Kevin Anderson wrote:
I don't think they run cooler, but I know that using nitrogen the pressure
stays more consistant as the tire heat up

Do you guys stay up late making this stuff up or do you really, honestly
believe that?

Have you ever heard of - much less read - the "gas laws'? Look up a
French chap named Charles and Gay-Lussac and their particular
contribution to the art.

Exactly how do you "know that using nitrogen the pressure stays more
consistant (sic) as the tire heats up"?

The reason nitrogen is used in high performance tires (usually aircraft)
is that it will not support combustion or oxidation of rubber compounds
in a very high temperature application. Compressed nitrogen is normally
dry, very low in moisture content as well as completely free of oil
which is a contaminant delivered by many air compressors. All the normal
gas laws still apply.

The only thing worse than the general lack of basic scientific knowledge
shown here is the willingness of people to post that they "know" that
the laws of physics simply don't apply.


Rick

"Rick" wrote in message
ink.net...
Kevin Anderson wrote:
I don't think they run cooler, but I know that using nitrogen the
pressure
stays more consistant as the tire heat up

Do you guys stay up late making this stuff up or do you really, honestly
believe that?

Have you ever heard of - much less read - the "gas laws'? Look up a
French chap named Charles and Gay-Lussac and their particular
contribution to the art.

Exactly how do you "know that using nitrogen the pressure stays more
consistant (sic) as the tire heats up"?

The reason nitrogen is used in high performance tires (usually aircraft)
is that it will not support combustion or oxidation of rubber compounds
in a very high temperature application. Compressed nitrogen is normally
dry, very low in moisture content as well as completely free of oil
which is a contaminant delivered by many air compressors. All the normal
gas laws still apply.

The only thing worse than the general lack of basic scientific knowledge
shown here is the willingness of people to post that they "know" that
the laws of physics simply don't apply.


Rick

Um, Rick,

Race car operators take a great deal of time and effort to first dry their
tires, then fill them with dry nitrogen. The reason is that the water in the
air does NOT act like an ideal gas. Think about what happens to the
pressure/volume curves as the tire reaches 100 degrees C.

http://www.porschenet.com/bruns04.html

There are other perceived benefits that may induce an operator to switch to
nitrogen.
I am not ready to support this other stuff, but throw it in just to cover
the subject more fully.

http://www.branick.com/n2/faq.html

Mark Browne

Mark Browne wrote:

Um, Rick,

Race car operators take a great deal of time and effort to first dry their
tires, then fill them with dry nitrogen. The reason is that the water in the
air does NOT act like an ideal gas.

yeah, and did you notice that I wrote:

Compressed nitrogen is normally
dry, very low in moisture content ...

Rick

"Rick" wrote in message
ink.net...
Mark Browne wrote:

Um, Rick,

Race car operators take a great deal of time and effort to first dry
their
tires, then fill them with dry nitrogen. The reason is that the water in
the
air does NOT act like an ideal gas.

yeah, and did you notice that I wrote:

Compressed nitrogen is normally
dry, very low in moisture content ...

Rick

Yes, but now the others on this group have a better understanding of the
factors involved.

Mark Browne

Mark Browne wrote:

Yes, but now the others on this group have a better understanding of the
factors involved.

I am not going to bother to run the numbers but the partial pressure of
any "normal" quantity of water vapor in a tire is not going to change
the tire pressure by an amount easily measured by anyone outside a
laboratory. It will have no significant influence.

Moisture will however contribute to corrosion and oxidation at elevated
temperatures in an oxygen bearing atmosphere. How much of a factor this
is in an application where tires are changed every few minutes anyway is
debatable.

I think your racer/writer/engineer friend might be disappointed when he
fails to see much, if any, measurable difference in his tire pressure.

Rick

"Rick" wrote in message
ink.net...
Mark Browne wrote:

Yes, but now the others on this group have a better understanding of the
factors involved.

I am not going to bother to run the numbers but the partial pressure of
any "normal" quantity of water vapor in a tire is not going to change
the tire pressure by an amount easily measured by anyone outside a
laboratory. It will have no significant influence.

Moisture will however contribute to corrosion and oxidation at elevated
temperatures in an oxygen bearing atmosphere. How much of a factor this
is in an application where tires are changed every few minutes anyway is
debatable.

I think your racer/writer/engineer friend might be disappointed when he
fails to see much, if any, measurable difference in his tire pressure.

Rick

Rick,
I believe that what you are neatly trying to side-step in your consideration
is the presence of liquid water. If all we were talking about is water
vapor, even at 100% humidity, then I would completely agree that you are
right.

Unfortunately there *can* be liquid water trapped inside the tire. Some of
this comes from tire mounting compound, some from air compressors without
suitable dryers, some from water inside the tire. This trapped water inside
the tire can be standing on the surface, or inside the rubber.

It is rather difficult to make a blanket statement about how much effect
each source can contribute. This makes an unassailable mathematical analysis
equally difficult. Not to worry - others have done it and I have read the
reports. In a Formula or NASCAR setting moisture can raise tire pressure
about 4 PSI in the corners. This is enough to mess up a finely tuned race
car chassis.

Whatever *it* is, either it works, or it does not. If *it* does not make
cars go faster or safer, most people don't put a lot of time and money into
it. Real race teams that have real physicists and engineers on their staff
go to considerable effort to control the presence of water inside the tire.
Tire moisture *is* a significant problem in racing; people worry about going
into a corner at 200 miles an hour and having their car go squirrelly in the
middle of the turn.

I spend a fair amount of time working around race tracks and see a lot of
people shoot their mouths off about how things *should* work. The nice thing
about racing is that most of this stuff gets sorted out on the track. If you
would like to field a car and fill the tires with normal air to prove that
there is no difference, by all means go ahead. The nice thing about racing
is that people that know what they are talking about go fast, and clueless
people watch 'em go by. It all gets sorted out when the rubber hits the
road!

Mark Browne

Mark Browne wrote:

I believe that what you are neatly trying to side-step in your consideration
is the presence of liquid water. If all we were talking about is water
vapor, even at 100% humidity, then I would completely agree that you are
right.

Unfortunately there *can* be liquid water trapped inside the tire. Some of
this comes from tire mounting compound, some from air compressors without
suitable dryers, some from water inside the tire. This trapped water inside
the tire can be standing on the surface, or inside the rubber.

Wasn't this discussion about using nitrogen in the tires? If the racers
are so particular why are they using wet air from a cheap air compressor
and still worry about the effects of moisture? Why are they using
practices and processes that are known to add worrisome quantities of
liquid water to a component that is so sensitive to moisture?

Which way do you guys want this? Perfectly predictable tire pressures
will be impossible to obtain when the mounting is done with shade tree
techniques as you describe.

If there is so much water in a tire despite the best efforts of "real
physicists and engineers on their staff (who)go to considerable effort
to control the presence of water inside the tire" then something is
missing in this equation.

In a Formula or NASCAR setting moisture can raise tire pressure
about 4 PSI in the corners.

I find this a bit hard to believe. If it is water vapor it will
respond exactly like the nitrogen or air and the pressure rise is due to
the temperature increase of the tire. That is one of the gas laws that
no one seems to want to follow. If there is liquid water in the tire a
whole new set of conditions exist that are still unlikely to produce the
effect you describe.

Look at it another way. If you can attribute that 4 psi increase to
moisture then why not control the amount of moisture in the tire ... dry
the tire and add a measured amount of water so that you can predict the
pressure increase and regulate accordingly? But if you can dry the tire
then why worry about moisture? If you cannot dry the tire then you can
measure the dew point of the filling gas and calculate the weight of the
water in the tire and predict accordingly. It sounds to me like you guys
are just using "rules of thumb" and are surprised when you get surprised.

What is the normal tire pressure on one of those cars? Thirty - forty
psig? Let's say the tire started out at 35 psi, for the water to boil
away and increase the pressure of the tire to 39 psi its temperature
would have to increase to somewhere around 285 degrees F. Do you run
your tires at those temperatures? For the tires to increase 4 psi in the
second or two of cornering due to boiling water the carcass temperature
of the tire would have to be damn near glowing since heat does not
transfer instantaneously to the water, nor does it cool instantaneously
as the car leaves the corner.

If the starting temperature and pressure of the tire in the pits was 35
psig at 80 degrees F and it heated up to 200 degrees in the corner its
pressure would raise to around 46 psig ... at that pressure any water
would still be water until it reached over 290 degrees ...

I have not even mentioned the fact that the heat to vaporize the water
comes from the tire and the other gases filling the tire. The transfer
of that heat actually cools the tire and the gas ... a minute amount,
yes, but the effect of water has to be an equally minute amount and I
have yet to be shown the mechanism whereby "normal" amounts of water in
a tire will produce the effect you describe in the conditions in which
tires operate.

If you can explain how race car tires somehow work differently than
other machines I would love to hear it. I am very open minded but this
smacks of voodoo engineering to me.

Rick

"Mark Browne" wrote in message
news:8H_mb.39146


The reason is that the water in the
air does NOT act like an ideal gas.

Gosh, I didn't realize that there had been a change in the laws of physics
since I went to college! When did this happen?

Man, things were easier back in my day when any gas obeyed the gas laws!
Remember when the steam tables were what you would use for any gas you
didn't know the properties of?

Think about what happens to the
pressure/volume curves as the tire reaches 100 degrees C.


The vapor pressure for water will vary over a very large temperature range.
Fortunately, it is predicatable and monotonic. If you didn't have liquid
water in the tires when they were cold, you won't have any liquid in them as
they heat up.

I can see reasons that a race car might want to use nitrogen in their tires.
It is a nice, safe gas. It is realatively cheap. The fact that it is
readily available in a very dry state can have its advantages: I can imagin
that avoiding any condesation when the tire was cold could be an issue,
especially during the winter. The issue would be maintaining a
"predictable" inflation pressure as the tires went from "colder than when
they were inflated" to nominal operating temperatures. I suppose that
condensation could also be an issue when the wheels were balanced.

Rod