It's been a while since I took general chemistry (7 years
😱), but I believe atoms generally get smaller as you move to the right within the same row of the periodic table. This occurs because the number of protons increases and creates a stronger 'pull' by the nucleus on the outermost orbital. Thus, while O2 may have a longer bond length, the 'radius of gyration' (i.e. the net total length of the molecule) is probably smaller. Another factor could be that oxygen has a higher affinity (i.e. solubility) for these rubbers, but that's just speculation.
Edit: I have all these textboks... I supposed that I could actually use them for a change. It looks like the 'kinetic diameter' of O2 is 0.346 nm, while N2 is 0.364. I tend to doubt that this small difference alone could possibly account for a three-fold difference in a diffusion coefficient, but I don't have the book that I need here to look into that. The little data I have suggest that the two have nearly identical diffusion coefficients in 'natural rubbers', but that is not really what tires are anymore, so it's hard to say for sure.
Now, for their four statements:
[1] Nitrogen is denser than Oxygen: This means the larger molecules escape less easily from tires resulting in a more gradual loss of pressure over time. According to the Michelin Tire Manual, a tire that is inflated with Nitrogen loses its pressure 3 times slower than if it were inflated with air.
Sure, nitrogen is very slightly denser than oxygen, but this doesn't tell us anything about how fast it will leave tires. It does mean that it takes more work for the tire to rotate, since the same volume has a higher mass. This will lower gas mileage, but probably not by much, and the effect will vary with average speed.
[2] Nitrogen is moisture free: Pure Nitrogen inflated tires experience less steel belt and rubber degradation. Nitrogen use also reduces valve and wheel corrosion.
There is no such thing as 'pure nitrogen'. My senior design project was to design a chemical plant that would produce 99.5% nitrogen, which is a pretty typical purity for nitrogen that you might get in a compressed gas cylinder or from a house nitrogen system in a lab. Contrary to what this guy says, the steps used to remove oxygen are not the same as those used to remove water in a nitrogen process. Oxygen is generally removed using an ethanolamine reduction reactor, while water is removed using molecular sieving, flash drums, or similar processes. Of course, this doesn't really matter because the compressed air you get from a gas station should also be run through a drier first (though I've seen gas stations that didn't do this and I ended up with a big mess).
[3] Nitrogen provides longer tire life: Nitrogen inflated tire run cooler and require less maintenance according to the Goodyear application bulletin.
Again this claim is misleading at best. Assuming that the thermal conductivity and heat capacity for nitrogen are higher than that of oxygen, a nitrogen-filled tire would run slightly cooler than the air-filled tire during short trips. However, once the tire reached equilibrium, it wouldn't matter which gas was filling the tire. This does raise a potential problem with nitrogen-filled tires: if a tire is designed to run using air and nitrogen is used, the equilibrium volume will be lower for the nitrogen-filled tire, causing a reduction in gas mileage and an increase in tire wear. In reality, this effect is probably too small to actually matter, but so are all the effects this guy is talking about, so I thought I'd throw it in there.
[4] Nitrogen is non-flammable: Nitrogen technology has been used in aircraft, military and race car technology for over thirty years.
Air is non-flammable as well. What's his point? Just more salesmanship. If you had a tire rupture, there would be enough ambient oxygen that whatever is filling your tire isn't going to matter. An existing flame will be fed just fine.
