80 mpg! Nitrogen Works ;)

Could another way of saying it be "money for old rope"? or "money for nothing"?

or a popular one from here;

"Snake oil"?

Just pump your tyres/tires upto the correct pressures (or higher if YOU are happy doing so) and you should get good economy from your car.

 

The advantage to N2 must just be because you can get it dry and so won't have issues with pressure changes from condensation temperatures for water vapour... that's my guess anyway.

I heard once that some airplanes used helium for tire inflation because on a big airliner they could save the weight of 2 passengers. Not sure if I believe it. As many of you know from buying He filled balloons, He will go through almost everything (it is the smallest atom) even lots of glasses won't hold it.

I did love that Westjet April fools gag linked above... they have a history of humourous marketing.

 

If there were a significant difference in leakage rates, it would be a self correcting problem because the Oxygen would leak out faster leaving pure Nitrogen.

 

Assuming there is preferential leakage of molecular oxygen (O2) over molecular nitrogen (N2), the result of repeated refillings of regular air will result in nearly pure molecular nitrogen (N2) -- thus nullifying the N2 advocates' reasoning for filling with pure molecular nitrogen (N2) in the first place.

In other words, either it doesn't make a difference, or it's the same difference.

 

This is true for dry nitrogen used in race cars and aircraft. Unfortunately, the "nitronized" stuff that they sell at tire stores is neither pure nitrogen or dry; at least not any drier than what you would get with a good compressor and moisture removal system. Even if it was dry, they brush on a bunch of water based lubricant when they mount the tires. Where do you suppose that water goes.

For aircraft it is important to not have condensed frozen water in the tires when the plane lands. Aircraft deal with seriously cold temperatures.

For race cars the main attribute is repeatability. All common gases expand when heated. Nitrogen is no exception. Race car drivers know that tire pressures will rise while they drive, but they want to know exactly how much they will rise. To do this you need a consistent gas, and dry nitrogen fits the bill.

Another reason that nitrogen is popular for aircraft and race cars is that you can conveniently store considerable amounts of the stuff in liquid form. When speed and convenience are important, it's faster and easier to carry a small Dewar than to lug a compressor and power cord.

Lastly, nitrogen will not support combustion. This can be handy with tires that are driven to extremes.

On paper O2 molecules are larger than N2. Because of quirks in nature, N2 appears to have a slightly slower diffusion rate than O2, but the difference is so small as to be completely irrelevant. Besides, the idea behind pneumatic tires is to keep air inside, not let it diffuse. The diffusion rate of air, O2, and N2 is essentially zero through modern tires.

Tom