As we all know, proper tire pressure is vital for tire life, proper handling of the vehicle, fuel milage, etc. It is also somewhat common knowledge that proper pressure is based on the cold pressure - i.e. when the tires are stabilized at ambient air pressure. In my case, my car is parked in my 60º garage overnight, and outside during the day. The outside temp is forecast to be getting down to -40 (ºF or ºC, take your pick, they are the same at that point) most of this week, so we are talking a 100º difference between the outside temperature and the temperature in my garage.
Searching the internet, I find that the rule of thumb is that tire pressure changes about 1 psi for every 10ºF change in temperature - so the pressure difference from when I leave in the morning from a 60º garage, to when I come home from work where my car has been sitting outside at -40º could be as much as 10psi - which, I would think, would be significant. Of course, the temperature right now is only about -15ºF, so not so cold.
My thinking is that given the low outside temperatures, I should be “over” inflating my tires somewhat when measuring the pressure in the warm garage, so when they cool down after sitting outside all day, I’ll still have sufficient pressure. The question, of course, is “how much”?
Using the rule of thumb and a cold temperature of -40 would say I should over inflate by 10psi - bringing the pressure in the tires up to 42/40 psi front/back (the car placard states 32/30). The maximum inflation pressure on the tires is listed as 50psi, so this should be safe, but is it best? At the current temperatures, that would still be over-inflated by at least a couple of psi, but that doesn’t sound bad to me, and definitely sounds better than being under-inflated. On the other hand, in the mornings the tires would be over-inflated by around 10psi, at least for the first part of the trip (depending on how the tire temperature changes as I drive) - could being that far over cause a problem?