Tires With Nitrogen

A member of the Dodge Challenger owners’ forum was buying a new car from a dealer and noticed green valve-stem caps on all four tires. The salesman told him that the tires had been filled with nitrogen, which would keep the tire pressure and temperature more consistent and that it would prevent tire rot from the inside out. It wasn’t a free add-on, though. The “nitrogen upgrade” was a $69 item on the supplemental window sticker. Another forum member later posted that his dealer was charging $179 for this same “upgrade.”

Some dealerships and tire stores claim that filling your tires with nitrogen will save you money on gas while offering better performance than air. But a closer look reveals that nitrogen has few benefits and much higher costs. For starters, a typical nitrogen fill-up will cost you about $6 per tire.

Why Nitrogen?
The Get Nitrogen Institute Web site says that with nitrogen tire inflation, drivers will note improvements in a vehicle’s handling, fuel efficiency and tire life. All this is achieved through better tire-pressure retention, improved fuel economy and cooler-running tire temperatures, the institute says.

This sounds great in theory but let’s take a closer look at each of those claims.

  • Better tire-pressure retention: Over time, a tire will gradually lose pressure. Changes in temperature will accelerate this. The general rule of thumb is a loss of 1 psi for every 10-degree rise or fall in temperature. The institute says that nitrogen has a more stable pressure, since it has larger molecules than oxygen that are less likely to seep through the permeable tire walls.In 2006, Consumer Reports conducted a year-long study to determine how much air loss was experienced in tires filled with nitrogen versus those filled with air. The results showed that nitrogen did reduce pressure loss over time, but it was only a 1.3 psi difference from air-filled tires. Among 31 pairs of tires, the average loss of air-filled tires was 3.5 psi from the initial 30 psi setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial setting. Nitrogen won the test, but not by a significant margin.
  • Improved fuel economy: The EPA says that under-inflated tires can lower gas mileage by 0.3 percent for every 1 psi drop in pressure of all four tires. The theory is that since nitrogen loses pressure at a slower rate than air, you are more likely to be at the correct psi and therefore get better fuel economy.If you are proactive and check your tire pressure at least once a month, you can offset this difference with free air, and you won’t need expensive nitrogen. We think this invalidates the “better fuel economy with nitrogen” argument.