I made a living building, preparing and sometimes driving race cars for over 10 years. Logic always prevailed over dead chickens.

Argon in the tires would almost certainly be better than nitrogen. The same gas laws apply, but the larger molecule will leak even less.

But racers don't use argon. That's an expensive gas. Nitrogen is dirt-cheap.

But racers don't use argon. That's an expensive gas. Nitrogen is dirt-cheap.[/quote]


Not in Mississippi it ain't!! And my wife has 4 tires to prove it!!LOL:)

Leakage of this sort is not an issue in racing. If it was, argon would be used.

Reality
 

Night air is even better than nitrogen or argon. Makes you go faster.

What happens when the tire loses pressure and you're not near a nitrogen source, say on a trip? Can compressed air be mixed to inflate to pressure?

Ya, for free too! Our atmosphere is somewhere around 78% N2.

If they used helium would that make the car lighter?

I guess I could take advantage of the sunny, dry, -10°F days of January here and exchange all the air in my tires with a regular compressor and achieve the same thing (or better).

When the shops fill tires with nitrogen, how do they flush out the original air that's in there? On a humid summer day that can leave more moisture in the tire than using conventional air during the Michigan winters. For those that understand dew points, you'd know what I am talking about.

Exactly! In fact I've done just that. On exceptionally dry days near the ocean in Southern California when the dew point drops to 10F or less. I've changed the air in my tires to ensure that it is as dry as possible so condensation will never be an issue.

Someone earlier made the following statement:

"Water vapor is not an "ideal gas" and-in the context of race tires- expands in an unpredictable manner."

You need to review a basic chemstry text. Like any other gas at normal temperatures and pressures, water vapor behaves to within one percent of Boyle's Law - same as nitrogen and oxygen. If you want more exacting approximations, review the Van der Waal equations for each gas.

The problem with high humidity in tire air is that if the tire temperature drops to below the dew point, water vapor condenses to liquid and the pressure drops. If the temperature is 80 and the dew point is 60 and the tire temperature drops below 60, like sitting out overnight, water vapor will condense and tire pressure drops.

Of course, when the tire heats up again, either from the heat of the day or operation, it will evaporate again.

Nitrogen - at the cost tire shops charge - is a ripoff, but astute automotive owners should take reasonable care to ensure that tire air is as dry as possible. Most shops have driers, but you never know. If you have your own compressor, install a decent drier on it, which will catch condensation that may form as the temperature drops going through the regulator. And fill your tank on dry days.

If you just use one of those little tire filling compressors that doesn't have a tank, check and add air as required when the dew point is low.

Claims that nitrogen's leak rate is less due to different molecule size is bunk, especially when you consider that air is 78 percent nitrogen. If a tire looses more than 1-2 psi per month is has a minor leak, but you may be chasing a ghost trying to find it unless the leak rate is higher.

And check tires when they are cold and not in the sun - preferably in the morning when temperatures are coolest and before the car is driven.

Duke

Yep. x2. And you also get those neat little green tire valve caps. Look at me, I'm riding on nitrogen! :D

'Twas I that made that statement and I'll stand by it.
Ideal gases can mixed in any ratio to form an homogenous mixture. Water vapor cannot be mixed so.
Air generally loses some water vapor as condensate when it is compressed. How much is lost is an unknown at the race track, so we have no idea how much water vapor is present inside a tire filled with compressed air. Tires filled with air in the morning could and most likely do, have a different amount of trapped water vapor than tires filled in the afternoon. Tires with different amounts of water vapor will produce different pressures when heated to the same temperature.

You do notice it in a race car. My Mazda starts at 34 psi cold and it rises to about 40-42 depending on outside air and track temp with air. With nitrogen the tires don't increase as much in pressure. At 32 psi my car slides around and is a handfull untill the pressure comes up in a few laps. With nitrogen I can start at 36 and it still rises to 42, but starting at 36 makes for a more controled first few laps.

For a street car it makes no difference, even if you do track days you can do a few laps to warm up the tires before realy getting on it.