Does anyone have experience with CO2 (or other compressed gas) for inflating tires? A friend of mine uses the 10# Smittybuilt tank and claims to get 16 fills out of each tank, which I assume is 16 individual tire fills. I'll also assume (after today's experiment) that he's inflating from 15->25 or so, not 13->32 as I did. I'll ask next time I see him.

So I did an experiment and did not have great results. First test is with a 5# CO2 tank and the second is a 40cuft nitrogen tank. Started at 13psi in all 4 tires and target was to inflate to 32psi. CO2 tank started at about 690psig and N2 at about 2030psig. The CO2 tank totally drained before finishing, the tank and tires were at 30psig. The nitrogen was much better, filled the tires and had 840psig remaining. However, each of these cylinders is about $20 to fill, so clearly this is not a cost effective method to inflate tires. How does this compare to anybody else's experience?

Let's check with math. Assuming the 35x12.50R15's have 1" of tread/wall & 1/4" side walls thus can be approximated as 33x12.00R15, we get a water capacity of 8143 cuin = 133 liters. The internet tells me that my 40 cuft N2 has a water capacity of 7.8 liters. At 2,030 psig, that's 15,834 psi-liters (weird units, I know, but the math works). So now we fill four 133 liter tires from 13 to 32 psig, that's 10,108 psi-liters. This should mean I have 5,726 psi-liters remaining, or 7.8 liters at 734 psig. 734 psi theoretical versus 840 psi measured is pretty close - with big assumptions like this I'd say an order of magnitude off is wrong and within a factor of 2 is right. In conclusion, the math and the experiment shows that this is a poor method to fill tires. So fill me in on your experience!

Because people like pictures:

I see this thread, but it did not answer my questions: http://www.frontrange4x4.com/forums/...tank-question/