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Info - Use of Nitrogen Gas in Tires #05-03-10-020 - (Dec 22, 2005)
Use of Nitrogen Gas in Tires
All 2006 and Prior GM Passenger Cars and Light/Medium Duty Trucks (including Saturn)

2003-2006 HUMMER H2

2006 HUMMER H3

2005-2006 Saab 9-7X

GM's Position on the Use of Nitrogen Gas in Tires
General Motors does not oppose the use of purified nitrogen as an inflation gas for tires. We expect the theoretical benefits to be reduced in practical use due to the lack of an existing infrastructure to continuously facilitate inflating tires with nearly pure nitrogen. Even occasional inflation with compressed atmospheric air will negate many of the theoretical benefits. Given those theoretical benefits, practical limitations, and the robust design of GM original equipment TPC tires, the realized benefits to our customer of inflating their tires with purified nitrogen are expected to be minimal.

The Promise of Nitrogen: Under Controlled Conditions
Recently, nitrogen gas (for use in inflating tires) has become available to the general consumer through some retailers. The use of nitrogen gas to inflate tires is a technology used in automobile racing. The following benefits under controlled conditions are attributed to nitrogen gas and its unique properties:

• A reduction in the expected loss of Tire Pressure over time.

• A reduction in the variance of Tire Pressures with temperature changes due to reduction of water vapor concentration.

• A reduction of long term rubber degradation due to a decrease in oxygen concentrations.
Important: These are obtainable performance improvements when relatively pure nitrogen gas is used to inflate tires under controlled conditions.



The Promise of Nitrogen: Real World Use
Nitrogen inflation can provide some benefit by reducing gas migration (pressure loss) at the molecular level through the tire structure. NHTSA (National Highway Traffic Safety Administration) has stated that the inflation pressure loss of tires can be up to 5% a month. Nitrogen molecules are larger than oxygen molecules and, therefore, are less prone to "seeping" through the tire casing. The actual obtainable benefits of nitrogen varies, based on the physical construction and the materials used in the manufacturing of the tire being inflated.

Another potential benefit of nitrogen is the reduced oxidation of tire components. Research has demonstrated that oxygen consumed in the oxidation process of the tire primarily comes from the inflation media. Therefore, it is reasonable to assume that oxidation of tire components can be reduced if the tire is inflated with pure nitrogen. However, only very small amounts of oxygen are required to begin the normal oxidation process. Even slight contamination of the tire inflation gas with compressed atmospheric air during normal inflation pressure maintenance, may negate the benefits of using nitrogen.


GM Tire Quality, Technology and Focus of Importance
Since 1972, General Motors has designed tires under the TPC (Tire Performance Criteria) specification system, which includes specific requirements that ensure robust tire performance under normal usage. General Motors works with tire suppliers to design and manufacture original equipment tires for GM vehicles. The GM TPC addresses required performance with respect to both inflation pressure retention, and endurance properties for original equipment tires. The inflation pressure retention requirements address availability of oxygen and oxidation concerns, while endurance requirements ensure the mechanical structure of the tire has sufficient strength. This combination has provided our customers with tires that maintain their structural integrity throughout their useful treadlife under normal operating conditions.

Regardless of the inflation media for tires (atmospheric air or nitrogen), inflation pressure maintenance of tires is critical for overall tire, and ultimately, vehicle performance. Maintaining the correct inflation pressure allows the tire to perform as intended by the vehicle manufacturer in many areas, including comfort, fuel economy, stopping distance, cornering, traction, treadwear, and noise. Since the load carrying capability of a tire is related to inflation pressure, proper inflation pressure maintenance is necessary for the tire to support the load imposed by the vehicle without excessive structural degradation.

Important: Regardless of the inflation media for tires (atmospheric air or nitrogen) inflation pressure maintenance of tires is critical for overall tire, and ultimately, vehicle performance.
 

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Wow, that one was written by the lawyers....:blahblah:


BEGIN :rant:

I don't really see the advantages of nitrogen for the average Joe. I wonder if most paying for nitrogen at Costco realize that the air they're breathing is 79% nitrogen already. By the way, I've never looked, what are people paying for that other 21%? How do they evacuate all the oxygen out of the tire before they fill it with nitrogen? The only way would be completely remove all the air from the tire before filling it (how do they do that in the race circles?). It's been a long day and I'm too tired to do the math, but I bet by filling with nitrogen, you're only upping the percentage to maybe 85-90%.

Maybe I'm way off base, but I just don't get it...

END :rant:

Doug
 

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A bit better than 90%, depending on your fill pressure.
For a passenger car tire at 32psi, assume you have 8 cubic feet of "air" at 14.7psi (sea level).
You bring the tire to 32psi, which is actually 46.7 absolute, so you now have a total of (8/14.7)*46.7 = 25.44 cubic feet of gas.
You have added 17.44 cubic feet of N2. Of the original 8cf, 6.32 was N2, so you now have a total of 17.44+6.32 or 23.76cf of N2 and 1.68cf of O2.
23.76/25.44 = 93.4% N2.

That's a 32psi... you'll do even better at 60psi on a truck tire. The actual cubic footage doesn't matter... just substitute "x" for 8cf and the percentage works out the same once you divide out "x" at the end.

I believe Costco includes the N2 fill for free... if they are charging for it, then ya, it's a sucker purchase.
 
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