Don't forget the laws of physics involving air pressure also includes ambient temperature. So when my bike sits in my car all day on a sunny day, I rarely have to pump the tires before my afternoon ride. But on cool mornings when I head out from the house, I need to add air.

More fun with air pressure - when I used to live and work at 7000 ft elevation, and we'd get an order of lab supplies, the boxes would be almost bursting open. All our pipets, tubes, and other such plasticware would be packed in sealed plastic bags, the difference in elevation change from the factory site (sea level) to the lab would make the sealed plastic bags expand. This also happens with air splints, so if you have an air splint and go up elevation - more pressure on your broken limb. Air splint going down elevation, loss of pressure, loss of splint function.

So Mr. Sliver - are you checking your air pressure the same time / every day? Has it been warmer or cooler than the day before? You could have all kinds of road trip fun checking pressure at various temperatures and elevations.