with RV tire expert Roger Marble
While air volume output might be a consideration, IMO if you are properly inflating your tires and properly monitoring inflation with a TPMS, I don’t understand how anyone can get in a position of needing more than about 5 psi unless you have an active leak.
As I have covered a number of times in this blog, I recommend your cold inflation pressure to be at least 10% above the minimum needed to support your actual measured tire loading. (Minimum inflation would be based on the heaviest loaded tire on any axle or, lacking individual tire loading numbers, then using an assumed 53/47% side-to-side split for motorhomes and trailers with big slides or residential refrigerators, and at least 51/49% load split for smaller trailers.)
So assuming you have LR-C or LR-D tires you would be inflating to 50 or 65 psi with your TPMS warning set to no lower than 49 or 64 with your minimum inflation in the load tables being 45 and 58. So how would you ever need to add more than 5 or 6 psi assuming you let your tires get that low? Why not do your “top-off” as soon as you need 3 psi? Now you do need to consider the 1 or 2 psi difference between your calibrated hand gauge and the TPMS reading. I set the warning based on the TPMS reading AFTER setting the tire using my certified hand gauge.
Yes, pressure changes with temperature (about 2% for change of 10° F temperature). A change in morning temperature of 40° F from day to day is unusual and that would only result in a pressure drop of 5 psi on your LR-D tires.
Motorhomes should be running a +10% margin on air pressure based on the measured tire loading, which means there would need to be a 50° F drop in temperature for them to need to add 10 psi (assuming a 100 psi minimum).
If you need to add more than 20% (20 psi) of the needed pressure in your tires with steel body ply, that means you have technically been operating on a “flat” tire, according to tire industry standards, and you should have a professional inspection and have them reinflate your tires AFTER the reason for the sir loss was identified and repaired. Large 19.5 and 22.5 tires should only be reinflated in a cage (watch the video) just in case there was damage to the steel body cords which can lead to an explosion (watch the video) due to zipper rupture.
LR-E (80 psi polyester body tires), as found on most Class C and some larger trailers, need to consider the above information and adjust for their higher cold inflation numbers. I would consider a 20% drop to put you in the safety cage reinflation level if you drove on the tires when that low. While they are not likely to suffer a true “zipper” failure from fatigued steel body cords, there can still be internal structural damage to your tires.
Bottom Line: Monitor your tire pressure and don’t let the pressure drop more than 10% before you reinflate your tires. Know why the pressure dropped and if not due to a drastic change in temperature overnight, inspect for leaks. I find that spray cleaner like Windex or other cleaners tend to foam at the location of the leak.