So I had an epiphany the other day. We have companies that charge you to have your tires drained of oxygen and filled with nitrogen. They sell this by saying that nitrogen molecules are larger than oxygen and will leak out of your tires less which in turn gives you “better gas mileage” by having properly inflated tires more often.
Let’s think this through… The single fact that folks forget is that our atmosphere and the air we breathe is NOT 100% oxygen. In fact, it’s barely 21% oxygen. 1% is a mix of argon, carbon dioxide, and other gasses… and 78% is… drumroll please… NITROGEN!
Point 1: We are already pumping our tires with compressed air comprised of 78% nitrogen.
Moving on… If we then take their claims to be true, that oxygen leaks out of tires and nitrogen doesn’t (or at least doesn’t as quickly), this means that only 21% of the contents of our tires can leak out… let’s pretend it does. We’re left with 100% nitrogen in the (albeit under-inflated) tire. So we fill the tire the rest of the way, with another 78% nitrogen / 21% oxygen mix. This brings the total nitrogen content to just over 94% and the oxygen content to under 5%.
Now only 5% can leak out (or is at least more likely to leak out) and once you do that and refill that 5% space with 78%/21% nitrogen/oxygen mix, you now have a tire with 98% nitrogen in it.
Point 2: Normal topping off of tires puts in 98% nitrogen after just 2 top-offs.
Neat, eh?
Let’s then pursue the alternative. Pay someone to put in nitrogen. Do you think they fully drain the tire of all gasses prior to filling with nitrogen? Nope. They don’t put a vacuum in there… they just remove all EXTRA pressure, leaving the tire with some normal air in there at normal atmospheric pressure… then pump it full of nitrogen the rest of the way up to 30psi or whatever your tire is rated for. What do you think that ratio ends up being? Do you think it’s 98% to 1%? Or maybe 94.4% to 4.6%? What are you really paying for here?
Snake oil my friends. Snake oil.
Point 3: Nitrogen inflated tires are not fully drained of oxygen before being filled with nitrogen anyway.
That being said, if you buy new tires at a place that offers free nitrogen inflation, and the cost of the tire is better than anywhere else that just uses air… then sure, go for it. It might save you a single top-off. But then again, it might not.
/end epiphany