Flints don't puncture bicycle tires?

[Tim McNamara]

In article <[email protected]>,
[email protected] wrote:

> The reduced penetration that accompanies lower tire pressures must be
> part of the reason why car tires at 25-35 psi don't suffer from the
> flint and rock chip problems mentioned by many posters in this
> thread, who probably run 60-120 psi in their bicycle tires.

Car tires having casings that are about four times thicker, rubber tread
that's about 20 times thicker, and steel puncture protection belts
explains most of it. But I have still had flat car tires from roofing
nails and woodscrews that got jammed through the tread. Back in my days
working in a gas station, I patched a lot of car tires that had been
punctured by one thing or another.

 

[[email protected]]

On Sat, 28 Oct 2006 06:25:56 -0500, "Earl Bollinger"
<[email protected]> wrote:

><[email protected]> wrote in message
>news:[email protected]...
>> On Fri, 27 Oct 2006 21:26:22 -0500, "Earl Bollinger"
>> <[email protected]> wrote:
>>
>>><[email protected]> wrote in message
>>>news:[email protected]...
>>>> Over in rec.bicycles.tech, Jobst Brandt argues that flint flats are
>>>> just a myth:
>>>>
>>>> "I keep hearing about these mysterious cherts [flints] yet have never
>>>> seen one on the road or in a tire. I ride many miles of rocky roads
>>>> here and in Europe and have not had a flat from these mysterious sharp
>>>> rocks that don't seem to cut car tires or we could find examples of
>>>> them embedded in the surface of car tires."
>>>>
>>>> http://groups.google.com/group/rec.bicycles.tech/msg/97f538aa81f0f1ed
>>>>
>>>> Primitive superstitions about flints still flourish in the UK and
>>>> Denmark, so I'm asking for your views on the matter, somewhat like a
>>>> sociologist asking about the Loch Ness monster.
>>>>
>>>> Any pictures of flints in tires and tubes would be interesting, even
>>>> though they must be obvious fakes.
>>>>
>>>> (Alas, the nearby sand and gravel pit closed a few years ago, so I'm no
>>>> longer able to photograph the flint flats whose existence Jobst
>>>> denies.)
>>>>
>>>> Cheers,
>>>>
>>>> Carl Fogel
>>>>
>>>
>>>In what way is a small sharp piece of flint different from a small piece
>>>of
>>>glass?
>>>If a small piece of a broken beer bottle can work its way into a tire and
>>>cause a flat, why can't a small piece of a flint do the same thing?
>>>I have had small sharp bits of gravel, damage a tire enough to cause a
>>>weak
>>>spot in the casing so that the tire tube blows out later.
>>>So I can see where a small sharp something can get in a bike tire and work
>>>its way through the tire and casing to puncture the tube.
>>
>> Dear Earl,
>>
>> Much the same thoughts occurred to me when I removed nasty little
>> green-Slime-covered rock chips from my flat tires, but read that
>> flint-flats were myth and lore.
>>
>> Obviously, my tongue-in-cheek style needs improvement.
>>
>> As penance, here's a earlier post with some older pictures, provoked
>> by the familiar flints-don't-cause-flats claim:
>>
>> http://groups.google.com/group/rec.bicycles.tech/msg/a4a0b6cb9a83e15e
>>
>> Fogel Labs has since replaced its $15 WalMart USB camera with a modern
>> marvel, but is still looking for a competent photographer. Here's one
>> of the nitwit's more embarrassing recent shots:
>>
>> http://server5.theimagehosting.com/image.php?img=314hawkb.jpg
>> or http://tinyurl.com/ygfaf7
>>
>> A magnificent prairie hawk flew across the road as I climbed up the
>> side of the dam, did some swooping, and then perched on a convenient
>> nearby stake, so I stopped and took several pictures of it, most of
>> which showed the hawk nicely.
>>
>> The picture above captures the breathtaking wild beauty of another
>> stake, neatly centered. (The part of the hawk that went over the fence
>> last is just visible on the extreme left, sitting on a different
>> stake.)
>>
>> Cheers,
>>
>> Carl Fogel
>
>Thanks,
>
>I got to thinking about it some more.
>Now I have had a delayed blow out effect. That is where some sort of a
>semi-sharp short object manages to punch through the outer tire casing and
>damage the plies underneath, but not enough to puncture the tube outright.
>It blew out quite spectacularly at work later in my quiet office almost
>giving me a heart attack. That was on a cheap brand tire, so I figured the
>cheaper tire with its cheaper low thread count casing probably made it
>susceptable to such things.
>Anyway I wonder if certain tires like the cheaper ones would be more
>susceptable to small semi-sharp objects embedded in Chip Seal roads etc.
>Heck I think older worn down good tires might even be susceptable too. The
>way they do the chip seal roads with the big heavy machines mashing down the
>gravel so well, I don't see much happening there as the sharp edges on the
>gravel seems to get knocked off or flattened out. But if there are cracks in
>the pavement and a sharp rock gets stuck in there just right, it could cause
>a tire to get damaged enough to blow out or go flat.

Dear Earl,

Like nails, which ought to lie flat and never puncture tires, little
rock chips may be bounced up by the front tire and waiting in an
upright position when the rear tire arrives a moment later.

Several things make flats more likely.

Worn tires offer a little less resistance to punctures.

More highly inflated tires provide more pressure against the debris.

Higher speeds and heavier riders, ditto. In addition to the pressure
provided by the gravity load pressing the inflated tire straight down,
there's the kinetic slamming effect of the tire rolling the contact
patch forward and downward onto the debris that's sticking up. It's
just the same as hitting a bump--the impact force rises with the speed
and mass that must be bumped upward.

So lighter, slower riders who use lower tire pressures may suffer
fewer flats than fatter--er, larger, faster, high-pressure riders.

Wet roads lubricate the debris, so sharp objects can plunge more
easily through the tremendous friction of the rubber tread. A wet road
also increases the amount of debris flung up by the front tire
enormously, so the odds of the rear tire hitting an upright nail,
chip, or piece of glass is also greatly increased.

Posters in this thread have mentioned that the flint chips may be
washed onto the roads by rain where they ride, so they may face an
extra wet-weather hazard until enough car traffic smashes the sharp
new debris.

Cheers,

Carl Fogel

 

[[email protected]]

On Sat, 28 Oct 2006 10:53:09 -0500, Tim McNamara
<[email protected]> wrote:

>In article <[email protected]>,
> [email protected] wrote:
>
>> The reduced penetration that accompanies lower tire pressures must be
>> part of the reason why car tires at 25-35 psi don't suffer from the
>> flint and rock chip problems mentioned by many posters in this
>> thread, who probably run 60-120 psi in their bicycle tires.
>
>Car tires having casings that are about four times thicker, rubber tread
>that's about 20 times thicker, and steel puncture protection belts
>explains most of it. But I have still had flat car tires from roofing
>nails and woodscrews that got jammed through the tread. Back in my days
>working in a gas station, I patched a lot of car tires that had been
>punctured by one thing or another.

Dear Ben, Tony, and Tim,

As I carefully said, "The reduced penetration that accompanies lower
tire pressures must be part of the reason why car tires at 25-35 psi
^^^^^^^^^^^^^^^^^^
don't suffer from the flint and rock chip problems . . ."

Yes, I'm aware that car tires are thicker and have steel belts.

But someone or other has repeatedly insisted that rock chips can't
cause bicycle flats because he doesn't see rock chips in car tires.

If car tires press down with only 25-35 psi, we should expect to see
fewer rock chips in them than we see in bicycle tires at 60-120 psi.

Cheers,

Carl Fogel

 

[Tony Raven]

[email protected] wrote on 28/10/2006 19:36 +0100:
>
> Dear Ben, Tony, and Tim,
>
> As I carefully said, "The reduced penetration that accompanies lower
> tire pressures must be part of the reason why car tires at 25-35 psi
> ^^^^^^^^^^^^^^^^^^

For a car tyre that's like saying that a T-shirt is part of the reason a
bullet doesn't kill someone wearing a bullet proof vest

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

 

[Tony Raven]

[email protected] wrote on 28/10/2006 20:32 +0100:
>
> The point is worth making, since one poster has repeatedly argued that
> rock chips cannot cause bicycle flats because a) he has never seen a
> rock chip cause a bicycle flat and b) he does not see rock chips in
> car tires.
>

Does the word "obsessing" mean anything to you?

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

 

[* * Chas]

"Tim McNamara" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>,
> [email protected] wrote:
>
> > The reduced penetration that accompanies lower tire pressures must
be
> > part of the reason why car tires at 25-35 psi don't suffer from the
> > flint and rock chip problems mentioned by many posters in this
> > thread, who probably run 60-120 psi in their bicycle tires.
>
> Car tires having casings that are about four times thicker, rubber
tread
> that's about 20 times thicker, and steel puncture protection belts
> explains most of it. But I have still had flat car tires from roofing
> nails and woodscrews that got jammed through the tread. Back in my
days
> working in a gas station, I patched a lot of car tires that had been
> punctured by one thing or another.

I once had a spark plug embedded upright into the tread one of my
Michelin steel belted radials!

Chas.

 

[* * Chas]

<[email protected]> wrote in message
news:[email protected]...
> On Sat, 28 Oct 2006 10:53:09 -0500, Tim McNamara
> <[email protected]> wrote:
>
> >In article <[email protected]>,
> > [email protected] wrote:
> >
> >> The reduced penetration that accompanies lower tire pressures must
be
> >> part of the reason why car tires at 25-35 psi don't suffer from the
> >> flint and rock chip problems mentioned by many posters in this
> >> thread, who probably run 60-120 psi in their bicycle tires.
> >
> >Car tires having casings that are about four times thicker, rubber
tread
> >that's about 20 times thicker, and steel puncture protection belts
> >explains most of it. But I have still had flat car tires from
roofing
> >nails and woodscrews that got jammed through the tread. Back in my
days
> >working in a gas station, I patched a lot of car tires that had been
> >punctured by one thing or another.
>
> Dear Ben, Tony, and Tim,
>
> As I carefully said, "The reduced penetration that accompanies lower
> tire pressures must be part of the reason why car tires at 25-35 psi
> ^^^^^^^^^^^^^^^^^^
> don't suffer from the flint and rock chip problems . . ."
>
> Yes, I'm aware that car tires are thicker and have steel belts.
>
> But someone or other has repeatedly insisted that rock chips can't
> cause bicycle flats because he doesn't see rock chips in car tires.
>
> If car tires press down with only 25-35 psi, we should expect to see
> fewer rock chips in them than we see in bicycle tires at 60-120 psi.
>
> Cheers,
>
> Carl Fogel

I haven't seen any mention of the effect of concentrated PSI of a
penetrating object entering a tire as a function of the surface area it
contacts. For example the amount of damage a 100 Lb. woman wearing spike
heeled shoes can do to flooring:a portion of her weight concentrated in
a 10mm -12mm area can create enormous PSI.

A roofing nail may be less likely to penetrate a bicycle tire than a car
tire because the size of the surface areas and pressures involved;
whereas a glass/stone chip or goathead has a smaller surface area and
can easily penetrate a bicycle tire.

There appears to be 2 different failure modes with flats caused by rocks
and glass. The first is catastrophic failure where an object
instantaneously cuts into the tire and punctures the tube. The second
mode is where a smaller object is picked up by the tread and works its
way through the casing and penetrates the tube. These failure mode
should be differentiated.

Chas.

 

[* * Chas]

"Tony Raven" <[email protected]> wrote in message
news:[email protected]...
> [email protected] wrote on 28/10/2006 20:32 +0100:
> >
> > The point is worth making, since one poster has repeatedly argued
that
> > rock chips cannot cause bicycle flats because a) he has never seen a
> > rock chip cause a bicycle flat and b) he does not see rock chips in
> > car tires.
> >
>
> Does the word "obsessing" mean anything to you?
>
> --
> Tony

OCD!

Chas.

 

[[email protected]]

On Sat, 28 Oct 2006 13:26:21 -0700, "* * Chas"
<[email protected]> wrote:

>
>"Tim McNamara" <[email protected]> wrote in message
>news:[email protected]...
>> In article <[email protected]>,
>> [email protected] wrote:
>>
>> > The reduced penetration that accompanies lower tire pressures must
>be
>> > part of the reason why car tires at 25-35 psi don't suffer from the
>> > flint and rock chip problems mentioned by many posters in this
>> > thread, who probably run 60-120 psi in their bicycle tires.
>>
>> Car tires having casings that are about four times thicker, rubber
>tread
>> that's about 20 times thicker, and steel puncture protection belts
>> explains most of it. But I have still had flat car tires from roofing
>> nails and woodscrews that got jammed through the tread. Back in my
>days
>> working in a gas station, I patched a lot of car tires that had been
>> punctured by one thing or another.
>
>I once had a spark plug embedded upright into the tread one of my
>Michelin steel belted radials!
>
>Chas.

Dear Chas,

A friend managed a railroad spike through a tire.

A fish-hook in a bicycle tire on a prairie highway is the oddest that
I ever managed. (The explanation is that there's a reservoir a few
miles away, so there's a steady stream of trucks towing boats.)

I've had two car flats that I can remember, both mysterious slow leaks
that would take a month to show up. They turned out to be wood screws
whose heads had been ground off almost immediately. As the mechanic
pointed out, if you had a punctured car tire and nothing else handy, a
wood screw would make a fair temporary plug.

Cheers,

Carl Fogel

 

[[email protected]]

On Sat, 28 Oct 2006 20:39:28 +0100, Tony Raven <[email protected]>
wrote:

>[email protected] wrote on 28/10/2006 20:32 +0100:
>>
>> The point is worth making, since one poster has repeatedly argued that
>> rock chips cannot cause bicycle flats because a) he has never seen a
>> rock chip cause a bicycle flat and b) he does not see rock chips in
>> car tires.
>>
>
>Does the word "obsessing" mean anything to you?

Dear Tony,

It's a shame that we aren't getting along.

I was tempted to reply "whoosh" earlier, but decided instead to
explain what you seemed to be missing.

Now I know that you're not missing it.

Cheers,

Carl Fogel

 

[[email protected]]

Chas who? writes:

>>> The reduced penetration that accompanies lower tire pressures must
>>> be part of the reason why car tires at 25-35 psi don't suffer from
>>> the flint and rock chip problems mentioned by many posters in this
>>> thread, who probably run 60-120 psi in their bicycle tires.

>> Car tires having casings that are about four times thicker, rubber
>> tread that's about 20 times thicker, and steel puncture protection
>> belts explains most of it. But I have still had flat car tires
>> from roofing nails and woodscrews that got jammed through the
>> tread. Back in my days working in a gas station, I patched a lot
>> of car tires that had been punctured by one thing or another.

> I once had a spark plug embedded upright into the tread one of my
> Michelin steel belted radials!

That's because you had your tires inflated too hard, no doubt.

Jobst Brandt

 

[[email protected]]

On 29 Oct 2006 01:28:11 GMT, [email protected] wrote:

>Chas who? writes:
>
>>>> The reduced penetration that accompanies lower tire pressures must
>>>> be part of the reason why car tires at 25-35 psi don't suffer from
>>>> the flint and rock chip problems mentioned by many posters in this
>>>> thread, who probably run 60-120 psi in their bicycle tires.
>
>>> Car tires having casings that are about four times thicker, rubber
>>> tread that's about 20 times thicker, and steel puncture protection
>>> belts explains most of it. But I have still had flat car tires
>>> from roofing nails and woodscrews that got jammed through the
>>> tread. Back in my days working in a gas station, I patched a lot
>>> of car tires that had been punctured by one thing or another.
>
>> I once had a spark plug embedded upright into the tread one of my
>> Michelin steel belted radials!
>
>That's because you had your tires inflated too hard, no doubt.
>
>Jobst Brandt

Dear Jobst,

Alas, my doubts are easily inflamed.

A) Spark plugs are stout and strong enough to raise tremendous tents
in a 25-35 psi car tire trying to roll over them. A car tire is big
enough to hide an upright 3-inch-high spark-plug in a dimple so big
that the pressure concentrated on the spark plug tip is enormous, far
more than a quarter-inch rock chip.

B) Back then, the upright end of a spark plug often lacked the
screw-on cap, leaving a surprisingly small threaded metal rod sticking
up. I knew I had one somewhere out on the leaf-covered carport
shelves:

http://server5.theimagehosting.com/image.php?img=335a_sparkplug.jpg
or http://tinyurl.com/yxdc9t

The ancient 3-inch motorcycle spark plug in the picture is normally
used with the screw-on metal cap removed, leaving the threads bare.
The threaded end is about 0.150 inches wide, roughly twice as wide as
the 14 gauge bicycle spoke at 0.078 inches.

C) A car tire often has considerably more velocity and always much
more mass than a bicycle tire, which is the other half of what causes
debris to puncture a tire. The upright spark plug is trying to lift a
heavy car tire and wheel three inches against gravity and the car
suspension in the moment that it slams across the plug at up 70-80
mph. The effect is exaggerated by the fact that the car tire is likely
to be smaller in diameter than the bicycle wheel. That's why smaller
wheels supporting greater loads at higher speeds (cars) need
suspension to survive the impacts on normal roads--smaller diameter
wheels strike bumps at sharper angles.

D) Think what would happen to a 100 psi bicycle tire that hit the
naked threaded end of a three-inch-high spark plug just right at 20
mph. The comparatively huge height of the 3-inch spark plug puts it
far outside the realm of the quarter-inch flints of this thread.

E) Luckily, spark plugs are much rarer than rock chips on roads and
are rarely flipped up just right to cause disaster.

Cheers,

Carl Fogel

 

[* * Chas]

<[email protected]> wrote in message
news:[email protected]...
> Chas who? writes:
>
> >>> The reduced penetration that accompanies lower tire pressures must
> >>> be part of the reason why car tires at 25-35 psi don't suffer from
> >>> the flint and rock chip problems mentioned by many posters in this
> >>> thread, who probably run 60-120 psi in their bicycle tires.
>
> >> Car tires having casings that are about four times thicker, rubber
> >> tread that's about 20 times thicker, and steel puncture protection
> >> belts explains most of it. But I have still had flat car tires
> >> from roofing nails and woodscrews that got jammed through the
> >> tread. Back in my days working in a gas station, I patched a lot
> >> of car tires that had been punctured by one thing or another.
>
> > I once had a spark plug embedded upright into the tread one of my
> > Michelin steel belted radials!
>
> That's because you had your tires inflated too hard, no doubt.
>
> Jobst Brandt

Nope! 36PSI front and 40PSI rear per the owner's manual! Michelin
205/50/16 ZR radials.

Chas.

Chas.

 

[* * Chas]

<[email protected]> wrote in message
news:[email protected]...
> On 29 Oct 2006 01:28:11 GMT, [email protected] wrote:
>
> >Chas who? writes:
> >
> >>>> The reduced penetration that accompanies lower tire pressures
must
> >>>> be part of the reason why car tires at 25-35 psi don't suffer
from
> >>>> the flint and rock chip problems mentioned by many posters in
this
> >>>> thread, who probably run 60-120 psi in their bicycle tires.
> >
> >>> Car tires having casings that are about four times thicker, rubber
> >>> tread that's about 20 times thicker, and steel puncture protection
> >>> belts explains most of it. But I have still had flat car tires
> >>> from roofing nails and woodscrews that got jammed through the
> >>> tread. Back in my days working in a gas station, I patched a lot
> >>> of car tires that had been punctured by one thing or another.
> >
> >> I once had a spark plug embedded upright into the tread one of my
> >> Michelin steel belted radials!
> >
> >That's because you had your tires inflated too hard, no doubt.
> >
> >Jobst Brandt
>
> Dear Jobst,
>
> Alas, my doubts are easily inflamed.
>
> A) Spark plugs are stout and strong enough to raise tremendous tents
> in a 25-35 psi car tire trying to roll over them. A car tire is big
> enough to hide an upright 3-inch-high spark-plug in a dimple so big
> that the pressure concentrated on the spark plug tip is enormous, far
> more than a quarter-inch rock chip.
>
> B) Back then, the upright end of a spark plug often lacked the
> screw-on cap, leaving a surprisingly small threaded metal rod sticking
> up. I knew I had one somewhere out on the leaf-covered carport
> shelves:
>
> http://server5.theimagehosting.com/image.php?img=335a_sparkplug.jpg
> or http://tinyurl.com/yxdc9t
>
> The ancient 3-inch motorcycle spark plug in the picture is normally
> used with the screw-on metal cap removed, leaving the threads bare.
> The threaded end is about 0.150 inches wide, roughly twice as wide as
> the 14 gauge bicycle spoke at 0.078 inches.
>
> C) A car tire often has considerably more velocity and always much
> more mass than a bicycle tire, which is the other half of what causes
> debris to puncture a tire. The upright spark plug is trying to lift a
> heavy car tire and wheel three inches against gravity and the car
> suspension in the moment that it slams across the plug at up 70-80
> mph. The effect is exaggerated by the fact that the car tire is likely
> to be smaller in diameter than the bicycle wheel. That's why smaller
> wheels supporting greater loads at higher speeds (cars) need
> suspension to survive the impacts on normal roads--smaller diameter
> wheels strike bumps at sharper angles.
>
> D) Think what would happen to a 100 psi bicycle tire that hit the
> naked threaded end of a three-inch-high spark plug just right at 20
> mph. The comparatively huge height of the 3-inch spark plug puts it
> far outside the realm of the quarter-inch flints of this thread.
>
> E) Luckily, spark plugs are much rarer than rock chips on roads and
> are rarely flipped up just right to cause disaster.
>
> Cheers,
>
> Carl Fogel


It was a relatively new Michelin 205/50/16 ZR rear tire running at 40
PSI on a '92 Volvo Turbo wagon with a tricked out suspension. The spark
plug was buried flush with the tread surface. It damaged the casing
enough that I scraped the tire.

There's always the possibility that I parked in someone's space and they
wedged the spark plug under my tire....

I frequently drive around in construction sites and shipping areas of
manufacturing facilities in my business car and I pick up nails and
screws 2-3 times a year. These usually result in slow leaks.

....but we are getting led way off topic by resident experts!

Chas.

 

[Tony Raven]

* * Chas wrote on 28/10/2006 21:26 +0100:
>
> I once had a spark plug embedded upright into the tread one of my
> Michelin steel belted radials!
>

The quality of auto mechanics is really deteriorating these days. Some
of them will fit parts anywhere they can ;-)

--
Tony

"Anyone who conducts an argument by appealing to authority is not using
his intelligence; he is just using his memory."
- Leonardo da Vinci

 

[Michael Press]

In article
<[email protected]>,
"* * Chas" <[email protected]> wrote:

> <[email protected]> wrote in message
> news:[email protected]...
> > Chas who? writes:
> >
> > >>> The reduced penetration that accompanies lower tire pressures must
> > >>> be part of the reason why car tires at 25-35 psi don't suffer from
> > >>> the flint and rock chip problems mentioned by many posters in this
> > >>> thread, who probably run 60-120 psi in their bicycle tires.
> >
> > >> Car tires having casings that are about four times thicker, rubber
> > >> tread that's about 20 times thicker, and steel puncture protection
> > >> belts explains most of it. But I have still had flat car tires
> > >> from roofing nails and woodscrews that got jammed through the
> > >> tread. Back in my days working in a gas station, I patched a lot
> > >> of car tires that had been punctured by one thing or another.
> >
> > > I once had a spark plug embedded upright into the tread one of my
> > > Michelin steel belted radials!
> >
> > That's because you had your tires inflated too hard, no doubt.
>
> Nope! 36PSI front and 40PSI rear per the owner's manual! Michelin
> 205/50/16 ZR radials.

That was a joke. Now it is road kill.

--
Michael Press

 

[mb]

[email protected] wrote:

> On 27 Oct 2006 04:22:56 GMT, [email protected] wrote:
>
> > Carl Fogel writes:
> >
> >>>> Why wouldn't sharp objects be less likely to penetrate tough
> >>>> materials like tires if the resistance is lowered to 60-90 psi
> >>>> instead of 90-120 psi?
> >
> >>> As I mentioned above. For this scenario to succeed, the tire
> would >>> need enough flexibility to allow a dimple several mm in
> diameter to >>> be supported on a thorn or sharp (knife like) object
> not more than >>> 2mm in length. Tires are not that flexible. Try
> that manually and >>> you'll see that even at 30psi there is enough
> pressure to puncture >>> through to the air chamber.
> >
> >>>> There is, after all, a lower limit of pressure below which the
> >>>> sharp object will not penetrate the tire.
> >
> >>> Describe that for an average tire. Just try that with any of
> yours.
> >
> >> [snip]
> >
> >> Okay, let's try it with an average tire, one of mine.
> >
> >> Here's about 4mm of small nail sticking up in a vise, with its twin
> >> brother lying beside it and spoke ruler. The nail point,
> >> considerably enlarged, appears to be less than half a millimeter
> >> wide:
> >
> > http://tinyurl.com/whahk
> >
> >> Here's a 700c x 26 tire inflated to 30 psi and about to test your
> >> theory, again considerably enlarged:
> >
> > http://tinyurl.com/y6g36w
> >
> >> And here's the result:
> >
> > http://tinyurl.com/y74wc8
> >
> >> As you can see, the tire is holding pressure, having flattened out
> >> and tented over the nail point quite flexibly--no puncture, not
> even >> a mark on the tread.
> >

How much weight were you putting on the wheel?

I bet if I went out on a test ride with a tyre inflated at 30 psi it
would soon get punctured, the first bump I went over.

--
Mike

 

[Mike Causer]

On Fri, 27 Oct 2006 02:19:56 -0600, carlfogel wrote:

> To return to the UK side of things, could flint-flats be worse in some
> parts of the UK? I confess that I have no notion of the geography, but
> posters have mentioned flint-flats in Grimes Graves,

Grimes Graves is the site of a major neolithic industrial enterprise,
turning out arrow heads and knives for the masses, made from flint
quarried there [1]. I have cycled there (on my first ever century) and
(hangs head) been there many more times with the help of stinkpot
transport. No punctures though.


Where I live the main causes of punctures are broken glass and the crushed
rock that Sustrans [2] use for some of their alleged "cycle paths" in this
area.


[1] http://www.english-heritage.org.uk/server/show/conProperty.24

[2] Sustrans is a charity that claims to encourage cycling. I think they
have sponsorship from Cure-C-Cure patches. (Not knocking Cure-C-Cure,
that's the make I use, but far too often IMO.)


Mike

 

[* * Chas]

"Tony Raven" <[email protected]> wrote in message
news:[email protected]...
> * * Chas wrote on 28/10/2006 21:26 +0100:
> >
> > I once had a spark plug embedded upright into the tread one of my
> > Michelin steel belted radials!
> >
>
> The quality of auto mechanics is really deteriorating these days.
Some
> of them will fit parts anywhere they can ;-)
>
> --
> Tony

Yes, I've heard of numerous incidents of unskilled "repair" people
adding oil to the windshield (windscreen) washer fluid bottle, oil to
the brake fluid reservoir and radiator overflow tank and so on.

Chas.

 

[[email protected]]

On Sun, 29 Oct 2006 03:44:03 -0600, "mb" <[email protected]>
wrote:

>[email protected] wrote:
>
>> On 27 Oct 2006 04:22:56 GMT, [email protected] wrote:
>>
>> > Carl Fogel writes:
>> >
>> >>>> Why wouldn't sharp objects be less likely to penetrate tough
>> >>>> materials like tires if the resistance is lowered to 60-90 psi
>> >>>> instead of 90-120 psi?
>> >
>> >>> As I mentioned above. For this scenario to succeed, the tire
>> would >>> need enough flexibility to allow a dimple several mm in
>> diameter to >>> be supported on a thorn or sharp (knife like) object
>> not more than >>> 2mm in length. Tires are not that flexible. Try
>> that manually and >>> you'll see that even at 30psi there is enough
>> pressure to puncture >>> through to the air chamber.
>> >
>> >>>> There is, after all, a lower limit of pressure below which the
>> >>>> sharp object will not penetrate the tire.
>> >
>> >>> Describe that for an average tire. Just try that with any of
>> yours.
>> >
>> >> [snip]
>> >
>> >> Okay, let's try it with an average tire, one of mine.
>> >
>> >> Here's about 4mm of small nail sticking up in a vise, with its twin
>> >> brother lying beside it and spoke ruler. The nail point,
>> >> considerably enlarged, appears to be less than half a millimeter
>> >> wide:
>> >
>> > http://tinyurl.com/whahk
>> >
>> >> Here's a 700c x 26 tire inflated to 30 psi and about to test your
>> >> theory, again considerably enlarged:
>> >
>> > http://tinyurl.com/y6g36w
>> >
>> >> And here's the result:
>> >
>> > http://tinyurl.com/y74wc8
>> >
>> >> As you can see, the tire is holding pressure, having flattened out
>> >> and tented over the nail point quite flexibly--no puncture, not
>> even >> a mark on the tread.
>> >
>
>How much weight were you putting on the wheel?
>
>I bet if I went out on a test ride with a tyre inflated at 30 psi it
>would soon get punctured, the first bump I went over.

Dear MB,

You'd think that more weight would matter, but it actually doesn't
after the wheel has flattened out on all sides of the nail.

More weight only flattens more tread against the ground elsewhere:
_ _
This _/|\_ is the same to the nail as this _______/|\_______

Yes, you'd probably suffer an impact flat very soon at 30 psi at
normal speeds on normal roads.

But:

A) That's the kinetic impact side of things. Slamming into an obstacle
at a higher speed provides more impact, which is why pros worry about
impact flats more than most of us--they hit things faster, so the same
bumps on the road are more powerful impacts on their tires.

B) Jobst specified 30 psi, not me.

C) Have a look at the results at 100 and 110 psi here:

http://groups.google.com/group/rec.bicycles.tech/msg/7c93e56242f3a16f

It's the same thread, but many posts away and easy-to-miss.

Briefly, I kept pumping the tire up at 10 psi increments and rolling
it over the nail.

At 100 psi, the nail began to penetrate into the tread with an audible
pop and left a hole, but the tire didn't go flat.

At 110 psi, the pop was even louder, but the tire still didn't go
flat, so I took the tire off the wheel and peeked inside to see what
was happening.

Cheers,

Carl Fogel