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Old 01-24-2014, 08:45 AM   #1 (permalink)
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Default Air in tires?

Is there any advantage to using nitrogen instead of compressed air in tires?
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Old 01-24-2014, 11:40 AM   #2 (permalink)
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Nope

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Old 01-24-2014, 11:56 AM   #3 (permalink)
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It's a gimmick. I've seen no proof that it's any better. Besides, if a tire gets low, aren't you going to refill with air? If so the "benefit" of nitrogen decreases over time so why bother?
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Old 01-24-2014, 12:03 PM   #4 (permalink)
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Default A racket

Since air is composed of 78% nitrogen naturally, it's another gimmick to add profits to the dealer.
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Old 01-24-2014, 03:45 PM   #5 (permalink)
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What benefit would pure nitrogen have over plain air?
It does not expand or contract more or less than air under pressure or temperature changes.

It has less mass - about 2.5 % less than air. A liter of air weighs just above a gram, and there may be some 50 liters of compressed air in a tire so the difference is less than 2 gram per tire.
Hydrogen gas, by contrast, would save you about 50 grams per tire. But hydrogen is volatile; the small molecules may seep out faster than you'd like.

The oxygen might react with the rubber and age it prematurely, I have heard. Oh yeah, but there is a lot of oxygen on the other side of the tire and apparently that holds well enough.
And even if the oxygen does react, it would soon be depleted - there is just some 15 gram of it in the tire. What remains is almost pure nitrogen then; but at no cost!

Air also holds a tiny bit of moisture which is bad for rubber. But again, the outside of the tire will have to hold up against a lot of it.

Finally, who can tell whether the gas bottle holds what it says? If they sell air for nitrogen it would be mostly true, just a 21% lie.
Sure they can order new nitrogen gas every time they run out.
Or they can put the compressor on and replenish it themselves for free, and let you pay for their 79% worth of honesty.
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Old 03-26-2014, 11:17 PM   #6 (permalink)
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Kind of an old thread, but I talked to a guy who fills tires with "nitrogen" at a local tire shop. It's true that 78% of our air is already Nitrogen. What he says they do, is dry the air, take the moisture out... which is what tends to expand and contract the most under influence of heat and cold.

The gist of it... tire pressure doesn't vary quite as much as normal "air" would as tire heats while driving on a hot day and then goes back to cool condition at rest at night.

That's what I found out talking to a tire guy that has a "Nitrogen" system.
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Old 03-27-2014, 09:10 AM   #7 (permalink)
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Nobody in the nitrogen business or having nitrogen in the tires is ever going to say that there really is no difference with plain air.
They will always say it is better or they would not be doing it.
They believe it works.

When it comes to the reason why they believe we can go fact checking.
First, they dry it/take the moisture out. Not the oxygen? Then they are basically selling dry air, not pure nitrogen.

But does it even really help to take the water out?
Water is the only component in air that is not a gas by itself under normal temperature and pressure
The water content is usually about 1-2% at sea level though it varies strongly depending on conditions.
It acts just like a gas, so as long as it does not condense it will expand and contract with temperature changes just like the other components.
When the temperature drops the air may become saturated and some water may condense (see Water vapor - Wikipedia, the free encyclopedia). Yet that amounts to just a few % of the whole, at most.

When you drive the tires get warm.
When the tires are warmer than the air was that got pumped in the water is totally vapourised and the air behaves like an ideal gas.

So I think the effect of water in the air is negligible.
Drying the air you put into the tires only makes sense when you fill them during a monsoon expecting to enter a cold area, and even then it will be hard to notice the effect.
Otherwise only your wallet will notice the difference between using air and nitrogen.
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Old 03-27-2014, 09:36 PM   #8 (permalink)
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Quote:
Originally Posted by RedDevil View Post
When you drive the tires get warm.
When the tires are warmer than the air was that got pumped in the water is totally vapourised and the air behaves like an ideal gas.

So I think the effect of water in the air is negligible.
Drying the air you put into the tires only makes sense when you fill them during a monsoon expecting to enter a cold area, and even then it will be hard to notice the effect.
Otherwise only your wallet will notice the difference between using air and nitrogen.
We all definitely need to find an "ideal gas" for our tires!!
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Old 03-27-2014, 10:36 PM   #9 (permalink)
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Quote:
Originally Posted by RedDevil View Post
But does it even really help to take the water out?
Water is the only component in air that is not a gas by itself under normal temperature and pressure
The water content is usually about 1-2% at sea level though it varies strongly depending on conditions.
It acts just like a gas, so as long as it does not condense it will expand and contract with temperature changes just like the other components.
When the temperature drops the air may become saturated and some water may condense (see Water vapor - Wikipedia, the free encyclopedia). Yet that amounts to just a few % of the whole, at most.

When you drive the tires get warm.
When the tires are warmer than the air was that got pumped in the water is totally vapourised and the air behaves like an ideal gas.

So I think the effect of water in the air is negligible.
The vapor pressure of the water moisture in a tire filled with "air" causes a nonlinear change in air pressure in the tire when it heats up. See this link,

http://www.epicentermotorsports.com/...icle_Rev_A.pdf

Also see,
http://www.popularmechanics.com/cars...ular Mechanics

TireRack has a long article about nitrogen in tires.

The following is in relation to water liquid water boiling to steam. I mention this because it gives and indication that if the internal temperature in the tire rises to 212+ F (under racing conditions this might be possible) how much the moisture vapor in the tire can affect the pressure. I found this at

Physics Help and Math Help - Physics Forums

"At 212F, 14.7 psia, liquid water has a specific volume of 0.016716 ft3/lbm and steam has a specfic volume of 26.80 3/lbm, which is a volume ratio of ~1603 : 1 of steam:water."

If your local gas station has liquid water in the air hose you got big trouble if you don't want a big change in tire pressure.

Even if you use dried air you will get an advantage in having a more stable tire pressure. On the other hand, having higher pressure in tires generally will increase the fuel mileage.
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Old 03-28-2014, 12:04 AM   #10 (permalink)
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Quote:
Originally Posted by olrowdy01 View Post
The vapor pressure of the water moisture in a tire filled with "air" causes a nonlinear change in air pressure in the tire when it heats up. See this link,

http://www.epicentermotorsports.com/...icle_Rev_A.pdf

Also see,
http://www.popularmechanics.com/cars...ular Mechanics

TireRack has a long article about nitrogen in tires.

The following is in relation to water liquid water boiling to steam. I mention this because it gives and indication that if the internal temperature in the tire rises to 212+ F (under racing conditions this might be possible) how much the moisture vapor in the tire can affect the pressure. I found this at

Physics Help and Math Help - Physics Forums

"At 212F, 14.7 psia, liquid water has a specific volume of 0.016716 ft3/lbm and steam has a specfic volume of 26.80 3/lbm, which is a volume ratio of ~1603 : 1 of steam:water."

If your local gas station has liquid water in the air hose you got big trouble if you don't want a big change in tire pressure.

Even if you use dried air you will get an advantage in having a more stable tire pressure. On the other hand, having higher pressure in tires generally will increase the fuel mileage.
Think I covered all that in more layman's terms, up above. I tried a "nitrogen"(dehumidified air) fill in my car's tires once to see if it worked as advertised. Noted that the pressure was a little more steady as temperatures varied and overall pressure was maintained about 3 weeks longer than usual before tires needed a refresh. Only did it once out of curiosity to see if it worked.

I check my tire pressure at least every two weeks. More often if we see big temperature changes. One of the best ways to maximize MPG and tire life. I see a lot of under inflated tires on all kinds of vehicles. So easy to resolve.
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