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Unread 09-09-2013, 08:23 PM   #1
Mfrancis
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Filling JK tires with air?

The JK I bought ten days ago has tires filled with nitrogen. If I deflate them to go wheelin' in sand, will it hurt anything to refill them with regular air?

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Unread 09-09-2013, 08:28 PM   #2
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Nope.
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Unread 09-09-2013, 08:29 PM   #3
ronjenx
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Quote:
Originally Posted by Mfrancis View Post
The JK I bought ten days ago has tires filled with nitrogen. If I deflate them to go wheelin' in sand, will it hurt anything to refill them with regular air?
No. It will not hurt a thing.

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Unread 09-09-2013, 08:38 PM   #4
MikeHoncho88
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Well technically, the oxygen in regular air will rot your tires from the inside out in about 10-20 years. So watch out for that. ;-)

Nitrogen fill to me seems like a scam, but what do I know.

By the way, regular, free air is like 70 some percent nitrogen. :-)

Edit: forgot to mention that the outside of your tires are exposed to regular air all day as well. Too funny.
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Unread 09-09-2013, 09:09 PM   #5
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I could see using pure nitrogen in high performance low profile (and low volume) tires. It is more stable and should leak out less.

But in a jeep it's stupid. Unless you plan to set the tire pressure once and never change it or air down etc.
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Unread 09-09-2013, 09:42 PM   #6
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Leave nitrogen filled tires to track cars and aircraft.
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Unread 09-09-2013, 10:01 PM   #7
SubAtomicGenius
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You get 76% nitrogen for free in your tires when you use air. You're paying a premium for the other 23-24%. That's even if you are actually getting nitrogen and not just the green caps. No benefit to the average driver whatsoever. Gimmick.
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Unread 09-09-2013, 11:02 PM   #8
Jiblet
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Nitrogen in automobile or truck tires is a scam.


The point of using nitrogen in certain tires is that the nitrogen can be delivered very dry (dehumidified). There is nothing special about the nitrogen (as noted, air is mostly nitrogen). It is cheap, plentiful, inert (enough), easily dried.

Water is the enemy. A tiny amount of liquid water heated will expand greatly. Much more so than a volume of a gas would under the same conditions. (A liquid phase changing to gas has a big increase in volume or pressure while a gas remaining gas, not so much.) Such expansion inside a closed system results in a rapid increase in volume and/or pressure.

Think of an aircraft tire suddenly contacting the ground. The sudden heating of the gas in the tire causes an increase in pressure but not nearly as much as the expansion of even a small amount of condensation (liquid water). The presence of even a minute amount of liquid water can result in catastrophic blow outs.



This video (and any of dozens more like it) show the exact opposite of what I'm trying to describe. Expanded water vapor in a heated, sealed system is cooled. The drop in volume of the water vapor decreases the internal pressure of the drum such that the external pressure crushes the drum.

It's the vaporized water that makes the difference. Heating a drum full of (somewhat dry) air, sealing it and letting it cool would not have the same catastrophic effect.
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Unread 09-10-2013, 05:02 AM   #9
mello
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Nitrogen filled tires on the vehicle where you my air down is definitely a waste. On Regular automobiles however where you will not be airing down nitrogen is a great thing specially for vehicles with TPMS. The nitrogen keeps you from having cold-weather low tire lights.
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Unread 09-10-2013, 07:19 AM   #10
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Originally Posted by mello View Post
... nitrogen is a great thing specially for vehicles with TPMS. The nitrogen keeps you from having cold-weather low tire lights.
But only if the nitrogen is dry. ANY dry gas or mix of gases will do, including dry air. Dryness is the key. The change in pressure in tires due to temperature fluctuations is almost entirely do to the presence of water in the fill.

All it takes is a drop of water... probably way less.

I doubt the local shop N machine is delivering particularly dry N or purging the tire sufficiently. Not the way the Air Force/NASA/airlines etc. do.

When you take a Helium-filled balloon from a warm house out into the winter-cold, it shrinks. That's not the helium, its the water vapor in the mix.

At the temp and pressure of tires all gases behave as Ideal gases (or very nearly so*). But with water the liquid/gas phase transition is so close to these conditions that it plays a big role.

At 0C/1atm (STP) the volume of a mole of liquid-water (18g) is about a cubic inch, the volume of the same amount of gas-water is over 1300 cubic inches.
at 100C the volume increase is over 1700X. (Firemen know the danger of hosing down a very hot fire.)

*deviation from ideal behavior increases with higher pressures (van der Waals equation) but its very small... Not enough to effect an auto's tires.
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Unread 09-10-2013, 07:38 AM   #11
Mfrancis
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Don't be offended, but I read that last post in Sheldon's voice from Big Bang Theory. Bazzinga!
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Unread 09-10-2013, 10:01 AM   #12
Tanimal
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Quote:
Originally Posted by SubAtomicGenius View Post
You get 76% nitrogen for free in your tires when you use air. You're paying a premium for the other 23-24%. That's even if you are actually getting nitrogen and not just the green caps. No benefit to the average driver whatsoever. Gimmick.
When I bought my Jeep I was charged $100 for nitrogen filled tires. Literally watched them top the tires off to proper pressure with a regular Craftsman air compressor. Got my ACE rock sliders with the money they gave me back after I was done speaking to the manager
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Unread 09-10-2013, 06:39 PM   #13
Jiblet
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Quote:
Originally Posted by Mfrancis
Don't be offended, but I read that last post in Sheldon's voice from Big Bang Theory. Bazzinga!
That's funny! No offense taken. Except that Sheldon is a physicist... I'm a chemist.
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Unread 09-10-2013, 06:41 PM   #14
SubAtomicGenius
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Quote:
Originally Posted by mello View Post
On Regular automobiles however where you will not be airing down nitrogen is a great thing specially for vehicles with TPMS. The nitrogen keeps you from having cold-weather low tire lights.


Mmmmmm... purple kool-aid.
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Unread 09-10-2013, 06:45 PM   #15
SubAtomicGenius
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Quote:
Originally Posted by Tanimal View Post
When I bought my Jeep I was charged $100 for nitrogen filled tires. Literally watched them top the tires off to proper pressure with a regular Craftsman air compressor. Got my ACE rock sliders with the money they gave me back after I was done speaking to the manager
Typical of the automotive industry's practice of fleecing the average customer - thankfully you proved more wiley than the average customer, Tanimal!
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