JPJ may be just busting my chops, but over far too many years of checking tire pressures I have developed some ideas of where my pressure losses come from.

The two most likely and common places my tires lose pressure is the valve core, and the place where the valve stem goes through the rim. To address the first I have always used good caps, and now I have the spring loaded caps that do not require removal to check or air up a tire. They seem to work much better than conventional caps as a second seal.

As far as the valve stem seal at the rim, there is no easy fix. If I notice a tire always needs a few more PSI, I soap around the seal to confirm that is the leak, and then I have to deflate the tire and either tighten it up, or replace the rubber seal completely. The good news is I don't have to remove the tire from the wheel as long as I can push the tire down (I use a hydraulic jack under my truck bumper to hold it) and get at the valve stem from the rear.

I always use the same gauge so I am not dealing with pressure variations from gauge to gauge. I also always fill my tires to the exact pressure each time so if one of my tires always needs more air than the others I know I have to find the reason for the leak. That helped me find a nail that had gone through the inner sidewall once and that I did not find by looking around the tread of the tire.

The Chinese tires hold air as well as the Michelins. They may turn out to hold air better because my Michelins will literally push away from the rim easily when deflated, and the Chinese tires need a fairly good push in order to break the bead. Time will tell.

Outside air temperatures have a huge impact on pressure, as does the sun. If you go from the frigid north to the warm south your tire pressures will be higher than they were, and the reverse is also true. The difference I have seen is as much as 7 PSI. It is useless to check tire pressures right after you have been driving, except to measure differences in pressures on the same axle. The values for a hot tire are going to be different by a lot. Similarly, if you check tire pressures after the sun has been shining on them for a while, those pressures are going to read high. So set your alarm and get up before the sun rises to check tire pressures.

Checking tire pressures is a royal pain in the butt, and nothing makes me madder than having to deal with a leaky valve core that was perfectly fine up until I messed it up by checking pressure. The alternative to checking pressures is poor tire wear (if you are lucky) or worse, a blowout. On our coaches if a tire blows out and starts to disassemble itself there is ahigh probability that besides the cost of the new tire and a service call you will be spending some serious Lewbucks if it tears up things like your airbags, brake lines or all of the other things that can be damaged by a heavy piece of rubber slamming around at 60 miles and hour in your wheel well.