Q: I have a tire question that I’ve had about six different answers on from RV dealers. We have a fifth-wheel trailer with a dry weight of 7,794 pounds and its tires came filled with nitrogen gas. The tire size is ST225/75R15 with a 65-psi-cold tire pressure printed on the tire. I have two questions: Can I mix the gas with air? (There is no one in the area who carries the gas.) How much air/gas pressure should I keep in the tires? (I had work done on it at a large RV service center and it now has 52 psi in all tires; previously, it had 62 psi.)
David Miller, Anchorage, Alaska
A: It doesn’t matter whether there is nitrogen or air in the tires; use the same pressure regardless. You can mix them as well, although the straight air will dilute the claimed advantages of using nitrogen. You may be able to find nitrogen at a local welding or industrial gas supplier if your local tire shops don’t have it available. In order to determine what pressure to use in the tires, you need to weigh the fully loaded trailer (both axles) and divide the weight by the number of tires. Then look this weight up in a load-inflation table, which is available on tire dealers’ and manufacturers’ websites. Until you know how much weight is actually on the tires, to be safe, you should run the pressure that is listed on the sidewalls.
— Ken Freund
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