Air is already almost 80% nitrogen anyway.

 

Until this forum, I was ready to switch to nitrogen ... thank you for both the web-link and the technical explanation. Together it's easy to see that I'd be wasting my time and money on something with such a miniscule difference for my street-use (primarily) sled.
Seems the best thing to do is fill the tires on a day with very high humidity.
Thanks all.

 

As those who understand the physics involved already understand, pure Nitrogen offers practically no benefit (aside from psychological) in a car tire. There is a tiny bit less theoretical leakdown, about one pound per YEAR, but that is the only benefit (air is already almost 80% nitrogen).
Since there is absolutely no difference in the heat expansion rate of pure nitrogen over compressed air, there is positively no performance benefit whatsoever.
I hope I used enough absolutes. Pure nitrogen is a P.T. Barnum special.
You know, "there's a sucker born every minute".
Please don't waste your money.

 

I've been running 79% Nitrogen for years, never had a problem
Seriously, there may be some very small benefit in a lower diffusion of Nitrogen than air or O2, but it is not significant on a street/DE car IMO. On a top level ALMS car maybe, but not the street.

 

Any of you know if they use nitrogen at the porsche dealerships?

 

Maybe Ti Lug nuts are a waste of money too , along with my Dymag Cf Wheels ?

I wonder why all aircraft have N2 in there tires ?

Gee-Bee

 

Yes

Completely different operating environments. You have tires that go from a stand still to very high rates of speed with hundreds of thousands of pounds exerting pressure on them. Then there are the extreme temperature changes as well.

 

If we're going into semantics, then anything more than a Honda Civic is a waste of money...

That being said, I think the point of this is more a "If it ain't broke, don't fix it" situation. No one is telling you not to spend 80 bucks to increase the N2 content of your tires by 20%.
That being said I think it's a worthwhile discussion to have for those who are being sold something under false pretenses and wouldn't want it other than for the claimed benefits.

Ti lugnuts, CF wheels, and mods in that category all in all are more about cosmetics than performance.
Few people can hardly extract all the potential out of a stock 997tt to run as fast as possible, much less need those types of parts to improve on their lap times. I would say less than 1% of drivers out there that casually track derive more than minute additions to performance from parts like that. A turbo kit/suspension/etc are obviously different.
If you are good enough to "need" Ti lugnuts and etc because you can drive to 100% of the stock vehicles potential, then more power to you. Otherwise, all car modding is basically for enjoyment...and if you really want to get the most bang for your buck "mod" then take a driving course.

In the case of Nitrogen in tires...I think it's a clever case of market and a lack of more than basic understanding of physics. I'd rather hold onto my 80 bucks in that case.

 

Well said! In addition, aircraft use Nitrogen gas primarily for corrosion resistance since it is not hygroscopic like compressed air. Even tiny amounts of corrosion must be avoided in something like an aircraft wheel that holds up a 747.

 

It also has a lot of water vapor in it, which is going to have a higher expansion rate then just straight nitrogen, this is going to effect the spring rate of the tire as it heats up which will effect handling of the car, this is why it is used in motorsports instead of compressed air, it is more consistent.
In racing with cars with high sidewall tires like NASCAR or Indycar 1 psi of tire pressure difference is close to a 10-15 lb spring rate change.

Kyle.

 

if you have ever worked in a shop that uses compressed air you would know how much water accumulates in your compressor lines...100cfm output at 100F is about 2 gallons an hour... or so ive heard....

 

Good grief! The moisture content in air is about 1%, even in the equatorial jungle. When air is compressed to 7 Bar or so, it gets very hot (Boyles Law).
When the air cools in a modern compressed air system, condensation occurs as the pressurized gas is no longer able to hold as much moisture (now about 1/7 of normal or .0015%). Modern compressed air systems use simple dryers to then remove the condensed moisture. So in fact the air is as dry as the Gobi frigging desert. Your suggestion that the tiny amount of water vapor remaining can affect the pressure in the tire as it heats is therefore scientifically impossible.
In addition: "First, the claim that pure N2 provides more "stable pressure" than air over a change in temperature. Not true, other than the aforementioned tiny 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."

It would seem the Nitrogen marketers have done an amazing job.
PLEASE do not waste your money.

 

I don't think anyone ever suggested that with N2 you don't have to check your tire pressures - you may not have to add air but you still have to check. I run N2 - no pressure leakage for 15 months during zero degree weather and 100 degree weather...but I still check my pressures before every drive with a manual gauge and monitor with TPMS display.

 

All great information. Good job guys.

 

Im talking about use in motorsports in my quote you use. I dont see a benefit for the street. and i dont care about moisture content of air im talking about expansion rates and nitrogen is more consistent having less moisture in it, and thats why it is used by every race team... they have been doing this for years, the tires are given to teams mounted by the tire manufacturer and the teams remove the air out of them and fill them with nitrogen.