[TR] Nitrogen in Tires

[Dave1massey at cs.com]

In a message dated 9/2/2008 9:19:21 AM Central Daylight Time, 
jeyoung_2 at yahoo.com writes: 
> >Why do you say that?  The molecular weight of nitrogen is
> >14 whereas oxygen 
> >is 16.  Since oxygen has a larger nuculas (the root word
> >for "nukular") and 
> >more electrons it sounds logical that nitrogen is actually
> >larger.

My typo.  What I meant to say is Oxygen is actually bigger.  Based on 
molecular weight and electron count.

> 
> It is actually smaller. The attraction of more electrons toward the nucleus 
> make the nitrogen atom smaller than the oxygen atom.

Now that makes sense.  But I guess absorption and permeation have little to 
do with the physical size of something approaching the scale quantum mechanics. 


> >
> >Besides don't they both follow the ideal gas law?
> 
> At these conditions, yes. 
> The only difference I can see that has not been mentioned so far is that the 
> Nitrogen is DRY. Water vapor certainly does not follow the gas laws at these 
> conditions and the water vapor may condense at ordinary temperatures and 
> vaporise at higher ones, thus changing the pressure slightly. It seems to me 
> that dry air would be just as good as dry Nitrogen.

I agree.  Getting your tires aired up on a hot, humid summer Satruday 
afternoon (a busy time for the local tire shop) may not be as good an idea than doing 
it first thing in the morning.  Other advantages to using nitrogen are that 
you can toss a cylinder of nitrogen in the truck and have a source of 
compressed air where there is no compressor handy.  But these are atypical 
circumstances.  If a garage wants to fill my tires with nitrogen, that's fine.  If they 
want me to pay extra...

Dave