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MA3 rim failure, where to now



 
 
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  #71  
Old September 21st 03, 12:53 PM
Just zis Guy, you know?
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Default MA3 rim failure, where to now

On Tue, 16 Sep 2003 18:46:54 +0000 (UTC), Ian Smith
wrote:

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.


Or, the biggest change in tension is exhibited in the lower spokes due
to rim deformation, but since the change in tension is reduced by
using a more rigid rim, the amount of hangingness / standingness
changes. In other words, it's not hanging or standing, it's supported
by the spokes in their entirety and there is a secondary effect due to
rim deformation, which is that the tension in the lower spokes changes
by much more than in any other spokes.

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.


Or rather, the change in tension resultant from rim deformation
remains concentrated in the lower spokes.

You haven't addressed this point, Ian. I am suggesting that the large
change in tension in the lower spokes is resultant from rim
deformation. To say that the hub "stands" is to imply that rim
deformation is the mechanism by which the hub is supported, rather
than being a secondary effect.

None of this disputes the FEA, or the large change in tension of the
lower spokes. The difference is and always has been semantic, to wit:
is it reasonable to say that the hub stands on spokes which cannot
carry a compressive load, and if their tension drops below zero the
wheel becomes unstable. The term "stand" isolates consideration of
the bottom spokes when it is perfectly clear that the wheel is
unstable unless it is complete, that all the spokes must be present in
order for the wheel to work.

I say the hub is held up by the spoke nipples pushing on the rim.

Guy
===
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  #72  
Old September 21st 03, 12:57 PM
Just zis Guy, you know?
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Default MA3 rim failure, where to now

On Tue, 16 Sep 2003 18:44:24 +0000 (UTC), Ian Smith
wrote:

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).


45 degrees is not "near the bottom" - it's well outside the zone of
huge tensile changes.

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.


Which I have. I maintain that this is a secondary effect.

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


Pedantic, because that's what the whole stupid argument is about. Is
it reasonable to use words like "stand" when the degree of
standingness is dependent on rim deformation, not the mass applied.

Guy
===
** WARNING ** This posting may contain traces of irony.
http://chapmancentral.demon.co.uk
  #74  
Old September 21st 03, 07:48 PM
Tim McNamara
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Default MA3 rim failure, where to now

In article ,
"Just zis Guy, you know?" wrote:

On Thu, 11 Sep 2003 15:07:46 GMT,
wrote:

I saw no response to the question. I assume those who quibble
about the function of spokes did not see the following or were
unable to access the URL. Please consider the question.


I don't think there is any dispute over the changes in tension and
which spokes exhibit the greatest change. The argument - which
appears to be a perennial one - is over whether it is reasonable to
use the specific term "standing" to describe the mechanism by which
the hub is supported.


As the lightning rod who initially used the term "stands" in this
particular thread- a descriptive term, developed from FEA analysis of
the bicycle wheel, that has been used for a long time and occasionally
arouses this oddly intense semantic quibbling, invective and ad
hominem- I "stand" by my use of the term. It's a simple and clear
description intended to combat the misconception that the hub "hangs"
from the upper spokes. That latter description is far, far more
semantically and phenomenologically inaccurate.

Because the of the pretensioning resulting from building the wheel,
the hub "hangs" equally from all the spokes in all directions. The
only spokes that change tension under load are those between the hub
and the ground- ergo, the wheel is standing on those spokes. The rest
of the spokes continue to do exactly what they were doing. The spokes
carrying the load, as evidenced by the change in tension, are those
between the hub and the ground and therefore it is correct to say that
the wheel is standing on those spokes.

The word "stand" implies to me at least that the change in tension
is the primary mechanism by which the hub is supported, rather than
being what would appear to me to be a secondary effect due to
deformation of the rim at he contact point.


You're not thinking of the wheel as an integrated system, apparently.
That seems to be what "hangs" up the understanding of a number of
objectors to the terminology of the wheel standing on its lower
spokes.

I remember a previous thread where one of the dissenters vociferously
demanded that we accept that the wheel stands on the ground and
nothing else. I'm surprised that didn't come up in this thread, too.
I once argued against this idea, having "known" for years that a hub
hangs from the upper spokes. Once I understood how a wheel supports a
load, the fallacy of my prior beliefs became obvious.
  #75  
Old September 21st 03, 10:18 PM
Ian Smith
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Default MA3 rim failure, where to now

On Sun, 21 Sep, Just zis Guy, you know? wrote:

deformation. To say that the hub "stands" is to imply that rim
deformation is the mechanism by which the hub is supported, rather
than being a secondary effect.


It says no such thing. How does saying 'spoke x carries the load'
mean that rim deformation carries the load?

If anything, your argument has more imploication of teh rim carrying
the laod, since you're requiring teh rim to conduct significant
proportions of teh load all around the wheel.

Consider teh trusty compressive-spoked cartwheel. I say that the
lower spoke carries the load. Aha, you say (you do above) saying teh
lower spoke carries the load implies that rim deformation is the
mechanism by which the hub is supported. Except, in this case, teh
load remains supported if you take away all teh other spokes and teh
rim, so the logic that says "saying a wheel stands must mnean rim
deformation is teh mechanism" must be horribly horribly broken.

regards, Ian SMith
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  #76  
Old September 22nd 03, 09:17 PM
Ian Smith
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Default MA3 rim failure, where to now

On Mon, 22 Sep 2003 09:05:02 GMT, Simon Brooke wrote:

Jobst, I respect, and as far as I can see Guy respects, your technical
knowledge of what happens in spokes in a wheel. But you _cannot_ abuse
the English language in this way. You can 'hang from' a structural
element which is in tension, but you cannot - you absolutely _cannot_
'stand on' it. Nor can you 'stand on' something which has no mechanism
other than tension to keep it in column.


But it's an ever greater abuse of teh english language to say
something 'hangs from' an object below it.

Do you hanbg from a chair when you sit on it? Do you hang from teh
floor when you stand up? If so, I'd lay off whatever it is you're
smoking.

regards, Ian SMith
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  #77  
Old September 23rd 03, 12:08 AM
AndyMorris
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Default MA3 rim failure, where to now

Simon Brooke wrote:

What you are _saying_ - not what you intend to say, but what your
abuse of English conveys - is the Indian Rope Trick, and it cannot be
done.

If you want to say the hub 'hangs from' all the spokes, do so; it
does. If you want to say it hangs slightly less from the bottom
spokes, I have no argument. If you want to say that the terms 'hangs
from' and 'stands on' are just unuseful with respect to bicycle
wheels, that would seem to me very sensible. But angels do not in the
real world dance on the heads of pins, and hubs in the real world do
not stand on spokes.

Even if you still think you're right and we're wrong, you still should
not use this terminology because it obviously miscommunicates with a
substantial subset of you audience.


The whole point of language in this discussion is to describe the situation
in a way that conveys the best understanding of the situation in the
listener.

To say that a hub hangs from the top spokes suggests that the top spokes
undergo more strain than the bottom ones, this is untrue.

To say that a hub stands on the bottom spokes suggests that the bottom
spokes undergo more strain than the bottom ones, this is true.

The words 'hangs' and 'stands' are very old and originated before the
existence of prestressed structure's. Our understanding of prestressed
structure means that we have to have a more subtle definition of those
terms.

--
Andy Morris

AndyAtJinkasDotFreeserve.Co.UK


Love this:
Put an end to Outlook Express's messy quotes
http://home.in.tum.de/~jain/software/oe-quotefix/


  #78  
Old September 23rd 03, 12:08 AM
AndyMorris
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Default MA3 rim failure, where to now

Simon Brooke wrote:

What you are _saying_ - not what you intend to say, but what your
abuse of English conveys - is the Indian Rope Trick, and it cannot be
done.

If you want to say the hub 'hangs from' all the spokes, do so; it
does. If you want to say it hangs slightly less from the bottom
spokes, I have no argument. If you want to say that the terms 'hangs
from' and 'stands on' are just unuseful with respect to bicycle
wheels, that would seem to me very sensible. But angels do not in the
real world dance on the heads of pins, and hubs in the real world do
not stand on spokes.

Even if you still think you're right and we're wrong, you still should
not use this terminology because it obviously miscommunicates with a
substantial subset of you audience.


The whole point of language in this discussion is to describe the situation
in a way that conveys the best understanding of the situation in the
listener.

To say that a hub hangs from the top spokes suggests that the top spokes
undergo more strain than the bottom ones, this is untrue.

To say that a hub stands on the bottom spokes suggests that the bottom
spokes undergo more strain than the bottom ones, this is true.

The words 'hangs' and 'stands' are very old and originated before the
existence of prestressed structure's. Our understanding of prestressed
structure means that we have to have a more subtle definition of those
terms.

--
Andy Morris

AndyAtJinkasDotFreeserve.Co.UK


Love this:
Put an end to Outlook Express's messy quotes
http://home.in.tum.de/~jain/software/oe-quotefix/


  #79  
Old September 23rd 03, 04:56 AM
Tim McNamara
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Posts: n/a
Default MA3 rim failure, where to now

In article ,
"AndyMorris" wrote:

The whole point of language in this discussion is to describe the
situation in a way that conveys the best understanding of the
situation in the listener.


Excellent! Much more elegantly put than my efforts at explaining my
use of the word "stands."

To say that a hub hangs from the top spokes suggests that the top
spokes undergo more strain than the bottom ones, this is untrue.

To say that a hub stands on the bottom spokes suggests that the
bottom spokes undergo more strain than the bottom ones, this is
true.


Not quite true, as the tension on those spokes is *reduced* when
loaded the wheel is loaded. It would be more accurate to say that the
tension of the spoke sat the top is unaffected by the load, whereas
the tension of the spokes below the hub is affected.

The words 'hangs' and 'stands' are very old and originated before
the existence of prestressed structure's. Our understanding of
prestressed structure means that we have to have a more subtle
definition of those terms.


Some people cannot tolerate a language adapting to new shades of
meaning.
  #80  
Old September 23rd 03, 04:56 AM
Tim McNamara
external usenet poster
 
Posts: n/a
Default MA3 rim failure, where to now

In article ,
"AndyMorris" wrote:

The whole point of language in this discussion is to describe the
situation in a way that conveys the best understanding of the
situation in the listener.


Excellent! Much more elegantly put than my efforts at explaining my
use of the word "stands."

To say that a hub hangs from the top spokes suggests that the top
spokes undergo more strain than the bottom ones, this is untrue.

To say that a hub stands on the bottom spokes suggests that the
bottom spokes undergo more strain than the bottom ones, this is
true.


Not quite true, as the tension on those spokes is *reduced* when
loaded the wheel is loaded. It would be more accurate to say that the
tension of the spoke sat the top is unaffected by the load, whereas
the tension of the spokes below the hub is affected.

The words 'hangs' and 'stands' are very old and originated before
the existence of prestressed structure's. Our understanding of
prestressed structure means that we have to have a more subtle
definition of those terms.


Some people cannot tolerate a language adapting to new shades of
meaning.
 




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