Not quite right.
Air is roughly 79% N2 and 21% O2 (ignoring CO2 and all the lesser gases).
N2 has a molecular weight of 28 while O2 has a molecular weight of 32. i.e. O2 is slightly larger not that it really matters.

 

Nitrogen In Tires
Here are a few other benefits of using Nitrogen in tires:
[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.
[2] Nitrogen is moisture free: Pure Nitrogen inflated tires experience less steel belt and rubber degradation. Nitrogen use also reduces valve and wheel corrosion.
[3] Nitrogen provides longer tire life: Nitrogen inflated tire run cooler and require less maintenance according to the Goodyear application bulletin.
[4] Nitrogen is non-flammable: Nitrogen technology has been used in aircraft, military and race car technology for over thirty years.

 

Ok educate me, I took only elementary chemistry in college and most I forgot.

Looking here:
http://www.corrosionsource.com/handb...odic_table.gif

I see Nitrogen (single atom not molecule) has an atomic number 7 and atomic weight of 14, while oxygen has an atomic number 8 and atomic weight of 16.

How can Nitrogen be more dense unless the molecular structure is different, eg. N3 vs O2? Are the Nitrogen atoms bonded to anything else that makes them more dense than Oxygen?

 

I'm not a scientist, but everything I've read (from the engineers and scientists) says the same thing. Nitrogen is heavier / larger and that's why it doesn't escape where the components in "breathing air" does. The earlier quote was from this article:
http://ezinearticles.com/?Selling-Ni...-Air?&id=38142

The literature my dealer gave me said the same thing, as do all other web sites, printed literature, etc.

http://www.getnitrogen.org/

Perhaps the 02 isn't the issue, it's the other gases and that Nitrogen is safer to use in tires than pure O2.

 

Yah O2 is a nasty molecule reacts with everything, I know that much!