
    someone in the 19th century analyzed it and understood it, back in the days when the bicycle was the
    state of the technical art. However, the book in question brought all that up to date for us
    come-latelys and may be worth your perusal.

    You can assure yourself of the load distributions by plucking the same spoke (for accurate tone
    repetition) in the front wheel when it is at the top of the wheel and at the bottom, before and
    after you put your full weight on the handlebars. It is best to have an assistant for this. Just in
    case it isn't obvious. The higher the tone the higher the tension.

    http://www.avocet.com/wheelbook/wheelbook.html

    Jobst Brandt [email protected] Palo Alto CA
     
  13. David Kerber

    David Kerber Guest

    In article <CeaJa.4412$%[email protected]>, [email protected] says...
    > David Kerber writes:
    >
    > >>> I haven't read the book, this might be covered there. A trick learned from a motorcycle wheel
    > >>> builder. Spokes "settle" at the bend were the go through the hub. First build and tension
    > >>> wheel as normal.
    >
    > >> They do that from tension all by themselves, the highest tension a spoke carries is when the
    > >> wheel is unloaded.
    >
    > > Huh? I would think the spokes at the top of the wheel rotation would have higher tension when
    > > loaded than they do unloaded. I can see why the bottoms might not carry any less load than their
    > > pre-load (assuming no elongation of the uppers), but the uppers would have to carry more. If
    > > they don't, then what is supporting the additional axle weight?
    >
    > Wire spoked wheels do not work the way we were led to believe for the past century although I'm
    > sure someone in the 19th century analyzed it and understood it, back in the days when the bicycle
    > was the state of the technical art. However, the book in question brought all that up to date for
    > us come-latelys and may be worth your perusal.
    >
    > You can assure yourself of the load distributions by plucking the same spoke (for accurate tone
    > repetition) in the front wheel when it is at the top of the wheel and at the bottom, before and
    > after you put your full weight on the handlebars. It is best to have an assistant for this. Just
    > in case it isn't obvious. The higher the tone the higher the tension.

    Instead of trying this on a normal wheel with lots of spokes, think about a 4-spoke wheel, with the
    wheel turned so that one of them is straignt up and down. If they are pre-tensioned to 200lbf, and
    you then set 200lbs of bike and rider on them, the tension in the top spoke MUST increase by 200lbf
    total (front and rear combined). It will likely be more in the rear than the front, but it the
    combined increase must equal the total weight of the load. A simple statics calculation will show
    you that. The interesting part of this calculation is that if the spokes don't stretch and the wheel
    doesn't distort, the tension in the bottom and side-facing spokes doesn't change at all.

    --
    Dave Kerber Fight spam: remove the ns_ from the return address before replying!

    REAL programmers write self-modifying code.
     
  14. David Kerber wrote:
    > In article <CeaJa.4412$%[email protected]>, [email protected] says...
    >
    >> David Kerber writes:
    >>
    >>
    >>>>>I haven't read the book, this might be covered there. A trick learned from a motorcycle wheel
    >>>>>builder. Spokes "settle" at the bend were the go through the hub. First build and tension wheel
    >>>>>as normal.
    >>>>
    >>>>They do that from tension all by themselves, the highest tension a spoke carries is when the
    >>>>wheel is unloaded.
    >>>
    >>>Huh? I would think the spokes at the top of the wheel rotation would have higher tension when
    >>>loaded than they do unloaded. I can see why the bottoms might not carry any less load than their
    >>>pre-load (assuming no elongation of the uppers), but the uppers would have to carry more. If they
    >>>don't, then what is supporting the additional axle weight?
    >>
    >>Wire spoked wheels do not work the way we were led to believe for the past century although I'm
    >>sure someone in the 19th century analyzed it and understood it, back in the days when the bicycle
    >>was the state of the technical art. However, the book in question brought all that up to date for
    >>us come-latelys and may be worth your perusal.
    >>
    >>You can assure yourself of the load distributions by plucking the same spoke (for accurate tone
    >>repetition) in the front wheel when it is at the top of the wheel and at the bottom, before and
    >>after you put your full weight on the handlebars. It is best to have an assistant for this. Just
    >>in case it isn't obvious. The higher the tone the higher the tension.
    >
    >
    > Instead of trying this on a normal wheel with lots of spokes, think about a 4-spoke wheel, with
    > the wheel turned so that one of them is straignt up and down. If they are pre-tensioned to 200lbf,
    > and you then set 200lbs of bike and rider on them, the tension in the top spoke MUST increase by
    > 200lbf total (front and rear combined). It will likely be more in the rear than the front, but it
    > the combined increase must equal the total weight of the load. A simple statics calculation will
    > show you that. The interesting part of this calculation is that if the spokes don't stretch and
    > the wheel doesn't distort, the tension in the bottom and side-facing spokes doesn't change at all.

    Holy moly, you've invented anti-gravity!

    Firstly, you've started with an incorrect assumption, that the rim is infinitely stiff as compared
    to the spokes. In actuality, the radial stiffness of the rim is much less than the radial stiffness
    of the spokes. So when you apply a load to the wheel, the bottom of the rim will easily bend inward
    allowing the bottom spokes to absorb the load, and very little of the load will be allowed to be
    transferred to the top of the wheel.

    But even if the rim were infinitely stiff, you've still got it all wrong. I think you'll agree that
    as you tension the spokes, they will elastically stretch in proportion. According to you, the top
    spokes increase tension, but the bottom spokes don't. Therefore the top spokes will stretch but the
    bottom spokes won't. This means that when you apply a load to the hub, the top of the rim will move
    upward (as the top spokes stretch from extra tension), but the hub won't get any closer to the
    ground (because the bottom spokes don't change tension). You've just invented anti-gravity!

    Before you get yourself further tripped up in half thought-out theory, I really suggest you try the
    spoke plucking experiment mentioned above. It can be very illuminating.

    By the way here's a hint: There are two ways to counter a load applied to the wheel's hub - you can
    either increase the tension in the top spokes, or decrease the tension in the bottom spokes. After
    you do the spoke plucking experiment, you'll know which one happens in a real wheel.

    Mark McMaster [email protected]
     
  15. David Kerber

    David Kerber Guest

    In article <[email protected]>, [email protected] says...

    ...

    > > Instead of trying this on a normal wheel with lots of spokes, think about a 4-spoke wheel, with
    > > the wheel turned so that one of them is straignt up and down. If they are pre-tensioned to
    > > 200lbf, and you then set 200lbs of bike and rider on them, the tension in the top spoke MUST
    > > increase by 200lbf total (front and rear combined). It will likely be more in the rear than the
    > > front, but it the combined increase must equal the total weight of the load. A simple statics
    > > calculation will show you that. The interesting part of this calculation is that if the spokes
    > > don't stretch and the wheel doesn't distort, the tension in the bottom and side-facing spokes
    > > doesn't change at all.
    >
    > Holy moly, you've invented anti-gravity!
    >
    > Firstly, you've started with an incorrect assumption, that the rim is infinitely stiff as compared
    > to the spokes. In

    That was only a simplifying assumption for illustration purposes. I am well aware that it is not the
    case in real life.

    > actuality, the radial stiffness of the rim is much less than the radial stiffness of the spokes.
    > So when you apply a load to the wheel, the bottom of the rim will easily bend inward allowing the
    > bottom spokes to absorb the load, and very little of the load will be allowed to be transferred to
    > the top of the wheel.

    SOME of it must be transferred, because the total vertical load on the axle must increast to equal
    the total weight of the load. That difference is spread out among lots of spokes, so the change in
    tension in any one spoke is probably only a few pounds. That's why you don't hear it.

    > But even if the rim were infinitely stiff, you've still got it all wrong. I think you'll agree
    > that as you tension the spokes, they will elastically stretch in proportion. According to you, the
    > top spokes increase tension, but the bottom spokes don't. Therefore the top spokes will stretch

    I didn't say they didn't stretch; I said that *If you make the simplifying assumption that nothing
    deformed* then the tension in the bottom wouldn't change. That is obviously not a real-life
    assumption. However, I still maintain the the tension in the top spokes MUST increase to handle the
    added load. Draw a simple free body diagram with a 4-spoke wheel and work out the calculations. As
    you said below, if you take the real life case in which the spokes and wheel deform under load, then
    the increase in tension in the upper is smaller, because it is partly counter-acted by the decrease
    in the lowers, but it CANNOT fully cancel out, or there would be nothing to support the added load
    on the axle.

    > Before you get yourself further tripped up in half thought-out theory, I really suggest you try
    > the spoke plucking experiment mentioned above. It can be very illuminating.

    It wouldn't surprise me a bit if you couldn't tell the difference in tension by the sound of a
    plucked spoke, especially in a high spoke- count wheel (because the load is distributed over so many
    spokes), but it MUST be there, and with a sensitive enough tensionometer, you could measure it. Do
    the calculations!!!

    ....

    --
    Dave Kerber Fight spam: remove the ns_ from the return address before replying!

    REAL programmers write self-modifying code.
     
  16. Tom Sherman

    Tom Sherman Guest

    David Kerber wrote:
    > ... I didn't say they didn't stretch; I said that *If you make the simplifying assumption that
    > nothing deformed* then the tension in the bottom wouldn't change. That is obviously not a
    > real-life assumption....

    I was not aware that it was possible to analyze a statically indeterminate system without taking the
    stiffness of the structural members into account. Or maybe the entire applied science/engineering
    profession is wrong on a fundamental issue?

    Tom Sherman - Quad Cities USA (Illinois side)
     
  17. Tom Ace

    Tom Ace Guest

    David Kerber wrote:

    > > Before you get yourself further tripped up in half thought-out theory, I really suggest you try
    > > the spoke plucking experiment mentioned above. It can be very illuminating.
    >
    > It wouldn't surprise me a bit if you couldn't tell the difference in tension by the sound of a
    > plucked spoke, especially in a high spoke- count wheel (because the load is distributed over so
    > many spokes), but it MUST be there, and with a sensitive enough tensionometer, you could measure
    > it. Do the calculations!!!

    Isn't it wild, how someone will argue at length (and talk about how small the difference probably
    is) rather than take the 5 minutes to do the spoke-plucking test and see (hear) for themselves.

    Tom Ace
     
  18. Peter

    Peter Guest

    David Kerber wrote:
    > In article <[email protected]>, [email protected] says...
    >
    > ...
    >
    >
    >>>Instead of trying this on a normal wheel with lots of spokes, think about a 4-spoke wheel, with
    >>>the wheel turned so that one of them is straignt up and down. If they are pre-tensioned to
    >>>200lbf, and you then set 200lbs of bike and rider on them, the tension in the top spoke MUST
    >>>increase by 200lbf total (front and rear combined). It will likely be more in the rear than the
    >>>front, but it the combined increase must equal the total weight of the load. A simple statics
    >>>calculation will show you that. The interesting part of this calculation is that if the spokes
    >>>don't stretch and the wheel doesn't distort, the tension in the bottom and side-facing spokes
    >>>doesn't change at all.
    >>
    >>Holy moly, you've invented anti-gravity!
    >>
    >>Firstly, you've started with an incorrect assumption, that the rim is infinitely stiff as compared
    >>to the spokes. In
    >
    >
    > That was only a simplifying assumption for illustration purposes. I am well aware that it is not
    > the case in real life.
    >
    >
    >>actuality, the radial stiffness of the rim is much less than the radial stiffness of the spokes.
    >>So when you apply a load to the wheel, the bottom of the rim will easily bend inward allowing the
    >>bottom spokes to absorb the load, and very little of the load will be allowed to be transferred to
    >>the top of the wheel.
    >
    >
    > SOME of it must be transferred, because the total vertical load on the axle must increast to equal
    > the total weight of the load. That difference is spread out among lots of spokes, so the change in
    > tension in any one spoke is probably only a few pounds. That's why you don't hear it.
    >
    >
    >
    >>But even if the rim were infinitely stiff, you've still got it all wrong. I think you'll agree
    >>that as you tension the spokes, they will elastically stretch in proportion. According to you, the
    >>top spokes increase tension, but the bottom spokes don't. Therefore the top spokes will stretch
    >
    >
    > I didn't say they didn't stretch; I said that *If you make the simplifying assumption that nothing
    > deformed* then the tension in the bottom wouldn't change. That is obviously not a real-life
    > assumption. However, I still maintain the the tension in the top spokes MUST increase to handle
    > the added load. Draw a simple free body diagram with a 4-spoke wheel and work out the
    > calculations. As you said below, if you take the real life case in which the spokes and wheel
    > deform under load, then the increase in tension in the upper is smaller, because it is partly
    > counter-acted by the decrease in the lowers, but it CANNOT fully cancel out, or there would be
    > nothing to support the added load on the axle.
    >
    >
    >>Before you get yourself further tripped up in half thought-out theory, I really suggest you try
    >>the spoke plucking experiment mentioned above. It can be very illuminating.
    >
    >
    > It wouldn't surprise me a bit if you couldn't tell the difference in tension by the sound of a
    > plucked spoke, especially in a high spoke- count wheel (because the load is distributed over so
    > many spokes), but it MUST be there, and with a sensitive enough tensionometer, you could measure
    > it. Do the calculations!!!

    The calculations will depend on what is assumed about the relative stiffness of the spokes vs. the
    rim. If we make the assumption that the rim is infinitely stiff and the spokes are elastic (as Mark
    pointed out this is a very poor assumption for a real wheel), then your 4-spoke wheel looks like a
    rigid hoop connected to the hub with strong 'rubber-band' spokes. The rubber bands each have a
    pre-load tension of 200 lbs-f, so the hub feels a pull of 200 lbs downward from the bottom rubber
    band, a force of 200 lbs upward from the top rubber band, and cancelling 200 lb forces forward and
    backward by the two side rubber bands. Now the hub axle is pushed down by the weight of rider + bike
    in the amount of 100 lbs-f. With a rigid hoop, the rubber band on the bottom will get shorter and
    have a reduced tension while the rubber band on the top will be stretched by an equal amount and
    have an increased tension. The two side rubber bands will only have an insignificant increase in
    their lengths, so they'll have very slight tension increases which we'll ignore. If the bottom and
    top rubber bands have the same spring constant, the reduction of tension from the bottom one will be
    equal to the increase of tension in the top and the sum of these two effects must balance the
    downward force on the hub of 100 lbs-f. So the bottom spoke sees a reduction of its preload from 200
    lbs-f to 150 lbs-f, the top spoke sees an increase from 200 lbs-f to 250 lbs-f and the net force on
    the hub is balanced as expected: 250 up - 150 down - 100 down from rider+bike = 0 net force.

    The other extreme is that the rim is very flexible and the spokes are more rigid. In this case when
    the wheel is pushed down by the weight of bike+rider, the bottom of the rim deforms while the rest
    of the rim maintains its shape. In this case the bottom spoke sees a decrease in tension but the top
    and side spokes will have no change. If the force from the weight of bike+rider is 100 lbs, then the
    tension in the bottom spoke must decrease by 100 lbs-f to balance it and therefore change from the
    initial preload value of 200 to 100 lbs-f while the tension in the top spoke remains at 200 lbs-f.
    The net forces on the hub are still properly balanced: 200 up - 100 down - 100 down from bike+rider
    = 0 net force.

    In the case of my actual bicycle wheels with a lightweight rim and 36 14 gauge spokes almost all of
    the radial rigidity comes from the spokes and very little from the rim (the rim alone would
    immediately collapse under my weight). Therefore it closely matches the second scenario and I'd
    expect almost no change in the tension of the top spokes when the wheel is loaded.
     
  19. David Kerber wrote:
    > In article <[email protected]>, [email protected] says...
    >
    > ...
    >
    >
    >>>Instead of trying this on a normal wheel with lots of spokes, think about a 4-spoke wheel, with
    >>>the wheel turned so that one of them is straignt up and down. If they are pre-tensioned to
    >>>200lbf, and you then set 200lbs of bike and rider on them, the tension in the top spoke MUST
    >>>increase by 200lbf total (front and rear combined). It will likely be more in the rear than the
    >>>front, but it the combined increase must equal the total weight of the load. A simple statics
    >>>calculation will show you that. The interesting part of this calculation is that if the spokes
    >>>don't stretch and the wheel doesn't distort, the tension in the bottom and side-facing spokes
    >>>doesn't change at all.
    >>
    >>Holy moly, you've invented anti-gravity!
    >>
    >>Firstly, you've started with an incorrect assumption, that the rim is infinitely stiff as compared
    >>to the spokes. In
    >
    >
    > That was only a simplifying assumption for illustration purposes. I am well aware that it is not
    > the case in real life.
    >
    >
    >>actuality, the radial stiffness of the rim is much less than the radial stiffness of the spokes.
    >>So when you apply a load to the wheel, the bottom of the rim will easily bend inward allowing the
    >>bottom spokes to absorb the load, and very little of the load will be allowed to be transferred to
    >>the top of the wheel.
    >
    >
    > SOME of it must be transferred, because the total vertical load on the axle must increast to equal
    > the total weight of the load. That difference is spread out among lots of spokes, so the change in
    > tension in any one spoke is probably only a few pounds. That's why you don't hear it.
    >
    >
    >
    >>But even if the rim were infinitely stiff, you've still got it all wrong. I think you'll agree
    >>that as you tension the spokes, they will elastically stretch in proportion. According to you, the
    >>top spokes increase tension, but the bottom spokes don't. Therefore the top spokes will stretch
    >
    >
    > I didn't say they didn't stretch; I said that *If you make the simplifying assumption that nothing
    > deformed* then the tension in the bottom wouldn't change. That is obviously not a real-life
    > assumption. However, I still maintain the the tension in the top spokes MUST increase to handle
    > the added load. Draw a simple free body diagram with a 4-spoke wheel and work out the
    > calculations. As you said below, if you take the real life case in which the spokes and wheel
    > deform under load, then the increase in tension in the upper is smaller, because it is partly
    > counter-acted by the decrease in the lowers, but it CANNOT fully cancel out, or there would be
    > nothing to support the added load on the axle.

    The tension in the top spokes does increase slightly - but not for the reasons you think. If you
    look closely, you'll see that as the rim flattens out at the very bottom of the wheel, the radius of
    the rim around the rest of the wheel (including the sides and top) increases slightly. It is this
    affect, and not the transfer of the external load to the top of the wheel, that accounts for the
    increase in tension in spokes on the sides and top of the wheel.

    >>Before you get yourself further tripped up in half thought-out theory, I really suggest you try
    >>the spoke plucking experiment mentioned above. It can be very illuminating.
    >
    >
    > It wouldn't surprise me a bit if you couldn't tell the difference in tension by the sound of a
    > plucked spoke, especially in a high spoke- count wheel (because the load is distributed over so
    > many spokes), but it MUST be there, and with a sensitive enough tensionometer, you could
    > measure it.

    This is starting to become tiresome. Theory and calculations mean nothing if they don't jibe with
    reality. Doing the spoke plucking experiment will show just what the reality is when it comes to the
    tension changes in a wheel to support a load. You have obviously not done the experiment, or else
    you wouldn't continue on this path.

    > Do the calculations!!!

    The calculations have been done many times. First, in "The Bicycle Wheel", by Jobst Brandt, and then
    by others. All analyses agree that there is very little change in tension in the top spokes, and
    that the total increase in tension in the top spokes don't even come close to equaling the load on
    the wheel. Here are a few analyses:

    http://www.rose-hulman.edu/~fine/FE2002/Projects/Hartz.pdf

    http://www.achrn.demon.co.uk/astounding/ian/wheel/

    Mark McMaster [email protected]
     
  20. Archer

    Archer Guest

    In article <[email protected]>, [email protected] says...
    >
    > David Kerber wrote:
    > > ... I didn't say they didn't stretch; I said that *If you make the simplifying assumption that
    > > nothing deformed* then the tension in the bottom wouldn't change. That is obviously not a
    > > real-life assumption....
    >
    > I was not aware that it was possible to analyze a statically indeterminate system without taking
    > the stiffness of the structural members into account. Or maybe the entire applied
    > science/engineering profession is wrong on a fundamental issue?

    For a detailed analysis, of course not. However, simplifying assumptions like this are valid and
    commonly used techniques to get a feel for the direction and rough magnitude of the effects
    under study.

    --
    David Kerber An optimist says "Good morning, Lord." While a pessimist says "Good Lord,
    it's morning".

    Remove the ns_ from the address before e-mailing.
     
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