How much does tension rise on squeezed spokes?

[[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.

Cheers,

Carl Fogel

 

[Leo Lichtman]

<[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)?

 

[[email protected]]

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

 

[Phil Holman]

<[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

 

[Joe Riel]

"Phil Holman" <piholmanc@yourservice> 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

 

[Leo Lichtman]

"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.

 

[Phil Holman]

"Joe Riel" <[email protected]> wrote in message
news:[email protected]...
> "Phil Holman" <piholmanc@yourservice> 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

 

[Phil Holman]

"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

 

[[email protected]]

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

 

[[email protected]]

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

 

[[email protected]]

On Sat, 6 May 2006 16:35:27 -0700, "Phil Holman"
<piholmanc@yourservice> 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

 

[[email protected]]

On Sat, 6 May 2006 16:35:27 -0700, "Phil Holman"
<piholmanc@yourservice> 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

 

[Phil Holman]

<[email protected]> wrote in message
news:[email protected]...
> On Sat, 6 May 2006 16:35:27 -0700, "Phil Holman"
> <piholmanc@yourservice> 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

 

[[email protected]]

[email protected] wrote:
> "Phil Holman" <piholmanc@yourservice> 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.

 

[[email protected]]

On Sun, 7 May 2006 06:41:20 -0700, "Phil Holman"
<piholmanc@yourservice> wrote:

>
><[email protected]> wrote in message
>news:[email protected]...
>> On Sat, 6 May 2006 16:35:27 -0700, "Phil Holman"
>> <piholmanc@yourservice> 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

 

[[email protected]]

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

>[email protected] wrote:
>> "Phil Holman" <piholmanc@yourservice> 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

 

[Leo Lichtman]

<[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.)

 

[[email protected]]

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

 

[[email protected]]

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

 

[[email protected]]

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