Craig Lalley wrote after Brice Yokem wrote:
> Leakage is a factor in such things.  There is no such thing as a
> perfect seal.  I am not an automotive expert, but I bet the
> leakage is more significant than the reactivity.
> ****************************************
My understanding is that the oxygen reacts with the moisture and can cause 
rust on a steel rim.Of course the amount of time it would take to cause 
significant damage would be longer than the life of the car.-Craig

I first came across this in 2007:

> These cops in North Carolina are filling their tires using nitrogen
to save money:
>
> http://www.wral.com/news/local/story/1713452/
>
> According to the car dealer:
>
> "It's been used on the space shuttle, commercial aircraft for
decades," said car dealer David Hurd. "Nitrogen is not affected by
normal cold and hot conditions, so you don't have any fluctuation in
the air pressure."
> As a result, nitrogen is reported to extend the life of a tire and
provide better fuel economy.
>

It sounded like a scam to me, because air and Nitrogen follow the same gas 
laws in terms of expansion/contraction due to changes in heat. But then 
someone pointed out this:

There's a grain of truth, though the article got the details wrong:
http://en.wikipedia.org/wiki/Nitrogen#Molecular_nitrogen_.28gas_and_liquid.29

It occurred to me after I posted the article that one possible advantage to
using nitrogen over air is that by removing the oxygen component you would
reduce the oxidation of the rubber. The wikipedia article says that it is
not necessary for consumer automobile tires, but I could see how it might
make a difference with aircraft tires where I assume we are dealing with
greater pressures.

The difference in diameter of nitrogen versus oxygen and it's effect on
diffusion through the rubber didn't occur to me but I would think its effect
would be fairly small. If it was very large then the oxygen would diffuse
out faster than the nitrogen and you'd end up with nitrogen filled tires
anyway :-)

Bruce (still thinking it's a scam) Collins 

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