Nitrogen or regular old air? If you’re confused about which to use in your tires, don’t panic – you’re not alone. The cacophony of claims in the war between air and nitrogen runs the gamut from nitrogen being the greatest technological advance since someone figured out how to use a wheel, to the use of nitrogen being a complete sham.
The truth of the matter is that nitrogen does have some scientific advantages over air, but they lie at the upper reaches of the tire performance spectrum, and it’s debatable if the average driver will reap any benefits from using nitrogen. Let’s take a closer look at some of the factors in the argument and see if we can help you decide which is right for you.
Air for tire inflation is almost universally available at a reasonable cost. Just about any service station or tire dealer anywhere will fill up your tires or let you adjust your tire pressure for free, or for a couple of dollars at the most. Not so with nitrogen. The infrastructure for nitrogen is not fully developed and, in many places, nitrogen is simply not available. Where it is available, nitrogen generally costs $5 - $7 for filling each tire, and some tire installers will charge $70 - $180 for a complete nitrogen upgrade. Converting air-filled tires to nitrogen requires filling and deflating the tires with nitrogen several times to purge all of the air (nitrogen must be 93-95% pure to be effective).
If you have nitrogen-filled tires and you encounter a tire deflation issue on the road where no nitrogen is available, you can top up the tire with air with no ill effects to the tire or your vehicle’s handling, but you may have to recharge the tire with nitrogen later to purge the air.
All tires have microscopic pores through which any inflating gas, air and nitrogen included, will seep out over an extended period of time, gradually lowering the inflation pressure. Nitrogen has larger molecules than air and will move through the tire more slowly than air, thus maintaining the inflation pressure longer.
Consumer Reports conducted a study comparing nitrogen versus air loss in tires to determine if this benefit of nitrogen was worth the extra cost. They used 31 pairs of various tire models, filled one tire of each pair to 30 psi with air and the other to the same pressure with nitrogen, then left them outside for a year. At the end of the year, they found that all tires lost pressure. The average pressure loss with air was 3.5 psi; with nitrogen the average loss was 2.2 psi – a difference of only 1.3 psi over a year.
Consumer Reports concluded that nitrogen’s slight improvement in tire inflation pressure retention was not a substitute for regular inflation checks. If you check your tire pressure regularly, you’ll be able to easily spot a pressure drop without incurring the extra cost of using nitrogen.
The EPA estimates a 0.3 % drop in gas mileage for every 1 psi drop in all four tires. A drop in tire pressure increases the rolling resistance of your tires, which is what causes the decrease in your gas mileage. An ExxonMobil study in 2008 found that using nitrogen to inflate tires does not change a tire’s rolling resistance – and that tells us that nitrogen won’t have an effect on your fuel economy. As always, check your tire pressure at least once a month and keep your tires at the recommended inflation pressure to minimize rolling resistance and maximize your gas mileage.
Air is 78% nitrogen and 21% oxygen, with the remainder being trace gases. Oxygen can retain moisture inside your tires and eventually can oxidize the internal tire wall casing, causing premature tire aging. In extreme cases, the moisture can even cause the tire’s steel reinforcing belts to rust. If the wheel’s paint protection is damaged, this can also promote rust in steel wheels.
Nitrogen, on the other hand, is an inert, dry gas and does not support moisture. The use of 93-95% pure nitrogen will prevent premature tire aging and wheel corrosion due to internal moisture. However, some experts say that under normal driving conditions, a tire’s tread will reach its minimum usable depth long before any effect of oxidation on the tire wall or wheel rust. Although nitrogen has the technological advantage here, the practical benefit is minimal under normal driving conditions. It may be beneficial if your car is not driven regularly or is placed in storage.
Just about every race car, airplane, and heavy equipment tire is filled with nitrogen. These vehicles subject tires to extreme temperature conditions, and the use of nitrogen allows better control over tire pressure as tire temperature increases. Compressed air holds moisture and the amount of moisture may vary from tire to tire. During extreme usage, the amount of moisture in the tire causes the tire temperature to increase more rapidly, and in a non-linear way that can be unpredictable.
With dry nitrogen, the effects of moisture are eliminated and the increase in tire pressure due to temperature is more linear and predictable than with air. The tires also run cooler, which is especially important in racing because the grip of race tires is highly dependent on tire temperature.
So where does all this information leave us? As we’ve seen, nitrogen does have some technological advantages over air for tire inflation. Whether or not those advantages will be of any practical use to you depends on how you use your car. Certainly, if you fall into one or more of the categories below, using nitrogen could be beneficial:
If you use your car on a regular basis for daily driving and don’t fall into any of the above categories, it’s difficult to see how using nitrogen gives you any practical benefits, especially compared to its cost and inconvenience. But it’s your call – nitrogen does no harm to your tires and if you’re interested, you can test it out – maybe on that new set of Michelin Pilot Sport 4S tires you’ve been eyeing. If you don’t like it or don’t see any benefits, you can always go back to the free (or almost free) alternative that we’ve all used successfully for years: air.