Re: Trailer tire quandry!
The Truths and Myths of nitrogen
Claim #1. "N2 doesn't expand with heat like air because it's drier so your tire pressures stay more constant through tire temperature changes." Here's a claim that we've heard more times than we';d like to admit. Bottled nitrogen is dry, drier than typical air, and it is said that a drier gas will exhibit less pressure change to temperature changes. This would mean that as my N2 filled tires heat up, the pressure will not go up as much as if they were filled with air. The dryness of CO2 is also put into question since it is a "liquid" gas under pressure. CO2 vapor is very dry. Don't forget that N2 is also a liquid gas under certain pressure and temperature. The truth is, the differences in thermal expansion values (TEV) between N2, air, and CO2 at automotive tire pressures is virtually undetectable to a driver. In our own tests we compared the pressure changes of N2, air, and CO2 through a wide temperature range and found that they all expanded (increased in pressure) at virtually the same rate (see Gas Test).
Claim #2. "N2 permeates (leaks) through tires slower than air therefore your tires will maintain their pressure longer and require less maintenance."
Although it is true that nitrogen does permeate through tire rubber slower than oxygen and CO2, there are two things to know. First, the gas permeation difference between oxygen, CO2 and nitrogen through a tire wall is very minute. Second, this difference is made even more insignificant for N2 since oxygen only makes up 17% of air and most of "air" (78%) is nitrogen. Diffusion speed through the walls of your tires has more to do with the quality, the wall thickness, and the age of your tires. More often, tire deflation is due to a leak in the stem core, the stem seal, cracks in the stem, a bad tire to wheel bead seal, cracks in the tire wall, or objects like nails stuck through the tire tread. Also, did you know that your tires may grow during the first 1-2 days as it gets used to being inflated which would reduce the tire pressure. Tire manufacturers recommend checking your tire pressures often no matter what type of gas you';re using to fill your tires. Bottom line: If gas permeation was the only way a tire would lose its "air" there would be very little detectable difference between air (which is already 80% nitrogen), nitrogen, and CO2.
POWERTANK - CO2 Air Systems
