Nitrogen in tires, what’s really driving the trend.

I don’t know if you’ve noticed it, but more and more places are offering pure (or more pure) nitrogen for filling your tires. When I dug into the whys of this, I found a bunch of BS, one good reason, and a lot of money…This subject has been popping up on a lot of the auto forums I frequent, and I’d never really understood the drivers for it. After all, room air is already 80% nitrogen, so really, we’re just talking about a change in the 20% that remains.

Well, I just read an article in Ward’s Dealer Business  about nitrogen in tires. Ward’s Dealer Business is trade magazine for the dealerships, and is not read by many in the auto-consuming public. As a sometimes Automotive Journalist, I read a wide range of stuff about cars, and thier newsletter is something I glance at from time to time.

Anyway, the article by James Clausen is called Nitrogen Can Pump Up Profits… You can see where this is going… Anyway, it starts by reviewing the benefits claimed by pervayors of nitrogen filling. And they are:

  • Slower Diffusion Rate through rubber that results in more stable tire pressure.
  • Elimination of water reduces corrosion of thing like steel wheels and tire pressure monitoring system (TPMS) sensors.

Well, the first is complete BS. Mr Clauses claims that the faster effusion (no, this isn’t a typo, effusion is the right word) rate of oxygen is due to the fact that oxygen is a smaller molecule. Well, N2 has a 7% faster effusion rate (Graham’s Law of Effusion), and O2 actually has a longer bond length (1.21 vs 1.112 Angstroms)!

But the claim about water has merit and this is because water can condense at lower tempuratures, this would lead to larger pressure fluctuations. The act of removing water seems to be the big benefit of going to pure nitrogen.

But really, enhancing tire lifetimes by reducing pressure fluctuation isn’t really in the interest of tire sales people, service stations or dealerships. That means that they sell less stuff over time. Really, the real reason that you’re seeing more of places offering nitrogen is money. They can sell the service (a back of the envelope shows that selling just one nitrogen fill at $30 per day will pay for the equipment, utility and labor costs of the service, the rest is just gravy…) or they can offer the service for free to drive business into thier shops, providing the perception of value or safety that will capture and keep customers.

So, if some place offers you nitrogen for your tires, go ahead and say sure, unless they’re asking you to pay for it. It really is about the money.

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