# What's with green valve stem caps?



## milobloom242 (Dec 28, 2004)

Lanc3r said:


> Upon Googling the claim is that Nitrogen bleeds through rubber at a slower rate the O2, so the tire pressures are maintained longer. My OP is apparantly wrong.


the N2 molecule is larger than O2 molecule, which could explain the slower bleed rate


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## Test_Engineer (Sep 11, 2004)

teh_jev said:


> I'm sure this has been answered before but why nitrogen? I can't imagine it lessening too much weight can it?


If you read enough technical opinions on it, you will find rather quickly that it is the newest snake oil product of the auto industry. If someone wants, I will go into detail, but most of it is very technical and it proves Nitrogen filling on a passenger car is complete BS.


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## obmd1 (Jan 17, 2005)

Test_Engineer said:


> If you read enough technical opinions on it, you will find rather quickly that it is the newest snake oil product of the auto industry. If someone wants, I will go into detail, but most of it is very technical and it proves Nitrogen filling on a passenger car is complete BS.


but it does explain why Discount Tire put those ugly green things on the wife's car.


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## dboy11 (Mar 6, 2006)

milobloom242 said:


> the N2 molecule is larger than O2 molecule, which could explain the slower bleed rate


This was how it was explained to me..


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## rehostman (Feb 10, 2008)

My winter tires were filled with nitrogen and the technician told me the green valve stem caps were green for this reason. He also mentioned that the tires would lose pressure less rapidly with nitrogen, for what it's worth.


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## geebeemer (Jul 2, 2005)

Well, well....

A month ago went to Colony Tire for the two front tires on my S10. Out the door for $165 or so. Go in yesterday to get the two back tires and check the paperwork after I leave and discover they've charged me $7.50 per tire for nitrogen. "Uh, beg your pardon? Did I ask for a $7.50 bump per tire for green caps?? No." :tsk:

Note to self: Next time I get tires, explicitly state I'm not paying extra for nitrogen. kthxbye


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## 1SCK530 (Apr 29, 2009)

because costco is a horrible company and they are all stupid


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## Andrew*Debbie (Jul 2, 2004)

milobloom242 said:


> the N2 molecule is larger than O2 molecule, which could explain the slower bleed rate


Dry air is about 78% Nitrogen. 20% is O2. The rest is mostly Argon.

There can be a fair amount of water too. Depends on local conditions. A good shop air system will trap much of the water.

One could argue that dry N2 is inert and won't do anything to the tire or wheel.


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