I was in Manhattan, Kan., waiting on my truck to be serviced about two years ago when the salesman at the service station brought me a brochure. It touted the benefits of filling my tires with nitrogen. I had never heard of such a practice, so I read the entire brochure with amazement.
It seems that there are companies that market nitrogen for use in automobile tires. The language on a brochure or a website from one of these companies reads just like that from any popular pseudoscience or scam. Phrases like “amazing benefits” and “high purity” could just as easily come from a vitamin supplement company. In the first couple of above-the-fold paragraphs on the website from one such popular company, it’s explained how the high cost of this technology – generating and delivering nitrogen – has kept it out of the hands and tires of the common folk until now. Lucky us. Seems it was the college kids with the nitrogen tanks for their kegorators who’ve had the secret this whole time.
Like any good skeptic, I’m not going to base an entire case against a product on poorly selected marketing tactics. Let’s think about what the product is trying to solve, decide if it makes sense and, if so, then decide if it’s economically viable.
The benefits for using nitrogen in tires comprise increases in fuel economy, tire life and safety.
Fuel economy
The hypothesis is that because nitrogen gas molecules are larger than those of oxygen, the natural seepage is reduced. Because lower-than-proper tire pressure has a negative impact on fuel economy, nitrogen must be better.
Tire life
The hypothesis is that the double bonds in the rubber of tires are susceptible to oxidation and that, over time, the anti-oxidants used by tire manufacturers to prevent this oxidation are degraded to the point that the oxygen in the tires begins to attack the rubber. Also, the moisture in air can cause corrosion on the rims. Because nitrogen doesn’t oxidize the rubber or corrode the wheels, nitrogen must be better.
Safety
The hypothesis is that because the expansion rate of nitrogen is less than that of air. Because varying pressures in tires can lead to problems in the consistency of handling, steering and braking, nitrogen must be better.
Let’s look at the difference between oxygen and nitrogen. I’m not a chemist, but from what I can find the difference in molecular size between the gasses of oxygen and nitrogen is about 3%. Furthermore, the air we breath – the same air that is compressed to fill most of our tires – contains nearly 80% nitrogen anyway.
Here’s some math from the Car Talk website.
Under-inflated tires lowers gas mileage by 0.4 percent for every one pound of drop in pressure of all four tires. So, if you’re down by 10 pounds… you’re losing 4 percent in fuel economy… For every drop of 10° Fahrenheit in air temperature, your tires will lose one pound of pressure.
I believe that nitrogen-filled tire pressure does change with temperature, perhaps just not as much as tires filled with air. If nitrogen pressure didn’t change at all with temperature, then by this math, properly inflating your tires with nitrogen during the summer can prevent this 4% loss in fuel economy if the temperature drops 100 degrees. Or you can simply check your tires every few months and adjust the pressure accordingly.
What about leakage? Does the 20% of the air in the tires that is 3% smaller than the rest really leak out so much faster that there is a change in pressure over the course of the few months between checks? I believe it may be slightly measurable – if using a highly accurate gauge – but I don’t believe it would be noticeable or significant to either the handling or the fuel economy.
We don’t drive our cars in a pure nitrogen environment, so the outside of our tires and our wheels are constantly exposed to oxygen, moisture and other more nefarious substances. I’ve never heard of anyone who had to replace a tire or rim due to holes rusting through from the inside of the wheels. Again, I suppose that it’s something that could be measured in the lab over the course of a very long time, but the wear on the tires will cause the need for a new tire long before the anti-oxidants (if this claim is even believable) go away. Likewise, the failure of other components on the car will cause the need for a new car long before the wheels corrode to the point that they need replaced.
The biggest logical fallacy noticeable in nearly all advertising for nitrogen in tires is an argument from authority. Because NASCAR and the US military use nitrogen in their tires, we average consumers should do the same. The high performance requirements – taking a turn at 150 mph or landing a bomber on a runway – require consistent, reliable air pressure. Both the military and NASCAR have large budgets, and at these extremes the slight benefit – only a percent or two based on the math above – of the nitrogen is worth the price which they don’t really care about anyway.
In summary, tires filled with air contain roughly 21% oxygen and 78% nitrogen and small amounts of water vapor and other trace gasses. Filling tires with dry nitrogen replaces that 21% oxygen with a molecule that is 3% larger and reduces moisture inside the tire. Does this practice increase fuel efficiency, tire and rim longevity, and safety? My guess is that it may be slightly measurable but certainly not noticeable – and most definitely not worth the additional cost for anyone who properly monitors tire pressure.
What did I miss? Let me know in the comments.
I guess there is practical reason to get that remaining 20% of nitrogen into the tires of precision vehicles, but there seems to be a very low benefit to using it in consumer level vehicles. Also, the cost to use nitrogen at your local service center seems to be far greater than what commodity prices for nitrogen gases are, so there definitely is a huge profit markup. I’d prefer the 100% discount on the low-grade nitrogen that is supplied out of your everyday air compressor or foot pump. :)
I worked as an airline mechanic on heavy aircraft. All the tires on a comercial airplane are filled with Nitrogen. Why, well it’s more stable and doesn’t overheat as rapidly as straight air. Landing and takeoff the tires get a bit hot. As for leakage well, we pre aired the replacement tires to 100 psi and every week checked the pressure when it dropped to 80 psi we refilled them to 100 psi. As for your car tires mine don’t last long enough to warrent it and for fuel savings, invest in a tire gague and use it weekly.
i would say that if it is that fuel saving on american hiways and biways then the trucking industry would be doing it and i have yet to see a nitrogen pump at a truck stop
I have a Ph.D. in Physical Chemistry, and I can tell you that nearly all of the N2 claims for tires are nonsense. First of all, N2 is more volatile than O2 (even though air is only ~18% oxygen, and about 78% Nitrogen anyway.
OK, maybe oxidation of the tire from the inside-out would be a concern, but the tread will wear out long before this is an issue.
When purchased in bulk, a “High Pressure” LN2 tank designed for High-pressure gas delivery is cheaper than an expensive, high-end air compressor… I’ll bet they use the HP-N2 to run their air-tools as well (you don’t have to worry about mechanical problems with your compressor during a pit-stop).
There are many physical and chemical problems with the claims of the N2 promoters, but basically they want your money, and will promote whatever it takes to convince people that it’s worth their money.
I use ~1,000 Liters of Liq. N2 in my research lab, and if there were ANY benefit to N2 in tires I would be filling a portable gas-tank in the lab to fill my tires… it’s not worth the hassle for free, let alone worth paying for.
Benefit would be since there is no oxygen then there is no rust or corrosion happening and your expensive rims on the inside should look as new as the day you bought them.
All the claims are false, or true only on the margins. Nitrogen and oxygen expand at the same rate with temperature (this is true for all gases). Never is a rim or a tyre replaced because of corrosion from the inside. Rubber just does not corrode quickly enough in air – witness the piles of old tyres everywhere. N2 and O2 molecules are so close in size there is no practical difference in leakage rates through the rubber. N2 is used on the race track and on 747s because when a tyre bursts thru high heat pure N2 will tend to put the flames out, or if a rim becomes red hot, then the tyre will not burn on the inside. This does not happen in cars. You are being scammed, often by well meaning but scientifically illiterate people, but often enough by downright crooks.
Nitrogen is non flammable.. so it is NOT more volatile. Seems like someone with a PhD in chem would know that!
Assuming that a tire filled with atmospheric gas leaks all the oxygen out. The tire is refilled with atmospheric gas and now instead of containing 20% oxygen it contains only 4% oxygen. When that two percent leaks out and the tire is refilled, it now contains only about 1% oxygen. It isn’t likely that the gas in a nitrogen filled tire is as pure as that, given that when the tire was first mounted, the tire was filled with atmospheric gas at ambient pressure.