MA3 rim failure, where to now

"Ian Smith" wrote in message
...

Actually, they elongate at teh bottom - alongside teh contact patch.
In fact, the greatest elongation is in the lower half of the wheel.
They have a negative modulus then?

No, the spoke in highest tension is near the bottom of the wheel.

Not according to the FEA. What that shows is that the spoke with the
biggest /change/ in tension is at the bottom, which is a completely
different matter.

What I said is accurate, and is discussed (with numerical values) on
my web page. I also state the value of modulus used, so you can see
what it is if you want. It now looks like you're deliberately
selectively misrepresenting what those that disagree with you said,
since I have trouble believing you seriously think I'd spontaneously
change the modulus of spokes as they move round the wheel.


Don't be absurd. I am perfectly capable of understanding the
technicalities, and the FEA shows that the spokes at the bottom undergo a
significant reduction in tension, primarily due to rim deformation.

You are now saying that the bottom spokes are under increased tension and
are elongated. That is not consistent with the page you have on your
website, or your previous comments. Ye canna' change the laws of physics!

--
Guy
===

WARNING: may contain traces of irony. Contents may settle after posting.
http://www.chapmancentral.com

"Ian Smith" wrote in message
...

It is worse than that: it is actively misleading. Consider a more
rigid
rim.
But we're discussing bicycle wheels, which have a very flexible rim.
Irrelevant.

It is not irrelevant.

It is. It is irrelevant because the amount of "hangingness" or
"standingness" varies with the ridigity of the rim. I have 20" wheels with
deep V rims on my bike, and on another bike I have relatively shallow
section 700c rims. If the former were not at least twice as rigid as the
latter I would be most surprised. The rigidity of the rim affects the
analysis in such a profound way that it becomes clear that the reduction in
tension in the lower spokes is not, after all, the primary mecahnism of
support of the hub - as would be suggested by "stand" and the baggage that
goes with it, but is a secondary effect. Place the wheel on a conformant
surface, and the hub no stands less hard on the lower spokes - while still
supporting exactly the same load. So "stand" is a classic case of post hoc
ergo propter hoc, I would say.

Still, I don't have a copy of Matlab, so why not run the FEA again using a
deep-V rim and see what happens?

--
Guy
===

WARNING: may contain traces of irony. Contents may settle after posting.
http://www.chapmancentral.com

"Ian Smith" wrote in message
...

If you remove the compressive spokes (of which tehre are several)
(which is what you proposed), the wheel is dramatically weakened.

But will it spontaneously collapse, as it will if you remove all the other
spokes?

All of which is angels dancing on the head of a pin. Nobody doubts the
numbers in the FEA, it's the terminology which is in dispute. This has
always been the case except for a few misguided souls who don't understand
the maths.

--
Guy
===

WARNING: may contain traces of irony. Contents may settle after posting.
http://www.chapmancentral.com

Just zis Guy, you know? wrote:
"Ian Smith" wrote in message
No, the spoke in highest tension is near the bottom of the wheel.
Not according to the FEA. What that shows is that the spoke with the
biggest /change/ in tension is at the bottom, which is a completely
different matter.

I think what's meant is that the spokes with the highest tension are next
to the bottom spokes, where the rim bulges outwards slightly.
--
David Damerell flcl?

On Tue, 16 Sep, Just zis Guy, you know? wrote:
"Ian Smith" wrote in message
...

Actually, they elongate at teh bottom - alongside teh contact patch.
In fact, the greatest elongation is in the lower half of the wheel.
They have a negative modulus then?

No, the spoke in highest tension is near the bottom of the wheel.

Not according to the FEA. What that shows is that the spoke with the
biggest /change/ in tension is at the bottom, which is a completely
different matter.

Yes according to the FEA. Have you really reviewed it in as much
detail as you claim? The most tensile spoke, the spoke with the
greatest value of tension, is in the bottom part of teh wheel - within
45 degrees of bottom dead centre (ie _well_ within "the lower half
of the wheel", actually within the bottom quarter of teh wheel).

What I said is accurate, and is discussed (with numerical values) on
my web page. I also state the value of modulus used, so you can see
what it is if you want. It now looks like you're deliberately
selectively misrepresenting what those that disagree with you said,
since I have trouble believing you seriously think I'd spontaneously
change the modulus of spokes as they move round the wheel.

Don't be absurd. I am perfectly capable of understanding the
technicalities, and the FEA shows that the spokes at the bottom undergo a
significant reduction in tension, primarily due to rim deformation.

The spokes in teh contact patch reduce in tension, most of the bottom
spokes (12 of the 17 or 18 in teh lower half) undergo an increase in
tension, as you'd know if you'd looked at the results.

I'm not being absurd, I'm being accurate. What are you being?

You are now saying that the bottom spokes are under increased tension and
are elongated. That is not consistent with the page you have on your
website, or your previous comments. Ye canna' change the laws of physics!

Yes it is - that is exactly what the web page shows - spoke number 33,
40 degrees round teh rim from bottom dead centre is the most tesnsile
spoke, being 40 .957 N more tensile than in the unloaded wheel. In
fact, the spoke which undergoes an increase in tension such as to have
the greatest impact on the lift force at the hub is also a bottom
spoke - spoke 5, the other spoke 40 degrees from bottom dead centre.

The lower half (in fact, lower quarter) of teh wheel contains both the
most compressive and teh most tensile spokes. It's very clear in teh
results on my web page you claim to have examined.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

On Tue, 16 Sep 2003 15:43:39 +0100, Just zis Guy, you know? wrote:
"Ian Smith" wrote in message
...

It is worse than that: it is actively misleading. Consider a more
rigid
rim.
But we're discussing bicycle wheels, which have a very flexible rim.
Irrelevant.

It is not irrelevant.

It is. It is irrelevant because the amount of "hangingness" or
"standingness" varies with the ridigity of the rim.

So what?

I have 20" wheels with
deep V rims on my bike, and on another bike I have relatively shallow
section 700c rims. If the former were not at least twice as rigid as the
latter I would be most surprised.

So what? The hub still predominantly stands on teh lower spokes. You
need to vary stiffness by 10 or 100 times to render the statement
invalid, and if you do that you don't have a bicycle wheel.

Still, I don't have a copy of Matlab, so why not run the FEA again using a
deep-V rim and see what happens?

The suport action remains concentrated in teh lower spokes.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

David Damerell writes:

Just zis Guy, you know? wrote:
"Ian Smith" wrote in message
No, the spoke in highest tension is near the bottom of the wheel.
Not according to the FEA. What that shows is that the spoke with the
biggest /change/ in tension is at the bottom, which is a completely
different matter.

I think what's meant is that the spokes with the highest tension are next
to the bottom spokes, where the rim bulges outwards slightly.

Ah! So it's not _standing_ on the bottom spokes, it's _being pulled_
_down_ by the spokes next to them?

What _were_ you guys doing at the Council of Nicaea?

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

;; no eternal reward will forgive us now for wasting the dawn.
;; Jim Morrison

In article ,
Simon Brooke wrote:

David Damerell writes:

Just zis Guy, you know? wrote:
"Ian Smith" wrote in message
No, the spoke in highest tension is near the bottom of the
wheel.
Not according to the FEA. What that shows is that the spoke
with the biggest /change/ in tension is at the bottom, which is
a completely different matter.

I think what's meant is that the spokes with the highest tension
are next to the bottom spokes, where the rim bulges outwards
slightly.

Ah! So it's not _standing_ on the bottom spokes, it's _being
pulled_ _down_ by the spokes next to them?

What _were_ you guys doing at the Council of Nicaea?

I think that the Council of Whitby in 664 would be more apropos.

Simon Brooke wrote:
David Damerell writes:
I think what's meant is that the spokes with the highest tension are next
to the bottom spokes, where the rim bulges outwards slightly.
I'm not disputing the maths, I never have disputed the maths; it's the
english I'm poking fun at.

So in fact I was perfectly correct in what I wrote. I wonder then why you
chose to respond in such a tone?
--
David Damerell Distortion Field!

On Wed, 10 Sep 2003 04:31:14 GMT,
Ted Bennett wrote:
Simon Brooke wrote:

What Simon has missed is that in a spoked wheel there is no compression
in absolute terms. Just a reduction in tension provides the upward
force on the hub.

In other words, it's hanging from the top, not standing on the
bottom. Yup, we all knew that already.

We did? If it hangs from the top, then the tension in the top spoke
would increase with load. But it doesn't; the tension in the lower
spoke decreases. A simple test, plucking a few spokes, may help
convince you.

Why would the tension in the top spoke increase?

(You can try this at home)

Take a helium balloon and a longish piece of stretchy elastic (say about
three feet). Attach a hook (paper clip) to the middle of the elastic and
then use the elastic to teather the balloon to the ground.
(do this indoors so air currents don't cause the balloon to bob around
too much). Ensure that the balloon isn't resting on the ceiling.

Carefully measure the length of the "two" pieces of elastic, one
from the ground to the hook and one from the hook to the balloon.

Now attach a small weight to the hook (something light enough that
it doesn't plummet to the ground but heavy enough that the height of
the balloon changes noticable).

Now measure the lengths of the two pieces of elastic again. You will,
by your reasoning, deduce that the weight is standing on the piece of
elastic at the bottom.

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H = J + @D/@t,"
and there was light.

http://tjw.hn.org/ http://www.locofungus.btinternet.co.uk/