I saw an ad for tires that gave a price for the tires with installation included. This was at Costco and included Michelins with a free fill with nitrogen. I have always heard this is just an upsell for the most part but was wondering if there is any real benefit. I hear it expands/contracts less with thermal changes and it less likely to slowly leak because the molecule is larger. Plus there is less oxygen to slowly degrade the insides of the tires. On the other hand, air is mostly nitrogen anyway. How big of a deal does this really make? I have been told that unless you race, it isn’t worthwhile at all.
Also, if you have tires that are on the car a long time but slowly leak as they all do, will oxygen preferentially leak over time and will the gas content in the tire become enriched with nitrogen as tires are topped off over time? Although the molecular weight of oxygen is larger, the molecule is smaller. I guess this could also reduce the rotational inertia of your tires by a TINY amount but again, we are splitting hairs. Is there any merit in this?