Are Nitrogen Molecules Really Larger Than Oxygen Molecules?

According to the "Get Nitrogen Institute" in their paper on N2 effusion
http://www.getnitrogen.org/pdf/graham.pdf

"The correct answer, with respect to 'permeation,' is yes."

So I imagine your question is why don't I support the effort to "sell" the idea of always inflating your tires with just Nitrogen. It comes down to effort and cost VS level of benefit.

Maybe one way to think of this would be to imagine dropping a penny as you walk away from making a small purchase at a store. If you dropped a number of coins you might stop, bend over and pick them all up. But what if you only dropped one penny and didn't discover the fact till you had walked to your car. Would you walk the 20' back to the store to look for the penny? I bet not.

There is no doubt that you would have more money if you picked up the penny but would you consider it worth the effort?

In general, tires lose about 1%  of their inflation pressure each month in laboratory testing. This is almost entirely Oxygen. It is also true that tire pressure changes about 2% for every change in temperature of 10F. This is true for Nitrogen or air.
I haven't tried to run a test but it is also true that every time you use a hand pressure gauge to check your air you let a little air out. How much air do you let out if you use a gauge to check your tires every day? Might it be 1% in a month's time? Might it be more?

Finally, what does it cost to inflate your tires with N2? Even if you have a deal with a dealer and can get your pressure "topped-off" for free, you still have to drive to the store location to get that "free" inflation.

Bottom Line:
IMO the small level of benefit of inflating with N2 just isn't worth the effort and cost. There is also the real negative of not checking your tire pressure simply because you believe that by inflating with N2 your tires will never lose pressure so you don't need to check. What about small punctures or leaking valves? If you don't check the pressure you will not learn about the leak till it is too late.

However, if you want to inflate your tires with N2 I see nothing wrong with doing that. After all, it's your time and money, not mine.



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When to replace tires? Can you drive on one "dual"?

Was reading a magazine aimed at motorhome owners and there was an item about a man that suffered a tire failure. It was one of his rear duals. The RV owner reported that he decided to drive to the nearest tire store where it was suggested that he replace all six tires. The tire dealer had to educate the RV owner about the life of tires in RV service being 10 years or less with many recommending that tires be replaced after six or seven years life.

The magazine did offer a brief explanation on how to "read" a tire DOT serial and learn it's age.

IMO the magazine missed an opportunity to further educate their readers with a warning of the damage that was probably being done to the mate of the tire that failed.

First off there is a good probability that the tire, being over 10 years old, failed from a belt/tread separation. We can't be sure, as the RV owner didn't have a TPMS, so we don't know if he could have avoided the problem of a "Blowout" or Run Low Flex Failure on the Interstate. We do know if there was a slow air loss, the tire that did not fail was being run with ever-increasing overload, for as the companion tire lost its air the load on that end of the axle was being transferred to the fully inflated tire.

In the tire industry, there are tables that provide information on how slow you need to drive as you increase the tire load above its normal load capacity.

Basically, you need to run no faster than 40 mph if you are running 107% of the rated load.
If you want to run 113% you can drive no faster than 30 and the max speed drops to 20 mph if the overload is +21%.

Since our RV owner was running at 200% load I would estimate that maximum speed he could travel without doing damage to the "good" tire to be no faster than 5 mph and even that is questionable as there are also distance limits for those conditions

BOTTOM LINE
If you have a tire failure, no matter the reason, you need to change out the failed tire and should not attempt to "limp" home on its companion. If you are concerned for your safety on the side of the road you need to be aware that driving over 5 mph means you need to have the companion tire also replaced. No matter its age. As always when changing tires in a dual position you must also match the pair as covered in THIS post.


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