One of the more common questions I get about nitrogen tire inflation is actually a pretty intriguing one. If oxygen leaks out of an air filled tire, wouldn't the driver end up with nitrogen inflated tires after a period of time? Good question, but what is the answer?
Air is comprised of 78.1% nitrogen, and nitrogen inflated tires typically have a purity of 95% nitrogen. I measured the nitrogen purity in air filled tires of various ages to determine how this oxgen migration affects nitrogen purity. Not one tire I measured had a nitrogen purity of 78.1%, every one was higher indicating significant oxygen permeation had occurred. The findings:
- Tires aged <1yr yielded purities ranging from 80% to 82% nitrogen.
- Tires aged 1-2 years yielded purities ranging from 82% to 84%.
- Tires aged >2years (but typically less than 5 yrs) yielded purities ranging from 83% to 88%.
A lot of the older tires seemed to be in pretty poor shape, with low quality rubber and inadequate tread. It appears tires would have to be in service for a long period of time to approach a respectable level of nitrogen. Not to mention that the air filled tire is still seeing significant ammounts of moisture and contamination over the life of the tire. Nitrogen filled tires have no moisture (-50F dewoint) and are contaminant (liquid & solid free).
So the answer is yes, normal migration of oxygen through an air filled tire yields a higher nitrogen purity. But the tire is only nitrogen enriched, not truly nitrogen inflated. And the benfits of a clean, dry inflation gas are not going to be realized.