Tire Pressure in Below Zero Weather?

Hey all, question.

Does extremely cold weather in the winter, say minus 20 or so, really contstrict air in your tires and mess up the pressure reading?

My 2004 Focus tires are supposed to be filled to 34psi. I checked today, they are all about 25psi. That's normal right?

I want to keep them that way? Not fill them up to 34? They will expand and be overinflated when they get up to highway speed or something, right?

Thanks!

yes and no.
I know, that helps right.
Yes tire pressure is affected by temp.
How to correct the issue. I live in northeast michigan and what I do is check my tire pressure every week. It never varies more than 3 psi. and that is ok with me. I am talking about extream changes in temp to. Up here it might be 13deg. right now, but tomorow it might be 50 so if I get a big change in the temp I do check my pressure expecially if I am traveling.
a 5 pis fluxuation in pressure is acceptable to tire manufactuers but it sure can mess up a good set of tires.
Low pressure is worse than overinflation so 32-37 would be good.

tire pressure is affected by temp.

The pressure goes up approximately 1 PSI for every 10 degrees fahrenheit.

Always adjust the tire pressure cold. It probably even says that on the sidewall somewhere if you read it. The tires don't get nearly as hot even on highway driving during the winter. I keep mine at the max on the sidewall year-round.

I'm not suggesting that you, or anyone, try this:
I had a set of 35 PSI tires that I put up to 45 PSI. I just wanted to see how much tolerance there was. Drove over 2,500 miles like that with no problem.

Here is how to do tire pressure.
I use a 60 foot poll barn with a concreet floor.
Set your tires to the factory recomended pressure.
Whipe off your tires tread with a rag.
drive the vehical forward about 20 feet, now look at the dirt/dust impression on the tread.
The dirt will attatch itself to the tread showing weather the tire is rideing flat on the surface and if they are equaly collecting dirt.
Say you have one of the tires with dirt from side to side on the tread and on the others the dirt rolls over the edge of the tread onto the sidewall of the tire. This tells you you need more air in the tires with the dirt showing up on the sidewall. the tire is under inflated
If the dirt shows one half way accross the tread (from center outward) and the outter part of the tread is not tutching the floor that tells you your tire is over inflated. When I do this it
Leaves me with different pressure in each tire, but the tires are toutching the ground equally.
And, FYI. I leave 1/4" of untuotched tread on the outside edge of the tire.
All my tires have worn equally. the pressure difference is only a few pounds, mabey 5 at the max.