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See this guy's write up below to a blog I have been following online for a while:
Quote:
Nitrogen vs. air. First, I’ve gotta say that there are an AWFUL lot of people spending way too much effort on this all – people with too much time on their hands perhaps. Maybe even me. Me? OK, like half of the people on this, I have an opinion – and a few facts. Maybe the tiniest of questions, but frankly, it’s not too significant anyway. In almost any ROAD vehicle application, It DOESN’T MATTER!! If you check your tires every couple of months in the spring and summer, and every month in the fall and early winter – IF you live in an area where it gets COLD – you’ll be fine with air. (why more as it gets cold? Because the gas laws are real …. It’s IMPORTANT [here in the Great Plains anyway] to know that TEMPERATURE will affect the pressure a lot. The “rule of thumb” is that a 10-degree change will give you about a one-psi change. SO, if the tires are “perfect” at (an example of) 32 psi on Sept. 1st, at 90 F. and then only 10 weeks later … on Nov. 15th … it gets down to 15 degrees F., you’ll likely have “lost” 7 or 8 psi. If they are now at 24 psi, THAT’S FAR TOO LOW! Nitrogen will make no difference.
I happen to be a bit over 60 and, having been a “farm boy”, I was working on vehicles and tires even 50 years ago. That’s a lot of tires over 50 years. I’m well over a million miles, and have owned at least 35 different vehicles plus lots of farm vehicles and 35 years of “company cars” too. I did go to Engineering college (Chem. E for a year, then Electrical) and to Uncle’s Air Force. While spending 3 years in Germany, I got involved in racing. Yes, the Formula One teams used Nitrogen !! I ran Formula V and Formula 3 – we didn’t use anything but air. We also didn’t $pend Million$ on a car. I had a friend who was on the ground crew for the F4 phantom – and HAD worked on a “secret spy plane” .. later disclosed to be the SR71 Blackbird. The SR71 was specked to use pure Nitrogen (N2) but the F4 specs (and other craft like the C-141 Starlifter) were for N2 OR for “pure dry air”. That’s the big deal!! Normal air has moisture. Ever been to Thailand (next to the Laotian/Vietnamese border) or ‘Nam in July? It’s HOT and it’s HUMID. If you fill a BIG tire to 200 or more psi with air, (I think he said the SR71 was something like 280!!) your compressor pumps in lots of moisture. At 80,000 feet, (yea, the Blackbird!) the moisture will freeze – where? -- in a pool at the bottom. Not a good thing for tire balance when you land.
More on the moisture. That’s the reason that heat -- as in a race car tire – will make “regular air” vary more than Nitrogen or “dry air”. The water vapor expands MORE with temp than does the Oxygen or Nitrogen
.
Yes, the moisture and Oxy. may also make corrosion at the rim worse on a tubeless tire, BUT if some store sells you Nitrogen, see if and how they PURGE the thing of all the air that’s there when the tire is mounted. Some aircraft wheels have TWO valves. (1.) It’s often more handy to check pressures. But (2.) after mounting, you can FILL at one valve while BLEEDING the other for a while. Can corrosion be a problem? Well, I’ve got a 16’ “utility trailer”. I put four USED tires on the cheap USED steel wheels. That was back in 1988, when I got new tires for a pickup. I annually set them to 35 psi. NEVER has one of the four gone flat in 20 years. One does have a leak more than the other three … over a YEAR, one will be down to 25 or 26, while the other 3 are at 30 or 31 psi. Do I seem concerned? Alloy wheels can corrode / oxidize too – look at the INSIDE of your “mags” especially if you live in “salt country”. When you get new tires at 30, 40, 50,000 miles, a good shop will look and lightly grind around the bead if it’s necessary.
Some of these posts say N2 is INERT !! Not hardly. Helium. Neon, Argon (etc) – those are inert. Nitrogen is the N in N2O, Nitrous Oxide. It is the N in N2H4, Hydrazine (a cool rocket fuel!). You think Ammonia is inert? NH3 is Ammonia. There are dozens of other compounds. That Nitric acid is really mean stuff. Most all explosives too ... why is Nitroglycerine called Nitro in the business? Anyway, it ain’t inert, but IS one step less active than Oxygen.
Here’s my question for a chemist – Is an N2 molecule REALLY bigger than an O2 molecule? (and really less likely to pass – by osmosis – through a tire’s sidewall?) I knew, but looked anyway – Oxygen is HEAVIER than Nitrogen. O is the 8th element .. with an atomic weight of 16. N is the 7th element .. with an atomic weight of 14. So how is the N2 molecule bigger when the Oxygen atom is bigger?
The Consumer Reports article does show a tiny difference in loss rates, but I don’t know why. They really don’t say. These people who insist they get higher gas mileage with N? It just can’t be. If somebody can prove that the rolling resistance at a given pressure with N is less than with air (which is 80% N, of course), PLEASE tell us how that is! If you want lower rolling resistance, call Union Pacific … they can prove that steel on steel is pretty good.
One more thing – I spent 35 years in electronic communications. There are both underground cables and “transmission lines” for broadcast towers – like TV, radio stations, cell towers, and microwave radio sites – that are “pressurized” or are called “air filled”. That’s not correct. It really isn’t “air”, it’s EITHER Nitrogen or it’s DRY AIR. Years ago we hauled Nitrogen tanks to the transmitter sites to pressurize the “Heliax”, but found that the transmission lines would leak and be a big problem. Also the tanks of N weren’t cheap Some of these lines are very high voltage, but there are now “air pumps” made that have dryers to take out the moisture. With the moisture removed, the dry air works just fine. In a race car, or an aircraft, DRY air has no more temperature effects than does pure Nitrogen. In any street car, it just doesn’t matter much. If it’s free, fine, it can’t hurt, but in NO WAY would I spend money for Nitrogen. Unless they “purge” the tire in some way, you are starting with Oxygen and water vapor in there – unless the humidity in the tire shop is zero."
End of quote.
posted by 98.169.149...
, Thu, 17 Jul 2008 10:07:50
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