[Guest]

Here's a practical puzzle... Lately, every time I take my truck into the shop, they try to sell me on the benefits of putting nitrogen in my tires instead of just compressed air. Touted benefits [among others] include better tire performance [handling], and longer wear. At $9 per tire I have been reluctant to buy since air is mostly nitrogen anyway.

So this puzzle has two parts: 1. caculate the concentration of water vapor and nitrogen at 40psi assuming assuming a fill at sea level in a tire with a volume of 10 liters. Further assume makeup of air in uncompressed volume of tire before fill is 78%Nitrogen, 21%Oxygen, 1%other inert, with 50% relative humidity. For simplicity sake, let's also hold the volume constant [compressed vs uncompress fill.]

2. Using your own knowlege, support or argue the theory of improved tire performance and wear.

[Guest]

AS I understand it, the Nitrogen they use is close to zero humidity, which is part of the "bonus" of using it. Therefore there is almost no water vapor at all in a Nitrogen fill. Also, my understanding of the physics behind it is that Nitrogen is a larger molecule than Oxygen, so it takes longer for seepage to occur for that extra 22% of the fill. Thus you maintain optimum PSI for a longer period of time.

Now, I've used Nitrogen fills in my Altima for the last three years. I have to say that I noticed a slight improvement in PSI mantenance, except for that time that I caught a nail, but that wasn't the N2's fault.

[Guest]

AS an aside: my N2 fills are free. I don't know that it makes enough difference that I'd spend $9 a tire for it.