OK, I last checked -my- tires a month ago. Temps were in the low 10s Celcius. I set the fronts to 40 PSI and the rears to 38 PSI and I set the TPMS. All was "hunky dory". Last night I was at a meeting, and Pearl was parked outside in -8C temps. Got in and noticed the TPMS light. Great, must have got a nail or something. Looked at the tires, they looked ok. Didn't want to be messing about in those temps so drove home with no issues. Pearl sleeps in the unheated but insulated garage, and temps in there were right around freezing. Just now I went out, got the Accugauge from the upper glove box, and checked the first tire. It read "L". ???? Messed around with it, then took it into the house to check the battery. Battery was fine. ???? Got out the spare electronic tire pressure gauge and a mechanical one, back out to the garage to check the tires. Meanwhile the Accugauge had warmed up. Appearantly it's a California piece of equipment. It worked fine when warm. Fronts were 34 PSI, rears were 33 PSI. Fired up the air compressor and pumped them back up to 40/38. I didn't see this last year. Moral? As Mario says, "Check your tires". I didn't think they would drop that much vs temp. Yet another reason the mileage drops when it gets cold out. CHECK YOUR TIRES!
Rule of thumb is 1 psi for every 10 degrees (F) change. I have found that to be pretty accurate in practice.
In 2 weeks mine managed to drop about 8 lbs. My fronts went from 42 to 34 and my back went from 40 to 32. The temp dropped about 25 degrees. Part of the drop is the temp and part is the time... These smaller tires tend to lose pressure faster than larger tires.
