When you see green caps on your tires' valve stems, it usually means that the tires are filled with nitrogen instead of air. Car dealers, tire dealers, repair shops and even some gas stations have touted nitrogen for several years as a better alternative to air based on claims that nitrogen doesn’t leak as much, so tires stay fully inflated longer. What’s the truth behind nitrogen?
Some people also claim that nitrogen improves fuel economy and allows vehicles to get a better gas mileage than those with tires that are filled with air. With gas prices always on the rise, the improved fuel efficiency alone may tempt you into considering switching to nitrogen. The catch is that topping off the nitrogen typically costs from about $5 to $10 per tire, and the initial charge for filling the tires can be much higher, so it’s also a revenue source for service outlets.
Does your vehicle really benefit when you choose nitrogen instead of oxygen or is it just a way for service stations to make more money?
Let’s take a closer look at the benefits of filling the tires on your vehicle with nitrogen.
Benefits of Nitrogen-Filled Tires.
It is true that pure nitrogen doesn’t leak out of tires as quickly as oxygen simply because a single molecule of nitrogen is larger than an oxygen molecule, so nitrogen-filled tires should remain at, or near their recommended inflation levels, or PSI, for longer. Fully inflated tires last longer and improve fuel economy and road-holding ability. It’s also true, however, that nitrogen will still leak out of tires over time, just not at the same volume as air. As a result, even if you use nitrogen, you will still need to stop and check your tire pressure from time to time to make sure they are still at the correct PSI.
Nitrogen fans also argue that air contains moisture, which can build up inside tires and possibly corrode the wheels and tire pressure monitoring systems (which track your PSI and alert you to any problems), as well as accelerate tire rot from the inside. Some air compressors use dryers that remove moisture before it gets into the hose you use to fill your tires, but many don’t. Nitrogen, in comparison, provides a “dryer” inflation. The absence of moisture in dry nitrogen ensures a more steady temperature inside the tire. This is why nitrogen tires are common on race cars. On the other hand, a nitrogen-filled tire isn’t 100 percent pure; about 93 to 95 percent of what’s inside is nitrogen, but the rest is air. Ordinary air is 78 percent nitrogen, so the difference isn’t huge, and compressed air is cheaper to use and still free in some places. In addition, whether a tire is filled with ordinary air or nitrogen, it will leak if the tire valve is faulty, if the tire isn’t properly mounted and sealed on the wheel, or if the tire has a nail in the tread or other damage. Nitrogen doesn’t fix damaged tires, so it’s still important to check your tire pressure regularly. Keep in mind, however, that not all roadside assistance providers carry nitrogen in their trucks, so air will be used to fill up your tire to the proper pressure.
Temperature changes may also still cause fluctuations in tire pressure even when you use nitrogen instead of oxygen.
The Bottom Line: Nitrogen vs Air
The Rubber Manufacturers Association, a trade group for tire manufacturers, says nitrogen “may contribute to minor reductions in an inflation pressure loss,” but also notes that “use of nitrogen alone is not a replacement for regular inflation pressure maintenance.” Tire maintenance is important whether you opt for nitrogen tire inflation or you prefer to use air. While you may be able to go longer between needing to add air, you still need to check your tire pressure regularly.