From what I've read, two reasons suggest that Nitrogen is better than
straight AIR. The tire/wheel unit is not impermeable, some air leaks
out regardless of attempts to keep it sealed and the Nitrogen
molecule is larger (less likely to squeeze through any pore) and also
inert in reaction to the rubber and steel.
        This brings into play the moisture content of regular air.
With increasing temperatures the water moisture in the air expands,
changing internal pressures as well as creating reactive agents that
may or may not cause corrosion or rubber deterioration.
        Nitrogen is 'DRY' and thus avoids both problems.
M2CW                            David (dsl82westy)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

>In a message dated 20/09/2007 6:15:56 A.M. Eastern Standard Time,
>WHalsey@sya.org writes:
>
>Why  nitrogen? I have never heard of that.
>
>
>
>Because that's what COSTCO is doing.  The  pamphlet I got from COSTCO says:
>Nitrogen helps stabilize a tire's  inflation pressure.
>
>Cheers,
>
>Frank  Condelli
>Almonte, Ontario, Canada
>'87 Westy & Lionel Trains (_Collection for sale_
>(http://members.aol.com/Fkc43/trainsal.htm) )
>_Frank Condelli &  Associates_ (http://members.aol.com/Fkc43/busindex.html)
>- Vanagon/Vanagon Westfalia Service in the Ottawa Valley
>_Vanagon Stainless Steel Exhaust  Systems_
>(http://members.aol.com/Fkc43/stebro.htm)
>_BusFusion_ (http://members.aol.com/BusFusion/bfhome.htm)  a VW Camper
>camping event, Almonte, ON, June 07 ~ 10,  2007