Dbracing New Reader
12/30/20 9:04 p.m.

What do you guys recommend as a process / tools for purging tires of air and filling them with nitrogen ?

bobzilla MegaDork
12/31/20 7:17 a.m.

well, they are already filled with nitrogen so........ 

bobzilla MegaDork
12/31/20 7:50 a.m.

at work on NYE and a little bored.... so correct my math if I'm wrong. 

a 195/55/15 tire should be approximately 240ci of volume at atmospheric pressure, which our tire gauge reads as 0. at 30psi, it's theoretically holding 7200ci of air. normal breathable air is ~78% nitrogen, or 5616ci of the air is already nitrogen. Even if you purged that to 0ci of volume (vacuum), and replaced that with 85% nitrogen (which is whats common in most tire shops), you're talking a 7% bump to 6120ci of nitrogen. 

It's a scam. I can say I've watched shops take off the black caps and put on the green caps and call it "nitrogen filled". 

boxedfox (Forum Supporter)
boxedfox (Forum Supporter) Reader
1/11/21 11:50 p.m.

Technically speaking, the way to do this is by installing a second valve stem on your wheel. You hook up a pump to one of the valve stems to draw air out of the tyre as while you fill it with Nitrogen (or whatever fancy CO2-based mixture that is in vogue these days) through the other one.

There are a few wheels out there that are pre-drilled specifically for this purpose. Like thisTR Motorsports C1M, for example:


Practically speaking, bobzilla is right. Some of these Nitrogen tire fill scams are so blatant that they make my face hurt.

Mr_Asa UltraDork
1/12/21 12:02 a.m.

Seat the bead, hook up a vacuum to it, pull it down as far as you can and then fill it with nitro.

WonkoTheSane (FS)
WonkoTheSane (FS) SuperDork
1/12/21 12:05 a.m.

The most important part of getting a good fill is to have a dryer on your site compressor line.  That will get you > 90% of the way there to the benefits of a (proper) nitrogen fill and way more benefit than just switching your valve stem color :)

Most of the increase of PSI is heat from the flexing sidewalls causing the water vapor on the air inside the tire to expand.  Remove the water vapor and there's not too much difference between o2 & N.

03Panther SuperDork
1/12/21 1:46 a.m.

In reply to WonkoTheSane (FS) :

You are correct. But a typo at the end. I don't know of anybody running O2 in their tires! but yes, there is very little difference in normal air, and the % of N available outside of a lab. I though of that wen I first saw his question, but I couldn't figure out how to say it without sounding like an azz.

Appleseed MegaDork
1/12/21 1:58 a.m.

You're stuck on this planet breathing 72% nitrogen.

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