Tuesday, August 01, 2006

When bad economics meets junk science

Some drivers are filling up their tires with nitrogen, instead of regular air, because tire shops have convinced them it improves gas mileage. Considering that our atmosphere is already 78% nitrogen, I side with the skeptics.

There can be a difference under NASCAR conditions, where nitrogen is used not to improve gas mileage, but to get consistent expansion in the tires and thus more consistent handling. The the tires are completely deflated, then filled with nitrogen, but it's not the nitrogen itself that does the trick. It's the fact that the nitrogen comes "dry" from the tanks, because atmospheric moisture is what makes tires inconsistent in expansion and contraction. Nitrogen is an ideal gas because it's already the great majority of our air, and it's very close in weight to oxygen, so the weight of the gas in the tires won't be much different than plain air. Hydrogen and helium are far too light, besides the fact that hydrogen is highly explosive. Pure oxygen is a very bad idea, and not because it's slightly heavier than air: oxygen is extremely combustible, and the tiniest spark would make the whole tire burst into a big flame. (That's the real reason hospitals started to ban smoking, because of pure oxygen sources.)

So ordinary drivers, i.e. people who aren't driving 200 m.p.h., probably won't notice the minimal improvement in handling consistency (which is not the same as an improvement in handling). And gas mileage? There needs to be better testing before I believe the "nitrogen activists" who claim a couple mpg more. Bourque's anecdotal 1.5-mpg increase has so many other variables at play, not the least of which is how carefully he filled up with regular air before, and how carefull now with nitrogen. It's like trying a new laundry detergent you badly want to believe in: did your clothes really come out cleaner, and like any good scientist asks, how can you reproduce the test?

There's also a high cost in filling up your tires, even with "lifetime free refills." How close is that tire shop? Are they charging more to cover the cost of the expensive nitrogen equipment? Instead of filling up anywhere that's convenient, is it worth your while to travel an extra distance just to get, say, 20 miles more per tank of gasoline? For some people, it might be very worthwhile. Hey, your mileage may vary (pun intended). But I'm pointing out that filling up with nitrogen is hardly at zero cost for most.

It's surprisingly true that nitrogen molecules are larger than oxygen molecules, but only slightly. Let's put it this way: nitrogen's atomic radius is 65 picometers, and oxygen's is 60 picometers. That 8.3% difference may seem like a lot, but the hydrogen atom's atomic radius is 25 picometers. Thus the difference in size between the nitrogen and oxygen atoms is one-fifth the size of hydrogen, the smallest atom. Besides, the sizes are so small and so negligible that the difference in "seeping" is minimal. Putting it in the other extreme, is there much of a difference if you're trampled by a 14,000-pound elephant or one weighing 15,000 pounds?
Marty Mailhot, manager of the Tire Warehouse in Topsham, said the idea is catching on with consumers, who are purchasing nitrogen for tires for cars, trucks, motor homes and lawn tractors. He has even tried it on footballs and inflatable tubes pulled behind boats.
And people also buy those little metal-imprinted stickers that you put on your cell phone battery, which supposedly improve reception. I've seen others that claim to lengthen battery life.

People will catch on to a new fad, thinking it'll help a lot, especially with cars. There are seemingly hundreds of different engine additives out there that are basically snake oil, but people buy them and swear they improved horsepower and fuel economy. Yet the Federal Trade Commission and others have done many studies that found no benefit whatsoever from these additives. The FTC has charged several of the big names with false advertising, receiving settlements from most, which I do think is part of good government's function: the companies were committing fraud by selling products based on untrue claims.
He has a retort for those who pooh-pooh the notion of paying for nitrogen when there's plenty of free air for the taking.

"I say, 'Why are you drinking that bottled water when there's a pond out back?'" he said.
I think Mailhot is expecting people to make the simple but foolish answer, "Because bottled is better/more pure." But I'm not breathing the air in my tires, so I don't care about the sanitary quality.

Also, as I pointed out, ordinary drivers won't see much difference between pure nitrogen and regular air. On the other hand, I live by some of the reservoirs that feed New York City as well as Westchester, and there is a difference between your ordinary bottle of Poland Spring and my tap water.


Anonymous David W said...

As someone who wouldn't bother with it myself, there is still a theoretical reason for nitrogen to perform better - it's about 4-5 times slower to seep through the tire than oxygen. It's not size of the molecule, that only matters when you have a hole, it's the amount that can dissolve in the rubber. So, nitrogen should keep your tire inflated longer. Of course, it only matters if everything else stays constant - you ought to be able to get the same improvement by just filling your tires more often, so it's still a fad.

Tuesday, August 01, 2006 2:39:00 PM  
Blogger Perry Eidelbus said...

In theory, but still at a pretty high cost compared to checking your tires on every other stop for gas.

Tuesday, August 01, 2006 9:54:00 PM  

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