Bill, Your statement is correct; however, the difference is that Nitrogen
filled tires do not get as hot as "dry" air filled tires...ergo, the
pressure does not increase.
Fred
-----Original Message-----
From: Diesel-RVs@yahoogro
Behalf Of Bill Halberstadt
Sent: Wednesday, January 02, 2008 8:08 AM
To: Diesel-RVs@yahoogro
Subject: [Diesel-RVs] Re: 07 Toyota/Nitrogen
That's just not true. Dry air and nitrogen have exactly the same
pressure rise with temperature. Air with some moisture in it will have
a very slightly higher pressure rise with temperature (negligible for
our uses). That's why I said you can avoid even that slight difference
by using the dry air that comes from your dryer-equipped motorhome air
system.
Warning: Technical trivia follows: The "ideal gas laws" show that, for
a fixed volume (roughly the case for our tires), with dry air,
nitrogen or any other ideal gas, if you double the temperature, you
will double the pressure. The "trick" is you have to use absolute
units for the measured temperature and pressure. E.G. psia and
kelvins. Temperature in kelvins is equal to degrees Celsius plus
273.15. Psia is psig plus 14.7 (with a slight correction for
altitude). Water vapor is not an "ideal gas", so it behaves somewhat
differently.
So, if you are really paranoid about pressure rise with temperature
(e.g. driving your rig in a NASCAR race, where 1/2 psi matters), the
trick is to use dry air. Nitrogen is one relatively expensive way to
do this. Having a dryer on your compressed air supply is another way.
Bill Halberstadt
--- In HYPERLINK
"mailto:Diesel-
"mydogscar" <markhovanec@
>
> Here's what I mean by stable. Check your tires temperature cold, and
> then hot. It will be different. With nitrogen it's the same.
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