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Discussion Starter · #1 ·
My Nissan store (garage) has been after me to have them replace the air in my tires with Nitrogen. The techs are really great guys, but I'm suspicious. They claim the gas will eliminate the need to frequently check air pressure - and the gas will extend milage on the tires due to the lower temps.

Thoughts? Experience? :cheers:
 

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Some interesting points:

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The question about nitrogen in tires has come up in other lists on the web as well. Let me clarrify a few points.

1. Air is 78% nitrogen, N2, and 21% oxygen, O2. So even if you put air in the tire, it's already 78% nitrogen. Many of the so called nitrogen generators don't produce much more than 90% nitrogen.

2. At relatively low pressures (ie tire pressures) N2, O2 and water vapor will all behave as ideal gases, and follow PV=nRT. Pressure will increase or decrease to the same extent as the temperature increases or decreases regardless of which gas is in the tire. (Even at 300 psi, which is about 20 atm, there is little deviation from ideality.) Therefore the comments about N2 not changing in pressure as the temperature changes are without merit.

3. The rate of effusion (or diffusion) of a gas through a porous membrane depends on the molar mass and to some degree on the molecular diameter. N2 and O2 are almost the same size and N2 is lighter than O2 (28 g/mol vs 32 g/mol) so if either gas were to effuse out of the tire, nitrogen would do it more quickly. Luckily, tires are designed not to be porous membranes.

4. N2 and O2 both have essentially the same specific heat capacity, about 1.0 J/gK, and thermal conductivity, about 0.00026 W/cmK. Water vapor has a specific heat capacity of about 2 J/gK. But remember, water vapor will constitute less than 1% of the air in the tire. So the idea that N2 has different heat handling properties is also without merit.

5. The ozone, O3, in the atmosphere, which is a ground level pollutant, will do a great deal more damage to your tires than the O2 inside the tire. For instance, don't leave a condom out in the air in Los Angeles for a few days. It will develop lots of tiny holes and weaken.

spdracer22 says that dry air is preferably to air with a lot of water vapor. As a tire heats up, the very small amount of H2O present will be in the vapor state which may contribute to the overall pressure very slightly.

Several have suggested that N2 in a high pressure tank is more portable and requires no electricity. That would make sense, particularly for aircraft tires.

I find no reason to believe that N2 is going to produce a "better ride" or "better handling".

The bottom line is that for general passenger car tires or truck tires there is nothing to be gained (other than portability) by using nitrogen rather than air. The biggest gain will be $$$ by the companies that sell nitrogen handling equipment and the tire merchants that appeal to ignorant customers. And who is the biggest loser? Yep, the consumer.


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The biggest reason to use compressed nitrogen *in a racing tire* is that it's dry, compared to typical compressed air.

When a tire heats up, the air and any moisture inside it heats up as well. When the moisture inside the tire heats up, the water molecules move further apart, increasing the tire pressure. By removing this moisture, the pressure stays more consistent over the entire heat cycle of the tire.

On a racecar, a 1/4 psi difference can change the handling of a car significantly. The humidity inside a tire does not have to be zero, but if it is not at least kept consistent from one set of tires to another, to equal a 1/4 psi increase in the current set, a 1 psi change may need to be made in another set because of the differing humidities.

Is nitrogen completely necessary? No. Air can be dried using inline air dryers and such. However, it's much easier to keep tire humidity consistent when all the tires can be filled from the same 1500 psi bottle of nitrogen delivered to the shop.

As far as race tires go, this is the reason to use nitrogen. Because of the short life of a race tire, how much air permiates out of a tire over a year is of no concern.

For a street car, I can see little benefit in using nitrogen. But then again, I check my pressures just about every week, and I'm not worried about whether my pressures increase 1 or 3 psi during my daily commute. For someone who "sets and forgets" it may help. As far as corrosion resistence, rusting will only occur when the oxygen in the air can reach bare metal. Unless for some reason your wheels didn't come painted or the surface was damaged before the tire was put on, the side of the wheel open to the ambient air will corrode much, much faster.
 

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My Nissan store (garage) has been after me to have them replace the air in my tires with Nitrogen. The techs are really great guys, but I'm suspicious. They claim the gas will eliminate the need to frequently check air pressure - and the gas will extend milage on the tires due to the lower temps.

Thoughts? Experience? :cheers:
If they want, it wont hurt anything, let them try it. As long as they don't charge you, I think it would be interesting to see the difference.

Has anyone done this? Any testimonials from members about the difference? I am curious if anyone has. I'll believe what people have to say over statistical data.
 

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Discussion Starter · #6 ·
Thanks, Illz - I appreciate the info. :cheers:
 

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Discussion Starter · #8 ·
I just bought a digital guage for $50 from Gritiot's Garage.
It displays tenths of a lb.
 
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