Nitrogen in your tires.. pros and cons PDF Print E-mail
Thursday, 22 May 2008 14:32

They say that tires rot from the  inside and the outside, but when the tires have moisture inside, aluminum wheels tend to corrode and oxidize around the bead which may lead to leaking or going flat.  Air that we breathe is 78% nitrogen and is an inert gas. All gasses expand and compress at the same rate, about 1/273rd for each change of one Kelvin degree. Nitrogen is dry but that's about it. 

 

 Tire gauge

 

Many race car teams use nitrogen instead of air in their tires because nitrogen has a much more consistent rate of expansion and contraction compared to the usual air. Often, a half- pound of pressure will radically affect traction and handling. With track and tire temperatures varying over the duration of a race, the consistency of nitrogen is needed. Nitrogen pressure is more consistent than normal air pressure, because air typically contains varying amounts of moisture due to changes in the relative humidity on race day. Water causes air to be inconsistent in its rate of expansion and contraction. So, a humid race in the southeast United States or a dry race in the desert western United States could make for unpredictable tire pressures if "dry" nitrogen were not used. 

 

 

Many race car teams use nitrogen instead of air in their tires because nitrogen has a much more consistent rate of expansion and contraction compared to the usual air. Often, a half- pound of pressure will radically affect traction and handling. With track and tire temperatures varying over the duration of a race, the consistency of nitrogen is needed. Nitrogen pressure is more consistent than normal air pressure, because air typically contains varying amounts of moisture due to changes in the relative humidity on race day. Water causes air to be inconsistent in its rate of expansion and contraction. So, a humid race in the southeast United States or a dry race in the desert western United States could make for unpredictable tire pressures if "dry" nitrogen were not used. 

 

Some racing teams use nitrogen in their shock reservoirs.  As you can see it’s not the gas expansion that keeps a more constant pressure, it’s the lack of moisture found in compressed air that rapidly expands when vaporizing from extreme heat associated with racing that causes the excess expansion and pressure. A racing shock on a motocross bike will get so hot you can’t touch it. Way to hot for compressed air. So a tire that is filled with compressed air at racing temperatures will absolutely expand more then a tire filled with nitrogen. Not because of the gas itself but because of the rapidly expanding moisture in compressed air. 

 

It is interesting that those looking for higher performance have been using Nitrogen for a while and in some cases doing even more exotic things. I have read that Ferrari is using a blend of a hydroflurocarbon (usually used as a refrigerant) and CO2 in the tires of the Formula 1 cars.

 

When water vapor in compressed air acts as a catalyst, accelerating rust and corrosion. Water vapor also absorbs and holds heat. And when it changes from liquid to vapor, water expands tremendously in volume. As a result, tires inflated with wet air tend to run hotter and fluctuate in pressure more. That's one of the reasons why racing tires, where fractions of a psi can radically change the handling characteristics, are inflated with dry nitrogen.  Nitrogen is also used in the high-pressure tires on large and small aircraft.  There are several grades of nitrogen even in high pressure cylinders, and then there are many specialty grades where the prices get really dicey.  The net effect may be that unless you drive consistently over 200 mph it is almost immeasurable. Nitrogen (absence of oxygen and moisture) won't build excessive pressure from heat buildup. If driving high speed over long distances, it may not be a bad thing, but for a 3000 pound a car, it may have no benefit if you check your tires on a regular basis 

 

Air is about 1/5 Oxygen, and oxygen, especially at high pressures and temperatures, is a very reactive element. When oxygen reacts with things, the process is called oxidation. When oxidation is extremely rapid, it's called "burning. That's one reason nitrogen is used in off-highway and aircraft tires. These tires run so hot they can actually catch on fire. Nitrogen doesn't support combustion, so nitrogen-filled tires don't add fuel to the flames. And nitrogen helps prevent slower forms of oxidation also. 

 

Nitrogen may be the next big thing. Soon it will be mandatory??? A representative of the International Tire and Rubber Association with 30 plus years of industry experience added. Nitrogen will not expand and contract as much as compressed air does so your inflation will remain the same for longer periods of time. In order to increase tire life and gas mileage; increase your tire pressuers by 2 to 3 PSI above the recomended air pressure located on the drivers side door post (door placard). Once you fill the tires with nitrogen you need to have them filled with nitrogen from then on. This can create a problem for the average consumer; you'd be better served by buying your self a $5.00 air gauge and checking your tire air pressuers once monthly. Rotate your tires every 2nd oil change, front to rear and have your wheel (suspension) alignment checked once every two years make sure your air filter is clean and you'll be money ahead. 

Before you argue this to death, another viable reason many of the manufacturers are suggesting nitrogen is by keeping the air press in the tires more stable you are not as apt to have a tire pressure monitor signal a problem because the temp dropped real low.  What about the Tire preasure monitors? How about the 100$+ replacement when the batteries in the transmitters go bad in 3 to 5 years. Don’t you wish that Bubba's gas station had a good moisture filter on his air line but he doesn't and a tire with a lot of water is not going to be real good on a tire pressure monitoring sensor.  You may have more moisture in your tires than you think. It depends on the type of water separator the shop uses.  Guess the Tire shops want to fill all your tires with nitrogen.

 

As for getting "old air" out of the tire, it’s easy enough to fill/purge, or hookup a small evacuation pump to it. Is the shop  careful to remove all the air from the tire before refilling them with nitrogen? Just exactly how do they do that? - that's the tough one. Fill the tire and then let the nitrogen out then refill. Some places use a vacuum to vacuum the air out.  The idea behind this was to remove the water vapor and prevent corrosion. To do this, you have to fill it, let the nitogen out, fill it again and do this three more times. It would take the moisture out with it, each time getting more of the vapor out.

 

As far as Nitrogen being more stable?  Those who claim to know about such things tell me that Nitrogen is less energetic than Oxygen. Therefore, Oxygen or regular air will escape  from your tires at a much faster rate,because the molecules in plain air are smaller then the ones contained in nitrogen so that after some period of time the gas/air pressure will be more stable in your tires will be higher in Nitrogen than normal air.  Remember! PV=nRT! Say we have 60g of Nitrogen in a tire. There are 28.0134g in one mole of Nitrogen. That gives us 2.14 moles Nitrogen rounded. That is our n Value. Say that our temperature is at 22.2 degrees celsius which is around 72 degrees fahrenheit. 

 

You need to convert to Kelvin, so add 273 to 22.2 which gives us a temperature of 295.2K. Say our pressure is at 1.00atm, which is the average sea level pressure, that is our P value. Since we are dealing with atm, R will be .0821atm*L/mol*K. So basically we are trying to find the value of V, or Volume. So V=nRT/P. So V=51.86Liters. Now say we increase our temperature to 120 degrees fahrenheit, or 321.9K. If you plug that in for T rather than 295.2K, you get a volume of 63.69L. So yes, Nitrogen gas does expand. Quite a bit actually. 

nitrogen does expand and contract with temperature according to some  silly law of physics like PV=NRT? (T is for temperature, R is a constant, n is the mass of the gas also a constant in a sealed tire, P is pressure, V is volume.) So if the temperature goes up, like when you are racing around a track @ 200 mph, the pressure and/or the volume increases porportionally. 

 

 

 

 

Last Updated on Sunday, 24 August 2008 20:30
 
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