Can nitrogen in tires reduce gas mileage?

Dear Driving for Dollars,
A while ago, I replaced the air in my tires with nitrogen at a cost of $20. Now I’ve noticed that I’m getting about 40 miles less per tank of gas.

Can nitrogen cause a drop in gas mileage?
— Esther

Dear Esther,
Using nitrogen in tires will not cause a drop in gas mileage. Have you checked your tire pressure lately? The most probable reason for the drop in fuel economy is that your tire pressure is low. Just because you replaced the air in your tires with nitrogen does not mean you no longer need to check your tire pressure.

While nitrogen in tires does equate to a slower loss of pressure, your tire pressure will still decrease over time, which translates to a loss in fuel economy. Check your tire pressure, and make sure that it is at the recommended pounds-per-square-inch level, which is listed in your owner’s manual or on the label on the driver’s side doorjamb, refilling your tires with nitrogen or air if necessary.

If you have a car shop refill your tires, immediately confirm that the pressure is set to the recommended level. Ask the shop to adjust the pressure if it’s not at the level. Check your tire pressure once a month to maintain optimum pressure.

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