Autos: nitrogen in tires

Self-tutoring about autos: the tutor mentions the idea of inflating tires with nitrogen.

I’ve noticed green tire caps on cars and wondered what they mean. Apparently it means the tires have been filled with nitrogen.

With new ways of doing things where the old ways seemed to work fine, I’m typically skeptical. Since it seems I’ve noticed green caps mainly on newer cars, I’m even more so: the cars in this household are from 2013 and 2016.

I’ve heard that nitrogen leaks slower from tires than oxygen, although perhaps the difference is small. I wondered what the reasoning might be for the idea that nitrogen would leak more slowly from tires.

It turns out, the reasoning is that the nitrogen molecule (N₂) is slightly larger (in volume) than the oxygen (O₂) one, perhaps by about 8%. [This is in spite of the fact that the oxygen molecule is heavier.] Theoretically, this does suggest tires filled with nitrogen should leak slower than ones filled with atmospheric air.

Consumer Reports agrees that nitrogen-filled tires lose pressure more slowly than ones filled with atmospheric air; from their test, it seems, they found that air-filled tires lost 3.5psi over a year, while nitrogen-filled ones lost 2.2psi.

There is more to tell about this issue; I hope to follow up in another post:)

consumerreports.org

inertion.org