Re: Is my tire bad? - Page 4

jim beam wrote:
> jobst.brandt@stanfordalumni.org wrote:
> > Peter Cole writes:
> >
> >
> >>>for a good quality rim in good condition, it is indeed most
> >>>unlikely that a tire can be pumped sufficiently to bend the rim
> >>>before blow-off, but that doesn't mean it can't happen - there has
> >>>to be some pressure at which it occurs. once that principle is
> >>>established, it's then a matter of quantification.
> >
> >
> >>If the 2 spots on the rim were folded down by the force of the tire
> >>bead after the bead lifted off but before the tube blew, I would
> >>think either the rim would have to be extremely fragile (and
> >>ductile) and/or the pressure very high. I wonder if the tire was
> >>being filled from a high pressure source (compressor)? It could
> >>theoretically be possible to get very high pressures (>200 psi)
> >>before liftoff.
> >
> >
> > This is not a reasonable pursuit. The rim would not bend at the
place
> > where the tire first lifted off because that is a region of reduced
> > stress, the tire bead no longer having a hold on the rim. I don't
see
> > why, in face of many years of experience by professional bicycle
> > people, this scenario is given so much consideration. This is all
> > based on a report from someone who believes this is what occurred
and
> > who asks, whether the scenario is probable.
> >
> > It isn't.
> >
> > Jobst.Brandt@stanfordalumni.org
>
> did you or peter ever bother to look at the cracks in the 3rd panel
of
> this pic?
>
> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>
> and have you two ever bothered to consider the effects of fatigue
caused
> by excess tire pressure, particularly with regard to the orientation
of
> the extrusion axis?

Yes, I did, but I was struck by the curvature of the rim edge, I
wouldn't have thought that it would bend so far in a simple crack
failure. It was also surprising to hear that there were 2 such spots on
the rim, that seems a little too coincidental for fatigue failure. I'd
also find it difficult to believe that an experienced rider would dent
a rim that badly without remembering an impact (or 2), so I'm baffled.

On 30 Mar 2005 07:30:21 -0800, "Peter Cole"
<peter_cole@comcast.net> wrote:

>
>jim beam wrote:
>> jobst.brandt@stanfordalumni.org wrote:
>> > Peter Cole writes:
>> >
>> >
>> >>>for a good quality rim in good condition, it is indeed most
>> >>>unlikely that a tire can be pumped sufficiently to bend the rim
>> >>>before blow-off, but that doesn't mean it can't happen - there has
>> >>>to be some pressure at which it occurs. once that principle is
>> >>>established, it's then a matter of quantification.
>> >
>> >
>> >>If the 2 spots on the rim were folded down by the force of the tire
>> >>bead after the bead lifted off but before the tube blew, I would
>> >>think either the rim would have to be extremely fragile (and
>> >>ductile) and/or the pressure very high. I wonder if the tire was
>> >>being filled from a high pressure source (compressor)? It could
>> >>theoretically be possible to get very high pressures (>200 psi)
>> >>before liftoff.
>> >
>> >
>> > This is not a reasonable pursuit. The rim would not bend at the
>place
>> > where the tire first lifted off because that is a region of reduced
>> > stress, the tire bead no longer having a hold on the rim. I don't
>see
>> > why, in face of many years of experience by professional bicycle
>> > people, this scenario is given so much consideration. This is all
>> > based on a report from someone who believes this is what occurred
>and
>> > who asks, whether the scenario is probable.
>> >
>> > It isn't.
>> >
>> > Jobst.Brandt@stanfordalumni.org
>>
>> did you or peter ever bother to look at the cracks in the 3rd panel
>of
>> this pic?
>>
>> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>>
>> and have you two ever bothered to consider the effects of fatigue
>caused
>> by excess tire pressure, particularly with regard to the orientation
>of
>> the extrusion axis?
>
>Yes, I did, but I was struck by the curvature of the rim edge, I
>wouldn't have thought that it would bend so far in a simple crack
>failure. It was also surprising to hear that there were 2 such spots on
>the rim, that seems a little too coincidental for fatigue failure. I'd
>also find it difficult to believe that an experienced rider would dent
>a rim that badly without remembering an impact (or 2), so I'm baffled.

Dear Peter,

I'm baffled, too--why is the damage on only one side, why
didn't the rider notice hitting anything, and why is the
damage so impressive?

A private email pointed out that rims can be bent that much
a single time without cracking. (This seems plausible, but I
hesitate to sacrifice a rim before hearing what others say.)

Could we be looking at a combination of Jim's fatigue crack
and Jobst's impact damage?

If Jim's a fatigue crack developed on one side, would the
rim then be weakened enough that the next healthy bump would
produce Jobst's impressive curled bend on only one side?

This would explain why the impressive damage is on only one
side and why the rider didn't notice the kind of impressive
impact that at first seems to be indicated.

Carl Fogel

On 30 Mar 2005 07:30:21 -0800, "Peter Cole"
<peter_cole@comcast.net> wrote:

>
>jim beam wrote:
>> jobst.brandt@stanfordalumni.org wrote:
>> > Peter Cole writes:
>> >
>> >
>> >>>for a good quality rim in good condition, it is indeed most
>> >>>unlikely that a tire can be pumped sufficiently to bend the rim
>> >>>before blow-off, but that doesn't mean it can't happen - there has
>> >>>to be some pressure at which it occurs. once that principle is
>> >>>established, it's then a matter of quantification.
>> >
>> >
>> >>If the 2 spots on the rim were folded down by the force of the tire
>> >>bead after the bead lifted off but before the tube blew, I would
>> >>think either the rim would have to be extremely fragile (and
>> >>ductile) and/or the pressure very high. I wonder if the tire was
>> >>being filled from a high pressure source (compressor)? It could
>> >>theoretically be possible to get very high pressures (>200 psi)
>> >>before liftoff.
>> >
>> >
>> > This is not a reasonable pursuit. The rim would not bend at the
>place
>> > where the tire first lifted off because that is a region of reduced
>> > stress, the tire bead no longer having a hold on the rim. I don't
>see
>> > why, in face of many years of experience by professional bicycle
>> > people, this scenario is given so much consideration. This is all
>> > based on a report from someone who believes this is what occurred
>and
>> > who asks, whether the scenario is probable.
>> >
>> > It isn't.
>> >
>> > Jobst.Brandt@stanfordalumni.org
>>
>> did you or peter ever bother to look at the cracks in the 3rd panel
>of
>> this pic?
>>
>> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>>
>> and have you two ever bothered to consider the effects of fatigue
>caused
>> by excess tire pressure, particularly with regard to the orientation
>of
>> the extrusion axis?
>
>Yes, I did, but I was struck by the curvature of the rim edge, I
>wouldn't have thought that it would bend so far in a simple crack
>failure. It was also surprising to hear that there were 2 such spots on
>the rim, that seems a little too coincidental for fatigue failure. I'd
>also find it difficult to believe that an experienced rider would dent
>a rim that badly without remembering an impact (or 2), so I'm baffled.

Dear Peter,

I'm baffled, too--why is the damage on only one side, why
didn't the rider notice hitting anything, and why is the
damage so impressive?

A private email pointed out that rims can be bent that much
a single time without cracking. (This seems plausible, but I
hesitate to sacrifice a rim before hearing what others say.)

Could we be looking at a combination of Jim's fatigue crack
and Jobst's impact damage?

If Jim's a fatigue crack developed on one side, would the
rim then be weakened enough that the next healthy bump would
produce Jobst's impressive curled bend on only one side?

This would explain why the impressive damage is on only one
side and why the rider didn't notice the kind of impressive
impact that at first seems to be indicated.

Carl Fogel

carlfogel@comcast.net wrote:

> If Jim's a fatigue crack developed on one side, would the
> rim then be weakened enough that the next healthy bump would
> produce Jobst's impressive curled bend on only one side?

No. If you look, especially at the second picture, you will notice that
the curl or bend goes all the way to the very edge, far away from the
crack site which is at the base of the sidewall. That means a severe
force was applied to that edge, i.e. by impact. The crack is far away
and has no control over the amount of force required there.

The explanation for this is rather obvious and relates to the fact that
the original poster blows at pressures as low as his tires.i

carlfogel@comcast.net wrote:

> If Jim's a fatigue crack developed on one side, would the
> rim then be weakened enough that the next healthy bump would
> produce Jobst's impressive curled bend on only one side?

No. If you look, especially at the second picture, you will notice that
the curl or bend goes all the way to the very edge, far away from the
crack site which is at the base of the sidewall. That means a severe
force was applied to that edge, i.e. by impact. The crack is far away
and has no control over the amount of force required there.

The explanation for this is rather obvious and relates to the fact that
the original poster blows at pressures as low as his tires.i

carlfogel@comcast.net wrote:

> If Jim's a fatigue crack developed on one side, would the
> rim then be weakened enough that the next healthy bump would
> produce Jobst's impressive curled bend on only one side?

No. If you look, especially at the second picture, you will notice that
the curl or bend goes all the way to the very edge, far away from the
crack site which is at the base of the sidewall. That means a severe
force was applied to that edge, i.e. by impact. The crack is far away
and has no control over the amount of force required there.

The explanation for this is rather obvious and relates to the fact that
the original poster blows at pressures as low as his tires.i

carlfogel@comcast.net wrote:

> If Jim's a fatigue crack developed on one side, would the
> rim then be weakened enough that the next healthy bump would
> produce Jobst's impressive curled bend on only one side?

No. If you look, especially at the second picture, you will notice that
the curl or bend goes all the way to the very edge, far away from the
crack site which is at the base of the sidewall. That means a severe
force was applied to that edge, i.e. by impact. The crack is far away
and has no control over the amount of force required there.

The explanation for this is rather obvious and relates to the fact that
the original poster blows at pressures as low as his tires.i

carlfogel@comcast.net writes:

> On 30 Mar 2005 07:30:21 -0800, "Peter Cole"
> <peter_cole@comcast.net> wrote:
>
>>
>>jim beam wrote:
>>> jobst.brandt@stanfordalumni.org wrote:
>>> > Peter Cole writes:
>>> >
>>> >
>>> >>>for a good quality rim in good condition, it is indeed most
>>> >>>unlikely that a tire can be pumped sufficiently to bend the rim
>>> >>>before blow-off, but that doesn't mean it can't happen - there has
>>> >>>to be some pressure at which it occurs. once that principle is
>>> >>>established, it's then a matter of quantification.
>>> >
>>> >
>>> >>If the 2 spots on the rim were folded down by the force of the tire
>>> >>bead after the bead lifted off but before the tube blew, I would
>>> >>think either the rim would have to be extremely fragile (and
>>> >>ductile) and/or the pressure very high. I wonder if the tire was
>>> >>being filled from a high pressure source (compressor)? It could
>>> >>theoretically be possible to get very high pressures (>200 psi)
>>> >>before liftoff.
>>> >
>>> >
>>> > This is not a reasonable pursuit. The rim would not bend at the
>>place
>>> > where the tire first lifted off because that is a region of reduced
>>> > stress, the tire bead no longer having a hold on the rim. I don't
>>see
>>> > why, in face of many years of experience by professional bicycle
>>> > people, this scenario is given so much consideration. This is all
>>> > based on a report from someone who believes this is what occurred
>>and
>>> > who asks, whether the scenario is probable.
>>> >
>>> > It isn't.
>>> >
>>> > Jobst.Brandt@stanfordalumni.org
>>>
>>> did you or peter ever bother to look at the cracks in the 3rd panel
>>of
>>> this pic?
>>>
>>> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>>>
>>> and have you two ever bothered to consider the effects of fatigue
>>caused
>>> by excess tire pressure, particularly with regard to the orientation
>>of
>>> the extrusion axis?
>>
>>Yes, I did, but I was struck by the curvature of the rim edge, I
>>wouldn't have thought that it would bend so far in a simple crack
>>failure. It was also surprising to hear that there were 2 such spots on
>>the rim, that seems a little too coincidental for fatigue failure. I'd
>>also find it difficult to believe that an experienced rider would dent
>>a rim that badly without remembering an impact (or 2), so I'm baffled.
>
> Dear Peter,
>
> I'm baffled, too--why is the damage on only one side, why
> didn't the rider notice hitting anything, and why is the
> damage so impressive?
>
> A private email pointed out that rims can be bent that much
> a single time without cracking. (This seems plausible, but I
> hesitate to sacrifice a rim before hearing what others say.)
>
> Could we be looking at a combination of Jim's fatigue crack
> and Jobst's impact damage?
>
> If Jim's a fatigue crack developed on one side, would the
> rim then be weakened enough that the next healthy bump would
> produce Jobst's impressive curled bend on only one side?
>
> This would explain why the impressive damage is on only one
> side and why the rider didn't notice the kind of impressive
> impact that at first seems to be indicated.

Of course you are missing the entire conspiracy theory/troll angle.
Notice that Mr. Hasselhoff jumped all over Jobst allmost immediately.
Perhaps the whole thing was a set up?

carlfogel@comcast.net writes:

> On 30 Mar 2005 07:30:21 -0800, "Peter Cole"
> <peter_cole@comcast.net> wrote:
>
>>
>>jim beam wrote:
>>> jobst.brandt@stanfordalumni.org wrote:
>>> > Peter Cole writes:
>>> >
>>> >
>>> >>>for a good quality rim in good condition, it is indeed most
>>> >>>unlikely that a tire can be pumped sufficiently to bend the rim
>>> >>>before blow-off, but that doesn't mean it can't happen - there has
>>> >>>to be some pressure at which it occurs. once that principle is
>>> >>>established, it's then a matter of quantification.
>>> >
>>> >
>>> >>If the 2 spots on the rim were folded down by the force of the tire
>>> >>bead after the bead lifted off but before the tube blew, I would
>>> >>think either the rim would have to be extremely fragile (and
>>> >>ductile) and/or the pressure very high. I wonder if the tire was
>>> >>being filled from a high pressure source (compressor)? It could
>>> >>theoretically be possible to get very high pressures (>200 psi)
>>> >>before liftoff.
>>> >
>>> >
>>> > This is not a reasonable pursuit. The rim would not bend at the
>>place
>>> > where the tire first lifted off because that is a region of reduced
>>> > stress, the tire bead no longer having a hold on the rim. I don't
>>see
>>> > why, in face of many years of experience by professional bicycle
>>> > people, this scenario is given so much consideration. This is all
>>> > based on a report from someone who believes this is what occurred
>>and
>>> > who asks, whether the scenario is probable.
>>> >
>>> > It isn't.
>>> >
>>> > Jobst.Brandt@stanfordalumni.org
>>>
>>> did you or peter ever bother to look at the cracks in the 3rd panel
>>of
>>> this pic?
>>>
>>> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>>>
>>> and have you two ever bothered to consider the effects of fatigue
>>caused
>>> by excess tire pressure, particularly with regard to the orientation
>>of
>>> the extrusion axis?
>>
>>Yes, I did, but I was struck by the curvature of the rim edge, I
>>wouldn't have thought that it would bend so far in a simple crack
>>failure. It was also surprising to hear that there were 2 such spots on
>>the rim, that seems a little too coincidental for fatigue failure. I'd
>>also find it difficult to believe that an experienced rider would dent
>>a rim that badly without remembering an impact (or 2), so I'm baffled.
>
> Dear Peter,
>
> I'm baffled, too--why is the damage on only one side, why
> didn't the rider notice hitting anything, and why is the
> damage so impressive?
>
> A private email pointed out that rims can be bent that much
> a single time without cracking. (This seems plausible, but I
> hesitate to sacrifice a rim before hearing what others say.)
>
> Could we be looking at a combination of Jim's fatigue crack
> and Jobst's impact damage?
>
> If Jim's a fatigue crack developed on one side, would the
> rim then be weakened enough that the next healthy bump would
> produce Jobst's impressive curled bend on only one side?
>
> This would explain why the impressive damage is on only one
> side and why the rider didn't notice the kind of impressive
> impact that at first seems to be indicated.

Of course you are missing the entire conspiracy theory/troll angle.
Notice that Mr. Hasselhoff jumped all over Jobst allmost immediately.
Perhaps the whole thing was a set up?

On 30 Mar 2005 15:20:46 -0800, "41" <KingGeorgeXLI@yahoo.fr>
wrote:

>
>carlfogel@comcast.net wrote:
>
>> If Jim's a fatigue crack developed on one side, would the
>> rim then be weakened enough that the next healthy bump would
>> produce Jobst's impressive curled bend on only one side?
>
>No. If you look, especially at the second picture, you will notice that
>the curl or bend goes all the way to the very edge, far away from the
>crack site which is at the base of the sidewall. That means a severe
>force was applied to that edge, i.e. by impact. The crack is far away
>and has no control over the amount of force required there.
>
>The explanation for this is rather obvious and relates to the fact that
>the original poster blows at pressures as low as his tires.i

Dear 41,

I don't know enough about this stuff to know who's right,
but I'm a little skeptical of your claim that the crack has
no control over the amount of force needed to bend the rim
above it. Doesn't the impact-only theory assume that the
bending caused the crack at the base? If so, doesn't that
suggest that cracking the rim at the base to start with
would weaken the rim, allowing a much gentler impact to
produce such dramatic damage?

I have little experience with bike rims bent like this, so
it would be nice if some bike shop people who see lots of
them would comment on the crack--is it normal for an impact
dent like this to crack the rim around the base of the
sidewall, is it unusual, or is it fifty-fifty, depends on
the rim and what you hit?

Come to think of it, don't rims worn thin by brake pads tend
to crack at the base of the sidewall and then start to bulge
outward because the rim has weakened?

I think that most threads about worn rims include posts
about how the bulging of the sidewalls can be felt when the
rim is worn enough to become weak, before there's even a
crack.

Carl Fogel

On 30 Mar 2005 15:20:46 -0800, "41" <KingGeorgeXLI@yahoo.fr>
wrote:

>
>carlfogel@comcast.net wrote:
>
>> If Jim's a fatigue crack developed on one side, would the
>> rim then be weakened enough that the next healthy bump would
>> produce Jobst's impressive curled bend on only one side?
>
>No. If you look, especially at the second picture, you will notice that
>the curl or bend goes all the way to the very edge, far away from the
>crack site which is at the base of the sidewall. That means a severe
>force was applied to that edge, i.e. by impact. The crack is far away
>and has no control over the amount of force required there.
>
>The explanation for this is rather obvious and relates to the fact that
>the original poster blows at pressures as low as his tires.i

Dear 41,

I don't know enough about this stuff to know who's right,
but I'm a little skeptical of your claim that the crack has
no control over the amount of force needed to bend the rim
above it. Doesn't the impact-only theory assume that the
bending caused the crack at the base? If so, doesn't that
suggest that cracking the rim at the base to start with
would weaken the rim, allowing a much gentler impact to
produce such dramatic damage?

I have little experience with bike rims bent like this, so
it would be nice if some bike shop people who see lots of
them would comment on the crack--is it normal for an impact
dent like this to crack the rim around the base of the
sidewall, is it unusual, or is it fifty-fifty, depends on
the rim and what you hit?

Come to think of it, don't rims worn thin by brake pads tend
to crack at the base of the sidewall and then start to bulge
outward because the rim has weakened?

I think that most threads about worn rims include posts
about how the bulging of the sidewalls can be felt when the
rim is worn enough to become weak, before there's even a
crack.

Carl Fogel

On Wed, 30 Mar 2005 17:56:26 -0600, Jim Smith
<3.141592six@gmail.com> wrote:

>carlfogel@comcast.net writes:
>
>> On 30 Mar 2005 07:30:21 -0800, "Peter Cole"
>> <peter_cole@comcast.net> wrote:
>>
>>>
>>>jim beam wrote:
>>>> jobst.brandt@stanfordalumni.org wrote:
>>>> > Peter Cole writes:
>>>> >
>>>> >
>>>> >>>for a good quality rim in good condition, it is indeed most
>>>> >>>unlikely that a tire can be pumped sufficiently to bend the rim
>>>> >>>before blow-off, but that doesn't mean it can't happen - there has
>>>> >>>to be some pressure at which it occurs. once that principle is
>>>> >>>established, it's then a matter of quantification.
>>>> >
>>>> >
>>>> >>If the 2 spots on the rim were folded down by the force of the tire
>>>> >>bead after the bead lifted off but before the tube blew, I would
>>>> >>think either the rim would have to be extremely fragile (and
>>>> >>ductile) and/or the pressure very high. I wonder if the tire was
>>>> >>being filled from a high pressure source (compressor)? It could
>>>> >>theoretically be possible to get very high pressures (>200 psi)
>>>> >>before liftoff.
>>>> >
>>>> >
>>>> > This is not a reasonable pursuit. The rim would not bend at the
>>>place
>>>> > where the tire first lifted off because that is a region of reduced
>>>> > stress, the tire bead no longer having a hold on the rim. I don't
>>>see
>>>> > why, in face of many years of experience by professional bicycle
>>>> > people, this scenario is given so much consideration. This is all
>>>> > based on a report from someone who believes this is what occurred
>>>and
>>>> > who asks, whether the scenario is probable.
>>>> >
>>>> > It isn't.
>>>> >
>>>> > Jobst.Brandt@stanfordalumni.org
>>>>
>>>> did you or peter ever bother to look at the cracks in the 3rd panel
>>>of
>>>> this pic?
>>>>
>>>> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>>>>
>>>> and have you two ever bothered to consider the effects of fatigue
>>>caused
>>>> by excess tire pressure, particularly with regard to the orientation
>>>of
>>>> the extrusion axis?
>>>
>>>Yes, I did, but I was struck by the curvature of the rim edge, I
>>>wouldn't have thought that it would bend so far in a simple crack
>>>failure. It was also surprising to hear that there were 2 such spots on
>>>the rim, that seems a little too coincidental for fatigue failure. I'd
>>>also find it difficult to believe that an experienced rider would dent
>>>a rim that badly without remembering an impact (or 2), so I'm baffled.
>>
>> Dear Peter,
>>
>> I'm baffled, too--why is the damage on only one side, why
>> didn't the rider notice hitting anything, and why is the
>> damage so impressive?
>>
>> A private email pointed out that rims can be bent that much
>> a single time without cracking. (This seems plausible, but I
>> hesitate to sacrifice a rim before hearing what others say.)
>>
>> Could we be looking at a combination of Jim's fatigue crack
>> and Jobst's impact damage?
>>
>> If Jim's a fatigue crack developed on one side, would the
>> rim then be weakened enough that the next healthy bump would
>> produce Jobst's impressive curled bend on only one side?
>>
>> This would explain why the impressive damage is on only one
>> side and why the rider didn't notice the kind of impressive
>> impact that at first seems to be indicated.
>
>Of course you are missing the entire conspiracy theory/troll angle.
>Notice that Mr. Hasselhoff jumped all over Jobst allmost immediately.
>Perhaps the whole thing was a set up?

Dear Jim,

To paraphrase Bierce's comment regarding the definition of
an inferior lexicographer, conspiracy theories tend to be
not the last but the first resort of--

Er, never mind.

And never mind who actually jumped on whom first.

The rim is more interesting.

If the dented rim is a fraud of some kind, how was it
produced?

That is, would a normal rim crack like that when bent out on
one side with a suitable soft-jawed tool that left no marks
(doubtless available under the counter from Harris Cyclery's
Covert Operation Catalogue), or would it just bend without
the crack?

Would the speed of the bending determine whether it cracked?

That is, would a real impact cushioned by a tire at high
speed tend to rupture, while a fake "impact" produced by a
comparatively slow twist with a pair of soft-jawed
channel-locks would leave no crack?

Carl Fogel

On Wed, 30 Mar 2005 17:56:26 -0600, Jim Smith
<3.141592six@gmail.com> wrote:

>carlfogel@comcast.net writes:
>
>> On 30 Mar 2005 07:30:21 -0800, "Peter Cole"
>> <peter_cole@comcast.net> wrote:
>>
>>>
>>>jim beam wrote:
>>>> jobst.brandt@stanfordalumni.org wrote:
>>>> > Peter Cole writes:
>>>> >
>>>> >
>>>> >>>for a good quality rim in good condition, it is indeed most
>>>> >>>unlikely that a tire can be pumped sufficiently to bend the rim
>>>> >>>before blow-off, but that doesn't mean it can't happen - there has
>>>> >>>to be some pressure at which it occurs. once that principle is
>>>> >>>established, it's then a matter of quantification.
>>>> >
>>>> >
>>>> >>If the 2 spots on the rim were folded down by the force of the tire
>>>> >>bead after the bead lifted off but before the tube blew, I would
>>>> >>think either the rim would have to be extremely fragile (and
>>>> >>ductile) and/or the pressure very high. I wonder if the tire was
>>>> >>being filled from a high pressure source (compressor)? It could
>>>> >>theoretically be possible to get very high pressures (>200 psi)
>>>> >>before liftoff.
>>>> >
>>>> >
>>>> > This is not a reasonable pursuit. The rim would not bend at the
>>>place
>>>> > where the tire first lifted off because that is a region of reduced
>>>> > stress, the tire bead no longer having a hold on the rim. I don't
>>>see
>>>> > why, in face of many years of experience by professional bicycle
>>>> > people, this scenario is given so much consideration. This is all
>>>> > based on a report from someone who believes this is what occurred
>>>and
>>>> > who asks, whether the scenario is probable.
>>>> >
>>>> > It isn't.
>>>> >
>>>> > Jobst.Brandt@stanfordalumni.org
>>>>
>>>> did you or peter ever bother to look at the cracks in the 3rd panel
>>>of
>>>> this pic?
>>>>
>>>> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>>>>
>>>> and have you two ever bothered to consider the effects of fatigue
>>>caused
>>>> by excess tire pressure, particularly with regard to the orientation
>>>of
>>>> the extrusion axis?
>>>
>>>Yes, I did, but I was struck by the curvature of the rim edge, I
>>>wouldn't have thought that it would bend so far in a simple crack
>>>failure. It was also surprising to hear that there were 2 such spots on
>>>the rim, that seems a little too coincidental for fatigue failure. I'd
>>>also find it difficult to believe that an experienced rider would dent
>>>a rim that badly without remembering an impact (or 2), so I'm baffled.
>>
>> Dear Peter,
>>
>> I'm baffled, too--why is the damage on only one side, why
>> didn't the rider notice hitting anything, and why is the
>> damage so impressive?
>>
>> A private email pointed out that rims can be bent that much
>> a single time without cracking. (This seems plausible, but I
>> hesitate to sacrifice a rim before hearing what others say.)
>>
>> Could we be looking at a combination of Jim's fatigue crack
>> and Jobst's impact damage?
>>
>> If Jim's a fatigue crack developed on one side, would the
>> rim then be weakened enough that the next healthy bump would
>> produce Jobst's impressive curled bend on only one side?
>>
>> This would explain why the impressive damage is on only one
>> side and why the rider didn't notice the kind of impressive
>> impact that at first seems to be indicated.
>
>Of course you are missing the entire conspiracy theory/troll angle.
>Notice that Mr. Hasselhoff jumped all over Jobst allmost immediately.
>Perhaps the whole thing was a set up?

Dear Jim,

To paraphrase Bierce's comment regarding the definition of
an inferior lexicographer, conspiracy theories tend to be
not the last but the first resort of--

Er, never mind.

And never mind who actually jumped on whom first.

The rim is more interesting.

If the dented rim is a fraud of some kind, how was it
produced?

That is, would a normal rim crack like that when bent out on
one side with a suitable soft-jawed tool that left no marks
(doubtless available under the counter from Harris Cyclery's
Covert Operation Catalogue), or would it just bend without
the crack?

Would the speed of the bending determine whether it cracked?

That is, would a real impact cushioned by a tire at high
speed tend to rupture, while a fake "impact" produced by a
comparatively slow twist with a pair of soft-jawed
channel-locks would leave no crack?

Carl Fogel

Carl Fogel writes:

> If the dented rim is a fraud of some kind, how was it produced?

> That is, would a normal rim crack like that when bent out on one
> side with a suitable soft-jawed tool that left no marks (doubtless
> available under the counter from Harris Cyclery's Covert Operation
> Catalogue), or would it just bend without the crack?

This is the usual form f a rim that encountered an object, like a
piece of RR ballast (granite) off center of the tire. I have several
rims that were fatally dented like this on one side in my collection
of scrap rims. The difference is that I didn't concoct a story that
it was the result of moderate inflation pressure and then call
everyone who doubted that a jerk.

> Would the speed of the bending determine whether it cracked?

No.

> That is, would a real impact cushioned by a tire at high
> speed tend to rupture, while a fake "impact" produced by a
> comparatively slow twist with a pair of soft-jawed
> channel-locks would leave no crack?

That is completely out of the question from my experience with such
dents. You can't make them that smooth without a tire on the rim and
exerting a radial overload.

The speed of the bicycle in conjunction with weight on the wheel,
needs to be only great enough that the inertial load will bend the
rim. This is not hard to do at speeds of even 15mph, although higher
speed ensures success. Curling the edge of a rim cannot be fatigue
related.

Jobst.Brandt@stanfordalumni.org

Carl Fogel writes:

> If the dented rim is a fraud of some kind, how was it produced?

> That is, would a normal rim crack like that when bent out on one
> side with a suitable soft-jawed tool that left no marks (doubtless
> available under the counter from Harris Cyclery's Covert Operation
> Catalogue), or would it just bend without the crack?

This is the usual form f a rim that encountered an object, like a
piece of RR ballast (granite) off center of the tire. I have several
rims that were fatally dented like this on one side in my collection
of scrap rims. The difference is that I didn't concoct a story that
it was the result of moderate inflation pressure and then call
everyone who doubted that a jerk.

> Would the speed of the bending determine whether it cracked?

No.

> That is, would a real impact cushioned by a tire at high
> speed tend to rupture, while a fake "impact" produced by a
> comparatively slow twist with a pair of soft-jawed
> channel-locks would leave no crack?

That is completely out of the question from my experience with such
dents. You can't make them that smooth without a tire on the rim and
exerting a radial overload.

The speed of the bicycle in conjunction with weight on the wheel,
needs to be only great enough that the inertial load will bend the
rim. This is not hard to do at speeds of even 15mph, although higher
speed ensures success. Curling the edge of a rim cannot be fatigue
related.

Jobst.Brandt@stanfordalumni.org