a year without air

A little over a year ago I was having frequent Tire Pressure Monitoring System (TPMS) light—related alerts on my Kia’s dashboard. Given the rather stupid government-mandated TPMS system I found myself having to replace at least one of the valve stems.  Instead, I opted for a new set of four tires, four new TPMS valve sensors and the vendor’s upgrade to fill each tire with nitrogen rather than the expected air most tires use.

Nitrogen isn’t that exotic of an element. In fact, 78% of air already is composed of it. The remainder of air is oxygen, water vapor, carbon dioxide and smaller concentrations of other gases. Probably the most compelling reason to fill a car tire with Nitrogen alone is that it’s a large molecule and is much less likely to escape through the rubber. Without the water vapor, the tire’s pressure remains constant over a wide range of temperatures. In fact, that’s the topic of this post:  I just drove an entire year all over the southwest U.S. and didn’t need to adjust my tire pressure, not even once.

I drove in weather over the past twelve months which ranged from freezing to above 100° through numerous deserts during the summer. And each tire remained within a pound of the recommended tire pressure all this time.

According to the U.S. Department of Energy’s website:

“You can improve your gas mileage by 0.6% on average—up to 3% in some cases—by keeping your tires inflated to the proper pressure. Under-inflated tires can lower gas mileage by about 0.2% for every 1 psi drop in the average pressure of all tires.”

If an average driver goes 12,000 miles per year and assuming $3/gallon for gasoline and my own 26 MPG average, under-inflated tires for that year equates to $88.38 (quite a bit more than what the upgrade cost for the Nitrogen-filled tires).