i don't get what you mean??? when you fill your tires according to the chart below you are putting in 78.08% nitrogen. are you thinking of helium to make the weight of the rim and tire lighter in weight???? and what did you mean by going back to the dealer for it?
Constant components in the earths atmosphere
(proportions remain the same over time and location)
Neon, Helium, Krypton
(amounts vary over time and location)
Carbon dioxide (CO2) 0.0003%
Water vapor (H20) 0-4%
Methane (CH4) trace
Sulfur dioxide (SO2) trace
Ozone (O3) trace
Nitrogen oxides (NO, NO2) trace
OK for a quick answer... Use Nitrogen because it does not expand when heated and the molecules are bigger so less air escapes from the tire.
Nitrogen is a nonmetal, with an electronegativity of 3.0. It has five electrons in its outer shell and is therefore trivalent in most compounds. The triple bond in molecular nitrogen (N2) is one of the strongest in nature. The resulting difficulty of converting (N2) into other compounds, and the ease (and associated high energy release) of converting nitrogen compounds into elemental N2, have dominated the role of nitrogen in both nature and human economic activities.
At atmospheric pressure molecular nitrogen condenses (liquifies) at 77 K (−195.8 °C) and freezes at 63 K (−210.0 °C) into the beta hexagonal close-packed crystal allotropic form. Below 35.4 K (−237.6 °C) nitrogen assumes the alpha cubic crystal allotropic form. Liquid nitrogen, a fluid resembling water, but with 80.8% of the density, is a common cryogen.
Unstable allotropes of nitrogen consisting of more than two nitrogen atoms have been produced in the laboratory, like N3 and N4. Under extremely high pressures (1.1 million atm) and high temperatures (2000 K), as produced under diamond anvil conditions, nitrogen polymerizes into the single bonded diamond crystal structure, an allotrope nicknamed "nitrogen diamond."
I'll get blasted by loyal nitrogen users for this but..........It's just another way of separating you and your money. It is useful in racing and aircraft, but of marginal effectiveness in passenger car (or truck) tires.
Some claim that normal air (and the oxygen in it) causes the rubber in you tire to deteriorate. What they fail to consider is that the entire outside of the tire is still sitting in normal air that contains oxygen. Sunlight is the real killer of tires (other than wear). Pull an old dry rotted tire off the rim and the interior always looks much better than the outside.
Others claim that the moisture level in compressed nitrogen is lower and keeps tire pressures more stable when the tire heats up. Dehumidified air will do the same thing, but honestly we don’t drive race cars where a half pound of tire pressure makes a big difference in the way the car handles.
Lastly nitrogen is nonflammable. Boy, I sure am glad to hear that! Now my worries about my tires spontaneously combusting are over.
If nitrogen was so good, every gas station in America would be selling it at ridiculously expensive prices.
Wait wait wait....
The most important information was in the first post, the reason to use Nitrogen in the tires is because of the molecule size, and thermal expansion. With nitrogen, you will not have your TPS light coming on every time the weather changes.
That being said, air at speedway = $0.75, what does that N2 run?
EDIT - This information is also available in the first line of the How Stuff works article. Sorry Quartz, I need to RTFA first.
Many of the aftermarket tire places around here are advertising that they fill ALL their tire replacements with nitrogen. So it's not just a dealer thing anymore. I'm not sure about the cost of refilling or topping off, but it's becoming more popular. Necessary? No, but that's up to the individual.
put nitrogen in my mom's 2002 Grand Prix 4 years ago and haven't had to add since and it's driven every day. molecules are larger and uniform compared to atmosphere and don't seep. tires are firmer and run cooler adding mileage before needed replacement.