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

On Dec 7, 6:30*pm, Dan O wrote:
On Dec 7, 4:38 pm, Chocobot wrote:

http://ganrin.blogspot.com/2008/11/i...-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?

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...7609868064447/
before they take the tire off.

Ben

Andrew Lee wrote:

Chocobot wrote:

http://ganrin.blogspot.com/2008/11/i...-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...14948/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...7609868064447/

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

On Sun, 7 Dec 2008 22:26:36 -0800 (PST), "
wrote:

On Dec 7, 6:30*pm, Dan O wrote:
On Dec 7, 4:38 pm, Chocobot wrote:

http://ganrin.blogspot.com/2008/11/i...-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?

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...7609868064447/
before they take the tire off.

Ben

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

On Dec 7, 11:53*pm, 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

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

On Dec 8, 8:58*am, "
wrote:
On Dec 7, 11:53*pm, 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. *

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.

"Andre Jute" wrote in message
...

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

Maybe a study of the ideal gas laws would help.

On Dec 8, 11:53*am, "Clive George" wrote:
"Andre Jute" wrote in message

...

(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".

Stop nitpicking, Clive.

Andre Jute
High on nitrogen

"Andre Jute" wrote in message
...
On Dec 8, 11:53 am, "Clive George" wrote:
"Andre Jute" wrote in message

...

(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, I complain when people
abuse simple science.

On Dec 8, 12:34*pm, "Clive George" wrote:
"Andre Jute" wrote in message

...

On Dec 8, 11:53 am, "Clive George" wrote:
"Andre Jute" wrote in message

....

(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