Wheelbuilding wisdom for the novice

[Archer]

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

...

> > It wouldn't surprise me a bit if you couldn't tell the difference in tension by the sound of a
> > plucked spoke, especially in a high spoke- count wheel (because the load is distributed over so
> > many spokes), but it MUST be there, and with a sensitive enough tensionometer, you could measure
> > it. Do the calculations!!!
>
> The calculations will depend on what is assumed about the relative stiffness of the spokes vs. the
> rim. If we make the assumption that the rim is infinitely stiff and the spokes are elastic (as
> Mark pointed out this is a very poor assumption for a real wheel), then your 4-spoke wheel looks
> like a rigid hoop connected to the hub with strong 'rubber-band' spokes. The rubber bands each
> have a pre-load tension of 200 lbs-f, so the hub feels a pull of 200 lbs downward from the bottom
> rubber band, a force of 200 lbs upward from the top rubber band, and cancelling 200 lb forces
> forward and backward by the two side rubber bands. Now the hub axle is pushed down by the weight
> of rider + bike in the amount of 100 lbs-f. With a rigid hoop, the rubber band on the bottom will
> get shorter and have a reduced tension while the rubber band on the top will be stretched by an
> equal amount and have an increased tension. The two side rubber bands will only have an
> insignificant increase in their lengths, so they'll have very slight tension increases which we'll
> ignore. If the bottom and top rubber bands have the same spring constant, the reduction of tension
> from the bottom one will be equal to the increase of tension in the top and the sum of these two
> effects must balance the downward force on the hub of 100 lbs-f. So the bottom spoke sees a
> reduction of its preload from 200 lbs-f to 150 lbs-f, the top spoke sees an increase from 200
> lbs-f to 250 lbs-f and the net force on the hub is balanced as expected: 250 up - 150 down - 100
> down from rider+bike = 0 net force.

Yes. That was my conclusion as well.

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

> In the case of my actual bicycle wheels with a lightweight rim and 36 14 gauge spokes almost all
> of the radial rigidity comes from the spokes and very little from the rim (the rim alone would
> immediately collapse under my weight). Therefore it closely matches the second scenario and I'd
> expect almost no change in the tension of the top spokes when the wheel is loaded.

I would tend to disagree with your assumptions about the rigidity of even a lightweight rim (let
alone a low-spoke-count one), and would expect the results to be somewhere near the middle between
the two cases, but your analysis is good (it must be; that's exactly the way I did ti <Grin>).

Now add one more step to the analysis, and pluck the spokes in each of the analyses above, and tell
me whether or not you can hear the difference in the 4-spoke wheels' spokes. I think you will. As
for the 36-spoke wheel, because the weight is spread out among so many spokes, I'll bet you can't
hear difference in tension between them, even though it is there.

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

Remove the ns_ from the address before e-mailing.

 

[Corvus Corvax]

David Kerber <ns_dkerber@ns_ids.net> wrote
>
> Do the calculations!!!

So have you tried it on a real bike yet?

CC

 

[Archer]

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

...

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

It has the same net effect though.

...

> >>Before you get yourself further tripped up in half thought-out theory, I really suggest you try
> >>the spoke plucking experiment mentioned above. It can be very illuminating.
> >
> >
> > It wouldn't surprise me a bit if you couldn't tell the difference in tension by the sound of a
> > plucked spoke, especially in a high spoke- count wheel (because the load is distributed over so
> > many spokes), but it MUST be there, and with a sensitive enough tensionometer, you could
> > measure it.
>
> This is starting to become tiresome. Theory and calculations mean nothing if they don't jibe with
> reality. Doing the spoke plucking experiment will show just what the reality is when it comes to
> the tension changes in a wheel to support a load. You have obviously not done the experiment, or
> else you wouldn't continue on this path.

My contention is that the pluck test doesn't tell you anything in most real life cases, because the
change in tension (which you are now saying is there) is not enough to cause a large enough change
in tone for any person who does not have a very sensitive ear.

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

I understand that, but that is not the same as saying that the spokes are under their greatest
tension when the wheel is unloaded, which is what set me off on this thread to start with.

> the wheel. Here are a few analyses:

Thank you for these.

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

Remove the ns_ from the address before e-mailing.

 

[Alex Rodriguez]

In article <[email protected]>, ns_dkerber@ns_ids.net says...
>

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

Instead of coming up with hypothetical ideas on non-existant wheels, try the experiment Jobst
suggested. You don't need any special instruments or non-existant equipment. You will see that your
theory is wrong.
-----------------
Alex __O _-\<,_ (_)/ (_)

 

[S. Delaire \"Ro]

The original question, if I understand it correctly, is, why does the tension of the wheel change
and how can it be prevented. Procedures I've outlined do work well and keeps the tension consistent
even when racing. A high school shop teacher saying: there is a right way, a wrong way, and a way
that works. Always choose the way that works. Wheels we build here probably see higher loads then
those on regular style bikes. They need to be stronger. My race averages are often over 35 MPH on
bikes that are heavier. Winning % so far this year is only 62.5% down from last years 85% 98% podium
finish results since 1995 Know how to win on motorcycles too Love the speed Which is why I ride
steamlined recumbents.

Steve "Speedy" Delaire

[email protected] wrote:

> S? Delaire writes:
>
> > I haven't read the book, this might be covered there. A trick learned from a motorcycle wheel
> > builder. Spokes "settle" at the bend were the go through the hub. First build and tension wheel
> > as normal.
>
> They do that from tension all by themselves, the highest tension a spoke carries is when the wheel
> is unloaded. Therefore you needn't worry about seating, especially after stress relieving,
> probably the most important part of wheel building.
>
> > Then to encourage the correct spoke bend take an aluminum punch and hammer the spoke, force it
> > into the flange at the hub. Outside spokes only.
>
> Don't do this! It damages trueness and integrity of hub flanges.
>
> > Check tension again Most wheels take another 1/2 to 1 full turn on the threads Install the tire
> > to proper pressure.
>
> > Check tension again Most wheels take another 1/2 to 1 full turn at the threads.
>
> This may apply to your M/C but not to bicycle wheels.
>
> Jobst Brandt [email protected] Palo Alto CA

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[Alex Rodriguez]

In article <[email protected]>, ns_dkerber@ns_ids.net says...

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

The tension change is on the bottom spokes and it is very easy to hear the differnce. It is very
obvious. Why don't you do the simplt experiment and prove it to yourself?
-----------------
Alex __O _-\<,_ (_)/ (_)

 

[Peter]

archer wrote:
> In article <[email protected]>, [email protected] says...
>>>It wouldn't surprise me a bit if you couldn't tell the difference in tension by the sound of a
>>>plucked spoke, especially in a high spoke- count wheel (because the load is distributed over so
>>>many spokes), but it MUST be there, and with a sensitive enough tensionometer, you could measure
>>>it. Do the calculations!!!
>>
>>The calculations will depend on what is assumed about the relative stiffness of the spokes vs. the
>>rim. If we make the assumption that the rim is infinitely stiff and the spokes are elastic (as
>>Mark pointed out this is a very poor assumption for a real wheel), then your 4-spoke wheel looks
>>like a rigid hoop connected to the hub with strong 'rubber-band' spokes. The rubber bands each
>>have a pre-load tension of 200 lbs-f, so the hub feels a pull of 200 lbs downward from the bottom
>>rubber band, a force of 200 lbs upward from the top rubber band, and cancelling 200 lb forces
>>forward and backward by the two side rubber bands. Now the hub axle is pushed down by the weight
>>of rider + bike in the amount of 100 lbs-f. With a rigid hoop, the rubber band on the bottom will
>>get shorter and have a reduced tension while the rubber band on the top will be stretched by an
>>equal amount and have an increased tension. The two side rubber bands will only have an
>>insignificant increase in their lengths, so they'll have very slight tension increases which we'll
>>ignore. If the bottom and top rubber bands have the same spring constant, the reduction of tension
>>from the bottom one will be equal to the increase of tension in the top and the sum of these two
>>effects must balance the downward force on the hub of 100 lbs-f. So the bottom spoke sees a
>>reduction of its preload from 200 lbs-f to 150 lbs-f, the top spoke sees an increase from 200
>>lbs-f to 250 lbs-f and the net force on the hub is balanced as expected: 250 up - 150 down - 100
>>down from rider+bike = 0 net force.
>
>
> Yes. That was my conclusion as well.

Really? It wasn't what you said before: "Instead of trying this on a normal wheel with lots of
spokes, think about a 4-spoke wheel, with the wheel turned so that one of them is straignt up and
down. If they are pre-tensioned to 200lbf, and you then set 200lbs of bike and rider on them, the
tension in the top spoke MUST increase by 200lbf total (front and rear combined). It will likely be
more in the rear than the front, but it the combined increase must equal the total weight of the
load. A simple statics calculation will show you that."

There you claimed that the increase in tension of the top spoke MUST equal the full load applied.
But the analysis you just agreed with indicates that in the unrealistic extreme of a rigid rim and
stretchy spokes the increase in tension of the top spoke is *only half* of the applied load. And in
the more nearly realistic case of a flexible rim and rigid spokes there is *no* increase in tension
of the top spoke.

>>The other extreme is that the rim is very flexible and the spokes are more rigid. In this case
>>when the wheel is pushed down by the weight of bike+rider, the bottom of the rim deforms while the
>>rest of the rim maintains its shape. In this case the bottom spoke sees a decrease in tension but
>>the top and side spokes will have no change. If the force from the weight of bike+rider is 100
>>lbs, then the tension in the bottom spoke must decrease by 100 lbs-f to balance it and therefore
>>change from the initial preload value of 200 to 100 lbs-f while the tension in the top spoke
>>remains at 200 lbs-f. The net forces on the hub are still properly balanced: 200 up - 100 down -
>>100 down from bike+rider = 0 net force.
>>
>>In the case of my actual bicycle wheels with a lightweight rim and 36 14 gauge spokes almost all
>>of the radial rigidity comes from the spokes and very little from the rim (the rim alone would
>>immediately collapse under my weight). Therefore it closely matches the second scenario and I'd
>>expect almost no change in the tension of the top spokes when the wheel is loaded.
>
> I would tend to disagree with your assumptions about the rigidity of even a lightweight rim (let
> alone a low-spoke-count one), and would expect the results to be somewhere near the middle between
> the two cases, but your analysis is good (it must be; that's exactly the way I did ti <Grin>).

Then why did you state that "the combined increase must equal the total weight of the load?" If you
had a situation halfway between the two extremes the combined increase in tension of the top spokes
would only be one fourth of the weight of the load. And I see no reason to change my opinion that
the real situation with my wheels is much closer to the second scenario resulting in far less of a
tension increase. The bare rim is quite easily deformed by pushing on it but I would need very
precise measuring tools to detect the amount that I could stretch even a single one of my spokes.

 

[Archer]

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

...

> >>The calculations will depend on what is assumed about the relative stiffness of the spokes vs.
> >>the rim. If we make the assumption that the rim is infinitely stiff and the spokes are elastic
> >>(as Mark pointed out this is a very poor assumption for a real wheel), then your 4-spoke wheel
> >>looks like a rigid hoop connected to the hub with strong 'rubber-band' spokes. The rubber bands
> >>each have a pre-load tension of 200 lbs-f, so the hub feels a pull of 200 lbs downward from the
> >>bottom rubber band, a force of 200 lbs upward from the top rubber band, and cancelling 200 lb
> >>forces forward and backward by the two side rubber bands. Now the hub axle is pushed down by the
> >>weight of rider + bike in the amount of 100 lbs-f. With a rigid hoop, the rubber band on the
> >>bottom will get shorter and have a reduced tension while the rubber band on the top will be
> >>stretched by an equal amount and have an increased tension. The two side rubber bands will only
> >>have an insignificant increase in their lengths, so they'll have very slight tension increases
> >>which we'll ignore. If the bottom and top rubber bands have the same spring constant, the
> >>reduction of tension from the bottom one will be equal to the increase of tension in the top and
> >>the sum of these two effects must balance the downward force on the hub of 100 lbs-f. So the
> >>bottom spoke sees a reduction of its preload from 200 lbs-f to 150 lbs-f, the top spoke sees an
> >>increase from 200 lbs-f to 250 lbs-f and the net force on the hub is balanced as expected: 250
> >>up - 150 down - 100 down from rider+bike = 0 net force.
> >
> >
> > Yes. That was my conclusion as well.
>
> Really? It wasn't what you said before: "Instead of trying this on a normal wheel with lots of
> spokes, think about a 4-spoke wheel, with the wheel turned so that one of them is straignt up and
> down. If they are pre-tensioned to 200lbf, and you then set 200lbs of bike and rider on them, the
> tension in the top spoke MUST increase by 200lbf total (front and rear combined). It will likely
> be more in the rear than the front, but it the combined increase must equal the total weight of
> the load. A simple statics calculation will show you that."
>
> There you claimed that the increase in tension of the top spoke MUST equal the full load applied.
> But the analysis you just agreed with indicates that in the unrealistic extreme of a rigid rim and
> stretchy spokes the increase in tension of the top spoke is *only half* of the applied load. And
> in the more nearly realistic case of a flexible rim and rigid spokes there is *no* increase in
> tension of the top spoke.

I didn't make it clear in my post, but my initial statement was based on the idealized case of
completely non-flexing rim and spokes. I still stand by that idealized analysis. I do agree that
when you make your spokes and rim real-world flexible, you see the type of results which I agreed
with above. As to how MUCH the tensions change, I am much less confident, but my gut feel tells me
that most of the posters here are over-stating their case, and I believe that there is a small but
measurable increase in tension in the upper spokes. It may not be audible on a pluck test except by
a trained ear, but I believe it's there. The one reference I have had time to look at so far did not
address the strain in the upper spokes at all.

...

> > I would tend to disagree with your assumptions about the rigidity of even a lightweight rim (let
> > alone a low-spoke-count one), and would expect the results to be somewhere near the middle
> > between the two cases, but your analysis is good (it must be; that's exactly the way I did ti
> > <Grin>).
>
> Then why did you state that "the combined increase must equal the total weight of the load?"

As I said above, that statement was based on idealized wheel materials.

> If you had a situation halfway between the two extremes the combined increase in tension of the
> top spokes would only be one fourth of the weight of the load. And I see no reason to change my
> opinion that the real situation with my wheels is much closer to the second scenario resulting in
> far less of a tension increase.

You may be correct, but my opinion is different for now (though I reserve the right to change it at
any time ;-).

> The bare rim is quite easily deformed by pushing on it but I would need very precise measuring
> tools to detect the amount that I could stretch even a single one of my spokes.

But the only way you can flex a spoked rim is by flexing the spokes which hold it in its shape,
isn't it? And flexing is required for the lower spokes to relax some of their tension.

Of course, none of this is any evidence for the original statement which started me on this
discussion, which was Jobst's statement that "... the highest tension a spoke carries is when the
wheel is unloaded."

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

Remove the ns_ from the address before e-mailing.

 

[Jasper Janssen]

On Mon, 23 Jun 2003 16:35:48 GMT, Peter <[email protected]> wrote:

>There you claimed that the increase in tension of the top spoke MUST equal the full load applied.
>But the analysis you just agreed with indicates that in the unrealistic extreme of a rigid rim and
>stretchy spokes the increase in tension of the top spoke is *only half* of the applied load. And in
>the more nearly realistic case of a flexible rim and rigid spokes there is *no* increase in tension
>of the top spoke.

And in the most realistic case of rim and spokes both being flexible to the extent dictated by the
material, I rather suspect the top spokes do get an increase in tension, even if you can't 'measure'
it by pinging them. I use 'measure' in quotes here because of the rather inaccurate method.

Jasper

 

[Archer]

In article <[email protected]>, [email protected] says...
> On Mon, 23 Jun 2003 16:35:48 GMT, Peter <[email protected]> wrote:
>
> >There you claimed that the increase in tension of the top spoke MUST equal the full load applied.
> >But the analysis you just agreed with indicates that in the unrealistic extreme of a rigid rim
> >and stretchy spokes the increase in tension of the top spoke is *only half* of the applied load.
> >And in the more nearly realistic case of a flexible rim and rigid spokes there is *no* increase
> >in tension of the top spoke.
>
> And in the most realistic case of rim and spokes both being flexible to the extent dictated
> by the material, I rather suspect the top spokes do get an increase in tension, even if you
> can't 'measure' it by pinging them. I use 'measure' in quotes here because of the rather
> inaccurate method.

I finally got around to checking the other reference which someone here posted, and it said exactly
that: There is a small increase in many of the the top spoke tensions, and a large decrease in a few
of the lower spoke tensions. I was not surprised by the general results, but found the magnitudes
and distributions rather striking.

The upper spokes with the greatest change in tension only increased about 2% of the applied load,
while the bottom ones were about -35%, -25%, - 25%, -7% and -7% (all percentages of the applied
load). What I found most surprising was the relatively large increase in tension in the spokes which
were about 40° on either side of the contact patch: they ncreased around 3% to 4%. If I had thought
through more carefully the distortion of a hoop under load, it shouldn't have surprised me, but it
did. Overall, though, only 5 spokes decreased their tension. All the rest increased to a greater or
lesser extent.

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

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

Remove the ns_ from the address before e-mailing.

 

[Archer]

In article <[email protected]>, ns_archer1960@ns_hotmail.com says...

...

> The upper spokes with the greatest change in tension only increased about 2% of the applied load,
> while the bottom ones were about -35%, -25%, - 25%, -7% and -7% (all percentages of the applied
> load). What I found most surprising was the relatively large increase in tension in the spokes
> which were about 40° on either side of the contact patch: they ncreased around 3% to 4%. If I had
> thought through more carefully the distortion of a hoop under load, it shouldn't have surprised
> me, but it
> did. Overall, though, only 5 spokes decreased their tension. All the rest increased to a greater
> or lesser extent.

P.S. I doubt if any but the most sensitive ears can detect an increase in pitch from an increase in
tension of only a 2 to 4 percent without being able to switch back and forth between them
repeatedly, which is what we are seeing here.

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

Remove the ns_ from the address before e-mailing.

 

[Mark Hickey]

Alex Rodriguez <[email protected]> wrote:

>In article <[email protected]>, ns_dkerber@ns_ids.net says...

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

Or you can examine the two positions taken in this thread to see which one matched with reality.

If the tension on the top spokes increases with load, spoke tension will never get lower, and
nipples on undertensioned wheels will never loosen up.

If the tension on the lower spoke decreases with load, spoke tension will get lower, and nipples on
undertensioned wheels will loosen up.

I think we know which is the case...

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[Archer]

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

...

> Or you can examine the two positions taken in this thread to see which one matched with reality.
>
> If the tension on the top spokes increases with load, spoke tension will never get lower, and
> nipples on undertensioned wheels will never loosen up.
>
> If the tension on the lower spoke decreases with load, spoke tension will get lower, and nipples
> on undertensioned wheels will loosen up.
>
> I think we know which is the case...

Actually, according to the finite element analyses someone pointed to, they both happen, though the
lower spokes lose far more tension than the uppers gain. That result surprised me, but I accept it.

All of these analyses appear to assume a properly tensioned wheel, one in which the tension never
goes to zero or even gets very close to it.

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

Remove the ns_ from the address before e-mailing.

 

[Tom Ace]

David Kerber wrote:

> P.S. I doubt if any but the most sensitive ears can detect an increase in pitch from an increase
> in tension of only a 2 to 4 percent without being able to switch back and forth between them
> repeatedly, which is what we are seeing here.

Frequency of vibration is proportional to the square root of the tension in the spoke. Thus a 2 to 4
percent change in tension is associated with a 1 to 2 percent change in pitch. Most people can
detect a 1% change in pitch.

A wheel can be loaded/plucked/unloaded/plucked rapidly and repeatedly with the help of
another person.

Tom Ace

 

[Archer]

In article <[email protected]>, [email protected] says...
> David Kerber wrote:
>
> > P.S. I doubt if any but the most sensitive ears can detect an increase in pitch from an
> > increase in tension of only a 2 to 4 percent without being able to switch back and forth
> > between them repeatedly, which is what we are seeing here.
>
> Frequency of vibration is proportional to the square root of the tension in the spoke. Thus a 2 to
> 4 percent change in tension is associated with a 1 to 2 percent change in pitch. Most people can
> detect a 1% change in pitch.
>
> A wheel can be loaded/plucked/unloaded/plucked rapidly and repeatedly with the help of
> another person.

That would probably work; it wouldn't be easy for most people to pick up the difference, though,
unless they were doing something like that. The difference between 400 Hz and 404 Hz is not easy to
hear unless you are paying close attention.

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

Remove the ns_ from the address before e-mailing.

 

[Just Zis Guy]

On Mon, 23 Jun 2003 11:43:24 -0400, Alex Rodriguez <[email protected]> wrote:

>>The interesting part of this calculation is that if the spokes don't stretch and the wheel doesn't
>>distort, the tension in the bottom and side-facing spokes doesn't change at all.

That would be because this model is unrealistic, notably in not taking into account deflection
of the rim.

I am undoubtedly a "hanger" - I would say the wheel "hangs" from the top of the rim because the
terms "hang" and "stand" describe the same force in opposite directions, and if the tension on the
bottom spokes drops below zero the wheel fails - but there is no doubt that the majority of the
cyclical change in tension occurs in the 30 degrees or so either side of bottom dead centre, and
this appears to be primarily due to rim deflection.

Which accords with the facts as observed, as Mark says.

Guy
===
** WARNING ** This posting may contain traces of irony. http://www.chapmancentral.com Advance
notice: ADSL service in process of transfer to a new ISP. Obviously there will be a week of downtime
between the engineer removing the BT service and the same engineer connecting the same equipment on
the same line in the same exchange and billing it to the new ISP.

 

[David Kunz]

David Kerber wrote: ...
> The interesting part of this calculation is that if the spokes don't stretch and the wheel doesn't
> distort, the tension in the bottom and side-facing spokes doesn't change at all.

I'm an engineer and until this moment, this point didn't occur to me!

David

 

[Archer]

In article <[email protected]>,
[email protected] says...
> David Kerber wrote: ...
> > The interesting part of this calculation is that if the spokes don't stretch and the wheel
> > doesn't distort, the tension in the bottom and side-facing spokes doesn't change at all.
>
> I'm an engineer and until this moment, this point didn't occur to me!

I love coming up with idealized situations; it makes the calculations ever so much easier <Grin>. Of
course, real-life electricity comes a lot closer to acting "ideally" than most mechanical equipment;
that's why I like being an EE!

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

Remove the ns_ from the address before e-mailing.

 

[Philip Ganderto]

I'll risk this question: The finite element analysis referred to in this thread uses a rim that is
25mm wide and 10mm tall in cross-section. The resulting analysis identifies rim deformation at the
contact zone as the source of tension changes in the spokes. The rims on my bike have cross-section
dimensions of 17mm wide and 35mm tall. Assuming the rims are made of similar material (aluminium
alloy), and all other factors constant (tire, tire pressure, etc.) can I expect a similar analysis
to show less compression (reduction in tension) in the lower spokes on my loaded rim compared to the
one in the example analysis?

thanks,

 

[Archer]

In article <[email protected]>, [email protected] says...
> I'll risk this question: The finite element analysis referred to in this thread uses a rim that is
> 25mm wide and 10mm tall in cross-section. The resulting analysis identifies rim deformation at the
> contact zone as the source of tension changes in the spokes. The rims on my bike have
> cross-section dimensions of 17mm wide and 35mm tall. Assuming the rims are made of similar
> material (aluminium alloy), and all other factors constant (tire, tire pressure, etc.) can I
> expect a similar analysis to show less compression (reduction in tension) in the lower spokes on
> my loaded rim compared to the one in the example analysis?

This is out of my main area of expertise, but I do have a little experience and training in the
subject, and I'm never afraid of offering an opinion <Grin>, so here goes: I would expect that,
since your rim has a larger box section than the one used in the calculations, that it wouldn't flex
quite as much. If that assumption is correct, then I would expect that it wouldn't have as large of
an effect on the tension in the bottom spokes. And then you should see a somewhat larger increase in
tension in the upper spokes.

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

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