On 11/07/2014 9:44 AM, SMS wrote:
....

It isn't just the fact that it's nitrogen versus a mix that includes
nitrogen, there are other reasons for using nitrogen versus air as well.

The reason that Costco doesn't charge for nitrogen is not a marketing
ploy, the use of nitrogen reduces failures and Costco is one tire store
that actually honors its road hazard and tread life warranties. The cost
to them of including nitrogen is trivial given the benefits to them.

....

While it is true there's a slight difference in partial pressures owing
to water vapor versus dry air, for normal fluctuations in temperature I
can't think it's more than about a per cent or so, perhaps. (I haven't
sat down and done a calculation, but I'm positive it's nothing even
close to the difference between cold and hot running temp unless you're
looking at from midwinter to midsummer swings).

I really still have a very hard time believing there could be
demonstrated a real return for normal passenger tires solely due to N
vis a vis air--the effects of O2 on rubber causing damage or the like
just ain't gonna' be there for a tire that's being driven routinely.

Granted low pressure will increase early tread wearout, but again I
don't believe the difference in air pressure solely to N vs air is going
to prevent it if the owner/operator doesn't make the necessary
maintenance checks.

Plus, how many once they leave the store have a flat repaired elsewhere
or just refill w/ the corner station and the like so the N at best gets
diluted between new installs, anyway.

I just don't see it possibly being able to be enough of a factor to ever
really matter other than for the specialty cases.

For commercial airliners I can see it's desirable to not lose that full
partial pressure regardless of how small it is owing to the fact that
the water vapor will freeze at altitude, but for a passenger car tire,
no way...

$0.02, ymmv, im(ns)ho, etc., etc., etc., ...

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