This has come up on other boards - I am a convert and have been watching the tires with absolutely no change in 6 months. It has been said much of the pressure variation of compressed "room" air vs nitrogen is the lack of water vapor (in the nitrogen tires) which is more expansile when heated hence the increased variation of pressure in a temp dependent manner. May also get the same effect with "dry" compressed air. I have also heard that the larger molecule size may play a role in less leakage- this i don't buy i don't think the atomic molecule size can't really be an issue.

 

Ok, the engineer in me needs to wade in here...any difference in pressure vs. temp is pretty much due to the moisture content in the gas (be it pure N2 or air (N2+O2)), and it's not that significant.

Molecular size does play a role in leak rates...this is why helium, which is a small molecule, is used for leak detection. It fits through holes that any gas other than hydrogen won't get through.

For the most part, the whole Nitrogen thing (wrt to tires) is a way for tire installers to separate you from your money. If you get it for free, great...otherwise you are wasting your money.

 

I agree completely. Thanks for the scientific view.
The marketing that has gone into this Nitrogen issue is amazing. However, this is absolute "Snake Oil" and of no value to performance enthusiasts or anyone else for that matter. Spend the money on a great tire pressure gauge instead.

 

In the Air, there is 78% of Nitrogen !!!

 

In my mind it's no more "snake oil" than a CAI and a CAI is much more expensive. I'm sure a lot of folks paid over $200 for a smooth red intake hose and a red cap for their airboxes. The only reason I like it is the consistency in airpressures I see across all temp extremes - haven't had to add any air in over 15 months - temps from 0 degrees to 100 degrees - for that reason alone it has been worth the $20 I paid.

 

The only reason I like it is the consistency in airpressures I see across all temp extremes - haven't had to add any air in over 15 months - temps from 0 degrees to 100 degrees - for that reason alone it has been worth the $20 I paid.

AMEN TO THAT!

 

The benefits of 100% Nitrogen in truck tire preservation are well documented.
In fact, nitrogen (oxygen free) environments have been used for decades to preserve artwork and documents.
Unfortunately, there is just no science to support the suggestion that 100% nitrogen provides the "anti-leakage" or "constant pressure over a wide temperature range" benefits that have been asserted.
Oxygen molecules are actually larger than Nitrogen molecules so Nitrogen would escape first from a microscopic hole.
Oxygen and Nitrogen have similar rates of thermal expansion so there is just no scientific evidence to support the "constant pressure" argument.
Only excessive moisture content could account for measurable pressure differences due to temperature and then only 1-2%.

 

I don't pretend to understand all the science...and I'm not trying to sell this stuff...only that I consider my $20 well spent. There may not be science to support my experience but I do have 15 months of usage and there has been no leakage.

 

I tried running helium in my tires, but suffered too much oversteer, both front and rear, during hard cornering.

 

HILARIOUS!!!!!!!!!!!!!!!!!!

 

OK, time to do some math and examine the claims. Liberal arts majors can stop reading now...

First, the claim that pure N2 provides more "stable pressure" than air over a change in temperature. Not true, other than the aforementioned contribution of moisture. Here's why: as a consquence of Avogadro's law, The ideal gas constant has the same value for all gases. This means that the constant k = P*V/T
where:
P is the pressure of the gas, V is the volume and T is the temperature of the gas has the same value for all gases, independent of the size or mass of the gas molecules. In other words, it doesn't matter what the gas is, the pressure change is going to be the same for a given change in temperature.

So let's apply this to the real world. If you're at a track day, and your tire temperature goes from up from ambient, e.g. 20C to 100C, the pressure is going to go up by the ratio of absolute temperature, i.e. (100 + 273) / (20+273), or a factor of 1.27. So if you start at 30 psi, you're going to be at 38 psi. Might be time to take a break in the pits! This pressure rise is going to be the same whether you've got air, pure N2, or any gas you choose in your tires.

Ok, with that settled, let's look at the benefit in terms of how often you need to add air (or pure N2) to your tires. There actually is a small benefit here, but it's not as big as the nitrogen proponents would have you believe.

N2 and O2 have similar molecular weights, but it turns out that even though O2's weight is higher, it's actually a slightly smaller molecule. This has to do with electron orbits, van der Waals forces, and so on. There some other factors at play such that the permeability rate of O2 through rubber is actually quite a bit higher than N2, namely 10 for O2 vs. 3 for N2. This usually where the marketing stops for the N2 machines, but let's take the next step.

Air is 78% N2 to begin with, so it's not going to leak out 10/3's faster. For pure N2 the rate is 3...how about for air? It's going to be .78*3 + .22*10 = 4.54. So, N2 will leak out more slowly than air, with a theoretical ratio of (3/4.54) or 0.66. Let's compare to the real world again. In the Consumer Reports article referenced earlier in the thread, they measured how much pressure a variety of tires lost over a year. Starting at 30 psi, the air filled tires lost 3.5 psi/year and the pure N2 tires lost 2.2 psi/year. How's this compare to the theory? 2.2/3.5 = .63, so both theory and empirical data are in good agreement here.

So, the ultimate question, is what's this worth to you? If losing 2.2 psi/year vs. 3.5 psi/year is worth $20 to you, go for it. If it's free, take it. I would submit, however, that you really ought to be checking the pressure in your tires more than once a year anyway with a high quality pressure gauge.

 

Thanks for the explanation - more than I wanted to know and not sure I understand all of it (liberal arts major) - however, I never said I didn't check my air pressures. I do it weekly with a good gauge - the pressures do not fluctuate. Same with my truck.

 

get that boy a pocket protector

 

I highly recommend it. I have used it on three different cars including my 05 C2. Tires' pressure always the same.