spoke tension changes under load

Carl Fogel said:

What happens to spoke tension on a motionless wheel when a normal
load is placed on the axle?

Quoted message said:

This page uses FEA to calculate spoke tension changes in newtons for
a 36-spoke cross-3 symmetrical (front) wheel with a very heavy 1,000
newton (225 lb) load:

http://www.astounding.org.uk/ian/wheel/index.html

Quoted message said:

Here's an extrapolated graph of the spoke tension changes that Ian
predicts, in pounds rather than newtons and for a more reasonable 95
pound load, with the spokes re-numbered from 1 at the bottom at 6
o'clock:

http://i16.tinypic.com/47ca8fm

Quoted message said:

How well does Ian's theoretical wheel match a real wheel?

Quoted message said:

Here's a rig to load a front wheel with 95 pounds on a bathroom
scale, just an old frame with its seat post trapped in a bench vise
and a pole and board attached to the top tube to hold weights over
the axle:

http://i9.tinypic.com/4p97ur7.jpg

Quoted message said:

First, I measured the tension changes in 36-spoke cross-3 aero rim
from a bike used by visitors. The wheel came nicely trued from the
factory.

Quoted message said:

Here's the graph of how spoke tension changed from that real wheel
with a tire inflated to 110 psi, first in the air and then standing
on a scale showing 95 pounds:

http://i8.tinypic.com/52at279.gif

Quoted message said:

Oops!

Quoted message said:

Obviously, twanging spokes on that wheel would not confirm the
theory that only the lowermost spokes change tension significantly
when the axle is loaded. It doesn't match Ian's predicted graph very
well. Instead of staying at about 3 pounds of increased tension,
spokes are jumping up and down between 30 pound gains and 20 pound
losses.

Quoted message said:

What's the explanation?

Quoted message said:

A) Gross incompetence at Fogel Labs must account for some of the
wild variation--the pay is scandalously low and attracts only
workers unable to find more rewarding jobs.

Quoted message said:

But if the discrepancy was just the result of inaccurate
measurements, then the bottom spokes probably wouldn't match Ian's
FEA prediction. And a 50-pound variation where the graph is
supposed to be nearly level at a 3 pound gain would be amazingly
inaccurate.

Quoted message said:

B) Theoretical wheel models don't include inflated tires
constricting the rim and lowering the spoke tension about 10% to
15%.

Quoted message said:

But I'm damned if I can see how that would change things. I just put
tires on the wheels to make them as real as possible.

Quoted message said:

C) Theoretical wheel models do not include one effect of
cross-lacing, namely that lowering the tension in any spoke must
lower the tension in the other spoke around which the first spoke
bends at the crossing.

Quoted message said:

But this effect, however large it might be, should be fairly even
and diminishing, without one spoke gaining and the next spoke losing
lots of tension.

Quoted message said:

D) Theoretical wheel models assume absolutely uniform initial spoke
tension that real wheels never achieve.

Quoted message said:

In fact, many real wheels show very uneven tension. Significant
random variations in initial spoke tension on a true rim might lead
to significant random variations in spoke tension changes under
load.

Quoted message said:

So I tested another 36-spoke cross-3 wheel, one that had more evenly
tensioned spokes than the first wheel, though nothing to boast
about:

http://i12.tinypic.com/67n6o1c.gif

Quoted message said:

Aha! The more even the initial spoke tension, the more the spoke
tension changes resemble the idealized FEA prediction on Ian's page.
Here's a graph with all three spoke-tension changes:

http://i13.tinypic.com/4qro8qx.gif

Quoted message said:

And here are graphs showing how even the initial spoke tension was,
with a level line showing Ian's idealized wheel set to the average
for the two real wheels:

http://i11.tinypic.com/4lp55cl.gif

http://i15.tinypic.com/4zxw03t.gif

http://i6.tinypic.com/4u1lesl.gif

Quoted message said:

A few conclusions...

Quoted message said:

A) Pay cuts may not be necessary at Fogel Labs, but workers should
still strive to improve accuracy. Marginal employees may be given
more suitable tasks, such as cleaning up after the guard dog.

Quoted message said:

B) On real wheels, spokes with uneven initial spoke tension may
indeed twang in very unexpected ways, even though the wheels are
true.

Quoted message said:

Anyone sinfully proud of his evenly tensioned spokes can arrange to
have his wheel tested--you pay to ship it, I'll pay to ship it back.

Quoted message said:

C) Uneven initial tension may be a bigger problem than expected.

Quoted message said:

A real spoke that gains or loses more tension than expected as soon
as you sit on the bike may lead a very exciting secret life when the
wheel starts rolling, with more or larger tension changes per
revolution than an idealized spoke.

Quoted message said:

D) Real testing often produces curious results. I wonder what spokes
do on rear wheels, which have inherently uneven tension? Maybe
someone will email me about testing a really beautifully tensioned
rear wheel?

Nice work. May I suggest measuring the same spoke as it is moved from
one position to the next, 10° at a time, with the graph going from 12:00
to 12:00 so that the "load affected zone" lies in the center of the plot.

Using the same spoke will avoid effects of varying initial spoke
tension that may confuse the diagram. It will show the continuity of
the salient feature in the center of the plot.

Thanks for the effort.

Jobst Brandt

Quoted message said:

Carl Fogel said:

What happens to spoke tension on a motionless wheel when a normal
load is placed on the axle?

Quoted message said:

This page uses FEA to calculate spoke tension changes in newtons for
a 36-spoke cross-3 symmetrical (front) wheel with a very heavy 1,000
newton (225 lb) load:

http://www.astounding.org.uk/ian/wheel/index.html

Quoted message said:

Here's an extrapolated graph of the spoke tension changes that Ian
predicts, in pounds rather than newtons and for a more reasonable 95
pound load, with the spokes re-numbered from 1 at the bottom at 6
o'clock:

http://i16.tinypic.com/47ca8fm

Quoted message said:

How well does Ian's theoretical wheel match a real wheel?

Quoted message said:

Here's a rig to load a front wheel with 95 pounds on a bathroom
scale, just an old frame with its seat post trapped in a bench vise
and a pole and board attached to the top tube to hold weights over
the axle:

http://i9.tinypic.com/4p97ur7.jpg

Quoted message said:

First, I measured the tension changes in 36-spoke cross-3 aero rim
from a bike used by visitors. The wheel came nicely trued from the
factory.

Quoted message said:

Here's the graph of how spoke tension changed from that real wheel
with a tire inflated to 110 psi, first in the air and then standing
on a scale showing 95 pounds:

http://i8.tinypic.com/52at279.gif

Quoted message said:

Oops!

Quoted message said:

Obviously, twanging spokes on that wheel would not confirm the
theory that only the lowermost spokes change tension significantly
when the axle is loaded. It doesn't match Ian's predicted graph very
well. Instead of staying at about 3 pounds of increased tension,
spokes are jumping up and down between 30 pound gains and 20 pound
losses.

Quoted message said:

What's the explanation?

Quoted message said:

A) Gross incompetence at Fogel Labs must account for some of the
wild variation--the pay is scandalously low and attracts only
workers unable to find more rewarding jobs.

Quoted message said:

But if the discrepancy was just the result of inaccurate
measurements, then the bottom spokes probably wouldn't match Ian's
FEA prediction. And a 50-pound variation where the graph is
supposed to be nearly level at a 3 pound gain would be amazingly
inaccurate.

Quoted message said:

B) Theoretical wheel models don't include inflated tires
constricting the rim and lowering the spoke tension about 10% to
15%.

Quoted message said:

But I'm damned if I can see how that would change things. I just put
tires on the wheels to make them as real as possible.

Quoted message said:

C) Theoretical wheel models do not include one effect of
cross-lacing, namely that lowering the tension in any spoke must
lower the tension in the other spoke around which the first spoke
bends at the crossing.

Quoted message said:

But this effect, however large it might be, should be fairly even
and diminishing, without one spoke gaining and the next spoke losing
lots of tension.

Quoted message said:

D) Theoretical wheel models assume absolutely uniform initial spoke
tension that real wheels never achieve.

Quoted message said:

In fact, many real wheels show very uneven tension. Significant
random variations in initial spoke tension on a true rim might lead
to significant random variations in spoke tension changes under
load.

Quoted message said:

So I tested another 36-spoke cross-3 wheel, one that had more evenly
tensioned spokes than the first wheel, though nothing to boast
about:

http://i12.tinypic.com/67n6o1c.gif

Quoted message said:

Aha! The more even the initial spoke tension, the more the spoke
tension changes resemble the idealized FEA prediction on Ian's page.
Here's a graph with all three spoke-tension changes:

http://i13.tinypic.com/4qro8qx.gif

Quoted message said:

And here are graphs showing how even the initial spoke tension was,
with a level line showing Ian's idealized wheel set to the average
for the two real wheels:

http://i11.tinypic.com/4lp55cl.gif

http://i15.tinypic.com/4zxw03t.gif

http://i6.tinypic.com/4u1lesl.gif

Quoted message said:

A few conclusions...

Quoted message said:

A) Pay cuts may not be necessary at Fogel Labs, but workers should
still strive to improve accuracy. Marginal employees may be given
more suitable tasks, such as cleaning up after the guard dog.

Quoted message said:

B) On real wheels, spokes with uneven initial spoke tension may
indeed twang in very unexpected ways, even though the wheels are
true.

Quoted message said:

Anyone sinfully proud of his evenly tensioned spokes can arrange to
have his wheel tested--you pay to ship it, I'll pay to ship it back.

Quoted message said:

C) Uneven initial tension may be a bigger problem than expected.

Quoted message said:

A real spoke that gains or loses more tension than expected as soon
as you sit on the bike may lead a very exciting secret life when the
wheel starts rolling, with more or larger tension changes per
revolution than an idealized spoke.

Quoted message said:

D) Real testing often produces curious results. I wonder what spokes
do on rear wheels, which have inherently uneven tension? Maybe
someone will email me about testing a really beautifully tensioned
rear wheel?

Nice work. May I suggest measuring the same spoke as it is moved from
one position to the next, 10° at a time, with the graph going from 12:00
to 12:00 so that the "load affected zone" lies in the center of the plot.

Using the same spoke will avoid effects of varying initial spoke
tension that may confuse the diagram. It will show the continuity of
the salient feature in the center of the plot.

Thanks for the effort.

Jobst Brandt

Dear Jobst,

I think that might miss the point of loading and testing a motionless
wheel (the familiar plucking test fails for uneven tension) versus
what happens to any single spoke once the wheel has been loaded and
starts rolling.

Given a motionless and unloaded wheel, we can't predict what the
tension changes will be when we load the wheel _if_ the initial spoke
tension varies significantly.

The 31 spokes not under the axle, which would show only a tiny ~3-lb
rise in tension and tone on an evenly tensioned wheel, may gain or
lose 20 to 30 lbs in tension when the wheel is unevenly tensioned.

This may be why some posters are unconvinced by the motionless
plucking test--it really doesn't work if the wheel isn't tensioned
evenly, even though the wheel may be as true as anyone could wish.

But once a wheel is loaded and starts rolling, any single spoke should
start to behave as predictably as Professor Gavin's measurements
showed, whether the initial tension was even or not. Any single spoke
should lose considerable tension as it rolls under the wheel for about
50 degrees and then return to its "normal" level for the rest of the
cycle.

The evidence for this is Professor Gavin's real-world test with a
strain gauge on a bicycle ridden around a course. He didn't measure
the change in tension in many spokes as the wheel was loaded. In
figures 9 & 10, he measured what happened to a single spoke _after_
the wheel was loaded and began rolling around the course:

http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf

I think that the test that you suggest will just duplicate Gavin's
results, which are better done with a strain gauge in real time, while
the motionless wheel test for unevenly tensioned spokes is probably
easier to do at my crude level.

Cheers,

Carl Fogel

On 2007-09-13, [email hidden] <[email hidden]> wrote:
[...]

Quoted message said:

Given a motionless and unloaded wheel, we can't predict what the
tension changes will be when we load the wheel _if_ the initial spoke
tension varies significantly.

We might be able to-- you could always jumble up the spoke tensions a
bit in the FEA and see what it came up with.

Or measure the actual spoke tensions, put those in the FEA, load the
wheel, measure them again, and compare against the FEA. This would help
validate the FEA and also the theory that it's the uneven spoke tension
that's the cause of the spikiness rather than some other unknown factor
or gremlin. I think Ron Ruff might have an FEA.

Quoted message said:

Quoted message said:

Carl Fogel said:

What happens to spoke tension on a motionless wheel when a normal
load is placed on the axle?
This page uses FEA to calculate spoke tension changes in newtons for
a 36-spoke cross-3 symmetrical (front) wheel with a very heavy 1,000
newton (225 lb) load:

http://www.astounding.org.uk/ian/wheel/index.html

Quoted message said:

Here's an extrapolated graph of the spoke tension changes that Ian
predicts, in pounds rather than newtons and for a more reasonable 95
pound load, with the spokes re-numbered from 1 at the bottom at 6
o'clock:

http://i16.tinypic.com/47ca8fm

-snip-

Quoted message said:

Quoted message said:

Quoted message said:

And here are graphs showing how even the initial spoke tension was,
with a level line showing Ian's idealized wheel set to the average
for the two real wheels:

http://i11.tinypic.com/4lp55cl.gif
http://i15.tinypic.com/4zxw03t.gif
http://i6.tinypic.com/4u1lesl.gif

-snip-

Quoted message said:

Quoted message said:

Quoted message said:

D) Real testing often produces curious results. I wonder what spokes
do on rear wheels, which have inherently uneven tension? Maybe
someone will email me about testing a really beautifully tensioned
rear wheel?

Quoted message said:

Quoted message said:

Nice work. May I suggest measuring the same spoke as it is moved from
one position to the next, 10° at a time, with the graph going from 12:00
to 12:00 so that the "load affected zone" lies in the center of the plot.

Using the same spoke will avoid effects of varying initial spoke
tension that may confuse the diagram. It will show the continuity of
the salient feature in the center of the plot.

Quoted message said:

I think that might miss the point of loading and testing a motionless
wheel (the familiar plucking test fails for uneven tension) versus
what happens to any single spoke once the wheel has been loaded and
starts rolling.

Given a motionless and unloaded wheel, we can't predict what the
tension changes will be when we load the wheel _if_ the initial spoke
tension varies significantly.

-snip-

Quoted message said:

I think that the test that you suggest will just duplicate Gavin's
results, which are better done with a strain gauge in real time, while
the motionless wheel test for unevenly tensioned spokes is probably
easier to do at my crude level.

Did I misread this or did you? I thought Jobst meant to mark each spoke,
measure one and then lift the apparatus to index the wheel 1/36
revolution, repeat measure, repeat index, etc
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

On Thu, 13 Sep 2007 16:18:43 -0500, A Muzi <[email hidden]>

Quoted message said:

Quoted message said:

Quoted message said:

Carl Fogel writes:
> What happens to spoke tension on a motionless wheel when a normal
> load is placed on the axle?
> This page uses FEA to calculate spoke tension changes in newtons for
> a 36-spoke cross-3 symmetrical (front) wheel with a very heavy 1,000
> newton (225 lb) load:
http://www.astounding.org.uk/ian/wheel/index.html

> Here's an extrapolated graph of the spoke tension changes that Ian
> predicts, in pounds rather than newtons and for a more reasonable 95
> pound load, with the spokes re-numbered from 1 at the bottom at 6
> o'clock:
http://i16.tinypic.com/47ca8fm

-snip-

Quoted message said:

Quoted message said:

> And here are graphs showing how even the initial spoke tension was,
> with a level line showing Ian's idealized wheel set to the average
> for the two real wheels:
http://i11.tinypic.com/4lp55cl.gif
http://i15.tinypic.com/4zxw03t.gif
http://i6.tinypic.com/4u1lesl.gif

-snip-

Quoted message said:

Quoted message said:

> D) Real testing often produces curious results. I wonder what spokes
> do on rear wheels, which have inherently uneven tension? Maybe
> someone will email me about testing a really beautifully tensioned
> rear wheel?

Quoted message said:

Quoted message said:

Nice work. May I suggest measuring the same spoke as it is moved from
one position to the next, 10° at a time, with the graph going from 12:00
to 12:00 so that the "load affected zone" lies in the center of the plot.

Using the same spoke will avoid effects of varying initial spoke
tension that may confuse the diagram. It will show the continuity of
the salient feature in the center of the plot.

Quoted message said:

I think that might miss the point of loading and testing a motionless
wheel (the familiar plucking test fails for uneven tension) versus
what happens to any single spoke once the wheel has been loaded and
starts rolling.

Given a motionless and unloaded wheel, we can't predict what the
tension changes will be when we load the wheel _if_ the initial spoke
tension varies significantly.

-snip-

Quoted message said:

I think that the test that you suggest will just duplicate Gavin's
results, which are better done with a strain gauge in real time, while
the motionless wheel test for unevenly tensioned spokes is probably
easier to do at my crude level.

Did I misread this or did you? I thought Jobst meant to mark each spoke,
measure one and then lift the apparatus to index the wheel 1/36
revolution, repeat measure, repeat index, etc

Dear Andrew,

Let's assume that I misread it, not you.

In any case, it involves either an awful lot of heavy lifting on
someone else's part, followed by groveling on the floor to measure the
most awkward spoke a few dozen times, or else a considerably improved
test rig.

My point, again, is that plucking spokes on a motionless wheel before
and after loading will not produce the idealized results that many
posters have been told to expect _if_ the spokes are unevenly
tensioned.

That was what prompted the whole test--SSTW wrote that he didn't hear
the predicted tone change when plucking motionless spokes and that a
much earlier test that I did showed weird tension changes in a
motionless wheel.

Once the wheel has been loaded and starts rolling, any single spoke
will likely show the expected dramatic tension drop as it rolls under
the axle.

Possibly a single spoke on an unevenly tensioned wheel will also
behave weirdly after it starts rolling, but there are 36 possible
suspects, an infinite variety of uneven tension levels, and each spoke
would have to be tested for a full revolution. The weirdness might
take the form of a narrower (or wider) span where tension drops (say
only 20 or 80 degrees instead of 50), a greater (or lesser) range of
tension drop under the axle (say half or twice as much as the next
spoke), or even strange spots where a particular spoke gains (or
loses) a lot of tension in the other 310 degrees.

The test does suggest how uneven tension may cause a greater range of
tension change for an oddball spoke and cause it to fail sooner, even
though it never loses all tension, which is the usual explanation.

Back to burning slits in the plastic U-skeleton of my seat bag with a
hot ice-pick to repair the failed strap.

Cheers,

Carl Fogel

Quoted message said:

Quoted message said:

Carl Fogel writes:

Quoted message said:

Quoted message said:

What happens to spoke tension on a motionless wheel when a normal
load is placed on the axle?

Quoted message said:

Quoted message said:

This page uses FEA to calculate spoke tension changes in newtons for
a 36-spoke cross-3 symmetrical (front) wheel with a very heavy 1,000
newton (225 lb) load:

Quoted message said:

http://www.astounding.org.uk/ian/wheel/index.html

Quoted message said:

Quoted message said:

Here's an extrapolated graph of the spoke tension changes that Ian
predicts, in pounds rather than newtons and for a more reasonable 95
pound load, with the spokes re-numbered from 1 at the bottom at 6
o'clock:

Quoted message said:

http://i16.tinypic.com/47ca8fm

Quoted message said:

Quoted message said:

How well does Ian's theoretical wheel match a real wheel?

Quoted message said:

Quoted message said:

Here's a rig to load a front wheel with 95 pounds on a bathroom
scale, just an old frame with its seat post trapped in a bench vise
and a pole and board attached to the top tube to hold weights over
the axle:

Quoted message said:

http://i9.tinypic.com/4p97ur7.jpg

Quoted message said:

Quoted message said:

First, I measured the tension changes in 36-spoke cross-3 aero rim
from a bike used by visitors. The wheel came nicely trued from the
factory.

Quoted message said:

Quoted message said:

Here's the graph of how spoke tension changed from that real wheel
with a tire inflated to 110 psi, first in the air and then standing
on a scale showing 95 pounds:

Quoted message said:

http://i8.tinypic.com/52at279.gif

Quoted message said:

Quoted message said:

Oops!

Quoted message said:

Quoted message said:

Obviously, twanging spokes on that wheel would not confirm the
theory that only the lowermost spokes change tension significantly
when the axle is loaded. It doesn't match Ian's predicted graph very
well. Instead of staying at about 3 pounds of increased tension,
spokes are jumping up and down between 30 pound gains and 20 pound
losses.

Quoted message said:

Quoted message said:

What's the explanation?

Quoted message said:

Quoted message said:

A) Gross incompetence at Fogel Labs must account for some of the
wild variation--the pay is scandalously low and attracts only
workers unable to find more rewarding jobs.

Quoted message said:

Quoted message said:

But if the discrepancy was just the result of inaccurate
measurements, then the bottom spokes probably wouldn't match Ian's
FEA prediction. And a 50-pound variation where the graph is
supposed to be nearly level at a 3 pound gain would be amazingly
inaccurate.

Quoted message said:

Quoted message said:

B) Theoretical wheel models don't include inflated tires
constricting the rim and lowering the spoke tension about 10% to
15%.

Quoted message said:

Quoted message said:

But I'm damned if I can see how that would change things. I just put
tires on the wheels to make them as real as possible.

Quoted message said:

Quoted message said:

C) Theoretical wheel models do not include one effect of
cross-lacing, namely that lowering the tension in any spoke must
lower the tension in the other spoke around which the first spoke
bends at the crossing.

Quoted message said:

Quoted message said:

But this effect, however large it might be, should be fairly even
and diminishing, without one spoke gaining and the next spoke losing
lots of tension.

Quoted message said:

Quoted message said:

D) Theoretical wheel models assume absolutely uniform initial spoke
tension that real wheels never achieve.

Quoted message said:

Quoted message said:

In fact, many real wheels show very uneven tension. Significant
random variations in initial spoke tension on a true rim might lead
to significant random variations in spoke tension changes under
load.

Quoted message said:

Quoted message said:

So I tested another 36-spoke cross-3 wheel, one that had more evenly
tensioned spokes than the first wheel, though nothing to boast
about:

Quoted message said:

http://i12.tinypic.com/67n6o1c.gif

Quoted message said:

Quoted message said:

Aha! The more even the initial spoke tension, the more the spoke
tension changes resemble the idealized FEA prediction on Ian's page.
Here's a graph with all three spoke-tension changes:

Quoted message said:

http://i13.tinypic.com/4qro8qx.gif

Quoted message said:

Quoted message said:

And here are graphs showing how even the initial spoke tension was,
with a level line showing Ian's idealized wheel set to the average
for the two real wheels:

Quoted message said:

http://i11.tinypic.com/4lp55cl.gif

Quoted message said:

http://i15.tinypic.com/4zxw03t.gif

Quoted message said:

http://i6.tinypic.com/4u1lesl.gif

Quoted message said:

Quoted message said:

A few conclusions...

Quoted message said:

Quoted message said:

A) Pay cuts may not be necessary at Fogel Labs, but workers should
still strive to improve accuracy. Marginal employees may be given
more suitable tasks, such as cleaning up after the guard dog.

Quoted message said:

Quoted message said:

B) On real wheels, spokes with uneven initial spoke tension may
indeed twang in very unexpected ways, even though the wheels are
true.

Quoted message said:

Quoted message said:

Anyone sinfully proud of his evenly tensioned spokes can arrange to
have his wheel tested--you pay to ship it, I'll pay to ship it back.

Quoted message said:

Quoted message said:

C) Uneven initial tension may be a bigger problem than expected.

Quoted message said:

Quoted message said:

A real spoke that gains or loses more tension than expected as soon
as you sit on the bike may lead a very exciting secret life when the
wheel starts rolling, with more or larger tension changes per
revolution than an idealized spoke.

Quoted message said:

Quoted message said:

D) Real testing often produces curious results. I wonder what spokes
do on rear wheels, which have inherently uneven tension? Maybe
someone will email me about testing a really beautifully tensioned
rear wheel?

Quoted message said:

Nice work. May I suggest measuring the same spoke as it is moved from
one position to the next, 10° at a time, with the graph going from 12:00
to 12:00 so that the "load affected zone" lies in the center of the plot.

Quoted message said:

Using the same spoke will avoid effects of varying initial spoke
tension that may confuse the diagram. It will show the continuity of
the salient feature in the center of the plot.

Quoted message said:

Thanks for the effort.

Quoted message said:

Jobst Brandt

Dear Jobst,

I think that might miss the point of loading and testing a motionless
wheel (the familiar plucking test fails for uneven tension) versus
what happens to any single spoke once the wheel has been loaded and
starts rolling.

Given a motionless and unloaded wheel, we can't predict what the
tension changes will be when we load the wheel _if_ the initial spoke
tension varies significantly.

The 31 spokes not under the axle, which would show only a tiny ~3-lb
rise in tension and tone on an evenly tensioned wheel, may gain or
lose 20 to 30 lbs in tension when the wheel is unevenly tensioned.

This may be why some posters are unconvinced by the motionless
plucking test--it really doesn't work if the wheel isn't tensioned
evenly, even though the wheel may be as true as anyone could wish.

But once a wheel is loaded and starts rolling, any single spoke should
start to behave as predictably as Professor Gavin's measurements
showed, whether the initial tension was even or not. Any single spoke
should lose considerable tension as it rolls under the wheel for about
50 degrees and then return to its "normal" level for the rest of the
cycle.

The evidence for this is Professor Gavin's real-world test with a
strain gauge on a bicycle ridden around a course. He didn't measure
the change in tension in many spokes as the wheel was loaded. In
figures 9 & 10, he measured what happened to a single spoke _after_
the wheel was loaded and began rolling around the course:

http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf

I think that the test that you suggest will just duplicate Gavin's
results, which are better done with a strain gauge in real time, while
the motionless wheel test for unevenly tensioned spokes is probably
easier to do at my crude level.

Cheers,

Carl Fogel

For the purposes of this test, why not take the wheel(s) off and set
all spokes to the same tension. Leave the brakes unconnected, remount
the wheel, put a load on (passenger / cargo hanging from the seat, and
make your measurements. After the test retrue the wheel.

email hidden said:

For the purposes of this test, why not take the wheel(s) off and set
all spokes to the same tension. Leave the brakes unconnected, remount
the wheel, put a load on (passenger / cargo hanging from the seat, and
make your measurements. After the test retrue the wheel.

Dear Mike,

Well, it's much less fuss and trouble to undo the quick releases on
two real wheels that have been ridden and stayed true and pop them in
a modifed test rig than to adjust 36 spokes before and after testing
with a surprisingly awkward unmodified bicycle.

Plus I'm interested in real wheels.

If you have a 700c front wheel that you can spare that's true enough
to suit you, email me about shipping it without any tuning up.

Cheers,

Carl Fogel