Not goatheads

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Hmmm . . . it may be a bad idea to ooze downhill dragging the rear
brake just to chat with a visiting friend.

Jobst has mentioned blowing a tire off surprisingly quickly that way:

"My latest experience with that was descending Grosse Scheidegg to
Grindelwald with some of the most famous mountains and glaciers
arrayed in front of me. My friend stopped to take pictures so I
waited for him riding the rear brake over the lever hood at less than
10mph when BAM! the tire that I had previously ridden over steep
curving descents blew off."

http://groups.google.com/group/rec.bicycles.tech/msg/840cb236d153481e

And I run stretchy Kevlar bead tires, while Jobst probably uses tires
with tight steel beads.

Plus I run 120 psi, while Jobst sensibly runs lower pressures--and
weighs less than I do.

So let go of the brake, tuck in, and start coasting . . .

What's that odd thump-thump-thump?

Better slow down and look at my tire--

Better not use the rear brake to slow down, idiot!

Look, the rear tire's just about to come off the rim there, right by
the valve stem!

If I can get the cap off the Presta valve in time--

Bang-splat!

http://server5.theimagehosting.com/image.php?img=269bsplat.jpg
or http://tinyurl.com/yy7hgm

My friend took the picture of what happens when a Slime tube goes bang
just as you're reaching for the Presta valve.

And here's what the Slime tube and Kevlar-bead tire look like:

http://server5.theimagehosting.com/image.php?img=279asplat.jpg
or http://tinyurl.com/yxewwh

The black blob holding the Kevlar bead away from the ripped tire is
just a handy cyclocomputer, while a spoke helps the split Slime tube
to pose à la Goya's Maja.

I was surprised that the bead ripped out of the tire. A moment before
the bang-splat, he tire edge was clearly visible and undamaged as it
crept up out of the rim well toward freedom.

But memories of a few similar disasters years ago on wire-bead 27-inch
tires remind me that the tire usually rips away from the bead when it
creeps comes off rim, though I'm damned if I know why.

I don't count this as a goathead flat.

On an unrelated matter, these aren't goatheads, either:

http://server5.theimagehosting.com/image.php?img=270btumbleweeds.jpg
or http://tinyurl.com/trz6g

There were so many tumbleweeds blowing briskly across the highway that
I had time to stop and take a picture.

They weren't bad tumbleweeds, since they were rolling on the ground
instead of kicking up at head-height and flying across the road.

But they're still a good example of local variation. I gather that
some posters will use snow to make snowmen at Christmas instead of
spray-painting stacked tumbleweeds white.

Cheers,

Carl Fogel

Tumbleweed AKA Russian Thistle is not native to North America. It was
introduced to the plains of Western Canada in the late 1800's by
immigrant farmers from the Ukraine. The seeds were mixed in with the
flax seed that they planted.

"Tumbleweeds were first reported in the United States around 1877 in Bon
Homme County, South Dakota, apparently transported in flax seed imported
by Ukrainian farmers. Within two decades it had tumbled into a dozen
states, and by 1900, it had reached the Pacific Coast."

http://www.desertusa.com/mag01/may/papr/tweed.html

Goatheads are also not native to North America. They came from Europe. A
friend of mine recently saw them growing in Beijing, China.

http://www.goatheads.com/

Chas.

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Hmmm . . . it may be a bad idea to ooze downhill dragging the rear
brake just to chat with a visiting friend.

Jobst has mentioned blowing a tire off surprisingly quickly that way:

"My latest experience with that was descending Grosse Scheidegg to
Grindelwald with some of the most famous mountains and glaciers
arrayed in front of me. My friend stopped to take pictures so I
waited for him riding the rear brake over the lever hood at less than
10mph when BAM! the tire that I had previously ridden over steep
curving descents blew off."

http://groups.google.com/group/rec.bicycles.tech/msg/840cb236d153481e

And I run stretchy Kevlar bead tires, while Jobst probably uses tires
with tight steel beads.

Plus I run 120 psi, while Jobst sensibly runs lower pressures--and
weighs less than I do.

So let go of the brake, tuck in, and start coasting . . .

What's that odd thump-thump-thump?

Better slow down and look at my tire--

Better not use the rear brake to slow down, idiot!

Look, the rear tire's just about to come off the rim there, right by
the valve stem!

If I can get the cap off the Presta valve in time--

Bang-splat!

http://server5.theimagehosting.com/image.php?img=269bsplat.jpg
or http://tinyurl.com/yy7hgm

My friend took the picture of what happens when a Slime tube goes bang
just as you're reaching for the Presta valve.

And here's what the Slime tube and Kevlar-bead tire look like:

http://server5.theimagehosting.com/image.php?img=279asplat.jpg
or http://tinyurl.com/yxewwh

The black blob holding the Kevlar bead away from the ripped tire is
just a handy cyclocomputer, while a spoke helps the split Slime tube
to pose à la Goya's Maja.

I was surprised that the bead ripped out of the tire. A moment before
the bang-splat, he tire edge was clearly visible and undamaged as it
crept up out of the rim well toward freedom.

But memories of a few similar disasters years ago on wire-bead 27-inch
tires remind me that the tire usually rips away from the bead when it
creeps comes off rim, though I'm damned if I know why.

I don't count this as a goathead flat.

On an unrelated matter, these aren't goatheads, either:

http://server5.theimagehosting.com/image.php?img=270btumbleweeds.jpg
or http://tinyurl.com/trz6g

There were so many tumbleweeds blowing briskly across the highway that
I had time to stop and take a picture.

They weren't bad tumbleweeds, since they were rolling on the ground
instead of kicking up at head-height and flying across the road.

But they're still a good example of local variation. I gather that
some posters will use snow to make snowmen at Christmas instead of
spray-painting stacked tumbleweeds white.

Cheers,

Carl Fogel

Very interesting.
Sounds like a good use for disc brakes.
Maybe both kinds of brakes just to be sure.

Quoted message said:

Hmmm . . . it may be a bad idea to ooze downhill dragging the rear
brake just to chat with a visiting friend.

To make your story short, if I got it right, your tyre slipped around
the rim dragging the tube along and made it bulge and suffer at the
valve.
Funny enough, I was recently asking around if anyone on
it.sport.ciclismo had ever noticed such a slippage (with or without
dragging of the tube) and all those who responded did so in the
negative.

Cheers, dear Carl.

Sergio
Pisa

Quoted message said:

Quoted message said:

Tumbleweed AKA Russian Thistle is not native to North America. It was
introduced to the plains of Western Canada in the late 1800's by
immigrant farmers from the Ukraine. The seeds were mixed in with the
flax seed that they planted.

Around here, Russian Thistle is a tall stalk with a purple thistle flower on
the top. Not at all like a tumble weed's bushy shape.

Pat in TX

Pat in TX said:

Quoted message said:

Tumbleweed AKA Russian Thistle is not native to North America. It was
introduced to the plains of Western Canada in the late 1800's by
immigrant farmers from the Ukraine. The seeds were mixed in with the
flax seed that they planted.

Around here, Russian Thistle is a tall stalk with a purple thistle flower on
the top. Not at all like a tumble weed's bushy shape.

Pat in TX

You're talking about the musk, milk, or bull thistle, not a Russian thistle.

Robin Hubert

Quoted message said:

Look, the rear tire's just about to come off the rim there, right by
the valve stem!

If I can get the cap off the Presta valve in time--

Bang-splat!

Interesting. Can you look at the rim closely to see if there's any
deformation where the bead crept out of the rim? I'm still curious about
Peter Cole's theory espoused in the old crow-eating thread from a few
years back [1].

Quoted message said:

And here's what the Slime tube and Kevlar-bead tire look like:

http://server5.theimagehosting.com/image.php?img=279asplat.jpg
or http://tinyurl.com/yxewwh

The black blob holding the Kevlar bead away from the ripped tire is
just a handy cyclocomputer, while a spoke helps the split Slime tube
to pose à la Goya's Maja.

I was surprised that the bead ripped out of the tire. A moment before
the bang-splat, he tire edge was clearly visible and undamaged as it
crept up out of the rim well toward freedom.

But memories of a few similar disasters years ago on wire-bead 27-inch
tires remind me that the tire usually rips away from the bead when it
creeps comes off rim, though I'm damned if I know why.

I've blown off a few tyres, probably through installation error, but
I've never had the bead separate from the rest of the tyre. I can't
remember blowing off any kevlar beaded tyres. Maybe the bead type makes
a difference. I wonder what causes that separation?

[1] http://tinyurl.com/yb4mus (links to Google Groups)

--
Dave
dvt at psu dot edu

"Robin Hubert" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Pat in TX said:

Quoted message said:

Tumbleweed AKA Russian Thistle is not native to North America. It

was

Quoted message said:

Quoted message said:

Quoted message said:

introduced to the plains of Western Canada in the late 1800's by
immigrant farmers from the Ukraine. The seeds were mixed in with

the

Quoted message said:

Quoted message said:

Quoted message said:

flax seed that they planted.

Around here, Russian Thistle is a tall stalk with a purple thistle

flower on

Quoted message said:

Quoted message said:

the top. Not at all like a tumble weed's bushy shape.

Pat in TX

You're talking about the musk, milk, or bull thistle, not a Russian

thistle.

Quoted message said:

Robin Hubert

Artichokes are in the same family as milk thistles.

I'm highly allergic to tumble weed pollen and suffer with hay fever from
July until the first frost.... That's why I hate the stuff. Semi trucks
have aided in spreading the [censored] throughout most of North America.

Bringing this back on topic, I once got a flat in a sewup from running
over a dry tumble weed. They have sharp little spines.

Chas.

Pat in TX said:

Quoted message said:

Tumbleweed AKA Russian Thistle is not native to North America. It was
introduced to the plains of Western Canada in the late 1800's by
immigrant farmers from the Ukraine. The seeds were mixed in with the
flax seed that they planted.

Around here, Russian Thistle is a tall stalk with a purple thistle flower on
the top. Not at all like a tumble weed's bushy shape.

Pat in TX

I have no idea who's correct, but this hyear tumbleweed looks like what
we used to use for Christmas decorations many decades ago and the page
calls it Russian Thistle.

http://www.blueplanetbiomes.org/tumbleweed.htm

Quoted message said:

So let go of the brake, tuck in, and start coasting . . .

What's that odd thump-thump-thump?

Better slow down and look at my tire--

Better not use the rear brake to slow down, idiot!

Look, the rear tire's just about to come off the rim there, right by
the valve stem!

If I can get the cap off the Presta valve in time--

Bang-splat!

http://server5.theimagehosting.com/image.php?img=269bsplat.jpg
or http://tinyurl.com/yy7hgm

My friend took the picture of what happens when a Slime tube goes bang
just as you're reaching for the Presta valve.

Slimed! Hey, at least you were already running aware of the fact that
you were in a risky mode; it could have been much worse had you been
on a long descent riding the brakes, and then decided to uncork and
blast for the last half mile or so. It might have popped at 40mph if
that had been the case.

Quoted message said:

I don't count this as a goathead flat.

On an unrelated matter, these aren't goatheads, either:

http://server5.theimagehosting.com/image.php?img=270btumbleweeds.jpg
or http://tinyurl.com/trz6g

There were so many tumbleweeds blowing briskly across the highway that
I had time to stop and take a picture.

They weren't bad tumbleweeds, since they were rolling on the ground
instead of kicking up at head-height and flying across the road.

These appear to be the spokejam variety instead of the facehugger
variant. It's a good thing that squirrels are arboreal and not found
in the same climes as tumbleweeds, or they'd probably be piloting the
rollers to improve the vegetation's targeting and achieve greater
effect than a squirrel can manage alone.

Quoted message said:

But they're still a good example of local variation. I gather that
some posters will use snow to make snowmen at Christmas instead of
spray-painting stacked tumbleweeds white.

Those of us here in verdant Southeast Texas must make do with stuffing
huge plastic bags full of leaves, and spray-painting *those* white.
It is also permissible to stuff a large clear plastic bag with white
packing peanuts, but those tend to either get stolen or punctured and
strewn about. I suspect that the local opossums think that anything
shaped like a peanut must be edible.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Quoted message said:

Quoted message said:

Hmmm . . . it may be a bad idea to ooze downhill dragging the rear
brake just to chat with a visiting friend.

To make your story short, if I got it right, your tyre slipped around
the rim dragging the tube along and made it bulge and suffer at the
valve.
Funny enough, I was recently asking around if anyone on
it.sport.ciclismo had ever noticed such a slippage (with or without
dragging of the tube) and all those who responded did so in the
negative.

It's also likely that the reason for the location of the failure is
due to the tube's thickness at that point; the tire may not have been
seated as deeply at that location because of the presence of the
valve's flange. This would tend to make the area adjacent to the
valve more favorably arranged for such a failure. At normal riding
pressures, I doubt that the tire could have crept around the rim
enough to make any difference, even had the interface been wet.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Quoted message said:

Quoted message said:

Hmmm . . . it may be a bad idea to ooze downhill dragging the rear
brake just to chat with a visiting friend.

To make your story short, if I got it right, your tyre slipped around
the rim dragging the tube along and made it bulge and suffer at the
valve.
Funny enough, I was recently asking around if anyone on
it.sport.ciclismo had ever noticed such a slippage (with or without
dragging of the tube) and all those who responded did so in the
negative.

Cheers, dear Carl.

Sergio
Pisa

Dear Sergio,

No, my tire didn't move relative to the valve.

A small section of the tire bead a few inches from the valve crept up
out of the rim well, the tube was exposed, and bang!

Probably my rim was heated from my foolish low-speed brake dragging.
The heat reduced the friction between the tire bead and the rim.
Without enough friction, my arguably over-inflated tire with its
stretchy Kevlar bead crept up and over the rim.

You may be thinking of tubular tires, which can creep in another
direction on hot rims, as Jobst has mentioned:

"One of the rituals of tubulars was to turn the front wheel around
after a descent so that the tire would creep back toward normal, the
valve stem leaning strongly from heat creep. As I related, in the
Alps this was not possible because the tire crept so much during a
descent that before expected the stem ripped out of the tube. To
counter that, I put epoxied insulator strips around all my rims."

http://groups.google.com/group/rec.bicycles.tech/msg/0260397e1bdbaa3e

As a sidelight, old-fashioned trials motorcycle tires with inner tubes
run at only 4 to 6 psi had to be anchored to prevent them from sliding
on the rim like tubulars and ripping the inner tube valves out.

The anchors, known as rim locks or security bolts, are padded V-shaped
blocks that are drawn by bolts through the rim and tightened by heavy
nuts. They're easily mistaken for valves:

rim lock
|
__+__
/ | \
//XXXX\\\
//XXXXXX\\\rim
/ \
| |
\_______/
tire

Modern trials machines use sticky tubeless rear tires and no longer
feature the traditional two rim locks, but the front tires with tubes
still have the single front rim lock. Most trials riders have made the
embarrassing mistake of trying to clap an air hose chuck onto a rim
lock.

Cheers,

Carl Fogel

Earl Bollinger said:

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Hmmm . . . it may be a bad idea to ooze downhill dragging the rear
brake just to chat with a visiting friend.

Jobst has mentioned blowing a tire off surprisingly quickly that way:

"My latest experience with that was descending Grosse Scheidegg to
Grindelwald with some of the most famous mountains and glaciers
arrayed in front of me. My friend stopped to take pictures so I
waited for him riding the rear brake over the lever hood at less than
10mph when BAM! the tire that I had previously ridden over steep
curving descents blew off."

http://groups.google.com/group/rec.bicycles.tech/msg/840cb236d153481e

And I run stretchy Kevlar bead tires, while Jobst probably uses tires
with tight steel beads.

Plus I run 120 psi, while Jobst sensibly runs lower pressures--and
weighs less than I do.

So let go of the brake, tuck in, and start coasting . . .

What's that odd thump-thump-thump?

Better slow down and look at my tire--

Better not use the rear brake to slow down, idiot!

Look, the rear tire's just about to come off the rim there, right by
the valve stem!

If I can get the cap off the Presta valve in time--

Bang-splat!

http://server5.theimagehosting.com/image.php?img=269bsplat.jpg
or http://tinyurl.com/yy7hgm

My friend took the picture of what happens when a Slime tube goes bang
just as you're reaching for the Presta valve.

And here's what the Slime tube and Kevlar-bead tire look like:

http://server5.theimagehosting.com/image.php?img=279asplat.jpg
or http://tinyurl.com/yxewwh

The black blob holding the Kevlar bead away from the ripped tire is
just a handy cyclocomputer, while a spoke helps the split Slime tube
to pose à la Goya's Maja.

I was surprised that the bead ripped out of the tire. A moment before
the bang-splat, he tire edge was clearly visible and undamaged as it
crept up out of the rim well toward freedom.

But memories of a few similar disasters years ago on wire-bead 27-inch
tires remind me that the tire usually rips away from the bead when it
creeps comes off rim, though I'm damned if I know why.

I don't count this as a goathead flat.

On an unrelated matter, these aren't goatheads, either:

http://server5.theimagehosting.com/image.php?img=270btumbleweeds.jpg
or http://tinyurl.com/trz6g

There were so many tumbleweeds blowing briskly across the highway that
I had time to stop and take a picture.

They weren't bad tumbleweeds, since they were rolling on the ground
instead of kicking up at head-height and flying across the road.

But they're still a good example of local variation. I gather that
some posters will use snow to make snowmen at Christmas instead of
spray-painting stacked tumbleweeds white.

Cheers,

Carl Fogel

Very interesting.
Sounds like a good use for disc brakes.
Maybe both kinds of brakes just to be sure.

Dear Earl,

Disk brakes that don't heat the rim are often recommended on RBT for
severe downhill riding. Many tandems use a third coaster or disk brake
to solve their considerably worse braking problems.

I was just dim-wittedly dragging my rear brake at about 10 mph because
I was chatting with a friend as we rolled off down a slope that I
normally never touch my brakes on--it's a 65 mph highway and good for
about 35-40 mph, tucked in.

The really embarrassing thing is that I'd read Jobst's post about
blowing a tire off in a similar fashion as he dragged his rear brake
at about 10 mph, so I really should have known better.

But it certainly entertained my friend. He weighs less than I do, was
running 20 psi lower tire pressures, was rolling on less stretchy
steel-bead tires, and was dumping heat into much larger box-section
aero rims, so his tires stayed on just fine.

Cheers,

Carl Fogel

Robin Hubert said:

Quoted message said:

Quoted message said:

Tumbleweed AKA Russian Thistle is not native to North America. It
was introduced to the plains of Western Canada in the late 1800's
by immigrant farmers from the Ukraine. The seeds were mixed in
with the flax seed that they planted.

Quoted message said:

Quoted message said:

Around here, Russian Thistle is a tall stalk with a purple thistle
flower on the top. Not at all like a tumble weed's bushy shape.
Pat in TX

Quoted message said:

You're talking about the musk, milk, or bull thistle, not a Russian
thistle.

Here's an array of plants in that group:

http://tinyurl.com/y7dgxr

Jobst Brandt

Sergio Servadio said:

Quoted message said:

Hmmm... it may be a bad idea to ooze downhill dragging the rear
brake just to chat with a visiting friend.

Quoted message said:

To make your story short, if I got it right, your tyre slipped
around the rim dragging the tube along and made it bulge and suffer
at the valve.

Quoted message said:

Funny enough, I was recently asking around if anyone on
it.sport.ciclismo had ever noticed such a slippage (with or without
dragging of the tube) and all those who responded did so in the
negative.

I am certain that clincher tires with reasonable inflation (>50psi)
cannot slip on the rim. Tires blow off at the valve more often
because tire beads are sometimes not properly seated there because the
stem bulge must be carefully pushed up into the tire.

In this event, it seems coincidence that it is near the stem. In any
event, when the tube is exposed from tire blow off, a large tear in
the rubber occurs and it makes a big bang.

It was tubulars that slipped on the rim and ripped out the stem when
rim glue got hot from braking. It was common in those days to turn
the front wheel around before reaching the bottom of a descent so that
it would slip the other way and straighten the valve stem, the
indicator of tire creep.

Jobst Brandt

On Tue, 17 Oct 2006 11:55:58 -0500, catzz66 <[email hidden]>

Quoted message said:

Pat in TX said:

Quoted message said:

Tumbleweed AKA Russian Thistle is not native to North America. It was
introduced to the plains of Western Canada in the late 1800's by
immigrant farmers from the Ukraine. The seeds were mixed in with the
flax seed that they planted.

Around here, Russian Thistle is a tall stalk with a purple thistle flower on
the top. Not at all like a tumble weed's bushy shape.

Pat in TX

I have no idea who's correct, but this hyear tumbleweed looks like what
we used to use for Christmas decorations many decades ago and the page
calls it Russian Thistle.

http://www.blueplanetbiomes.org/tumbleweed.htm

Dear Cat,

Whatever it is, the desert snow-man plant also makes a good crayfish
trap.

If you yank a mossy tumbleweed out of a pond or ditch, the waterlogged
arms sag and close, trapping lots of tasty little freshwater lobsters
that are otherwise too quick to catch easily.

Once the crayfish wriggle out of the impromptu trap, you can pick them
up, take them home, and introduce them to the melted butter.

Cheers,

Carl Fogel

dvt said:

Quoted message said:

Look, the rear tire's just about to come off the rim there, right by
the valve stem!

If I can get the cap off the Presta valve in time--

Bang-splat!

Interesting. Can you look at the rim closely to see if there's any
deformation where the bead crept out of the rim? I'm still curious about
Peter Cole's theory espoused in the old crow-eating thread from a few
years back [1].

Quoted message said:

And here's what the Slime tube and Kevlar-bead tire look like:

http://server5.theimagehosting.com/image.php?img=279asplat.jpg
or http://tinyurl.com/yxewwh

The black blob holding the Kevlar bead away from the ripped tire is
just a handy cyclocomputer, while a spoke helps the split Slime tube
to pose à la Goya's Maja.

I was surprised that the bead ripped out of the tire. A moment before
the bang-splat, he tire edge was clearly visible and undamaged as it
crept up out of the rim well toward freedom.

But memories of a few similar disasters years ago on wire-bead 27-inch
tires remind me that the tire usually rips away from the bead when it
creeps comes off rim, though I'm damned if I know why.

I've blown off a few tyres, probably through installation error, but
I've never had the bead separate from the rest of the tyre. I can't
remember blowing off any kevlar beaded tyres. Maybe the bead type makes
a difference. I wonder what causes that separation?

[1] http://tinyurl.com/yb4mus (links to Google Groups)

Dear Dave,

I'm just as puzzled as you by the bead ripping out of the carcass. The
bead isn't even being pried over the lip of the rim--it just stretches
up and out smoothly, further and further.

As for whether there's any rim deformation where the bead crept out,
the short answer is no. Probably it's just a matter of which section
starts to give first, based on the rolling tire squashing and flexing
under the rider's weight and the bumps. Once it starts to go, it pulls
every other part of the bead tighter and is doomed.

Long answer, I pulled the tire off and applied dial calipers inside
the rim at 36 spokes after seeing nothing of interest where the bead
crept off, apart from some traces of green Slime that confirmed that
it came off at the spokes numbered 2-3-4 below. The widths were so
similar, around 0.650 inches, that I can indent them to make a crude
graph:

valve
hole
56780123
1 0.648
2 0.648 x tire
3 0.648 x blew
4 0.651 x off here
5 0.649
6 0.652
7 0.647
8 0.653
9 0.648
10 0.652
11 0.645
12 0.650
13 0.650
14 0.651
15 0.649
16 0.650
17 0.650
18 0.648
19 0.645
20 0.649
21 0.649
22 0.651
23 0.650
24 0.648
25 0.649
26 0.649
27 0.649
28 0.650
29 0.649
30 0.652
31 0.650
32 0.649
33 0.649
34 0.649
35 0.651
36 0.651

I doubt that the rim is unusually wide or narrow at spokes 2-3-4. If
anything, they seem to be pretty much average. Rim flange thickness is
about the same all the way around, since the rim is fairly new and I
brake only about 8 times on my daily 15-mile ride, mostly just to slow
down to about 15 mph for sharp corners. (Rim wear from braking is
mostly theoretical for me.)

Cheers,

Carl Fogel

Quoted message said:

Sergio Servadio said:

Quoted message said:

Hmmm... it may be a bad idea to ooze downhill dragging the rear
brake just to chat with a visiting friend.

Quoted message said:

To make your story short, if I got it right, your tyre slipped
around the rim dragging the tube along and made it bulge and suffer
at the valve.

Quoted message said:

Funny enough, I was recently asking around if anyone on
it.sport.ciclismo had ever noticed such a slippage (with or without
dragging of the tube) and all those who responded did so in the
negative.

I am certain that clincher tires with reasonable inflation (>50psi)
cannot slip on the rim. Tires blow off at the valve more often
because tire beads are sometimes not properly seated there because the
stem bulge must be carefully pushed up into the tire.

In this event, it seems coincidence that it is near the stem. In any
event, when the tube is exposed from tire blow off, a large tear in
the rubber occurs and it makes a big bang.

It was tubulars that slipped on the rim and ripped out the stem when
rim glue got hot from braking. It was common in those days to turn
the front wheel around before reaching the bottom of a descent so that
it would slip the other way and straighten the valve stem, the
indicator of tire creep.

Jobst Brandt

Dear Jobst,

Do you have any idea why the bead rips out of the carcass?

My only guess so far is that the bulging tube smoothly hoists the
carcass and contained bead up onto the rim flange, all in one piece.

When the tube is exposed and explodes, the enormous tension is
abruptly released. I'm wondering if the carcass section with the bead
in it catches on the rim, while the rest of the carcass is stretched
back across the lip of the rim and tears free.

sidewall
x sidewall
x x
x x
bead. x
/\ bang! bead./\x
/ \ ---> / \
rim rim

It isn't clear from the aftermath if this is the case, since the whole
tire deflates and pulls out of shape.

Cheers,

Carl Fogel

Carl Fogel said:

Quoted message said:

Quoted message said:

> Hmmm... it may be a bad idea to ooze downhill dragging the rear
> brake just to chat with a visiting friend.

Quoted message said:

Quoted message said:

Quoted message said:

To make your story short, if I got it right, your tyre slipped
around the rim dragging the tube along and made it bulge and
suffer at the valve.

Quoted message said:

Quoted message said:

Quoted message said:

Funny enough, I was recently asking around if anyone on
it.sport.ciclismo had ever noticed such a slippage (with or
without dragging of the tube) and all those who responded did so
in the negative.

Quoted message said:

Quoted message said:

I am certain that clincher tires with reasonable inflation (>50psi)
cannot slip on the rim. Tires blow off at the valve more often
because tire beads are sometimes not properly seated there because
the stem bulge must be carefully pushed up into the tire.

Quoted message said:

Quoted message said:

In this event, it seems coincidence that it is near the stem. In
any event, when the tube is exposed from tire blow off, a large
tear in the rubber occurs and it makes a big bang.

Quoted message said:

Quoted message said:

It was tubulars that slipped on the rim and ripped out the stem
when rim glue got hot from braking. It was common in those days to
turn the front wheel around before reaching the bottom of a descent
so that it would slip the other way and straighten the valve stem,
the indicator of tire creep.

Quoted message said:

Do you have any idea why the bead rips out of the carcass?

I think the term is tire casing, carcasses being those bald and
damaged tires that lie in heaps at dead tire repositories.

Quoted message said:

My only guess so far is that the bulging tube smoothly hoists the
carcass and contained bead up onto the rim flange, all in one piece.

I believe it can only be caused by a misplaced or worn out chafing
strip. Alternatively, the rim may be non standard in how high it
reaches on the chafing strip. Riding with extra low pressure also
could cause the casing cords to chafe on the rim bead.

Quoted message said:

When the tube is exposed and explodes, the enormous tension is
abruptly released. I'm wondering if the carcass section with the
bead in it catches on the rim, while the rest of the carcass is
stretched back across the lip of the rim and tears free.

That's not reasonable. Besides, I have inspected enough blown off
tires and have never seen that. How about inspecting the casing cords
in the area of failure and note whether there is any aluminum wear
debris on them. That would indicate such wear.

It also occurs to me that a dual pivot brake has serious cosine error
and sweeps its short-arm pad up into the tire as it wears. That has
caused casing failure just above the bead for centerpull brakes that
have similar geometry.

Jobst Brandt

Quoted message said:

I'm just as puzzled as you by the bead ripping out of the carcass. The
bead isn't even being pried over the lip of the rim--it just stretches
up and out smoothly, further and further.

Yeah, that's an odd one. You mentioned prior experience with this bead
ripping phenomena... have you always used kevlar beads? As I mentioned,
I've always used wire beads, and I've never had that happen. If it is
more prevalent with kevlar beads, perhaps that's a clue.

Quoted message said:

As for whether there's any rim deformation where the bead crept out,
the short answer is no. Probably it's just a matter of which section
starts to give first, based on the rolling tire squashing and flexing
under the rider's weight and the bumps. Once it starts to go, it pulls
every other part of the bead tighter and is doomed.

Long answer, I pulled the tire off and applied dial calipers inside
the rim at 36 spokes after seeing nothing of interest where the bead
crept off, apart from some traces of green Slime that confirmed that
it came off at the spokes numbered 2-3-4 below. The widths were so
similar, around 0.650 inches, that I can indent them to make a crude
graph:

valve
hole
56780123
1 0.648
2 0.648 x tire
3 0.648 x blew
4 0.651 x off here
5 0.649
6 0.652
7 0.647
8 0.653
9 0.648
10 0.652
11 0.645
12 0.650
13 0.650
14 0.651
15 0.649
16 0.650
17 0.650
18 0.648
19 0.645
20 0.649
21 0.649
22 0.651
23 0.650
24 0.648
25 0.649
26 0.649
27 0.649
28 0.650
29 0.649
30 0.652
31 0.650
32 0.649
33 0.649
34 0.649
35 0.651
36 0.651

I doubt that the rim is unusually wide or narrow at spokes 2-3-4. If
anything, they seem to be pretty much average. Rim flange thickness is
about the same all the way around, since the rim is fairly new and I
brake only about 8 times on my daily 15-mile ride, mostly just to slow
down to about 15 mph for sharp corners. (Rim wear from braking is
mostly theoretical for me.)

Thanks for the measurements. If anything, I was expecting deformation on
a much smaller scale. Maybe two little "dings" in the rim at the two
points where the tyre bead escaped the rim. As Peter calculated in the
prior thread, there's a lot of force on those two points.

I should have been more clear in my original post. If these dings were
present, I imagine you'd be able to feel them by running your fingers
along the inside of the rim. No calipers required. Sorry to make you go
through that extra work with the calipers.

--
Dave
dvt at psu dot edu

Everyone confesses that exertion which brings out all the powers of body
and mind is the best thing for us; but most people do all they can to
get rid of it, and as a general rule nobody does much more than
circumstances drive them to do. -Harriet Beecher Stowe, abolitionist and
novelist (1811-1896)