When is it the best time to air tires? in the heat or cold? I notice that at night, the pressure drops about 2-3 psi when cold

 

Should be cold when you check them, and also make sure the sun wasn't beating on them either, because it's possible in such a case that right/left don't match. Always use a pressure gauge. I've got a VDO that my friend gave me, which came with his Porsche. Funny thing is that Consumer Reports tested them a while back and the VDO showed as being very expensive and no better than the others. But dial gauges were preferred to the pencil type.

What you can do is if you check them while hot, give it a little extra. Then, go to your car early in the morning and you can adjust the pressures downward by letting some air out. I personally use a 36 front/ 33 rear setup myself. Guy at the tire shop said I should use at least 42 in the front because they're 235/40-18, but I never heard that from anyone else.