Nitrogen-Filled Tires & Better Gas Mileage?

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When I bought my tires from Costco, I noticed the caps for the valve stems were a flourescent green and asked about them – it means the tires are filled with Nitrogen. After reading a friend’s blog claiming that nitrogen-filled tires get 0.5 mi/gal better gas mileage and have a longer tire lifespan, I wanted to find some “proof” to these claims. The belief, also pushed by Costco in their tire brochures, is that the larger nitrogen molecules don’t react to temperature changes (better tread life and mileage) and lack moisture (won’t corrode the tire from the inside). It doesn’t affect my decision if these claims can’t be proven because there is a miniscule increased cost for using nitrogen (I can only “fill” my tires at a Costco, most gas stations only have air, but the service is free).

The theory is that the oxygen in the air inside the tire, when heated as a result of driving, can oxidize and rot the inside of the tire over time. A nitrogen filled tire won’t oxidize for obvious reasons, no oxygen. This is all anecdotal though and for most people, I think the tread of the tire wears out before the tire does from internal rot.

As for the nitrogen not reacting to temperature as much as compressed air, it’s probably a bit of snake oil magic going on there. At such low pressures, the nitrogen behaves like an ideal gas (just as oxygen and water vapor) so that means pure nitrogen will act just like regular air. A 0.5 mi/gal improvement in gas mileage is 1.6% improvement (on my car, which gets a little more than 30 mpg) which seems way too much.

It sounds like the “nitrogen is better than air” theory is not entirely true but since it costs me very little (if at all really) I won’t be complaining much about it. As long as you don’t pay for nitrogen, fill it with nitrogen; but if it costs you money, ask for regular air.

{ 167 comments, please add your thoughts now! }

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167 Responses to “Nitrogen-Filled Tires & Better Gas Mileage?”

  1. Chris says:

    Ok, i think its funny seeing all these rediculous stories and people who are all so scared of something new. I work in a Costco tire center. We never make any outrageous claims as the ones that people are sworn they are told here. The only thing we claim is that nitrogen is more stable then air when it comes to CLIMATE CHANGE such as when the weather is hot, the air expands in the tires just as after driving on your tires. Or when its cold out and the air condenses in tires. The nitrogen WILL fluctuate, just no where near as much as normal air would. As many have said above, YOU STILL NEED TO CHECK YOUR PRESSURE REGULARLY! Nitrogen is just there to keep fuel consumption and tire wear to a minimum between intervals of checking tire pressure. Another thing, COSTCO HAS NEVER CHARGED TO PUT NITROGEN INTO YOUR TIRES! Nitrogen inflation was something decided to be done once there were “BENEFITS” to it being claimed. We modified our systems for the MEMBERS benefit. With it being free, whats the downside of putting pure nitrogen compared to normal air? It cant make it any worse so all there is is room for improvement. Now Stealerships and small shops charge for Nitrogen but COSTCO has never charged a single person for Nitrogen. And to finalize for all you worried people about mixing nitrogen and air, THERE IS NITROGEN IN AIR! 78% ACTUALLY! Mixing them together just reduces/nullifies the claimed benefits of pure nitrogen. BUT IT IS 100% SAFE TO MIX THEM! No less safe in ANY way then normal air.

    • Nitrogen Happy! says:

      Everything you just said is precisely what I was told by Costco Tire Center when I was getting my new tires. No outrageous claims were made at all. I have noticed a consistent 4mpg increase since getting the new tires but I’m sure it’s due to a combination of the new tires, proper inflation, nitrogen and getting them rotated when I’m supposed to. I’ll add that I’m still impressed with the increased mileage though considering my car is 11 1/2 years old!

      • TT6 says:

        You have to be careful with the claim that nitrogen helps improve mpg.
        MPG is not improved due to having nitrogen in the tires, as there is nothing magical about nitrogen where it will affect rolling resistance.

        The potential MPG improvement comes by having a more stable psi in the tires over time, as pure nitrogen “leaks” out at a slower rate. So, by having a more consistent psi over time, that’s where the potential mpg increase comes from.
        With air only the cars tires may lose more psi over time. That under inflation will result in greater rolling resistance resulting in lower mpg.

        The way that air or nitrogen only can help increase MPG, is if you increase your tires psi to your car labels “high speed” or “high load” psi rating. The increase in psi will stiffen the sidewall keeping the tread from flattening as much as it does with the standard psi rating. As there is less tread meeting the road, the rolling resistance is lowered, and that can help increase MPG. So, it’s not the air or nitrogen that helps in this case. It’s the effect of increased psi in the tire.

  2. Nitrogen Happy! says:

    I regularly check my gas mileage when I fill up. I have to say I noticed an immediate difference in my gas mileage going from about 32mpg to about 36mpg (and consistently 35-36mph since then) when I got the new tires filled with nitrogren. I believe the tires installed were also bridgestone fuel/energy efficient tires but nontheless, there has been a consistent and maintained increase in my mpg’s since installed 6 months ago and I commute 150mi round trip per day so the numbers don’t lie…

  3. Mark says:

    Nitrogen filled tires cannot possibly increase MPG compared to air if both have the same tire pressure. The advantage of nitrogen is that tires lose pressure much slower with 95%+ nitrogen compared to air (with about 80% nitrogen) and your tires are less likely to be under-inflated (the major cause of poor MPG).

    New tires are much more likely to be “energy saver” designs with less rolling resistance than older tires. This is another factor in improved MPG.

    Also, the tire installers where you purchased new tires may have inflated your tires to a higher PSI level than you had before (even when your old tires were “properly” inflated). Even a difference of 1 PSI can make a difference in MPG.

  4. Whudy Goard says:

    I have 2010 Prius with nito fill. I added regular air in winter while on the road The nito fill was only 20 lbs at 20 degrees outside. Later my dealer replaced all the air with new nitro and I had 38 lbs. air instead of 35 lbs. I was getting 50 mpg and it went to 55 mpg. I think it was due to the extra air presure. Getting new tire soon from tire place and they think I should get the nitro fill for 20 dollars. After reading five hours on the internet i’ve decided to use the old regular air.

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