Ballast How to top off nitrogen rear tires

[Mace Canute]

oxygens atomic number is 8, nitrogens is 7. So oxygen is indeed bigger and heavier.

That's not correct. An oxygen molecule is smaller than a nitrogen molecule.

http://www.getnitrogen.org/pdf/graham.pdf

 

[bigdeano]

The oxygen in air will rust a tubeless rim where nitrogen won't. It would depend on what fluid the tire is filled with, if any, as well. A repeated new supply of oxygen from airing up would tend to promote rust, seems to me.