Funny you should ask.

[TandW]

This thread, if it survives, would be open to those asking oddball questions.
My opener. Does anyone have green valve caps or stems? And if the whole point of it is to be at 100%, how is that achieved when the operation is open to the atmosphere?

[MevetS]

What, item that would have green valve stem cap, or valve stem, are you at 100% ?

[TandW]

Thought that's how it would start. I've had two entire sets of Goodyears installed in the last 16 months and neither dealer asked if I wanted nitrogen. And it was just this morning when I finally thought about it.

[glwinger]

The green valve caps indicate that the tires are filled with nitrogen. It does not mean they are filled to 100% of their rating. just that they are filled with nitrogen. The theory is that since nitrogen molecules are larger, the tire is less likely to need air as often and the tires will run cooler and nitrogen and is void of moisture.
The problem is that when you do need to increase the pressure in the tires. you HAVE to use nitrogen again. Try to find some place that has nitrogen for tires, and get ready to pay a premium for it. When I bought my trailer it had the green caps, 'supposedly' nitrogen was used.
Checking and maintaining correct tire pressure is the best way to prevent problems. I just check my tires before every trip and then again before I pull out of a campground. I use a small 110 volt air pump that will deliver 125 PSI.

BTW, normal air is 78% nitrogen. 21 % oxygen and trace amounts of other gases.

[Mudfrog]

My wheels have the green caps on them. Checked the other day and added air via my compressor. Didn't think about it at the time but now I'm wondering if I voided my N warranty? Is it ok to mix nitrogen and air? Will my tires be ok running just regular old air?

[TandW]

So atmospheric air is 78% nitrogen. And in a passenger car tire, typically at <30>psi that air is compressed to 1/2 the original volume. So then we can assume that a tire "filled" with nitrogen still has 10.5% oxygen in it. Am I wrong?

[Gary RVRoamer]

Originally Posted by TandW

So atmospheric air is 78% nitrogen. And in a passenger car tire, typically at <30>psi that air is compressed to 1/2 the original volume. So then we can assume that a tire "filled" with nitrogen still has 10.5% oxygen in it. Am I wrong?

If it was truly filled with 100% nitrogen, then the "air" was displaced and there is no oxygen left. If it was filled with "air", then it still has 22% oxygen no matter how much it is compressed. Compressing doesn't change the proportions.


In a more likely scenario, the tire was filled with air at normal pressure and more-or-less pure nitrogen was added until the desired psi was reached. That would lead to a blend of air & nitrogen, so your 10.5% oxygen could well be correct.


In my opinion the value in filling with nitrogen is that it is always dry. If you have an air source that is dried the same as the nitrogen, you would get much the same benefit. I think the difference in molecule size is academic.

[Xmcdog]

Originally Posted by TandW

So atmospheric air is 78% nitrogen. And in a passenger car tire, typically at <30>psi that air is compressed to 1/2 the original volume. So then we can assume that a tire "filled" with nitrogen still has 10.5% oxygen in it. Am I wrong?

Nope. The tire before inflation contains air at atmospheric pressure. So unless a vacuum pump is used you will have contaminated nitrogen. Pulling a vacuum I think would be impossible as the bead seal would collapse.
So to me using nitrogen is not worth it. Yes for race cars, sure but for me, not so much.

[TandW]

So, is it common for tire dealers to propose a nitrogen fill anymore? And when and if they do, do they do a partial fill and purge before a final fill, similar to what is done with a brand-new propane tank?

[JohnBike]

I beg to differ with y’all. When I saw the green caps on two of our new TT tires, I asked the tech about N2 fill. He replied, “Nah, you we’re missing a coupla caps and that’s what I found in the parts bucket.”

[96 Wideglide]

First time I've heard of that!

My Kia came with green valve stem caps.

[johninsd]

The whole nitrogen in the tires deal is just a scam for tire dealers to make a little more money. One friend told me that her tire dealer had said that modern tires can't be filled with air, only nitrogen, and that she needed to come in once a month or so and pay him to top off her tires with nitrogen. If she were driving a Formula 1 car or an F35 as her daily driver that would probably make sense, but for an SUV it only makes for more $ in the pocket of the dishonest tire dealer.

[W4KMA]

Unless you drive NASCAR, just use air.

[Old-Biscuit]

O2 is 'heavier' then N2 so my tires weigh less which helps when taking one off and having to handle it