How much does tension rise on squeezed spokes?

Discussion in 'Cycling Equipment' started by [email protected], May 6, 2006.

  1. Elsewhere we've wandered off into how to calculate and test
    the rise in tension when a spoke is squeezed. That thread
    (as usual) is getting a bit large and awkward for people to
    follow, so here's a new thread.

    Joe Riel has a page with calculations indicating that rim
    stiffness plays a large role in the rise in tension when a
    tensioned spoke is displaced sideways:

    www.k-online.com/~joer/cycling/spoke-tension.pdf

    Joe recently commented:

    "I think it's pretty clear from the final graph that there
    is a large variation in the final tension, dependent upon
    the rim stiffness---that was the point of the article."

    Testing the rise in tension is a little trickier than you'd
    expect. The gauge is so large that it gets in the way, you
    could use another pair of hands, it's hard to do two spokes
    on one side with your left hand and two on the other with
    your right for balance, and everything will vary with the
    next tester--initial tension, strength of squeeze, kind of
    spoke, stiffness of rim.

    But I took a stab at it with an old 36-spoke 700c rim,
    straight 2mm spokes, and probably less initial tension than
    it ought to have.

    Unsqueezed, the spoke registered 15 on my Park gauge, which
    is probably around a pathetic 41 kgf (the Park conversion
    chart doesn't go below 17 for such spokes.)

    Squeezed as hard as I could manage with a rope, the spoke
    tension increased to 20 on the Park gauge, 68 kgf.

    (In both measurements, I squeezed and released the gauge
    three times--without that, it would have stayed on 15
    instead of rising to 20.)

    I think that this roughly 30 kgf (65-lb) tension increase is
    far less than most people expect from spoke squeezing, but I
    hasten to add that a greater increase might be obtained with
    better techniques--which is what this post is meant to
    provoke.

    A stiffer rim, hauling harder on the rope, more initial
    tension, and perhaps a more sensitive gauge might improve
    the results.

    The rim is plain and not boxed, so it may not be very stiff.

    The rope squeeze may not be as good as one hand, even though
    it looks pretty good. The rope is right in the midspan of
    the spoke, but the area squeezed is much smaller than a
    hand, which might affect leverage. (With the gauge on the
    spoke, I can't get my whole hand in to squeeze.)

    The initial tension was embarrassingly low, which could
    confuse the rim stiffness and other factors.

    The Park gauge is said to use a lot of force itself (you can
    see the bending within the gauge in the picture) and might
    confuse things).

    Here's a Park tension gauge showing 15 on the target spoke:
    http://www.filelodge.com/files/room19/497501/spoke1.jpg

    Here it shows 20 with the spoke squeezed with a rope:
    http://www.filelodge.com/files/room19/497501/spoke2.jpg

    A blurry picture of gauge and rope setup:
    http://www.filelodge.com/files/room19/497501/spoke3.jpg

    Better focus of gauge and rope setup:
    http://www.filelodge.com/files/room19/497501/spoke4.jpg

    Closer view of gauge and rope, showing bending of spoke:
    http://www.filelodge.com/files/room19/497501/spoke5.jpg

    Here's Park's 0-50 scale conversion chart for 2mm straight
    round steel spokes:

    scale_marking
    Park_kgf
    estimate_kgf
    13 --
    14 --
    15 -- (41?) <--initial tension
    16 -- (46?)
    17 51
    18 56
    19 62
    20 68 <--squeezed tension
    21 76
    22 85
    23 95 <--recommended tension for most wheels
    24 107
    25 121
    26 137
    27 156
    28 178
    29 ---
    30 ---

    I hope that this provokes pictures from people with better
    cameras, wheels, grips, and testing techniques. If nothing
    else, I learned that the rope will stay in place, unknotted,
    under heavy tension because the spokes are so thin that the
    loop jams solid.

    If anyone lacking a gauge can suggest a different way to do
    it, I'll give it a try, with the obvious warning that my
    experimental skills are already pushing their limits.

    Cheers,

    Carl Fogel
     
    Tags:


  2. Leo Lichtman

    Leo Lichtman Guest

    <[email protected]> wrote: (clip) If anyone lacking a gauge can suggest
    a different way to do it, I'll give it a try, with the obvious warning that
    my experimental skills are already pushing their limits.
    ^^^^^^^^^^^^^^^^
    An infinitely stiff rim would put a limit on the data. I suggest
    constructing such a "rim" by welding a pair of lugs on a steel plate, and
    installing a spoke between them. The finger squeeze could be simulated by a
    c-clamp pulling to a third lug, welded beside the spoke near the middle.

    I could build the testing jib, but I don't have a tensiometer. Does anyone
    have both a welder and a tensiometer (and the interest)?
     
  3. Carl Fogel writes:

    > Elsewhere we've wandered off into how to calculate and test the rise
    > in tension when a spoke is squeezed. That thread (as usual) is
    > getting a bit large and awkward for people to follow, so here's a
    > new thread.


    > Joe Riel has a page with calculations indicating that rim stiffness
    > plays a large role in the rise in tension when a tensioned spoke is
    > displaced sideways:


    www.k-online.com/~joer/cycling/spoke-tension.pdf

    > Joe recently commented:


    > "I think it's pretty clear from the final graph that there is a
    > large variation in the final tension, dependent upon the rim
    > stiffness---that was the point of the article."


    That depends on what your starting position is and that is easier to
    determine or quantify than rim stiffness. Spokes under final tension
    in a wheel are straight from hub to rim. Grasping pairs of spokes at
    midspan with a firm grip is limited to the person's strength assuming
    either calloused hands or gloves. That force is fairly constant
    regardless of the wheel and type of rim and is generally sufficiently
    high to increase spoke tension by at least a half.

    I realize that one can argue that "we're not all supermen" but for the
    riders I know this isn't a problem. Assuming only a 25% increase is
    achieved, this will definitely yield any place on the spoke that is
    already at yield, like the elbow of an outbound spoke that has been
    freshly installed. That these are at yield has been explained often.
    When you remove these spokes from a wheel they have an acute angle
    elbow, one that was obtuse. Therefore it yielded when installed and
    tensioned and nothing was there to relax that stress unless the
    builder stretched the spokes by the now commonly known method.

    > Testing the rise in tension is a little trickier than you'd
    > expect. The gauge is so large that it gets in the way, you could use
    > another pair of hands, it's hard to do two spokes on one side with
    > your left hand and two on the other with your right for balance, and
    > everything will vary with the next tester--initial tension, strength
    > of squeeze, kind of spoke, stiffness of rim.


    Why worry about it? That a significant rise can be achieved is known
    and readily calculable. The process has two effects. It yields high
    stress points on spokes and it assures that when braking the rim will
    not buckle, that being the only use that causes increased spoke
    tension and therefore increased rim compression... column buckling.

    > But I took a stab at it with an old 36-spoke 700c rim, straight 2mm
    > spokes, and probably less initial tension than it ought to have.


    > Squeezed, the spoke registered 15 on my Park gauge, which is
    > probably around a pathetic 41 kgf (the Park conversion chart doesn't
    > go below 17 for such spokes.)


    > Squeezed as hard as I could manage with a rope, the spoke tension
    > increased to 20 on the Park gauge, 68 kgf.


    > (In both measurements, I squeezed and released the gauge three
    > times--without that, it would have stayed on 15 instead of rising to
    > 20.)


    > I think that this roughly 30 kgf (65-lb) tension increase is
    > far less than most people expect from spoke squeezing, but I
    > hasten to add that a greater increase might be obtained with
    > better techniques--which is what this post is meant to
    > provoke.


    I find that amazingly small. I can apply a much force as much as that
    laterally on a 300mm long spoke with my grip that will cause a 15mm
    deflection. That {atan(15/150)=5.7deg} the force applied through a
    tangent function gives a force translation T=(F/(2tan(Th)).

    Looking at the deflection instead of the force applied may give the
    incorrect appearance that the force varies greatly with rim stregth.
    If the input force is held constant then tension increase does not
    change as rapidly because the tangent function is relatively flat at
    smaller angles (<10 deg).

    > A stiffer rim, hauling harder on the rope, more initial tension, and
    > perhaps a more sensitive gauge might improve the results.


    That is probably another serendipity of spoking wheels tightly.

    > The rim is plain and not boxed, so it may not be very stiff.


    It is the depth of the rim that defines bending stiffness, The inner
    wall roughly in the neutral axis does not add much to bending
    stiffness in the plane of the wheel.

    > The rope squeeze may not be as good as one hand, even though it
    > looks pretty good. The rope is right in the midspan of the spoke,
    > but the area squeezed is much smaller than a hand, which might
    > affect leverage. (With the gauge on the spoke, I can't get my whole
    > hand in to squeeze.)


    I don't visualize the rope trick. Xplain?

    > The initial tension was embarrassingly low, which could confuse the
    > rim stiffness and other factors.


    Jobst Brandt
     
  4. Phil Holman

    Phil Holman Guest

    <[email protected]> wrote in message
    news:[email protected]
    > Elsewhere we've wandered off into how to calculate and test
    > the rise in tension when a spoke is squeezed. That thread
    > (as usual) is getting a bit large and awkward for people to
    > follow, so here's a new thread.
    >
    > Joe Riel has a page with calculations indicating that rim
    > stiffness plays a large role in the rise in tension when a
    > tensioned spoke is displaced sideways:
    >
    > www.k-online.com/~joer/cycling/spoke-tension.pdf
    >
    > Joe recently commented:
    >
    > "I think it's pretty clear from the final graph that there
    > is a large variation in the final tension, dependent upon
    > the rim stiffness---that was the point of the article."
    >
    > Testing the rise in tension is a little trickier than you'd
    > expect. The gauge is so large that it gets in the way, you
    > could use another pair of hands, it's hard to do two spokes
    > on one side with your left hand and two on the other with
    > your right for balance, and everything will vary with the
    > next tester--initial tension, strength of squeeze, kind of
    > spoke, stiffness of rim.
    >
    > But I took a stab at it with an old 36-spoke 700c rim,
    > straight 2mm spokes, and probably less initial tension than
    > it ought to have.
    >
    > Unsqueezed, the spoke registered 15 on my Park gauge, which
    > is probably around a pathetic 41 kgf (the Park conversion
    > chart doesn't go below 17 for such spokes.)
    >
    > Squeezed as hard as I could manage with a rope, the spoke
    > tension increased to 20 on the Park gauge, 68 kgf.
    >
    > (In both measurements, I squeezed and released the gauge
    > three times--without that, it would have stayed on 15
    > instead of rising to 20.)
    >
    > I think that this roughly 30 kgf (65-lb) tension increase is
    > far less than most people expect from spoke squeezing, but I
    > hasten to add that a greater increase might be obtained with
    > better techniques--which is what this post is meant to
    > provoke.
    >
    > A stiffer rim, hauling harder on the rope, more initial
    > tension, and perhaps a more sensitive gauge might improve
    > the results.
    >
    > The rim is plain and not boxed, so it may not be very stiff.
    >
    > The rope squeeze may not be as good as one hand, even though
    > it looks pretty good. The rope is right in the midspan of
    > the spoke, but the area squeezed is much smaller than a
    > hand, which might affect leverage. (With the gauge on the
    > spoke, I can't get my whole hand in to squeeze.)
    >
    > The initial tension was embarrassingly low, which could
    > confuse the rim stiffness and other factors.
    >
    > The Park gauge is said to use a lot of force itself (you can
    > see the bending within the gauge in the picture) and might
    > confuse things).
    >
    > Here's a Park tension gauge showing 15 on the target spoke:
    > http://www.filelodge.com/files/room19/497501/spoke1.jpg
    >
    > Here it shows 20 with the spoke squeezed with a rope:
    > http://www.filelodge.com/files/room19/497501/spoke2.jpg
    >
    > A blurry picture of gauge and rope setup:
    > http://www.filelodge.com/files/room19/497501/spoke3.jpg
    >
    > Better focus of gauge and rope setup:
    > http://www.filelodge.com/files/room19/497501/spoke4.jpg
    >
    > Closer view of gauge and rope, showing bending of spoke:
    > http://www.filelodge.com/files/room19/497501/spoke5.jpg
    >
    > Here's Park's 0-50 scale conversion chart for 2mm straight
    > round steel spokes:
    >
    > scale_marking
    > Park_kgf
    > estimate_kgf
    > 13 --
    > 14 --
    > 15 -- (41?) <--initial tension
    > 16 -- (46?)
    > 17 51
    > 18 56
    > 19 62
    > 20 68 <--squeezed tension
    > 21 76
    > 22 85
    > 23 95 <--recommended tension for most wheels
    > 24 107
    > 25 121
    > 26 137
    > 27 156
    > 28 178
    > 29 ---
    > 30 ---
    >
    > I hope that this provokes pictures from people with better
    > cameras, wheels, grips, and testing techniques. If nothing
    > else, I learned that the rope will stay in place, unknotted,
    > under heavy tension because the spokes are so thin that the
    > loop jams solid.
    >
    > If anyone lacking a gauge can suggest a different way to do
    > it, I'll give it a try, with the obvious warning that my
    > experimental skills are already pushing their limits.
    >


    Carl,
    the increase in tension should be directly proportional to the
    magnitude of the squeeze load. Is there a way you can input a couple of
    known squeeze loads? Maybe by hanging known weights on the rope. You
    would then have two data points which if plotted, should go through (0,
    0) on a graph.

    Phil H
     
  5. Joe Riel

    Joe Riel Guest

    "Phil Holman" <[email protected]> writes:

    > the increase in tension should be directly proportional to the
    > magnitude of the squeeze load.


    True (to a close enough approximation). However, the constant of
    proportionality depends on the rim/wheel. As shown in the quoted pdf,
    that "constant" varies widely with the rim.

    > Is there a way you can input a couple of
    > known squeeze loads? Maybe by hanging known weights on the rope. You
    > would then have two data points which if plotted, should go through (0,
    > 0) on a graph.


    Attempting to measure it is reasonable. In the past I have done so
    using a pocket fishing scale connected between the pair
    of spokes. I was doing that in lieu of a tensiometer in a crude
    attempt to estimate the spoke tension (from the measured deflection).

    --
    Joe Riel
     
  6. Leo Lichtman

    Leo Lichtman Guest

    "Phil Holman" wrote: (clip) You would then have two data points which if
    plotted, should go through (0, 0) on a graph.
    ^^^^^^^^^^^^^^^^^
    Actually, Phil, the plot would have a Y-intercept, equal to the tensiometer
    reading with no applied side pull. In order to know whether you have
    scatter in the data, you would need at least three points.
     
  7. Phil Holman

    Phil Holman Guest

    "Joe Riel" <[email protected]> wrote in message
    news:[email protected]
    > "Phil Holman" <[email protected]> writes:
    >
    >> the increase in tension should be directly proportional to
    >> the
    >> magnitude of the squeeze load.

    >
    > True (to a close enough approximation). However, the constant of
    > proportionality depends on the rim/wheel. As shown in the quoted pdf,
    > that "constant" varies widely with the rim.


    I agree. It is mostly rim deflection we are seeing and not spoke
    stretch.

    >
    >> Is there a way you can input a couple of
    >> known squeeze loads? Maybe by hanging known weights on the rope. You
    >> would then have two data points which if plotted, should go through
    >> (0,
    >> 0) on a graph.

    >
    > Attempting to measure it is reasonable. In the past I have done so
    > using a pocket fishing scale connected between the pair
    > of spokes. I was doing that in lieu of a tensiometer in a crude
    > attempt to estimate the spoke tension (from the measured deflection).
    >

    I have a larger scale which is good up to 50 lb. I can reasonably pull
    with a 30lb force and the spoke deflects 5mm at the midpoint (270mm
    spoke length).

    Phil H
     
  8. Phil Holman

    Phil Holman Guest

    "Leo Lichtman" <[email protected]> wrote in message
    news:[email protected]
    >
    > "Phil Holman" wrote: (clip) You would then have two data points which
    > if plotted, should go through (0, 0) on a graph.
    > ^^^^^^^^^^^^^^^^^
    > Actually, Phil, the plot would have a Y-intercept, equal to the
    > tensiometer reading with no applied side pull. In order to know
    > whether you have scatter in the data, you would need at least three
    > points.

    Sorry Leo, I was suggesting a plot of spoke tension increase (not
    absolute tension) and lateral deflection which will pass through (0, 0).
    If the two data points do not line up with the origin, a best fit 2nd
    order polynomial would work quite well and take into account the
    non-linearity.

    Phil H
     
  9. On Sat, 06 May 2006 22:49:45 GMT, "Leo Lichtman"
    <[email protected]> wrote:

    >
    ><[email protected]> wrote: (clip) If anyone lacking a gauge can suggest
    >a different way to do it, I'll give it a try, with the obvious warning that
    >my experimental skills are already pushing their limits.
    >^^^^^^^^^^^^^^^^
    >An infinitely stiff rim would put a limit on the data. I suggest
    >constructing such a "rim" by welding a pair of lugs on a steel plate, and
    >installing a spoke between them. The finger squeeze could be simulated by a
    >c-clamp pulling to a third lug, welded beside the spoke near the middle.
    >
    >I could build the testing jib, but I don't have a tensiometer. Does anyone
    >have both a welder and a tensiometer (and the interest)?
    >


    Dear Leo,

    I appreciate the idea, but actually the point is finding out
    what happens to spokes squeezed on real rims, which are not
    likely to be infinitely stiff.

    That is, Joe Riel's calculations and graph suggest that the
    less stiff the rim is, the less the spoke tension will
    increase when the spoke is squeezed sideways.

    (Or so I think--blame me, not Joe, for any misunderstanding
    of his paper.)

    Here's the relevant part and the link again:

    www.k-online.com/~joer/cycling/spoke-tension.pdf

    Joe recently commented:

    "I think it's pretty clear from the final graph that there
    is a large variation in the final tension, dependent upon
    the rim stiffness---that was the point of the article."

    In any case, I'm afraid that I'm not allowed out without my
    mittens on a string, much less given access to the welding
    equipment.

    Cheers,

    Carl Fogel
     
  10. On 06 May 2006 22:58:31 GMT, [email protected]
    wrote:

    [snip]

    >> The rope squeeze may not be as good as one hand, even though it
    >> looks pretty good. The rope is right in the midspan of the spoke,
    >> but the area squeezed is much smaller than a hand, which might
    >> affect leverage. (With the gauge on the spoke, I can't get my whole
    >> hand in to squeeze.)

    >
    >I don't visualize the rope trick. Xplain?


    Dear Jobst,

    The problem is to squeeze the spokes together roughly as
    hard as one hand can squeeze, while the Park gauge is
    hanging on the spoke.

    I can't even get my whole hand to squeeze if the gauge is on
    the spoke.

    I'm sure there are better solutions, but I just ran a loop
    of rope around the two spokes at their mid-span, pulled the
    two free ends through the loop, and pulled on them:

    http://www.filelodge.com/files/room19/497501/spoke5.jpg

    In the picture, the white rope on the right is pulling two
    parallel spokes together, with the Park gauge hanging upside
    down from the upper spoke.

    The loop of the rope is facing the camera.

    Both its ends rise and go over the top spoke, come back down
    behind, and exit toward the camera through the loop, and
    hang down.

    I hauled the rope tight, squeezed with my other hand as best
    I could, hauled some more, and got a fair bend on the spoke

    Sorry, but the worst assignment in technical writing is to
    describe how to tie a knot without a diagram. If you think
    of the two parallel spokes as the upright pole, it's the cow
    hitch on the upper right here:

    http://www.realknots.com/knots/hitches.htm

    Curiously, with that much rope tension, the friction around
    the thin spoke is so great that it's still just sitting
    there--I'm not pulling on it in the pictures.

    Since the rope just sits there, pulling the spokes together,
    I belatedly realized that I could apply my calipers and
    compare things.

    The parallel spokes are now 44 mm apart on the right edge of
    the rope toward the hub of a front 700c 36-spoke, 150mm in
    from the rim on what I think is a 294mm spoke, some of which
    is lost to the nipple.

    The roughly opposite pair of parallel spokes on the same
    side are 71mm apart at the same 150mm in from the rim.

    There's a little additional bend, of course, from the Park
    gauge, which can be seen in the pictures.

    So the 71mm distance dropped to 44mm, a sideways deflection
    of about 13mm for each spoke.

    At first, the Park gauge rises to only 19, but I always
    squeeze and release it three times, which usually raises it
    a bit, in this case to 20, probably because of friction.

    Cheers,

    Carl Fogel
     
  11. On Sat, 6 May 2006 16:35:27 -0700, "Phil Holman"
    <[email protected]> wrote:

    >Carl,
    > the increase in tension should be directly proportional to the
    >magnitude of the squeeze load. Is there a way you can input a couple of
    >known squeeze loads? Maybe by hanging known weights on the rope. You
    >would then have two data points which if plotted, should go through (0,
    >0) on a graph.
    >
    >Phil H


    Dear Phil,

    I bet there is, but I couldn't figure out the details.

    If the wheel is anchored so it can't spin, then we could
    dangle a known weight from one spoke as you suggest and get
    a repeatable amount of "sideways" force.

    Unfortunately, trying to dangle a 50 to 100 pound weight off
    one side of the bike wheel proved to be beyond the skilled
    technicians at Fogel Labs, who wanted to leave for their
    daily bike ride and then take the high-security dog out to
    see a turkey and two white-tail deer west of town.

    Lighter weights occurred to some of the lighter weights at
    Fogel Labs, but this scheme was scrapped when it was pointed
    out that the Park tension gauge is good enough for quick and
    dirty measurements, but indicates about 15-45 pounds per
    mark as it reads higher up the scale.

    In a reply trying to explain the rope details to Jobst, I
    mentioned that I can get a pair of calipers on this silly
    rig--the rope happily stays taut without any knot, and the
    original distance can be compared with the squeezed-together
    distance, divided by two, and adjusted for the little bit of
    extra visible bend at the Park gauge.

    For roughly 294mm spokes on this wheel, parallel spokes are
    about 71 mm apart 150mm in from the rim at the right-hand
    edge of the rope in the pictures.

    Roped together as in the picture, the spokes are 45mm apart,
    about 13mm "sideways" movement for each spoke.

    Again, the initial trouble with a graph is that the Park
    gauge's marks represent increasingly large steps of 5 to 7
    kgf tension down around 40-70 kgf, and 13 kgf by the time
    that we reach 27-28 at the end of the known values of the
    scale.

    (The chart scale goes from 0 to 50, but only 17-28 have
    values for a 2.0mm straight round steel spoke. Much
    stretchier round aluminum 3.3mm spokes give similar kgf
    tension way up around 33-40 on the chart.)

    So I think that any graphing efforts with such a coarse
    scale would be close to wishful thinking on my part. The
    other problem is that the rim may deform more and more as
    the spokes are pulled together.

    I'll try to think of some improvements.

    Hmmm . . . what if the wheel was mounted on a really narrow
    stand and table, anchored so it couldn't spin, and not one
    but two heavy weights dangled from a single rope looped over
    one spoke?

    Or some kind of C-clamp with ends to hold two spokes, count
    the turns tightened?

    Cheers,

    Carl Fogel
     
  12. On Sat, 6 May 2006 16:35:27 -0700, "Phil Holman"
    <[email protected]> wrote:

    [snip]

    >Carl,
    > the increase in tension should be directly proportional to the
    >magnitude of the squeeze load. Is there a way you can input a couple of
    >known squeeze loads? Maybe by hanging known weights on the rope. You
    >would then have two data points which if plotted, should go through (0,
    >0) on a graph.
    >
    >Phil H


    Dear Phil,

    D'oh!

    Sling the wheel at eye level from a couple of stout ropes
    from the ceiling!

    __________ceiling
    \ /
    \ /
    \ /
    O wheel
    |
    O weight on rope hanging from spoke

    Adjust things, perhaps with a trailing stay rope, hang rope
    with known increasing known weights from middle of spoke,
    check tension changes.

    Seems extremely simple, shouldn't take more than a day or so
    with available unskilled labor.

    Of course, the wheel will hang from the upper spokes . . .

    Cheers,

    Carl Fogel
     
  13. Phil Holman

    Phil Holman Guest

    <[email protected]> wrote in message
    news:[email protected]
    > On Sat, 6 May 2006 16:35:27 -0700, "Phil Holman"
    > <[email protected]> wrote:
    >
    > [snip]
    >
    >>Carl,
    >> the increase in tension should be directly proportional to the
    >>magnitude of the squeeze load. Is there a way you can input a couple
    >>of
    >>known squeeze loads? Maybe by hanging known weights on the rope. You
    >>would then have two data points which if plotted, should go through
    >>(0,
    >>0) on a graph.
    >>
    >>Phil H

    >
    > Dear Phil,
    >
    > D'oh!
    >
    > Sling the wheel at eye level from a couple of stout ropes
    > from the ceiling!
    >
    > __________ceiling
    > \ /
    > \ /
    > \ /
    > O wheel
    > |
    > O weight on rope hanging from spoke
    >
    > Adjust things, perhaps with a trailing stay rope, hang rope
    > with known increasing known weights from middle of spoke,
    > check tension changes.
    >
    > Seems extremely simple, shouldn't take more than a day or so
    > with available unskilled labor.
    >

    <Snip inflammatory remark> :)

    Carl, my bicycle was in the work stand and I had the front brake applied
    while I pulled the spoke with my spring scale. You could wrap the brake
    lever with a bungee or somesuch. If you let me know a couple of tension
    changes per applied load, I'll plot then in excel and determine a trend
    line with an equation.
    Phil H
     
  14. [email protected] wrote:
    > "Phil Holman" <[email protected]> wrote:


    > >Carl,
    > > the increase in tension should be directly proportional to the
    > >magnitude of the squeeze load. Is there a way you can input a couple of
    > >known squeeze loads? Maybe by hanging known weights on the rope. You
    > >would then have two data points which if plotted, should go through (0,
    > >0) on a graph.


    > Sling the wheel at eye level from a couple of stout ropes
    > from the ceiling!
    >
    > __________ceiling
    > \ /
    > \ /
    > \ /
    > O wheel
    > |
    > O weight on rope hanging from spoke
    >
    > Adjust things, perhaps with a trailing stay rope, hang rope
    > with known increasing known weights from middle of spoke,
    > check tension changes.


    Too complicated. Try attaching a fish scale or other
    spring balance in the middle of the section of rope that
    you are pulling on to get a direct measurement
    of the tension in the rope.
    You need to make sure that there is not a lot of
    friction in the rope where it wraps around the spokes.

    Also, I didn't have any problem grabbing four spokes
    at the crossing (as one would do while stress relieving)
    and attaching the tensiometer further up the spoke.
    There is plenty of room.
     
  15. On Sun, 7 May 2006 06:41:20 -0700, "Phil Holman"
    <[email protected]> wrote:

    >
    ><[email protected]> wrote in message
    >news:[email protected]
    >> On Sat, 6 May 2006 16:35:27 -0700, "Phil Holman"
    >> <[email protected]> wrote:
    >>
    >> [snip]
    >>
    >>>Carl,
    >>> the increase in tension should be directly proportional to the
    >>>magnitude of the squeeze load. Is there a way you can input a couple
    >>>of
    >>>known squeeze loads? Maybe by hanging known weights on the rope. You
    >>>would then have two data points which if plotted, should go through
    >>>(0,
    >>>0) on a graph.
    >>>
    >>>Phil H

    >>
    >> Dear Phil,
    >>
    >> D'oh!
    >>
    >> Sling the wheel at eye level from a couple of stout ropes
    >> from the ceiling!
    >>
    >> __________ceiling
    >> \ /
    >> \ /
    >> \ /
    >> O wheel
    >> |
    >> O weight on rope hanging from spoke
    >>
    >> Adjust things, perhaps with a trailing stay rope, hang rope
    >> with known increasing known weights from middle of spoke,
    >> check tension changes.
    >>
    >> Seems extremely simple, shouldn't take more than a day or so
    >> with available unskilled labor.
    >>

    ><Snip inflammatory remark> :)
    >
    >Carl, my bicycle was in the work stand and I had the front brake applied
    >while I pulled the spoke with my spring scale. You could wrap the brake
    >lever with a bungee or somesuch. If you let me know a couple of tension
    >changes per applied load, I'll plot then in excel and determine a trend
    >line with an equation.
    >Phil H


    Dear Phil,

    Victory is in sight.

    I'm awake now, rather than being struck by a sudden
    insomniac inspiration.

    I have a whole bicycle upside down on my workbench, back
    wheel sticking out over the edge. A massive rotary vise will
    clamp the seat post once I get a piece of plastic pipe to
    protect the post from the pipe-jaws.

    The brake pads should clamp the wheel nicely against the
    loads.

    I plan to use a pair of non-drive-side rear spokes at 90
    degrees to the valve hole in the rim--half the spokes are
    closer to it and half are further from it, so that should be
    close to average.

    I also plan to squeeze the spokes instead of hanging the
    weight on a rope from just one. The scheme is to tie the end
    of the rope around the midspan of the lower parallel spoke,
    run it up and over the upper spoke, and let the weight pull
    the two spokes together, which should mimic hand-squeezing
    better than just pulling down on one rope.

    The impressive friction of the rope around the upper spoke
    will probably goof things up for each separate spoke, but
    checking and recording the tension changes on both should
    average things out.

    The fuss with the valve hole and doing 2 spokes at once
    seems worth while, since Joe Riel's calculations involve rim
    stiffness and in the real world we just grab the spokes and
    squeeze them together instead of pulling sideways on only
    one.

    I thought about a pulley to get rid of the friction where
    the rope goes around the upper spoke, but I doubt that I can
    come up with any pulley that will work well under a heavy
    load on a 2mm shaft. I might smear some grease on the rope
    at the spoke, just in case it helps even things up.

    Having fixed the minor difficulty of a dying hard drive that
    complicated things at 5 a.m., I'm off to find some plastic
    pipe.

    Let me know if you have any suggestions.

    Cheers,

    Carl Fogel
     
  16. On 7 May 2006 09:09:06 -0700, "[email protected]"
    <[email protected]> wrote:

    >[email protected] wrote:
    >> "Phil Holman" <[email protected]> wrote:

    >
    >> >Carl,
    >> > the increase in tension should be directly proportional to the
    >> >magnitude of the squeeze load. Is there a way you can input a couple of
    >> >known squeeze loads? Maybe by hanging known weights on the rope. You
    >> >would then have two data points which if plotted, should go through (0,
    >> >0) on a graph.

    >
    >> Sling the wheel at eye level from a couple of stout ropes
    >> from the ceiling!
    >>
    >> __________ceiling
    >> \ /
    >> \ /
    >> \ /
    >> O wheel
    >> |
    >> O weight on rope hanging from spoke
    >>
    >> Adjust things, perhaps with a trailing stay rope, hang rope
    >> with known increasing known weights from middle of spoke,
    >> check tension changes.

    >
    >Too complicated. Try attaching a fish scale or other
    >spring balance in the middle of the section of rope that
    >you are pulling on to get a direct measurement
    >of the tension in the rope.
    >You need to make sure that there is not a lot of
    >friction in the rope where it wraps around the spokes.
    >
    >Also, I didn't have any problem grabbing four spokes
    >at the crossing (as one would do while stress relieving)
    >and attaching the tensiometer further up the spoke.
    >There is plenty of room.


    Dear B,

    Our hands, gauges, wheels, or technique are different.

    On my 700c wheel, there's only about 8 usable inches of
    spoke-span, and over 4 inches are used by the gauge. I can't
    fit my fingers into the space that's left next to the gauge.

    Maybe if I tried to hook my thumb into the tight spot or
    reversed my approach or something like that, I'd see how
    you're doing things, but in any case I think that we'd end
    up squeezing a good deal higher or lower than where we'd
    normally squeeze.

    You may have misunderstood my quick, crude diagram of the
    rope-hanging scheme. The idea was to hang a wheel by its rim
    from two ropes at roughly 45 degree angles.

    Then tie a rope with a weight to one spoke.

    The real problem is supporting the stupid wheel with enough
    room to work with a rope hanging below the wheel and a bunch
    of heavy weights--the stack that I have in mind is almost
    two feet high.

    Luckily, I woke up and found that I can put a whole bike
    upside down on a workbench, with the rear wheel sticking out
    over the edge and the seat post clamped in a rotary vise, so
    I think that things will be easier than I expected when I
    was trying to sling hammocks from the ceiling.

    I do plan to change the way that the weight dangles. The
    rope will be tied to the lower parallel spoke and then
    passed up and around the top spoke, so that the rope
    squeezes them together as close as possible to what we do in
    real life. The friction of a rope making a 180-degree turn
    over a 2mm spoke is tremendous, so I plan to grease it, just
    for luck, and then record the tension changes on both
    spokes, whose average should reflect the weight and
    eliminate the friction problem.

    If I get things to work, I'll try to take a picture that
    shows the whole weird setup.

    Cheers,

    Carl Fogel
     
  17. Leo Lichtman

    Leo Lichtman Guest

    <[email protected]> wrote: (clip) The friction of a rope making a
    180-degree turn over a 2mm spoke is tremendous, so I plan to grease it, just
    for luck, (clip)
    ^^^^^^^^^^^^^^^
    I am sure you are right about the friction. and I am afraid that the pull on
    the two spokes will not be equal, nor in the proper plane. I suggest that
    the rope from the lower spoke be passed over a pulley (suspended above the
    wheel) and down to some weights. A separate rope would be attached to the
    upper spoke, and weights would and directly from it, below the wheel.

    As I visualize the setup you propose, the upper spoke serves as a surrogate
    pulley, and the lubrication you plan to use helps it approach a pulley-like
    function. If I remember my high school physics, that would tend to DOUBLE
    the force on the upper spoke.*
    _____________________
    *If this is not clear, please let me explain further in another post.
    _____________________
    I just had a /brilliant/ idea. Attach a spring scale above the wheel, and
    hook it to the lower spoke. You will rotate the wheel by hand to apply
    tension. Hang a weight from the upper spoke. You can adjust the position
    of the wheel to make the scale match the hung weight. You can use the brake
    to hold it, while you go in with both hands and use the tensiometer. (You
    will need a volunteer or a bungee cord on the brake lever.)
     
  18. On Sat, 06 May 2006 15:49:51 -0600, [email protected]
    wrote:

    I clamped a bike by its seatpost in a rotary vise on a
    workbench with its rear wheel sticking out and anchored by
    the rear brake.

    Then I tied a rope around one spoke, looped it over the
    spoke above it, and hung more and more weights on the rope
    at 5-pound increments, checking both spokes with a Park
    tension gauge.

    The lower spoke didn't change much--in fact, the stupid
    thing actually dropped.

    The upper spoke increased in tension as shown in the ancient
    lotus 123 spreadsheet (most other spreadsheets should be
    able to import it) and its text printout:

    http://home.comcast.net/~carlfogel/download/spoke_tension.wk1

    http://home.comcast.net/~carlfogel/do700cwnload/spoke_tension.txt

    Here's the text, probably readable for most fixed-spce
    browsers:

    rear wheel, test non-drive-side spokes
    2.0mm straight stainless steel
    parallel pair @ 90 degrees to valve hole
    clamp bike upside-down in rotary vise
    back of wheel sticks out over edge of workbench
    clamp rear brake lever with vise-grips
    tire inflated to 110 psi
    tie rope to midspan of lower spoke in parallel pair
    loop over upper spoke
    add 5-pound weights from 0 to 100 pounds
    rope greased over top spoke in hopes of reducing friction
    fat chance!
    main effect was probably helping ropes slide toward hub
    noticed rope sneaked off around 45 and 75 pounds
    weight added to rope, all weight lifted, then lowered gently
    to hang
    Park spoke tension gauge squeezed 3 times, left edge near
    spoke nipple
    weight of rope trivial
    at midspan, gap narrowed from ~75mm to ~31mm
    stupid lower spoke went the wrong way!
    showed little change, rope friction plus rim deformation?
    decimal points only generallly reliable
    just best estimate, obviously influenced by memory of
    previous estimate
    extrapolate Park chart to decimal values

    raw data convert park mark to spoke
    tension

    (squeeze)
    upper lower weight upper lower upper lower
    spoke spoke in spoke spoke spoke spoke
    gauge gauge pounds kgf kgf lbs lbs

    21.5 20.0 0 80.5 68.0 177 150
    21.9 20.0 5 84.1 68.0 185 150
    22.0 19.2 10 85.0 63.2 187 139
    22.0 19.1 15 85.0 62.6 187 138
    22.5 19.0 20 90.0 62.0 198 136
    22.9 18.8 25 94.0 60.8 207 134
    23.2 18.5 30 97.4 59.0 214 130
    23.6 18.2 35 102.2 57.2 225 126
    23.9 18.1 40 105.8 56.6 233 125
    24.7 18.0 45 116.8 56.0 257 123
    24.9 17.9 50 119.6 55.4 263 122
    24.9 18.1 55 119.6 56.6 263 125
    25.1 18.2 60 122.6 57.2 270 126
    25.0 18.4 65 121.0 59.0 266 130
    25.7 19.0 70 132.2 62.0 291 136
    25.9 19.1 75 135.4 62.6 298 138
    26.1 19.3 80 138.9 63.8 306 140
    26.2 19.5 85 140.8 65.0 310 143
    26.2 19.5 90 140.8 65.0 310 143
    26.8 19.5 95 152.2 65.0 335 143
    26.9 20.2 100 154.1 69.6 339 153

    gauge chart gauge chart
    mark kgf mark kgf
    estimate extrapolated
    17 51
    18 56 18.0 56 0.6
    19 62 18.1 56.6
    20 68 18.2 57.2
    21 76 18.3 57.8
    22 85 18.4 58.4
    23 95 18.5 59.0
    24 107 18.6 59.6
    25 121 18.7 60.2
    26 137 18.8 60.8
    27 156 18.9 61.4
    28 179 19.0 62 0.6
    19.1 62.6
    19.2 63.2
    19.3 63.8
    19.4 64.4
    19.5 65.0
    19.6 65.6
    19.7 66.2
    19.8 66.8
    19.9 67.4
    20.0 68 0.8
    20.1 68.8
    20.2 69.6
    20.3 70.4
    20.4 71.2
    20.5 72.0
    20.6 72.8
    20.7 73.6
    20.8 74.4
    20.9 75.2
    21.0 76 0.9
    21.1 76.9
    21.2 77.8
    21.3 78.7
    21.4 79.6
    21.5 80.5
    21.6 81.4
    21.7 82.3
    21.8 83.2
    21.9 84.1
    22.0 85 1
    22.1 86.0
    22.2 87.0
    22.3 88.0
    22.4 89.0
    22.5 90.0
    22.6 91.0
    22.7 92.0
    22.8 93.0
    22.9 94.0
    23.0 95 1.2
    23.1 96.2
    23.2 97.4
    23.3 98.6
    23.4 99.8
    23.5 101.0
    23.6 102.2
    23.7 103.4
    23.8 104.6
    23.9 105.8
    24.0 107 1.4
    24.1 108.4
    24.2 109.8
    24.3 111.2
    24.4 112.6
    24.5 114.0
    24.6 115.4
    24.7 116.8
    24.8 118.2
    24.9 119.6
    25.0 121 1.6
    25.1 122.6
    25.2 124.2
    25.3 125.8
    25.4 127.4
    25.5 129.0
    25.6 130.6
    25.7 132.2
    25.8 133.8
    25.9 135.4
    26.0 137 1.9
    26.1 138.9
    26.2 140.8
    26.3 142.7
    26.4 144.6
    26.5 146.5
    26.6 148.4
    26.7 150.3
    26.8 152.2
    26.9 154.1
    27.0 156
    end of printout
     
  19. On Sun, 07 May 2006 20:39:01 GMT, "Leo Lichtman"
    <[email protected]> wrote:

    >
    ><[email protected]> wrote: (clip) The friction of a rope making a
    >180-degree turn over a 2mm spoke is tremendous, so I plan to grease it, just
    >for luck, (clip)
    >^^^^^^^^^^^^^^^
    >I am sure you are right about the friction. and I am afraid that the pull on
    >the two spokes will not be equal, nor in the proper plane. I suggest that
    >the rope from the lower spoke be passed over a pulley (suspended above the
    >wheel) and down to some weights. A separate rope would be attached to the
    >upper spoke, and weights would and directly from it, below the wheel.
    >
    >As I visualize the setup you propose, the upper spoke serves as a surrogate
    >pulley, and the lubrication you plan to use helps it approach a pulley-like
    >function. If I remember my high school physics, that would tend to DOUBLE
    >the force on the upper spoke.*
    >_____________________
    >*If this is not clear, please let me explain further in another post.
    >_____________________
    >I just had a /brilliant/ idea. Attach a spring scale above the wheel, and
    >hook it to the lower spoke. You will rotate the wheel by hand to apply
    >tension. Hang a weight from the upper spoke. You can adjust the position
    >of the wheel to make the scale match the hung weight. You can use the brake
    >to hold it, while you go in with both hands and use the tensiometer. (You
    >will need a volunteer or a bungee cord on the brake lever.)


    Dear Leo,

    Fears about friction proved to be true--the lower spoke
    actually lost tension!

    I suspect that only a light tension on the rope from the
    lower to the upper spoke was enough to jam the rope
    solid--it makes a 180-degree turn around a 2mm spoke and
    flattening to more a strip than a tube.

    As to why the damned lower spoke lost tension, I'm baffled.

    It looked as if it was bent slightly upward, but the gauge
    kept dropping for quite a while as I added 5 pound weights.

    Maybe the heavy deformation of the rim at the heavily loaded
    upper spoke did something weird to the nearby rim section?

    Given my experimental skills and lack of anything like an
    accurate spring scale, I settled for a bike upside-down on a
    workbench, clamped by the seatpost into a heavy rotary vise,
    locked the wheel with the rear brakes, and hung more and
    more weights on the rope. A dangling pinata of four 15-lb,
    two 10-lb, and four 5-lb weights looks silly, but there's no
    question that the two spokes from which they're hanging are
    support 100 lbs--and you have all the time in the world to
    squeeze and release the Park tension gauge and wonder why
    the hell the lower spoke is losing tension.

    Cheers,

    Carl Fogel
     
  20. On Sun, 07 May 2006 17:02:58 -0600, [email protected]
    wrote:

    Oops! I don't see the hasty note that I thought I scribbled
    about the crude extrapolation of the decimal marks to kgf.

    I just told the spreadsheet to add the apparent average kgf
    between each mark in steps of 10.

    That is, if two marks are x and y 10 kgf apart, then mark
    x.1 through x.9 will step up in crude 0.1 kgf increments.

    Actually, the increase is not linear, so x.1 to x.2 should
    be less than 0.1 kgf, and x.8 to x.9 should be bigger than
    0.1 kgf.

    The result is that for a smoothly climbing set of Park
    marks, using the crudely extrapolated conversion scale will
    give a stair-step graphs values toward a.1 are larger than
    they should be, while values toward a.9 are smaller than
    they should be, and the process repeats for b.1 to b.9, c.1
    to c.9, and so on.

    (The Park-calibrated chart's range from mark 17 to mark 18
    is only 5 kgf for a 2mm straight spoke, but rises to 19 kgf
    between mark 26 and mark 27.)

    I expect that this is obvious to the sort of folks who know
    how to do a smoother, more accurate conversion.

    Cheers,

    Carl Fogel
     
Loading...
Loading...