http://en.wikipedia.org/wiki/Earth's_atmosphere#Composition

Regular air is already 78% nitrogen. As said above regular top offs will increase this amount. There seems to be very little need for this.

About all I can see as the advantage is the lower moisture content.

The question becomes feasibility and costs. It seems to be a waste to use such gas generating technology just for tire inflation. Perhaps resulting the O2 rich gas (air stripped of N2 is O2 rich) can be use for something, like diesel electric generator.

Nitrogen gas is usually produced by chilling air until the N2 fraction liquefies. Whoever came up with this idea should specify the energy cost to produce & distribute the nitrogen gas and demonstrate a significant net benefit due to improved tire inflation and life.

Note that all cars equipped with ABS (and very few are not) already measure the radial velocity of each wheel and the steering angle. This information permits the inference of unequal tire pressures. The requisite software is an available options on certain cars on the European market today, to alert the driver to a leak.

If the bulk of pressure loss is equal on all four tires, automated detection requires extra hardware, e.g. pressure transducers with wireless transceivers mounted on the inside of the rims. I don't know if such hardware can already be implemented as a passively powered RFID.

Rafael, a large and increasing number of cars and trucks (especially SUVs with their perceived and real rollover risks) sold in the US have the same sort of tire pressure monitoring you describe. As you note, it won't detect if all four tires are equally low. I believe that some form of tire pressure monitoring is going to be required for all new vehicles sold in the US within a year or two. I'm not sure whether the ABS-sensor type system will satisfy this given its inability to detect four low tires, but I suspect that will be the dominant system if it is permitted.

As for the main discussion, I see the benefit of having pure N2 free of water vapor in the tires, but I just wonder if it is a significant enough benefit to justify the cost and hassle. It sounds a lot like a scheme to corner the market on tire inflation, something which has historically been 100% free from an air compressor hose at most gas stations in the US (aka "service stations" back from the day when they offered something that could be termed service).

The most common reason for tire replacement is tread wear. The second common reason for tire replacement is side-wall puncture that is not repairable in tubeless tires. Since N2 tire inflation can't address these two most common reasons for tire replacement, then its benefit may not be significant, unless proven otherwise by a randomize controlled study of thousands of cars, similar to a large medical trial involving randomized placebo-controlled methodology with sufficient N number of subjects to arrive at a statistically significant result.

Now, if large studies prove a statistically significant advantage of N2 vs air inflation, would a mixture of 78% N2 and 21% CO2 be just as good, since O2 is not present, and CO2 is a larger molecule than O2 and hence less permeable and is totally inert? If so, then this new mixture can be very cheaply obtained by low-temp catalytic reaction of propane or LPG with air to produce CO2 and N2 mixture, and chilled enough to remove nearly all the moisture (H2O). Should be a lot cheaper than pure N2.

TPMS also becomes required by law on all vehicles in 2008 or something, so underinflated tires will become less and less common since drivers will be alerted to the situation by the car's monitoring now.

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Rafael,
Agree that incorrect inflation can cause abnormal tire wear. However, how much an impact would N2 inflation help to reduce incorrect inflation remains to be seen. This is because both N2 and O2 permeate thru the tire, both being gases, with N2 a little less permeable, only 35% less.

In the Ford pdf document, the emphasis seems to be on preventing rubber oxidative degradation rather than reducing air loss. Of course, if oxidation occurs, the O2 will be consumed and perhaps incorporated into the rubber and will be loss.

But, at any rate, the owner should still check tire pressure at regular interval and can't depend solely on any other way. I found that a quick vision inspection can be quite good at estimating the degree of air loss if an air gauge is not immediately available. That's how I've been able to keep my tire always adequately inflated. This skill should be taught to all drivers, and tires should be inspect at every fueling or before every ride if time permitting, to avoid potential dangerous hazard due to tire blow-out. Too much hype on pure N2 tire inflation can give the driver a false sense of security, and IF this will lead to less frequent tire inspection, visually or with an airgauge, then it may do more harm than good!

There are a number of tubeless tire systems for bicycles that use aqueous sealants in quantities of ~60ml for a mountain bike wheel. This quantity of water will typically diffuse out over a span of weeks to several months. I would expect water introduced into a car tire to diffuse as well, especially given the much higher temperatures involved. My understanding of the reason for N2 inflation is that it is mainly about dryness. Water in a tire undergoes a huge PV change as the tire warms because of the phase change. Obviously this would be something you would prefer to avoid. It would seem that one could simply use a dryer on the compressed air line. The fact that the tire installers drench the bead in soapy stuff is a bit of an issue, eh? Regarding N2 diffusing 35% slower than O2, is that measured in a relevant experimental setup, or did that come from the marketing department? Thermal conductivity differences between air and N2 are negligible. air = 0.026 W/mK, N2 = 0.026, pure O2 = 0.027. If you want better thermal conductivity, fill your tires with helium or hydrogen. Be prepared to fill often, because those little suckers leak like crazy. Chemical degradation? Ozone is probably more of a problem than oxygen, and the exterior of the tire is constantly bathed in air and zapped with uv. Nevertheless, I don't find rubber degradation to be the problem it once was. I think that tire makers may have that problem solved. IMHO, the N2 inflation thing is a scam, other than the fact that it's dry.

I myself have been looking around this is some good information