Continental Gatorskins get ugly

[Michael Press]

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

> On 2007-04-04, Michael Press <[email protected]> wrote:
> > In article <[email protected]>,
> > G?nther Schwarz <[email protected]> wrote:
> >
> >> Michael Press wrote:
> >>
> >> > I do not like hand pumps, even floor pumps. I do not want to
> >> > maintain an air compressor. What inflation scheme do I
> >> > use?
> >>
> >> Petrol stations? The adaptor for filling with Presta and Dunlop valves
> >> lives in my wallet.
> >
> > I keep an 80 cubic foot (2.25 m^3) tank of compressed
> > nitrogen, with a regulator and a hose with a valve and
> > presta head. Set the regulator and fill the tires. I
> > also put N2 in the air space of half empty wine bottles.
>
> Do you find the tyres hold their pressure for longer using pure
> Nitrogen? There's some theory about partial pressures I half-remember
> that never seemed to make much sense in the first place; but it's
> claimed that truckers fill their truck tyres with Nitrogen, possibly to
> reduce corrosion.

I do not know about longer. I put in 115-120 psi, then
let the pressure drop to under 90 psi, then repeat. The
cycle is about 2-3 weeks.

Suppose we started with tires inflated to running
pressure with pure N2. The ambient atmosphere is about
18% O2 with some H2O and CO2. The tubes are porous. O2
etc will leak _into_ the tube. The the process is
osmosis. If the tire were inflated with SF6 (sulfur
hexafluoride) the SF6 would leak out so slowly and the
atmospheric gases leak in so quickly that the tire
could pressure could rise above the initial inflation
pressure by about 1 bar. Since I top off the tires that
are at equilibrium composition with the ambient
atmosphere, the osmotic effect is likely negligible.

Some racers use N2 to attain finer control of pressure
as the gas changes temperature. When inflating with a
compressor you get whatever the inlet sucks up including
H2O, CO2, and various hydrocarbons, all of which have
very non-linear responses to pressure and temperature
changes. Those in the compressed gas trade call CO2 a
`wet' gas.
--
Michael Press

 

[Ben C]

On 2007-04-04, Michael Press <[email protected]> wrote:
> In article <[email protected]>,
> Ben C <[email protected]> wrote:
[...]
>> Do you find the tyres hold their pressure for longer using pure
>> Nitrogen? There's some theory about partial pressures I half-remember
>> that never seemed to make much sense in the first place; but it's
>> claimed that truckers fill their truck tyres with Nitrogen, possibly to
>> reduce corrosion.
>
> I do not know about longer. I put in 115-120 psi, then
> let the pressure drop to under 90 psi, then repeat. The
> cycle is about 2-3 weeks.

That sounds about par for air-filled tyres.

> Suppose we started with tires inflated to running
> pressure with pure N2. The ambient atmosphere is about
> 18% O2 with some H2O and CO2. The tubes are porous. O2
> etc will leak _into_ the tube.

I see, makes sense. You've got O2 leaking in, but then again a higher
partial pressure of N2 trying to get out than with the air-filled tyre,
so it's not clear that you're better off.

> The the process is osmosis.

Isn't it osmosis only when concentrations of things in water are
involved?

> If the tire were inflated with SF6 (sulfur
> hexafluoride) the SF6 would leak out so slowly and the
> atmospheric gases leak in so quickly that the tire
> could pressure could rise above the initial inflation
> pressure by about 1 bar.

Why would the SF6 leak out slowly?

 

[[email protected]]

On Wed, 04 Apr 2007 02:37:10 -0500, Ben C <[email protected]> wrote:

>On 2007-04-04, Michael Press <[email protected]> wrote:
>> In article <[email protected]>,
>> G? Schwarz <[email protected]> wrote:
>>
>>> Michael Press wrote:
>>>
>>> > I do not like hand pumps, even floor pumps. I do not want to
>>> > maintain an air compressor. What inflation scheme do I
>>> > use?
>>>
>>> Petrol stations? The adaptor for filling with Presta and Dunlop valves
>>> lives in my wallet.
>>
>> I keep an 80 cubic foot (2.25 m^3) tank of compressed
>> nitrogen, with a regulator and a hose with a valve and
>> presta head. Set the regulator and fill the tires. I
>> also put N2 in the air space of half empty wine bottles.
>
>Do you find the tyres hold their pressure for longer using pure
>Nitrogen? There's some theory about partial pressures I half-remember
>that never seemed to make much sense in the first place; but it's
>claimed that truckers fill their truck tyres with Nitrogen, possibly to
>reduce corrosion.

Dear Ben,

The air is about 80% N2 and 20% 02, with 1% in the cracks consisting
mostly of CO2, water vapor, argon, methane, and so forth.

N2 is soluble in butyl rubber at a rate of ~10, O2 at a rate of about
~23, and CO2 at a whopping ~150:

http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html

So CO2 escapes from butyl tubes filled with CO2 cartridges about
fifteen times as fast as normally pumped tubes (80/20 N2/O2). That's
why flats pumped up with CO2 cartridges lose pressure so quickly.

O2 escapes about twice as fast as N2, but it's only 20% of a normally
pumped tube, so the effect is greatly lessened.

The gases are even more soluble in latex rubber, which is why latex
tubes need pumping up so often.

The chief advantage of pure N2 gas is that you're not putting water
vapor into the tires. An air compressor tank has a drain valve on the
bottom for rusty water.

Apart from corrosion, the water vapor in ordinary compressed air is
sensitive to temperature changes, so it affects tire pressure in race
cars, where temperature changes are considerable and tiny pressure
differences can make a difference.

Cheers,

Carl Fogel

 

[Michael Press]

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

> On 2007-04-04, Michael Press <[email protected]> wrote:
> > In article <[email protected]>,
> > Ben C <[email protected]> wrote:
> [...]
> >> Do you find the tyres hold their pressure for longer using pure
> >> Nitrogen? There's some theory about partial pressures I half-remember
> >> that never seemed to make much sense in the first place; but it's
> >> claimed that truckers fill their truck tyres with Nitrogen, possibly to
> >> reduce corrosion.
> >
> > I do not know about longer. I put in 115-120 psi, then
> > let the pressure drop to under 90 psi, then repeat. The
> > cycle is about 2-3 weeks.
>
> That sounds about par for air-filled tyres.
>
> > Suppose we started with tires inflated to running
> > pressure with pure N2. The ambient atmosphere is about
> > 18% O2 with some H2O and CO2. The tubes are porous. O2
> > etc will leak _into_ the tube.
>
> I see, makes sense. You've got O2 leaking in, but then again a higher
> partial pressure of N2 trying to get out than with the air-filled tyre,
> so it's not clear that you're better off.
>
> > The the process is osmosis.
>
> Isn't it osmosis only when concentrations of things in water are
> involved?

Yes, I misspoke. The concept is the same.

>
> > If the tire were inflated with SF6 (sulfur
> > hexafluoride) the SF6 would leak out so slowly and the
> > atmospheric gases leak in so quickly that the tire
> > could pressure could rise above the initial inflation
> > pressure by about 1 bar.
>
> Why would the SF6 leak out slowly?

It is more massive, so it moves more slowly
--
Michael Press

 

[Ben C]

On 2007-04-04, [email protected] <[email protected]> wrote:
> On Wed, 04 Apr 2007 02:37:10 -0500, Ben C <[email protected]> wrote:
[...]
>>Do you find the tyres hold their pressure for longer using pure
>>Nitrogen? There's some theory about partial pressures I half-remember
>>that never seemed to make much sense in the first place; but it's
>>claimed that truckers fill their truck tyres with Nitrogen, possibly to
>>reduce corrosion.
>
> Dear Ben,
>
> The air is about 80% N2 and 20% 02, with 1% in the cracks consisting
> mostly of CO2, water vapor, argon, methane, and so forth.
>
> N2 is soluble in butyl rubber at a rate of ~10, O2 at a rate of about
> ~23, and CO2 at a whopping ~150:
>
> http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html
>
> So CO2 escapes from butyl tubes filled with CO2 cartridges about
> fifteen times as fast as normally pumped tubes (80/20 N2/O2). That's
> why flats pumped up with CO2 cartridges lose pressure so quickly.
>
> O2 escapes about twice as fast as N2, but it's only 20% of a normally
> pumped tube, so the effect is greatly lessened.
>
> The gases are even more soluble in latex rubber, which is why latex
> tubes need pumping up so often.
>
> The chief advantage of pure N2 gas is that you're not putting water
> vapor into the tires. An air compressor tank has a drain valve on the
> bottom for rusty water.
>
> Apart from corrosion, the water vapor in ordinary compressed air is
> sensitive to temperature changes, so it affects tire pressure in race
> cars, where temperature changes are considerable and tiny pressure
> differences can make a difference.
>
> Cheers,
>
> Carl Fogel

Thanks for the explanation!

 

[Matt O'Toole]

On Wed, 04 Apr 2007 02:37:10 -0500, Ben C wrote:

> Do you find the tyres hold their pressure for longer using pure
> Nitrogen? There's some theory about partial pressures I half-remember
> that never seemed to make much sense in the first place; but it's
> claimed that truckers fill their truck tyres with Nitrogen, possibly to
> reduce corrosion.

They should hold pressure longer, if you consider this an issue. Many
automakers, notably Honda, fill tires with nitrogen at the factory. This
is mostly so they don't lose pressure while sitting around until the car
is sold.

Matt O.

 

[Mark Hickey]

[email protected] wrote:

>N2 is soluble in butyl rubber at a rate of ~10, O2 at a rate of about
>~23, and CO2 at a whopping ~150:
>
>http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html
>
>So CO2 escapes from butyl tubes filled with CO2 cartridges about
>fifteen times as fast as normally pumped tubes (80/20 N2/O2). That's
>why flats pumped up with CO2 cartridges lose pressure so quickly.

Hmmmm. Then it would follow that after many cycles of topping off a
tire, the contents of the tube would end up being almost entirely
nitrogen (the oxygen having been lost at a substantially greater
rate).

Cooool - sounds exotic. Can't wait to tell my riding buddies that my
tires are filled with 95% plus pure nitrogen!

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

 

[Michael Press]

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

> >>> Michael Press wrote:
> >>>> I do not like hand pumps, even floor pumps. I do not want to
> >>>> maintain an air compressor. What inflation scheme do I
> >>>> use?
>
> >> G?nther Schwarz <[email protected]> wrote:
> >>> Petrol stations? The adaptor for filling with Presta and Dunlop valves
> >>> lives in my wallet.
>
> > Michael Press wrote:
> >> I keep an 80 cubic foot (2.25 m^3) tank of compressed
> >> nitrogen, with a regulator and a hose with a valve and
> >> presta head. Set the regulator and fill the tires. I
> >> also put N2 in the air space of half empty wine bottles.
>
> jim beam wrote:
> > just for the bike and wine? that's a little extravagant isn't it?
>
> When one reaches a certain age, one companion isn't enough help to kill
> a bottle at dinner.

Could be the remains of the second bottle.

(but it is not)
--
Michael Press

 

[jim beam]

Michael Press wrote:
> In article <[email protected]>,
> Ben C <[email protected]> wrote:
>
>> On 2007-04-04, Michael Press <[email protected]> wrote:
>>> In article <[email protected]>,
>>> Ben C <[email protected]> wrote:
>> [...]
>>>> Do you find the tyres hold their pressure for longer using pure
>>>> Nitrogen? There's some theory about partial pressures I half-remember
>>>> that never seemed to make much sense in the first place; but it's
>>>> claimed that truckers fill their truck tyres with Nitrogen, possibly to
>>>> reduce corrosion.
>>> I do not know about longer. I put in 115-120 psi, then
>>> let the pressure drop to under 90 psi, then repeat. The
>>> cycle is about 2-3 weeks.
>> That sounds about par for air-filled tyres.
>>
>>> Suppose we started with tires inflated to running
>>> pressure with pure N2. The ambient atmosphere is about
>>> 18% O2 with some H2O and CO2. The tubes are porous. O2
>>> etc will leak _into_ the tube.
>> I see, makes sense. You've got O2 leaking in, but then again a higher
>> partial pressure of N2 trying to get out than with the air-filled tyre,
>> so it's not clear that you're better off.
>>
>>> The the process is osmosis.
>> Isn't it osmosis only when concentrations of things in water are
>> involved?
>
> Yes, I misspoke. The concept is the same.

it's diffusion. [osmosis is a subset of diffusion.]

>
>>> If the tire were inflated with SF6 (sulfur
>>> hexafluoride) the SF6 would leak out so slowly and the
>>> atmospheric gases leak in so quickly that the tire
>>> could pressure could rise above the initial inflation
>>> pressure by about 1 bar.
>> Why would the SF6 leak out slowly?
>
> It is more massive, so it moves more slowly

 

[jim beam]

[email protected] wrote:
> On Wed, 04 Apr 2007 02:37:10 -0500, Ben C <[email protected]> wrote:
>
>> On 2007-04-04, Michael Press <[email protected]> wrote:
>>> In article <[email protected]>,
>>> G? Schwarz <[email protected]> wrote:
>>>
>>>> Michael Press wrote:
>>>>
>>>>> I do not like hand pumps, even floor pumps. I do not want to
>>>>> maintain an air compressor. What inflation scheme do I
>>>>> use?
>>>> Petrol stations? The adaptor for filling with Presta and Dunlop valves
>>>> lives in my wallet.
>>> I keep an 80 cubic foot (2.25 m^3) tank of compressed
>>> nitrogen, with a regulator and a hose with a valve and
>>> presta head. Set the regulator and fill the tires. I
>>> also put N2 in the air space of half empty wine bottles.
>> Do you find the tyres hold their pressure for longer using pure
>> Nitrogen? There's some theory about partial pressures I half-remember
>> that never seemed to make much sense in the first place; but it's
>> claimed that truckers fill their truck tyres with Nitrogen, possibly to
>> reduce corrosion.
>
> Dear Ben,
>
> The air is about 80% N2 and 20% 02, with 1% in the cracks consisting
> mostly of CO2, water vapor, argon, methane, and so forth.
>
> N2 is soluble in butyl rubber at a rate of ~10, O2 at a rate of about
> ~23, and CO2 at a whopping ~150:
>
> http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html

in that cite, "soluble" is in quotes for a reason - the gas is not
dissolving in the rubber like sugar in a cup of tea, it's diffusing
/through/ the rubber, from one interface to the other. diffusion is the
word of the day. happens in gases, liquids and solids.

>
> So CO2 escapes from butyl tubes filled with CO2 cartridges about
> fifteen times as fast as normally pumped tubes (80/20 N2/O2). That's
> why flats pumped up with CO2 cartridges lose pressure so quickly.
>
> O2 escapes about twice as fast as N2, but it's only 20% of a normally
> pumped tube, so the effect is greatly lessened.
>
> The gases are even more soluble in latex rubber, which is why latex
> tubes need pumping up so often.
>
> The chief advantage of pure N2 gas is that you're not putting water
> vapor into the tires. An air compressor tank has a drain valve on the
> bottom for rusty water.
>
> Apart from corrosion, the water vapor in ordinary compressed air is
> sensitive to temperature changes, so it affects tire pressure in race
> cars, where temperature changes are considerable and tiny pressure
> differences can make a difference.
>
> Cheers,
>
> Carl Fogel

 

[jim beam]

Matt O'Toole wrote:
> On Wed, 04 Apr 2007 02:37:10 -0500, Ben C wrote:
>
>> Do you find the tyres hold their pressure for longer using pure
>> Nitrogen? There's some theory about partial pressures I half-remember
>> that never seemed to make much sense in the first place; but it's
>> claimed that truckers fill their truck tyres with Nitrogen, possibly to
>> reduce corrosion.
>
> They should hold pressure longer, if you consider this an issue. Many
> automakers, notably Honda, fill tires with nitrogen at the factory. This
> is mostly so they don't lose pressure while sitting around until the car
> is sold.
>
> Matt O.
>
that may be true, but i doubt it for reasons of economics. modern car
tires on new rims hold their pressure very well. they are lined with [i
think] chlorinated butyl which is all but impermeable. when i check the
tire pressures on my car, they're barely 2# off in 6 months. yes, i
/should/ check them more regularly, but given this experience, rarely do
- i have performed this "long term test" a number of times now.

 

[Ben C]

On 2007-04-05, Mark Hickey <[email protected]> wrote:
> [email protected] wrote:
>
>>N2 is soluble in butyl rubber at a rate of ~10, O2 at a rate of about
>>~23, and CO2 at a whopping ~150:
>>
>>http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html
>>
>>So CO2 escapes from butyl tubes filled with CO2 cartridges about
>>fifteen times as fast as normally pumped tubes (80/20 N2/O2). That's
>>why flats pumped up with CO2 cartridges lose pressure so quickly.
>
> Hmmmm. Then it would follow that after many cycles of topping off a
> tire, the contents of the tube would end up being almost entirely
> nitrogen (the oxygen having been lost at a substantially greater
> rate).
>
> Cooool - sounds exotic. Can't wait to tell my riding buddies that my
> tires are filled with 95% plus pure nitrogen!

That's an interesting thought, and may be what happens. After I
installed a new inner tube on my front wheel I was quite disappointed
with how soft it got after a few days, more so than the rear tyre. After
topping it up a few times it now seems to hold its pressure now for
about the same length of time as the rear. I thought vaguely that there
might be some molecular changes in the rubber going on, as it was a new
inner tube, but this gas ratio theory sounds like a better one.

 

[D'ohBoy]

On Mar 31, 1:01 pm, "[email protected]"
<[email protected]> wrote:
> On Mar 31, 1:39 pm, "Phil, Non-Squid" <[email protected]>
> wrote:
>
> > "Snakeskin" tire on the rear. Nice commuter tire. Holds 130psi fine.
>
> >http://img9.imagevenue.com/img.php?image=73741_tire_122_445lo.jpg
>
> > --
> > Phil
>
> That is how the Continental Gatorskni tires look after several years
> and thousands of miles. The outer layer of the Duraskin wears like
> that. But the inner layer of Duraskin is still going strong. Very
> tough sidewalls.


Gave up on Conti Gatorskins after I lost one with thousands of miles
left AND a brand new one to sidewall cuts within two rides.

D'ohBoy, who rides Michelins now.

 

[Ben C]

On 2007-04-05, jim beam <[email protected]> wrote:
> Ben C wrote:
>> On 2007-04-05, Mark Hickey <[email protected]> wrote:
[...]
>>> Cooool - sounds exotic. Can't wait to tell my riding buddies that my
>>> tires are filled with 95% plus pure nitrogen!
>>
>> That's an interesting thought, and may be what happens. After I
>> installed a new inner tube on my front wheel I was quite disappointed
>> with how soft it got after a few days, more so than the rear tyre. After
>> topping it up a few times it now seems to hold its pressure now for
>> about the same length of time as the rear. I thought vaguely that there
>> might be some molecular changes in the rubber going on, as it was a new
>> inner tube, but this gas ratio theory sounds like a better one.
>
> it's not just that - small pores are frequent in manufacture. these are
> genuine slow leaks, not the product of diffusion.

But would they be affected by time? What would make a tyre need less
frequent topping up after the first few times it was topped up?

The only confound here is that it was also a new inner tube, and also a
new outer tyre now I come to think of it. Perhaps the outer tyre was
"creeping" a bit and getting slightly larger over the first two days,
although I'm not sure whether that would affect the pressure
significantly.

 

[[email protected]]

On Thu, 05 Apr 2007 08:52:34 -0500, Ben C <[email protected]> wrote:

>On 2007-04-05, jim beam <[email protected]> wrote:
>> Ben C wrote:
>>> On 2007-04-05, Mark Hickey <[email protected]> wrote:
>[...]
>>>> Cooool - sounds exotic. Can't wait to tell my riding buddies that my
>>>> tires are filled with 95% plus pure nitrogen!
>>>
>>> That's an interesting thought, and may be what happens. After I
>>> installed a new inner tube on my front wheel I was quite disappointed
>>> with how soft it got after a few days, more so than the rear tyre. After
>>> topping it up a few times it now seems to hold its pressure now for
>>> about the same length of time as the rear. I thought vaguely that there
>>> might be some molecular changes in the rubber going on, as it was a new
>>> inner tube, but this gas ratio theory sounds like a better one.
>>
>> it's not just that - small pores are frequent in manufacture. these are
>> genuine slow leaks, not the product of diffusion.
>
>But would they be affected by time? What would make a tyre need less
>frequent topping up after the first few times it was topped up?
>
>The only confound here is that it was also a new inner tube, and also a
>new outer tyre now I come to think of it. Perhaps the outer tyre was
>"creeping" a bit and getting slightly larger over the first two days,
>although I'm not sure whether that would affect the pressure
>significantly.

Dear Ben,

A less exciting explanation is that repeated opening, closing, and
tightening of the Presta valve sometimes result in a better seal.

That is, all rubber balloons lose air through the rubber, but quite a
few benefit from a better knot.

Cheers,

Carl Fogel

 

[jim beam]

[email protected] wrote:
> On Thu, 05 Apr 2007 08:52:34 -0500, Ben C <[email protected]> wrote:
>
>> On 2007-04-05, jim beam <[email protected]> wrote:
>>> Ben C wrote:
>>>> On 2007-04-05, Mark Hickey <[email protected]> wrote:
>> [...]
>>>>> Cooool - sounds exotic. Can't wait to tell my riding buddies that my
>>>>> tires are filled with 95% plus pure nitrogen!
>>>> That's an interesting thought, and may be what happens. After I
>>>> installed a new inner tube on my front wheel I was quite disappointed
>>>> with how soft it got after a few days, more so than the rear tyre. After
>>>> topping it up a few times it now seems to hold its pressure now for
>>>> about the same length of time as the rear. I thought vaguely that there
>>>> might be some molecular changes in the rubber going on, as it was a new
>>>> inner tube, but this gas ratio theory sounds like a better one.
>>> it's not just that - small pores are frequent in manufacture. these are
>>> genuine slow leaks, not the product of diffusion.
>> But would they be affected by time? What would make a tyre need less
>> frequent topping up after the first few times it was topped up?
>>
>> The only confound here is that it was also a new inner tube, and also a
>> new outer tyre now I come to think of it. Perhaps the outer tyre was
>> "creeping" a bit and getting slightly larger over the first two days,
>> although I'm not sure whether that would affect the pressure
>> significantly.
>
> Dear Ben,
>
> A less exciting explanation is that repeated opening, closing, and
> tightening of the Presta valve sometimes result in a better seal.
>
> That is, all rubber balloons lose air through the rubber, but quite a
> few benefit from a better knot.
>
> Cheers,
>
> Carl Fogel

indeed.