H+Son rim failure, Mr. Brandt, your thoughts?

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Chocobot

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Dec 7, 2008, 7:38:21 PM12/7/08
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http://ganrin.blogspot.com/2008/11/its-not-mine-but.html

That is the story. Does this seem right?

- chris

jobst....@stanfordalumni.org

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Dec 7, 2008, 7:57:20 PM12/7/08
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Chris Allick wrote:

http://ganrin.blogspot.com/2008/11/its-not-mine-but.html

> That is the story. Does this seem right?

It's not right but the story may be correct. From the pictures it
seems the rim split down the center of its bed between sidewalls, but
I can't be sure because the lighting is poor and the rim black.

That's another point. I haven't seen such a split since black hard
anodized rims first appeared on the market in the 1970's. What brand
rim is it and is there a better picture of the wheel with no tire
remains obscuring the rim? I can see that it must have been loud
because the split in the inner tube is the reult of an instant
"air-out" like ones that I have heard.

So when was this wheel bought (built) and how about a closeup of the
fractured surface.

Jobst Brandt

carl...@comcast.net

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Dec 7, 2008, 8:22:52 PM12/7/08
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Dear Chris,

What was the tire width and inflation?

Cheers,

Carl Fogel

Dan O

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Dec 7, 2008, 8:30:28 PM12/7/08
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On Dec 7, 4:38 pm, Chocobot <chrisall...@gmail.com> wrote:
> http://ganrin.blogspot.com/2008/11/its-not-mine-but.html
>
> That is the story. Does this seem right?
>

Totally WAG: Fixed gear? Doing a skid? Forces of braking from hub
added spoke tension and longitudinal force at rim? Possibly existing
crack at spoke nipple bed split open. Then inner tube blew up forcing
crack further apart?

Mike Jacoubowsky

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Dec 7, 2008, 11:26:36 PM12/7/08
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<carl...@comcast.net> wrote in message
news:iltoj4dtlq95iit6g...@4ax.com...

You're on the right path, but it probably still needed a bit of help to
split like that, probably caused by an issue with the die such that the
rim was scored (a groove cut into it lengthwise) as it was extruded.
I've see it before.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


Chalo

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Dec 7, 2008, 11:40:45 PM12/7/08
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On Dec 7, 10:26 pm, "Mike Jacoubowsky" <mik...@ix.netcom.com> wrote:
> <carlfo...@comcast.net> wrote in message

>
> news:iltoj4dtlq95iit6g...@4ax.com...
>
>
>
> > On Sun, 7 Dec 2008 16:38:21 -0800 (PST), Chocobot
> > <chrisall...@gmail.com> wrote:
>
> >>http://ganrin.blogspot.com/2008/11/its-not-mine-but.html
>
> >>That is the story.  Does this seem right?
>
> >> - chris
>
> > Dear Chris,
>
> > What was the tire width and inflation?
>
> > Cheers,
>
> > Carl Fogel
>
> You're on the right path, but it probably still needed a bit of help to
> split like that, probably caused by an issue with the die such that the
> rim was scored (a groove cut into it lengthwise) as it was extruded.
> I've see it before.

When I was in the mechanic business, there was a run of hard anodized
26" Ritchey Vantage Comps that had just such a problem-- a groove
running down the inside rim wall, so distinct and centered that it
looked intentional. I saw a couple of those things crack and split
along the groove, though nothing that spread wide open like the H+Son
rim.

Chalo

carl...@comcast.net

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Dec 8, 2008, 1:12:24 AM12/8/08
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Dear Mike,

If it turns out to be just an ordinary narrow tire and ordinary
pressure, then a bad rim is the most likely explanation.

But running an over-width tire at excessive pressure is likely to
split a good rim the same way:
http://groups.google.com/group/rec.bicycles.tech/msg/17ce37398fc401ff

The rider doesn't look like the 265-lb Clydesdale in that old thread,
but skidding sideways might make up for the lighter weight.

If it turns out to be a 38 mm tire at 80 psi, ouch!

Cheers,

Carl Fogel

Andrew Lee

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Dec 8, 2008, 1:19:26 AM12/8/08
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Chocobot <chris...@gmail.com> wrote:
> http://ganrin.blogspot.com/2008/11/its-not-mine-but.html
>
> That is the story. Does this seem right?

I clicked on the second photo and found a link to a larger size:

http://www.flickr.com/photos/ganring/3055814948/sizes/l/

The inner rim wall is very thin looking. Just eyeball estimating, it looks less than 1/2 or even 1/3 mm to me.

bjwe...@gmail.com

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Dec 8, 2008, 1:26:36 AM12/8/08
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No.
This is a deep section aluminum rim.
Several of the pictures make it clear that the
rim is split at the channel bed, but the spoke
nipple bed is way down at the inner edge of
the rim and appears more or less undamaged.

http://hplusson.com/
http://www.flickr.com/photos/30185145@N04/

The tension increase from braking in a skidding
brake is not that big, because skidding is not a
particularly effective way to brake. (In a
deliberate-skidding contest, one unweights the
rear wheel.) And just because everybody on rbr
is obsessed with spoke tension and cracks at
the nipples does not make a few-week-old rim
likely to have fatal cracks at the nipples.

The more likely mechanism is that the skid locally
heated the air in the tube and momentarily increased
the hoop stress enough to pull the rim hooks apart
by tearing the channel bed in half. The failure
might have initiated at one of the hole drillings.
With the hooks bent out, the tire would then
lift off and the tube blow out with a big rip as
Jobst noted.

If I am right about this, the flat-spot on the tire caused
by skidding would be aligned with the rim failure,
which appears to be true, look at the first couple
of pictures:
http://www.flickr.com/photos/ganring/sets/72157609868064447/
before they take the tire off.

Ben

Andrew Lee

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Dec 8, 2008, 1:39:34 AM12/8/08
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Found a better photo:

http://www.flickr.com/photos/ganring/3054982423/sizes/o/in/set-72157609868064447/

The ruptured section looks about half the thickness of the same location on some lightweight Velocity Aerohead rims that I have on hand.

carl...@comcast.net

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Dec 8, 2008, 1:53:51 AM12/8/08
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Dear Ben,

When a rider deliberately skids a fixie's rear tire, he's shredding a
small section of rubber tire against the pavement.

It's a short skid, with very little heat transferred through the small
section of rubber tire to the air inside the tire.

The fixie comes to a stop in a moment or two, and then has to be sped
up again--even the small section of heated-up tire cools off again.
Despite the dramatics, there's very little heat and plenty of cooling
off time.

Think of someone waving a heat gun at at tire for about two seconds,
which is about all the skidding that a fixie is going to generate. The
tire isn't likely to see much pressure rise, much less tear a rim
apart.

In contrast, prolonged downhill rim braking presses rubber pads
against the metal for much longer periods, heating the metal rim and
the air inside the tire so much that the tire blows off the rim.

(Jobst was doing some testing that may cause doubt about even that--he
never got a tire to come off the rim with pressure alone, suggesting
that the heated rim flange and tire bead surface may be the real
problem, becoming very slippery.)

I don't recall any posts in which the slow heating did anything but
blow the rim off--the tire creeps off long before the rim fails.

An over-inflated, oversize tire can cause such rim failures, but we
don't know what the tire size was.

As Mike and Chalo have pointed out, ordinary hoop stress is enough to
split defective rims. If the original poster has the rim examined and
finds a nasty groove running down the inside of the rim, oops!

Cheers,

Carl Fogel

bjwe...@gmail.com

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Dec 8, 2008, 3:58:39 AM12/8/08
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On Dec 7, 11:53 pm, carlfo...@comcast.net wrote:
>
> When a rider deliberately skids a fixie's rear tire, he's shredding a
> small section of rubber tire against the pavement.
>
> It's a short skid, with very little heat transferred through the small
> section of rubber tire to the air inside the tire.
>
> The fixie comes to a stop in a moment or two, and then has to be sped
> up again--even the small section of heated-up tire cools off again.
> Despite the dramatics, there's very little heat and plenty of cooling
> off time.
>
> Think of someone waving a heat gun at at tire for about two seconds,
> which is about all the skidding that a fixie is going to generate. The
> tire isn't likely to see much pressure rise, much less tear a rim
> apart.

Skidding friction is much more efficient at transferring
heat to the tire than a heat gun would be. I don't think
that's a useful analogy.

The skidding stop dissipates the kinetic energy of the
rider in a small patch of rubber (some of it goes into
the skid patch of asphalt). The KE is easily estimated,
for 80 kg of rider plus bike going 15 mph=6.7 m/s,
the KE is 1800 Joules. That's not much unless it all
has to be taken up in a small patch. The heat capacity
of an entire tire+tube would take that up easily and
only rise a couple of degrees, but if it all gets dumped
into a few grams of rubber at the contact patch, that
is another story. (Heat capacity of rubber is about
2.0 kJ/kg/degree Kelvin; I think this number is for
natural rubber, and butyl may be less.)

> In contrast, prolonged downhill rim braking presses rubber pads
> against the metal for much longer periods, heating the metal rim and
> the air inside the tire so much that the tire blows off the rim.
>
> (Jobst was doing some testing that may cause doubt about even that--he
> never got a tire to come off the rim with pressure alone, suggesting
> that the heated rim flange and tire bead surface may be the real
> problem, becoming very slippery.)
>

Rim braking tests do not carry over well to this situation:
1. Extended rim braking dumps the heat uniformly into
the entire circumference of the rim rather than a small
skid patch.
2. Rim braking puts the heat into an aluminum rim which
has decent heat capacity and radiates heat well.
The skid issue is not extended slow heating.

> I don't recall any posts in which the slow heating did anything but
> blow the rim off--the tire creeps off long before the rim fails.
>
> An over-inflated, oversize tire can cause such rim failures, but we
> don't know what the tire size was.
>
> As Mike and Chalo have pointed out, ordinary hoop stress is enough to
> split defective rims. If the original poster has the rim examined and
> finds a nasty groove running down the inside of the rim, oops!
>

But why did this rim split at this particular time,
at this particular place (right at the contact patch)?
I certainly don't think that I've proved it was heat
from skidding. I do think that heat from skidding
is real - go out and do a rubber-burning skid, and
I'm sure the tire will be warm at the patch. Even a
pencil eraser gets warm from rubbing.

Ben

jobst....@stanfordalumni.org

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Dec 8, 2008, 5:18:16 AM12/8/08
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Ben Weiner wrote:

>> When a rider deliberately skids a fixie's rear tire, he's shredding
>> a small section of rubber tire against the pavement.

>> It's a short skid, with very little heat transferred through the
>> small section of rubber tire to the air inside the tire.

>> The fixie comes to a stop in a moment or two, and then has to be
>> sped up again--even the small section of heated-up tire cools off
>> again. Despite the dramatics, there's very little heat and plenty
>> of cooling off time.

>> Think of someone waving a heat gun at at tire for about two
>> seconds, which is about all the skidding that a fixie is going to
>> generate. The tire isn't likely to see much pressure rise, much
>> less tear a rim apart.

> Skidding friction is much more efficient at transferring heat to the
> tire than a heat gun would be. I don't think that's a useful
> analogy.

Whereas the rim is in contact with the thin rubber wall of the inner
tube, tire tread is relatively thick and the tread even thicker.
Skidding may tear some rubber from the tread but it does not heat it
significantly. Not enough to feel by hand. It isn't like white smoke
from a burnout on a motor vehicle and even that doesn't heat the air in
the tire much.

> The skidding stop dissipates the kinetic energy of the rider in a
> small patch of rubber (some of it goes into the skid patch of
> asphalt). The KE is easily estimated, for 80 kg of rider plus bike
> going 15 mph=6.7 m/s, the KE is 1800 Joules. That's not much unless
> it all has to be taken up in a small patch. The heat capacity of an
> entire tire+tube would take that up easily and only rise a couple of
> degrees, but if it all gets dumped into a few grams of rubber at the
> contact patch, that is another story. (Heat capacity of rubber is
> about 2.0 kJ/kg/degree Kelvin; I think this number is for natural
> rubber, and butyl may be less.)

Skidding when crossed-up is not a useful means of slowing down, it
being done with the rear wheel that is partially unloaded by the
method, the bicycle still being headed mainly forward.

>> In contrast, prolonged downhill rim braking presses rubber pads
>> against the metal for much longer periods, heating the metal rim
>> and the air inside the tire so much that the tire blows off the
>> rim.

>> (Jobst was doing some testing that may cause doubt about even
>> that--he never got a tire to come off the rim with pressure alone,
>> suggesting that the heated rim flange and tire bead surface may be
>> the real problem, becoming very slippery.)

> Rim braking tests do not carry over well to this situation:
> 1. Extended rim braking dumps the heat uniformly into
> the entire circumference of the rim rather than a small
> skid patch.

> 2. Rim braking puts the heat into an aluminum rim which has decent
> heat capacity and radiates heat well. The skid issue is not
> extended slow heating.

Well rims get over water boiling temperatures rapidly as I have tested
in alpine descents. You cannot touch such a rim without burning the
skin of a finger.

>> I don't recall any posts in which the slow heating did anything but
>> blow the rim off--the tire creeps off long before the rim fails.

>> An over-inflated, oversize tire can cause such rim failures, but we
>> don't know what the tire size was.

>> As Mike and Chalo have pointed out, ordinary hoop stress is enough
>> to split defective rims. If the original poster has the rim
>> examined and finds a nasty groove running down the inside of the
>> rim, oops!

> But why did this rim split at this particular time, at this
> particular place (right at the contact patch)? I certainly don't
> think that I've proved it was heat from skidding. I do think that
> heat from skidding is real - go out and do a rubber-burning skid,
> and I'm sure the tire will be warm at the patch. Even a pencil
> eraser gets warm from rubbing.

This looks much more like a mechanical failure at constant pressure.
The side force of a broadside skid must be supported by the rim and
that is what I believe is what we see here. Not heating and over
pressure.

Jobst Brandt

Andre Jute

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Dec 8, 2008, 6:37:22 AM12/8/08
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On Dec 8, 8:58 am, "b...@mambo.ucolick.org" <bjwei...@gmail.com>
wrote:

No you haven't.

> I do think that heat from skidding
> is real - go out and do a rubber-burning skid, and
> I'm sure the tire will be warm at the patch.  

I'll throw this into the pot: An automobile tyre run hard on a skidpad
despite the cooling effect of the liquid on the pad still warms up
enough to make the use of nitrogen in the tyres a useful option.
(Nitrogen doesn't expand with heat and thereby interfere with the
handling.) But the bicycle tyre skidding isn't analogous: too short a
period and probably other factors too that I can work out if I
unsheath my slide rule. To name just one hypothesis to be confirmed on
calculation: in relation to the weight it carries, it appears to me
that there might be more air mass in a bicycle tyre than in a car
tyre.

>Even a
> pencil eraser gets warm from rubbing.

Some of the most interesting people I know don't know when to give
up...

> Ben

I think Chalo and Mike J are right, this is a mechanical failure
caused by a defect in the rim, buggerall to do with heated,
overpressured air.

It doesn't take much to burst a fully inflated tyre. One night, riding
on a path with my lights turned down so as not to shine in the eyes of
pedestrians, I swerved for a fat lady bearing down on me determinedly
-- and hit a tree. I was riding at most at 10kph, yet the tyre popped.
The next day I was there again, looking for a piece that popped out of
the chaincase from the impact, and I leaned against this young tree to
test the give, and there was perceptible resilience only 18" above the
ground. I concluded at the time that my tyre was possibly
overinflated, which might have happened at that time because a
mailorder dealer sent me the wrong valves on my tubes and I was
waiting for a compatible pressure gauge to arrive (1), or possibly
defective already, or simply just too thin (I shortly went back to the
heavier weight of tube). But there was no rim damage whatsoever. If
the rim deflected more than some notional "normal" amount, it popped
right back.

Andre Jute
Tubes tend to make people believe in a god, and SS leads them to the
devil. -- Patrick Turner

(1) Yeah, I know, horny-handed cyclists just feel the tube and know
the pressure to within a millibar -- or so they claim; I put my faith
only in cash and a calibrated pressure guage. I ride on panzered
Marathon Plus (or the Bontrager equivalent), with anti-puncture rubber
and Kevlar and Aramid layers that make the top of the thing as stiff
to pressure uninflated as when inflated to the maximum. All the give
is in the sidewalls, and the give has too little range for finger
pressure to "measure" anything.

Clive George

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Dec 8, 2008, 6:53:13 AM12/8/08
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"Andre Jute" <fiul...@yahoo.com> wrote in message
news:ca6a4093-638e-4afa...@t39g2000prh.googlegroups.com...

>(Nitrogen doesn't expand with heat and thereby interfere with the
>handling.)

Maybe a study of the ideal gas laws would help.


Andre Jute

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Dec 8, 2008, 7:26:33 AM12/8/08
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On Dec 8, 11:53 am, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> "Andre Jute" <fiult...@yahoo.com> wrote in message

It surely would. And when you finish your study of ideal gas laws,
Clive, you should go on to study nitrogen in particular, when you will
find that nitrogen has a more consistent rate of expansion and
contraction than air, normally shorthanded by racing mechanics as
"doesn't expand like air".

Stop nitpicking, Clive.

Andre Jute
High on nitrogen

Clive George

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Dec 8, 2008, 7:34:02 AM12/8/08
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"Andre Jute" <fiul...@yahoo.com> wrote in message
news:85c01988-568c-4d1d...@k24g2000pri.googlegroups.com...

What would explain that difference?

>Stop nitpicking, Clive.

You complain when people use words you don't like, I complain when people
abuse simple science.


Andre Jute

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Dec 8, 2008, 8:12:06 AM12/8/08
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On Dec 8, 12:34 pm, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> "Andre Jute" <fiult...@yahoo.com> wrote in message
>
> news:85c01988-568c-4d1d...@k24g2000pri.googlegroups.com...
>
> >On Dec 8, 11:53 am, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> >> "Andre Jute" <fiult...@yahoo.com> wrote in message
>
> >>news:ca6a4093-638e-4afa...@t39g2000prh.googlegroups.com...
>
> >> >(Nitrogen doesn't expand with heat and thereby interfere with the
> >> >handling.)
>
> >> Maybe a study of the ideal gas laws would help.
>
> >It surely would. And when you finish your study of ideal gas laws,
> >Clive, you should go on to study nitrogen in particular, when you will
> >find that nitrogen has a more consistent rate of expansion and
> >contraction than air, normally shorthanded by racing mechanics as
> >"doesn't expand like air".
>
> What would explain that difference?
>
> >Stop nitpicking, Clive.
>
> You complain when people use words you don't like,

No, I don't; it's a free world and if people want to blare out the
lacunae in their background and education, that's their business.
Rarely I might correct them if they use words wrongly, and only when
the wrong choice changes the meaning of the discussion.

> I complain when people
> abuse simple science.

Well, I didn't abuse simple science. You are simply ignorant about the
qualities of gases: they don't all expand at the same rate.

If you have a real beef with someone abusing science, I'll join you in
correcting his miscomprehension. But nitpicking is another matter
altogether.

Andre Jute
Now let us honour the immutable laws of physics

Clive George

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Dec 8, 2008, 8:19:36 AM12/8/08
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"Andre Jute" <fiul...@yahoo.com> wrote in message
news:7985d680-96f1-423f...@w1g2000prm.googlegroups.com...

>Well, I didn't abuse simple science. You are simply ignorant about the
>qualities of gases: they don't all expand at the same rate.

Sometimes your ignorance is pure comedy.

What makes nitrogen expand at a different rate from air in conditions such
as may be found in the atmosphere and a car tyre?

Answer that question, and you'll understand the humour unintentionally
provided by your statement above.

Andre Jute

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Dec 8, 2008, 9:25:47 AM12/8/08
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On Dec 8, 1:19 pm, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> "Andre Jute" <fiult...@yahoo.com> wrote in message

Happiest days of your life when you were the Bully of the Upper
Fourth, eh, Clive, beating up the smaller boys until they did your
homework for you? But I don't mind helping even a bully with his
homework. The answer you want is: "Free air has varyng amounts of
water vapour in it, depending on local humidity, which causes it to
expand differentially, thereby affecting traction and handling when
used in racing tyres. 'Dry' nitrogen expands much less than
atmospheric air and therefore leads to more predictable traction and
handling. There are also leakage consideraitons, which together with
the more constant pressure, can lead to savings when fleets of trucks
use nitro rather than air." Go show that to the teacher and get a pat
on the back for someone else's work.

And mechanics still say, for practical purposes perfectly correctly,
"nitro doesn't expand when it heats up" -- and so do engineers from
Stanford to MIT, Stuttgart to Padua and Bristol to Melbourne, to name
just universities whose graduates I have heard speak those precise
words. God know why you, who claims to be a scientist, needs all the
eyes dotted and all the tees crossed.

Want me to do your math homework for you as well?

Andre Jute
Bored with this mindless pedant

Clive George

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Dec 8, 2008, 9:41:48 AM12/8/08
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"Andre Jute" <fiul...@yahoo.com> wrote in message
news:7c161c37-aef5-4750...@r15g2000prh.googlegroups.com...

On Dec 8, 1:19 pm, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
>> "Andre Jute" <fiult...@yahoo.com> wrote in message
>>
>> news:7985d680-96f1-423f...@w1g2000prm.googlegroups.com...
>>
>> >Well, I didn't abuse simple science. You are simply ignorant about the
>> >qualities of gases: they don't all expand at the same rate.
>>
>> Sometimes your ignorance is pure comedy.
>>
>> What makes nitrogen expand at a different rate from air in conditions
>> such
>> as may be found in the atmosphere and a car tyre?
>>
>> Answer that question, and you'll understand the humour unintentionally
>> provided by your statement above.

> But I don't mind helping even a bully with his homework.

You previously gloated that you much prefer other people to do your work for
you. I thought you may appreciate the chance to do some googling of your own
for a change.

>The answer you want is: "Free air has varyng amounts of
>water vapour in it, depending on local humidity, which causes it to
>expand differentially, thereby affecting traction and handling when
>used in racing tyres.

Well done. Now you should know where you went wrong. The difference is
caused by the water being in liquid phase in the cold air. It's not a gas.
Gases do expand at the same rate under the conditions I mentioned, contrary
to what you wrote.

Andre Jute

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Dec 8, 2008, 10:54:46 AM12/8/08
to

Pfft! I didn't see you state any condiitons at all, Clive, whereas the
conditions under which my original statement held true, holds true and
will forever hold true are clearly implied in the statement that we're
talking about automobile tyres: free air, full of water vapour. Under
those conditions, gases do not expand at the same rate, and every
mechanic knows it, so why don't you?

You're a nitpicker, Clive, and a bully besides. The purpose of your
misbehaviour is to make you seem smarter than your betters. It doesn't
work. But, to avoid this sort of dull, unproductive acrimony in
future, why don't we just agree that you're smarter than me, know more
about every subject under the sun, have better bikes and is more
handsome too? Then you'll be happy and I can continue to use you as my
bike research assistant when Fogel is lying down with a migraine.

Andre Jute
If you have to be a pedant, at least be an amusing pedant

Clive George

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Dec 8, 2008, 11:03:15 AM12/8/08
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"Andre Jute" <fiul...@yahoo.com> wrote in message
news:dd705df9-5b06-49d0...@p2g2000prn.googlegroups.com...

Perhaps you ought to read what others write more carefully then. My
conditions are still quoted above.

>You're a nitpicker, Clive, and a bully besides. The purpose of your
>misbehaviour is to make you seem smarter than your betters.

Once again your unintentional humour strikes.


Andre Jute

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Dec 8, 2008, 11:56:10 AM12/8/08
to

You win, Clive. You are always right. You're so clever and so
beautiful. I apologize for not having seen Your Luminosity before.
Please don't hit me any more.


Jay Beattie

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Dec 8, 2008, 12:09:18 PM12/8/08
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On Dec 7, 10:12 pm, carlfo...@comcast.net wrote:
> On Sun, 7 Dec 2008 20:26:36 -0800, "Mike Jacoubowsky"
>
>
>
>
>
> <mik...@ix.netcom.com> wrote:
> ><carlfo...@comcast.net> wrote in message

The rim strip was too tight. Look at the pictures Andrew Lee posted.
It was so tight, it split the tire bed. Should have used Velox. --
Jay Beattie.

Ben C

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Dec 8, 2008, 12:22:04 PM12/8/08
to
On 2008-12-08, Clive George <cl...@xxxx-x.fsnet.co.uk> wrote:
> "Andre Jute" <fiul...@yahoo.com> wrote in message
> news:85c01988-568c-4d1d...@k24g2000pri.googlegroups.com...
>>On Dec 8, 11:53 am, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
>>> "Andre Jute" <fiult...@yahoo.com> wrote in message
>>>
>>> news:ca6a4093-638e-4afa...@t39g2000prh.googlegroups.com...
>>>
>>> >(Nitrogen doesn't expand with heat and thereby interfere with the
>>> >handling.)
>>>
>>> Maybe a study of the ideal gas laws would help.
>>
>>It surely would. And when you finish your study of ideal gas laws,
>>Clive, you should go on to study nitrogen in particular, when you will
>>find that nitrogen has a more consistent rate of expansion and
>>contraction than air, normally shorthanded by racing mechanics as
>>"doesn't expand like air".
>
> What would explain that difference?

I think it's all the water in air that makes the difference. Not sure
exactly what happens: maybe water droplets evaporate as the tyre heats
up.

Dry air would work just as well as Nitrogen. Air is mostly nitrogen
anyway.

bjwe...@gmail.com

unread,
Dec 8, 2008, 1:01:26 PM12/8/08
to
On Dec 7, 5:57 pm, jobst.bra...@stanfordalumni.org wrote:

> This looks much more like a mechanical failure at constant pressure.
> The side force of a broadside skid must be supported by the rim and
> that is what I believe is what we see here.  Not heating and over
> pressure.

I can believe side loading at the contact patch
of a sideways skid as a trigger for this failure
instead of heating.

Although I think the skidding must have been
the immediate cause of the failure, I also agree
the rim must have been underbuilt at the channel
bed to begin with. Lots of people skid bikes and
very few rip their rims apart.

Ben

Chalo

unread,
Dec 8, 2008, 2:05:50 PM12/8/08
to
Carl Fogel wrote:
>
> Mike Jacoubowsky wrote:

> >
> > Carl Fogel wrote:
> >>
> >> What was the tire width and inflation?
> >
> >You're on the right path, but it probably still needed a bit of help to
> >split like that, probably caused by an issue with the die such that the
> >rim was scored (a groove cut into it lengthwise) as it was extruded.
> >I've see it before.
>
> If it turns out to be just an ordinary narrow tire and ordinary
> pressure, then a bad rim is the most likely explanation.
>
> But running an over-width tire at excessive pressure is likely to
> split a good rim the same way:
> http://groups.google.com/group/rec.bicycles.tech/msg/17ce37398fc401ff
>
> The rider doesn't look like the 265-lb Clydesdale in that old thread,
> but skidding sideways might make up for the lighter weight.
>
> If it turns out to be a 38 mm tire at 80 psi, ouch!

Your reasoning, and Sheldon's, and Georg's, are all quite
respectable. But there's this one problem. "Good" rims do what y'all
suggest they can't over and over again, every day. If we look at the
rider-miles logged on 2" or larger tires inflated to 60 or more psi
and mounted on rims of 13 to 18mm inside width, we either have to
regard the guidelines as faulty or cycling in the '90s as an anomaly.
(I'm not saying this is a great idea from a ride quality standpoint,
but I am observing that it is common practice, and has been so for a
long time.)

The split rims Mike and I have seen bore what was, in effect, a
"detach on dotted line"-type perforation. The rim in the thread to
which you linked is, not surprisingly, a Mavic. That they have a
little-known table of size and pressure limits comes across to me as
an admission of substandard physical integrity, like their little-
known spoke tension table. I don't think we have a body of evidence
showing that good rims (which is to say, widely used and proven rims
made by manufacturers other than Mavic) fail this way, regardless of
inflation pressure or tire size.

Chalo

carl...@comcast.net

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Dec 8, 2008, 3:26:50 PM12/8/08
to

Dear Ben,

The original poster's link doesn't really tell us much, so it's hard
to tell if a single skid or many were involved:

"last night, we rode bikes and had tons of fun. but when he was doing
skid, i heard big explosion i've never heard. then, the rim has
bursted."

The skid damage that's visible may be just one of many skid marks.
Like you, I wonder if it was the kind of sideways skid that would put
a side load on the rim, but I don't know whether the side loads could
be significant--my guess is that the wheel would taco long before any
load would split a rim, but that's just a guess.

We do know that the rim has been in use for about two weeks:

"Inside of rim has collapsed and tube was bursted. but tire has not
bursted. rim was just only two weeks used. it's almost new."

http://ganrin.blogspot.com/2008/11/its-not-mine-but.html

That's the kind of early catastrophic failure for a new rim in the
thread that I mentioned elsewhere in this thread:
http://groups.google.com/group/rec.bicycles.tech/msg/17ce37398fc401ff

The same early failure is expected with normal tires and pressures
with a severe manufacturing defect, the kind of unintended grooving of
the rim that Mike and Chalo suspect. It doesn't take very many stress
cycles to split defective rims.

As for the heat from skidding, yes, rubber heats up when it skids. But
there's not much temperature rise--water doesn't boil off a fixie tire
that's skidded, in contrast to Jobst's rims on descents.

Nor is there much rubber involved. The pressure in a tire with 80+
inches of tread isn't going to rise significantly from only two
seconds of fixie skidding on a roughly 1-square-inch contact patch,
about half an inch by two inches. It's just not the kind of prolonged
descent braking against metal rims that causes significant heat build
up and noticeably higher tire pressures.

Slam a two-inch wide belt sander across an inflated 700c tire for two
seconds to mimic a fixie skid tearing rubber off the tire. The tire
pressure won't rise significantly. There's too much air and rubber
involved.

Cheers,

Carl Fogel

Tim McNamara

unread,
Dec 8, 2008, 6:45:04 PM12/8/08
to
In article <L7OdnfeK4oCqiaDU...@posted.plusnet>,
"Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:

> "Andre Jute" <fiul...@yahoo.com> wrote in message
> news:85c01988-568c-4d1d...@k24g2000pri.googlegroups.com
> ...
> >On Dec 8, 11:53 am, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> >> "Andre Jute" <fiult...@yahoo.com> wrote in message
> >>
> >> news:ca6a4093-638e-4afa...@t39g2000prh.googlegroups.
> >> com...
> >>
> >> >(Nitrogen doesn't expand with heat and thereby interfere with the
> >> >handling.)
> >>
> >> Maybe a study of the ideal gas laws would help.
> >
> >It surely would. And when you finish your study of ideal gas laws,
> >Clive, you should go on to study nitrogen in particular, when you
> >will find that nitrogen has a more consistent rate of expansion and
> >contraction than air, normally shorthanded by racing mechanics as
> >"doesn't expand like air".

There goes Jute again. Dodge, weave, dodge, weave. Makes an incorrect
statement and blames it on the other person. LOL! His next alias
should be "john jameson."

> What would explain that difference?
>
> >Stop nitpicking, Clive.
>
> You complain when people use words you don't like, I complain when
> people abuse simple science.

And rightfully so

Michael Press

unread,
Dec 8, 2008, 6:47:49 PM12/8/08
to
In article
<f36c953c-8262-43d0...@k19g2000yqg.googlegroups.com>,
"b...@mambo.ucolick.org" <bjwe...@gmail.com> wrote:

> And just because everybody on rbr
> is obsessed with spoke tension and cracks at
> the nipples does

Good one.

--
Michael Press

Tim McNamara

unread,
Dec 8, 2008, 6:49:02 PM12/8/08
to
In article
<5900f0ee-3471-45c0...@z1g2000yqn.googlegroups.com>,
"b...@mambo.ucolick.org" <bjwe...@gmail.com> wrote:

It's hard to judge from the very low quality photos, but the metal of
the rim bed looked awfully thin. The rim section is so large, however,
that this could be an optical illusion. I also note that the failure
happened at the valve stem hole, possibly the weakest point of the rim
the direction of concern.

Tim McNamara

unread,
Dec 8, 2008, 6:50:25 PM12/8/08
to
In article
<d594b3ea-f471-4748...@l16g2000yqo.googlegroups.com>,
Chalo <chalo....@gmail.com> wrote:

> On Dec 7, 10:26 pm, "Mike Jacoubowsky" <mik...@ix.netcom.com> wrote:
> > <carlfo...@comcast.net> wrote in message
> >
> > news:iltoj4dtlq95iit6g...@4ax.com...
> >
> >
> >
> > > On Sun, 7 Dec 2008 16:38:21 -0800 (PST), Chocobot
> > > <chrisall...@gmail.com> wrote:
> >
> > >>http://ganrin.blogspot.com/2008/11/its-not-mine-but.html
> >
> > >>That is the story.  Does this seem right?
> >
> > >> - chris
> >
> > > Dear Chris,
> >

> > > What was the tire width and inflation?
> >

> > > Cheers,
> >
> > > Carl Fogel


> >
> > You're on the right path, but it probably still needed a bit of
> > help to split like that, probably caused by an issue with the die
> > such that the rim was scored (a groove cut into it lengthwise) as
> > it was extruded. I've see it before.
>

> When I was in the mechanic business, there was a run of hard anodized
> 26" Ritchey Vantage Comps that had just such a problem-- a groove
> running down the inside rim wall, so distinct and centered that it
> looked intentional. I saw a couple of those things crack and split
> along the groove, though nothing that spread wide open like the H+Son
> rim.

If the rim tore and punctured the tube, would the release of air into
the chamber of the rim add to the damage?

Michael Press

unread,
Dec 8, 2008, 6:56:48 PM12/8/08
to
In article
<85c01988-568c-4d1d...@k24g2000pri.googlegroups.com>,
Andre Jute <fiul...@yahoo.com> wrote:

> On Dec 8, 11:53 am, "Clive George" <cl...@xxxx-x.fsnet.co.uk> wrote:
> > "Andre Jute" <fiult...@yahoo.com> wrote in message
> >
> > news:ca6a4093-638e-4afa...@t39g2000prh.googlegroups.com...
> >
> > >
> >

> > Maybe a study of the ideal gas laws would help.
>
> It surely would. And when you finish your study of ideal gas laws,
> Clive, you should go on to study nitrogen in particular, when you will
> find that nitrogen has a more consistent rate of expansion and
> contraction than air, normally shorthanded by racing mechanics as
> "doesn't expand like air".

When you said "Nitrogen doesn't expand with heat"
you made yourself perfectly clear. You do not know
whereof you speak.

--
Michael Press

Mike Jacoubowsky

unread,
Dec 8, 2008, 6:57:45 PM12/8/08
to
> I don't think we have a body of evidence
> showing that good rims (which is to say, widely used and proven rims
> made by manufacturers other than Mavic) fail this way, regardless of
> inflation pressure or tire size.
>
> Chalo

We have seen sidewalls blown apart due to too-wide a tire at too-high
air pressure. Usually not split down the middle though. It does happen.

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA


Michael Press

unread,
Dec 8, 2008, 7:02:35 PM12/8/08
to
In article <ghiffe$lmm$1...@aioe.org>,
"Andrew Lee" <whatsu...@hotmail.com> wrote:

> Andrew Lee wrote:


> > Chocobot <chris...@gmail.com> wrote:
> >> http://ganrin.blogspot.com/2008/11/its-not-mine-but.html
> >>
> >> That is the story. Does this seem right?
> >

> > I clicked on the second photo and found a link to a larger size:
> >
> > http://www.flickr.com/photos/ganring/3055814948/sizes/l/
> >
> > The inner rim wall is very thin looking. Just eyeball estimating, it looks less than 1/2 or even 1/3 mm to me.
>
> Found a better photo:
>
> http://www.flickr.com/photos/ganring/3054982423/sizes/o/in/set-72157609868064447/

A tenth of a billion bits and fewer than a tenth are in focus.
The floor appears to be made out of foil.
A perfect engineering solution to minimize weight.

> The ruptured section looks about half the thickness of the same location on some lightweight Velocity Aerohead rims that I have on hand.

--
Michael Press

_

unread,
Dec 8, 2008, 7:09:23 PM12/8/08
to
On Mon, 08 Dec 2008 17:45:04 -0600, Tim McNamara wrote:


>>>>
>>>> >(Nitrogen doesn't expand with heat and thereby interfere with the
>>>> >handling.)
>>>>
>>>> Maybe a study of the ideal gas laws would help.
>>>
>>>It surely would. And when you finish your study of ideal gas laws,
>>>Clive, you should go on to study nitrogen in particular, when you
>>>will find that nitrogen has a more consistent rate of expansion and
>>>contraction than air, normally shorthanded by racing mechanics as
>>>"doesn't expand like air".
>
> There goes Jute again. Dodge, weave, dodge, weave. Makes an incorrect
> statement and blames it on the other person. LOL! His next alias
> should be "john jameson."
>

A goal-post move worthy of jim beam - "doesn't expand with heat" becomes
"somebody else says it doesn't expand like air".

Aside from that obvious error, whether there is and if any how much
difference between a 100% N2 gas and a 78% N2 gas, and whether any such
difference is at all a factor in the original question...

Andre Jute

unread,
Dec 8, 2008, 7:23:01 PM12/8/08
to
And here we have the little fellow-travelling bullies piling in, a
right litlle RBT gangbang:

On Dec 8, 11:56 pm, Michael Press <rub...@pacbell.net> wrote:
> In article
> <85c01988-568c-4d1d-8ef4-e39913202...@k24g2000pri.googlegroups.com>,

My original made it quite clear that a comparison was intended, and
that the comparison was with free air. It was hacked about by the
school bully Clive George in order to "prove" I made a mistake. Now
you're doing the same hack-job either out of ignorance or stupidity. I
leave it to your to find the original.

Unsigned out of contempt

jobst....@stanfordalumni.org

unread,
Dec 8, 2008, 7:25:17 PM12/8/08
to
Tim McNamara wrote:

http://ganrin.blogspot.com/2008/11/its-not-mine-but.html

>>>>> That is the story. ?Does this seem right?

>>>> What was the tire width and inflation?

>>> You're on the right path, but it probably still needed a bit of


>>> help to split like that, probably caused by an issue with the die
>>> such that the rim was scored (a groove cut into it lengthwise) as
>>> it was extruded. I've see it before.

>> When I was in the mechanic business, there was a run of hard
>> anodized 26" Ritchey Vantage Comps that had just such a problem-- a
>> groove running down the inside rim wall, so distinct and centered
>> that it looked intentional. I saw a couple of those things crack
>> and split along the groove, though nothing that spread wide open
>> like the H+Son rim.

> If the rim tore and punctured the tube, would the release of air
> into the chamber of the rim add to the damage?

It didn't. As is apparent from the picture, the tube burst with the
typical long clean slash of an inflated tube exposed outside the tire
casing, classic for a tire blow-off, regardless of blow-off cause.

Jobst Brandt

_

unread,
Dec 8, 2008, 7:29:36 PM12/8/08
to

Found it:

p(t) = p(0) * (1+[g*t])

where

p(o) = pressure at starting temp
p(t) = pressure at ending temp
g = 1/273.15 for ideal gas

turning g into a decimal number we get

366.099andabunchofextradigits *10^-5 for an ideal gas

and measured values for some other gasses are

Argon 368
Helium 366
Krypton 369
Neon 366
Xenon 372
CO 367
O(2) 367
N(2) 367
Air 367
NO 368
H(2) 366
CO2 373
Ammonia 377
Ethane 375
Azetylene 373
Chlorine 383
Chlorhydrogen 372
Methane 368
Sulfur Dioxide 385

Hey lookie lookie - no difference between air and nitrogen.

Whoodah thunkit? Well, surely not the experts that Andrew McCoy listens
to...

Andre Jute

unread,
Dec 8, 2008, 7:37:01 PM12/8/08
to
On Dec 9, 12:09 am, _ <jtayNOSPAM...@hfDONTSENDMESPAMx.andara.com>
wrote:

Gee, Mr NoName, now we have Timmie McNamara, who didn't read my
original, commenting on remarks by the school bully Clive George that
appear to stand up only because Georged hacked my text about. And you
confirm the remarks by the public idiot McNamara, presumably without
reading my original either.

You guys are like the pale shadow of a child resulting from the
travelling salesman sleeping on the other side of the sheet from the
farmer's daughter. No wonder you're ashamed of your name,

Andre Jute
Zero tolerance for trash

jobst....@stanfordalumni.org

unread,
Dec 8, 2008, 7:37:23 PM12/8/08
to
Mike Jacoubowsky <Mi...@chainreaction.com> wrote:

>> I don't think we have a body of evidence showing that good rims
>> (which is to say, widely used and proven rims made by manufacturers
>> other than Mavic) fail this way, regardless of inflation pressure
>> or tire size.

> We have seen sidewalls blown apart due to too-wide a tire at


> too-high air pressure. Usually not split down the middle though.
> It does happen.

Hoop stress at any cross section is proportional to tire cross section
diameter for a given pressure and lateral bead force depends on the
angle at which the tire casing departs from the rim. I think these
considerations should be apparent. Hoop stress is easy to visualize
because it arises from inflation pressure times the inside cross
section diameter of the tire casing.

Jobst Brandt

Andre Jute

unread,
Dec 8, 2008, 7:44:38 PM12/8/08
to
On Dec 9, 12:29 am, _ <jtayNOSPAM...@hfDONTSENDMESPAMx.andara.com>
wrote:

A set of data tha makes a different comparison to the one I made. I
compared free, atmospheric air to nitrogen, you are comparing dry air
to nitrogen. Of course your measurement by such trickery proves
something different. You're another idiot, No-Name. The only
alternative is that you're a liar.

> Whoodah thunkit?  

No one who knew what I was talking about.

>Well, surely not the experts that Andrew McCoy listens
> to...

Nah. Those practical men would never be so dumb as to drag the wrong,
artificially dried air into an argument about free air v. nitrogen in
car tires. Furthermore, those decent men wouldn't lie that those are
the only words I spoke, they would give the full context. Thirdly,
those intelligent men, unlike you dumb morons, wouldn't ever dream
that they could get away with such dishonesty. Finally, those
accomplished chaps had their own achievements and therefore no need to
prove what big men they are by tearing down someone else.

Those are really rather heavyweight reasons for listening to them
rather than you.

Unsigned out of contempt

jobst....@stanfordalumni.org

unread,
Dec 8, 2008, 7:50:12 PM12/8/08
to
Jay Taylor wrote:

It gives some to contribute blowing smoke filled with scientifical
sounding verbiage and look smart in front of the masses, hoping not to
be called on it. I don't think these guys are aware of the gass laws:

P*V=N*R*T for all gasses. Pressure times Volume equals (Number of
mols [molecular weight]) times the universal gas constant R times the
absolute Temperature.

http://en.wikipedia.org/wiki/Gas_constant

Jobst Brandt

Andre Jute

unread,
Dec 8, 2008, 7:52:39 PM12/8/08
to
On Dec 9, 12:09 am, _ <jtayNOSPAM...@hfDONTSENDMESPAMx.andara.com>
wrote:

> Aside from that obvious error,

Why don't you point to the obvious error in my own text, rather than
in something hacked out of context?

>whether there is and if any how much
> difference between a 100% N2 gas and a 78% N2 gas, and whether any such
> difference is at all a factor in the original question...

And when you do point to my own text, rather than what the bullyboy
Clive George claims I said, you will find that the matters you raise
are alluded to, and in fact justify my comparison.

Given on the basis that you are intelligent enough and have an
attention span long enough to connect the rear end of a short
paragraph to the front end, which on the evidence of your post is
exceedingly doubtful.

Andre Jute
Zero tolerance for fools

Andre Jute

unread,
Dec 8, 2008, 8:03:16 PM12/8/08
to
On Dec 9, 12:50 am, jobst.bra...@stanfordalumni.org wrote:

> Jay Taylor wrote:
>
> > Aside from that obvious error, whether there is and if any how much
> > difference between a 100% N2 gas and a 78% N2 gas, and whether any
> > such difference is at all a factor in the original question...
>
> It gives some to contribute blowing smoke filled with scientifical
> sounding verbiage and look smart in front of the masses, hoping not to
> be called on it.

Huh? "It give some to contibute" -- what does it give some, Jobst? And
what are they "contributing"?

> I don't think these guys are aware of the gass laws:
>
> P*V=N*R*T for all gasses.  Pressure times Volume equals (Number of
> mols [molecular weight]) times the universal gas constant R times the
> absolute Temperature.

If you knew what this was about, you would say "ideal gas laws". Your
extract from a textbook proves you don't know what this is about.

>  http://en.wikipedia.org/wiki/Gas_constant

There are wretched lies, wicked lies, and wikipedia.

> Jobst Brandt

Have you actually read what I said, Jobst, rather than what Clive
George hacked entirely out of context? No, I thought not. When you
have, come back and apologize.

Andre Jute
There's no fool like a geriatric blusterer joining a gangbang

jobst....@stanfordalumni.org

unread,
Dec 8, 2008, 8:09:30 PM12/8/08
to
Jay Taylor wrote:

It gives some the opportunity to blow smoke filled with scientifical


sounding verbiage and look smart in front of the masses, hoping not to

be called on it. I don't think these guys are aware of the gas laws:

P*V=N*R*T for all gasses. Pressure times Volume equals (Number of
mols [molecular weight]) times the universal gas constant R times the
absolute Temperature.

http://en.wikipedia.org/wiki/Gas_constant

Jobst Brandt

_

unread,
Dec 8, 2008, 8:10:45 PM12/8/08
to
On Mon, 8 Dec 2008 16:52:39 -0800 (PST), Andre Jute wrote:

> Andre Jute
> Zero tolerance for fools

You mis-spelt "facts".

Frank Krygowski

unread,
Dec 8, 2008, 8:15:28 PM12/8/08
to
On Dec 8, 7:44 pm, Andre Jute <fiult...@yahoo.com> wrote:
> On Dec 9, 12:29 am, _ <jtayNOSPAM...@hfDONTSENDMESPAMx.andara.com>
> wrote:
> ...

>
> > Argon 368
> > Helium 366
> > Krypton 369
> > Neon 366
> > Xenon 372
> > CO 367
> > O(2) 367
> > N(2) 367
> > Air 367
> > NO 368
> > H(2) 366
> > CO2 373
> > Ammonia 377
> > Ethane 375
> > Azetylene 373
> > Chlorine 383
> > Chlorhydrogen 372
> > Methane 368
> > Sulfur Dioxide 385
>
> > Hey lookie lookie - no difference between air and nitrogen.  
>
> A set of data tha makes a different comparison to the one I made. I
> compared free, atmospheric air to nitrogen, you are comparing dry air
> to nitrogen.

Well, do give us the value for air at 50% relative humidity, then. Or
if you prefer, 90% relative humidity.

But please be concise. I suspect I'm not the only one that reads less
than one screen-worth of your posts.

- Frank Krygowski

Andre Jute

unread,
Dec 8, 2008, 8:17:42 PM12/8/08
to
This is for the record, so that when Jobst has to retract this, I can
say I predicted it.

On Dec 9, 12:50 am, jobst.bra...@stanfordalumni.org wrote:

> It gives some to contribute blowing smoke filled with scientifical
> sounding verbiage and look smart in front of the masses, hoping not to
> be called on it.  I don't think these guys are aware of the gass laws:
>
> P*V=N*R*T for all gasses.  Pressure times Volume equals (Number of
> mols [molecular weight]) times the universal gas constant R times the
> absolute Temperature.
>
>  http://en.wikipedia.org/wiki/Gas_constant
>
> Jobst Brandt

In the context of the particular argument on which you're commenting,
Jobst, what you're saying here is that injected in a hard-used
automobile tyre free air and nitrogen will expand at the same rate
regardless of the amount of water vapour in the free air.

I said the opposite, that experience shows free air will expand more
than the nitrogen, and am abused for it. You rather inchoately abused
me for it above.

You can of course change your mind and agree with me at any time. I
always welcome conversions to righteousnous and truthfulness.

Andre Jute
Experience counts, every time

Andre Jute

unread,
Dec 8, 2008, 8:24:11 PM12/8/08
to

Eh? You want the facts, you look them up, Franki. I already provided a
paragraph of fact and opinion, which no one in this thread appears to
have read, including you. Why should I help dig a bunch of wannabe
gangbangers out of the hole one of their own, Clive George, dug for
them?

> But please be concise.  I suspect I'm not the only one that reads less
> than one screen-worth of your posts.

That's all right, Franki. I expect you need the time to shave your
legs. I don't really write for people who shave their legs.

> - Frank Krygowski

Andre Jute
Zero tolerance for legshavers

Andre Jute

unread,
Dec 8, 2008, 8:28:19 PM12/8/08
to
On Dec 9, 1:10 am, _ <jtayNOSPAM...@hfDONTSENDMESPAMx.andara.com>
wrote:

Uh-huh? You abused me on a false set of facts, and when faced with it
you don't have the grace to apologize, you merely abuse me some more.
You're scum, Taylor.

For the record, this is where I exposed this clown, whose name is
apparently Taylor, as a fellow-travelling bullyboy *who doesn't even
know what the argy-bargy is about but runs in all the same to get in
his kicks*, in short, scum:

********

Andre Jute
Zero tolerance for fools
*********

jim beam

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Dec 8, 2008, 11:38:33 PM12/8/08
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On Mon, 08 Dec 2008 10:18:16 +0000, jobst.brandt wrote:

> Ben Weiner wrote:
>
>>> When a rider deliberately skids a fixie's rear tire, he's shredding a
>>> small section of rubber tire against the pavement.
>
>>> It's a short skid, with very little heat transferred through the small
>>> section of rubber tire to the air inside the tire.
>
>>> The fixie comes to a stop in a moment or two, and then has to be sped
>>> up again--even the small section of heated-up tire cools off again.
>>> Despite the dramatics, there's very little heat and plenty of cooling
>>> off time.
>
>>> Think of someone waving a heat gun at at tire for about two seconds,
>>> which is about all the skidding that a fixie is going to generate. The
>>> tire isn't likely to see much pressure rise, much less tear a rim
>>> apart.
>
>> Skidding friction is much more efficient at transferring heat to the
>> tire than a heat gun would be. I don't think that's a useful analogy.
>

> Whereas the rim is in contact with the thin rubber wall of the inner
> tube, tire tread is relatively thick and the tread even thicker.
> Skidding may tear some rubber from the tread but it does not heat it
> significantly. Not enough to feel by hand. It isn't like white smoke
> from a burnout on a motor vehicle and even that doesn't heat the air in
> the tire much.


>
>> The skidding stop dissipates the kinetic energy of the rider in a small
>> patch of rubber (some of it goes into the skid patch of asphalt). The
>> KE is easily estimated, for 80 kg of rider plus bike going 15 mph=6.7
>> m/s, the KE is 1800 Joules. That's not much unless it all has to be
>> taken up in a small patch. The heat capacity of an entire tire+tube
>> would take that up easily and only rise a couple of degrees, but if it
>> all gets dumped into a few grams of rubber at the contact patch, that
>> is another story. (Heat capacity of rubber is about 2.0 kJ/kg/degree
>> Kelvin; I think this number is for natural rubber, and butyl may be
>> less.)
>

> Skidding when crossed-up is not a useful means of slowing down, it being
> done with the rear wheel that is partially unloaded by the method, the
> bicycle still being headed mainly forward.


>
>>> In contrast, prolonged downhill rim braking presses rubber pads
>>> against the metal for much longer periods, heating the metal rim and
>>> the air inside the tire so much that the tire blows off the rim.
>
>>> (Jobst was doing some testing that may cause doubt about even that--he
>>> never got a tire to come off the rim with pressure alone, suggesting
>>> that the heated rim flange and tire bead surface may be the real
>>> problem, becoming very slippery.)
>
>> Rim braking tests do not carry over well to this situation: 1. Extended
>> rim braking dumps the heat uniformly into the entire circumference of
>> the rim rather than a small skid patch.
>
>> 2. Rim braking puts the heat into an aluminum rim which has decent heat
>> capacity and radiates heat well. The skid issue is not extended slow
>> heating.
>

> Well rims get over water boiling temperatures rapidly as I have tested
> in alpine descents. You cannot touch such a rim without burning the
> skin of a finger.


>
>>> I don't recall any posts in which the slow heating did anything but
>>> blow the rim off--the tire creeps off long before the rim fails.
>
>>> An over-inflated, oversize tire can cause such rim failures, but we
>>> don't know what the tire size was.
>
>>> As Mike and Chalo have pointed out, ordinary hoop stress is enough to
>>> split defective rims. If the original poster has the rim examined and
>>> finds a nasty groove running down the inside of the rim, oops!
>
>> But why did this rim split at this particular time, at this particular
>> place (right at the contact patch)? I certainly don't think that I've
>> proved it was heat from skidding. I do think that heat from skidding
>> is real - go out and do a rubber-burning skid, and I'm sure the tire
>> will be warm at the patch. Even a pencil eraser gets warm from
>> rubbing.
>

> This looks much more like a mechanical failure at constant pressure. The
> side force of a broadside skid must be supported by the rim and that is
> what I believe is what we see here. Not heating and over pressure.
>

red herring. look at the pictures again. thin web between the hook
beads. excessively large spoke holes. excess tire pressure. easy.



Mike McGuire

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Dec 9, 2008, 12:33:00 AM12/9/08
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Andre Jute wrote:
> ...

> I'll throw this into the pot: An automobile tyre run hard on a skidpad
> despite the cooling effect of the liquid on the pad still warms up
> enough to make the use of nitrogen in the tyres a useful option.


> (Nitrogen doesn't expand with heat and thereby interfere with the

> handling.) But the bicycle tyre skidding isn't analogous: too short a
> period and probably other factors too that I can work out if I
> unsheath my slide rule. To name just one hypothesis to be confirmed on
> calculation: in relation to the weight it carries, it appears to me
> that there might be more air mass in a bicycle tyre than in a car
> tyre.
>
,,,>
> Andre Jute

What's been left unsaid here is that if there is sufficient liquid water
in a tire, the equation of state will be the ideal gas law _plus_ the
vapor pressure law for water at least until it's all vaporized. Putting
some numbers together, say a 25 liter volume for a tire, at 100C, and
of course 1 atm partial pressure of water vapor, you would have about 15
grams of water vaporized in that volume if there was sufficient liquid
water to start. So this 25 liter tire with say 2 atm in it a 20C plus 15
grams of water, on reaching 100C would have 2.5 atm due to ideal gas law
plus an additional 1 atm of water vapor. That 15 grams might be a
credible amount of water to have accumulated into a tire, filling
indiscriminately from various sources. But I don't think just deflating
a tire and refilling with dry gas would get the liquid water out. I
would be surprised if the temperature rise on a skid pad was great
enough to have a noticeable effect.

Mike McGuire

_

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Dec 9, 2008, 4:27:50 AM12/9/08
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Goodness - you must have enormous bicycle tyres - 25 litres!

Or are you subtly making the point that Mccoy is wrong, both in claiming
that "Nitrogen doesn't expand with heat... (a direct quote) and then later
admitting that well, yes it does, just *differently* from air and that
difference is enough to affect bicycle handling?

What do you think the difference in pressure would be for a typical bicycle
tyre inflated with typically humid air to normal initial pressures, which
then was ridden down a reasonably-sized hill and then heated by
rim-braking, and how much do you think that difference - if any - would
affect handling?

(The above question is esentially equivalent to "How many Macoys can dodge,
weave, and wave their hands on the head of a pin?")

Ben C

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Dec 9, 2008, 5:27:33 AM12/9/08
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On 2008-12-09, jobst....@stanfordalumni.org <jobst....@stanfordalumni.org> wrote:
> Mike Jacoubowsky <Mi...@chainreaction.com> wrote:
>
>>> I don't think we have a body of evidence showing that good rims
>>> (which is to say, widely used and proven rims made by manufacturers
>>> other than Mavic) fail this way, regardless of inflation pressure
>>> or tire size.
>
>> We have seen sidewalls blown apart due to too-wide a tire at
>> too-high air pressure. Usually not split down the middle though.
>> It does happen.
>
> Hoop stress at any cross section is proportional to tire cross section
> diameter for a given pressure and lateral bead force depends on the
> angle at which the tire casing departs from the rim. I think these
> considerations should be apparent.

It's not apparent to me why the angle at which the tyre casing departs
from the rim makes any difference.

Surely the rim has to oppose exactly the same force to keep everything
in equilibrium whatever that angle is?

Andre Jute

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Dec 9, 2008, 5:43:26 AM12/9/08
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On Dec 9, 5:33 am, Mike McGuire <mm...@sonic.net> wrote:
> Andre Jute wrote:
> > ...
> > I'll throw this into the pot: An automobile tyre run hard on a skidpad
> > despite the cooling effect of the liquid on the pad still warms up
> > enough to make the use of nitrogen in the tyres a useful option.
> > (Nitrogen doesn't expand with heat and thereby interfere with the
> > handling.) But the bicycle tyre skidding isn't analogous: too short a
> > period and probably other factors too that I can work out if I
> > unsheath my slide rule. To name just one hypothesis to be confirmed on
> > calculation: in relation to the weight it carries, it appears to me
> > that there might be more air mass in a bicycle tyre than in a car
> > tyre.
>
> ,,,>
> > Andre Jute

At last, someone actually responding to the point I made and not to
that idiot Clive George's distortion of it. Good on you, Mike.

> What's been left unsaid

Well, I'm not standing in a lecture room before a bunch of freshers,
I'm writing to my hobby group and making an aside. When I dot all the
eyes and cross all the tees, Smoothlegs Krygo whines that my posts are
too long, when I don't, the Georgeite wing of the same bunch of
bullyboys screech that I'm ignorant. Water and its vapour is pretty
obvious when you speak of air in car tyres; there isn't a racing
mechanic in the world to whom I would need to spell out the
conditions. But a bunch of guys, not including you, who brag about
their scientific approach, but offer no science among the abuse, have
now wasted huge bandwidth whining about it.

>here is that if there is sufficient liquid water
> in a tire, the equation of state will be the ideal gas law _plus_ the
> vapor pressure law for water at least until it's all vaporized. Putting
> some numbers together,  say a 25 liter volume for a tire, at 100C, and
> of course 1 atm partial pressure of water vapor, you would have about 15
> grams of water vaporized in that volume if there was sufficient liquid
> water to start. So this 25 liter tire with say 2 atm in it a 20C plus 15
> grams of water, on reaching 100C would have 2.5 atm due to ideal gas law
>   plus an additional 1 atm of water vapor. That 15 grams might be a
> credible amount of water to have accumulated into a tire, filling
> indiscriminately from various sources. But I don't think just deflating
> a tire and refilling with dry gas would get the liquid water out. I
> would be surprised if the temperature rise on a skid pad was great
> enough to have a noticeable effect.
>
> Mike McGuire

The effect of changing from free air to nitro is on handling where
very small changes make a big perceptible difference when the margin
of control is approached. I'm sure you know that automobile tyre
rubber does not behave in a linear manner, and the nearer the margin,
the less linear.

If you're right, NASCAR will probably pay you for your insight, and
other racing formulae as well. And you can set up in business advising
huge fleet operators that the savings they have been seeing "going
nitro" are all vapourware (pun <tm>).

Thanks for injecting some sanity into another thread made wretched by
the blustering myopia of the usual suspects.

Andre Jute
In the land of the blind, one-eye is king -- (did Dean Swift say that?)

Andre Jute

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Dec 9, 2008, 6:06:37 AM12/9/08
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On Dec 9, 9:27 am, _ <jtayNOSPAM...@hfDONTSENDMESPAMx.andara.com>
wrote: