nitrogen in tires?
10-02-2004, 09:43 AM
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nitrogen in tires?
My bro just told me about Costco offering to fill tires with nitrogen instead of the usual air.
anyone ever hear of this? benefits are supposed to be less temperature variation and less leakage (?!) Apparently it's popular in Europe already...
Is this just some kind of joke or is there real benefits/drawbacks?
TIA.
anyone ever hear of this? benefits are supposed to be less temperature variation and less leakage (?!) Apparently it's popular in Europe already...
Is this just some kind of joke or is there real benefits/drawbacks?
TIA.
10-02-2004, 06:25 PM
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Some hardcore auto-xers do it...
they are also rich! It costs more than air, but your tires wont change pressure when they get hot. not worth doing on a street driven car though.
10-02-2004, 07:35 PM
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Um, you can't beat physics: pressure still changes, the same amount as normal air.
Ideal gas law is PV=nRT, and it applies to ALL gases.
You can perhaps make a case for nitrogen being marginally lighter than air, which is only 78% nitrogen, with 20% heavier oxygen.
You can perhaps make a case for nitrogen being marginally lighter than air, which is only 78% nitrogen, with 20% heavier oxygen.
10-03-2004, 01:51 AM
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The benefit is less pressure variation. ...
Nitrogen is strongly recommended for racing where tires often run 200 oF or hotter.
The problem with air is that it's normally not just air. More often than not, the "air" in your tires contains liquid water from the air compressor and/or the lubricant used on the bead when the tire was mounted on the wheel. Normally the air (or nitrogen) pressure in a tire increases predictably about 1 psi for every 10 oF of temp. If there's liquid water in the tire (and water is usually present if you're filling the tires with "air"), pressures sky-rocket unpredictably as the water turns to steam.
On the street, there little benefit from using nitrogen; the tires normally don't run hot enough to cause a problem. On track at Mid-Ohio however, the left-front tire on my S8 has hit 240 oF. With a starting cold pressure of 36 psi, I normally expect a 47 psi hot pressure. My tires were filled with (wet) air however, and that LF tire was almost 60 psi. When I let "air" out, I was burned by the steam.
The problem with air is that it's normally not just air. More often than not, the "air" in your tires contains liquid water from the air compressor and/or the lubricant used on the bead when the tire was mounted on the wheel. Normally the air (or nitrogen) pressure in a tire increases predictably about 1 psi for every 10 oF of temp. If there's liquid water in the tire (and water is usually present if you're filling the tires with "air"), pressures sky-rocket unpredictably as the water turns to steam.
On the street, there little benefit from using nitrogen; the tires normally don't run hot enough to cause a problem. On track at Mid-Ohio however, the left-front tire on my S8 has hit 240 oF. With a starting cold pressure of 36 psi, I normally expect a 47 psi hot pressure. My tires were filled with (wet) air however, and that LF tire was almost 60 psi. When I let "air" out, I was burned by the steam.
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10-03-2004, 01:39 PM
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And with wet air, handling often spirals out of control.
The tire is also a spring, an air spring in series with the steel coil spring. A rule of thumb is that a 1 psi increase in tire pressure increases the spring rate at that corner by ~ 25 lb/inch.
The following undesireable chain of events is often the result with wet air,
1. Assume that the outside front tire runs 4 psi higher than it should.
2. This increases the spring rate of only that corner by ~ 100 lb/in.
3. The additional LF corner spring rate increases understeer and the load on the LF tire.
4. Because of the increased load on the LF front tire, it runs hotter.
5. Go back to #1 ...
The end point is usually reached when the tire is overheated so much that the tread starts melting, the greasy front tires make the car an understeering pig, and slow laps are the result. Been there, done that, as this pic of my left front overheated S-03 shows.
<img src="http://pictureposter.audiworld.com/42891/meltedtires.jpg">
The following undesireable chain of events is often the result with wet air,
1. Assume that the outside front tire runs 4 psi higher than it should.
2. This increases the spring rate of only that corner by ~ 100 lb/in.
3. The additional LF corner spring rate increases understeer and the load on the LF tire.
4. Because of the increased load on the LF front tire, it runs hotter.
5. Go back to #1 ...
The end point is usually reached when the tire is overheated so much that the tread starts melting, the greasy front tires make the car an understeering pig, and slow laps are the result. Been there, done that, as this pic of my left front overheated S-03 shows.
<img src="http://pictureposter.audiworld.com/42891/meltedtires.jpg">