I'm surprised that no one has mentioned that you should run a little higher PSI for sustained high speed driving (70 MPH +) for certain speed rated tires (T and below). I run my vehicles tires at a +3 at x degrees outside temp for the lowest expected temp for a given season. For example, my Matrix calls for 32 PSI. I have AEM Eagle F1's (94W) which call for 35 PSI. The lowest temp I would be driving at in SC is about 20 degrees. Therefore, I run 38 PSI at 20 degrees. Now before everyone jumps, the max PSI on the side wall is 51 so I'm well within that. As the seasons change, you adjust to compensate. Also, for every +/- 10 degrees in outside temp, there is a +/- 1 PSI change. If you inflate your tires to 30 PSI in a warm garage (say 60 degrees) and then go for a drive in 30 degree weather, your pressure will drop 3 PSI. Your tires will be underinflated. Will the PSI increase with tire temp? Probably but I wouldn't want to ride that long to find out. As a former LEO, I trusted my life to tires. The V rated RSA's we ran on the Vic's were set for 35 (up from Ford's 32) to allow for high speed driving at speeds in excess of 100MPH for extended periods. This is just my 2 cents on the topic.