Why Is Nitrogen Good for Tires?

The Get Nitrogen Institute, a nonprofit group that promotes nitrogen, says that with nitrogen tire inflation, drivers will note improvements in a vehicle's handling, fuel efficiency and tire life. All these benefits are achieved through better tire-pressure retention and cooler-running tire temperatures, the institute says.

It 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 accelerate this loss. The 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 than oxygen since its larger molecules are less likely to seep through the permeable tire walls. But what does that mean in the real world?

Consumer Reports conducted a yearlong study to determine how much pressure was lost 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 Environmental Protection Agency says that underinflated 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.

For many people, however, this kind of maintenance is easier said than done. Most forget to check and top off their tires regularly or they never learned how to do it in the first place.

And though tire-pressure monitoring systems (TPMS) now come standard on cars, a National Highway Transportation Safety Administration study found that only 57 percent of vehicles with TPMS had the correct tire pressure. That's because most systems are only meant to signal that a tire has very low pressure, not to show that the pressure is optimal. Presumably, nitrogen-filled tires would save us from our own laziness, but at a price.