i just started noticing this as the weather gets colder, but it seems if my car has been sitting out in the cold for a while, and i start the car, the low tire pressure light comes on. at first i thought i had a puncture somewhere, but i checked the pressure and all the tires are fine! what's more, after driving for a while with the light on, the light turns off on its own, until the next time when it's cold and i have my car sitting out for a while.

so what's going on here? is it the air getting cold inside the tire so it's losing just enough pressure to trigger the light? or the calibration is a bit off?

 

You filled up at 70*F. Its not 50*F. The air takes up less space in the tire. For every 10*F drop, expect about 1 psi drop. So if 70 is what temp you filled up at, its 50 now - 2 psi lower.

 

Et Voila!!!

 

Mine do the same thing. The TPMS is pretty sensitive in the EVOs I find. If it lowers more than 4 PSI than it's calibrated amount, the light will come on.

 

Physics 101, Ideal Gas Law:
PV=nRT

/thread

 

that's what i figured, but if it triggers after just a 2 psi drop...i dunno, it's sensitive.

 

Have you checked what psi they are when you go out to your car in the morning?

If the tire pressure drops to around 26psi / 20% of the calibrated value of 32psi, the TPMS light goes off. So if your tires are sitting around 26psi and then you start driving, depending on how cold it is, the air in the tires will raise a few psi putting it above the trigger point of the TPMS but would still be considered under inflated.

You want to fill your tires when they are cold (at your house or closest gas station) and try to fill them when its hovering around the average temperature your area see's or when you are typically driving, and then when the temp changes a lot either warmer or colder, do it again so that you’re not driving on under inflated or over inflated tires and cause uneven wear.

Lol I am **** about it and do it every other day, but then I have a compressor at my house and it take 2 seconds, but as a result I went 10,000kms this past summer on the OEM tires and never rotated them and all 4 have worn exactly the same amount.