"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