N is actually smaller than O. Like Doof said, air is already 78% N2, 21% O2. The case for N2 is that it's inert, like a noble gas.
Nitrogen vs Air in Tires: Which Is Better? | Firestone Complete Auto Care
When it comes to tire pressure, is inflating your tires with nitrogen better than air? Learn more about your options, from Firestone Complete Auto Care.
www.firestonecompleteautocare.com
“Nitrogen molecules are larger and slower moving than those of compressed air. “