Originally Posted by RangerJoe
Definitely go recommended pressure. And make sure you are checking the pressure when the tires are warm, not cold. Drive on them for 20 minutes and check. It likely won't make more than a few pounds of difference, but it can effect tire wear.
That's wrong. For a passenger car, tire pressures should be measured when the tires are cold.
If I underinflate my tires, the excess flexing of the carcass will heat the tire, thereby increasing the pressure, and it will register the recommended pressure if I measure when the tire is warm (after driving on it). But the tire will be underinflated. That's why tire pressures are specified for cold tires.
On a race car you're trying to achieve certain spring rates with tire pressure, so the tire pressure when the tire comes up to temperature matters (though unless you've got tire warmers you're setting the pressure when the tire is cold, and calculating where it will be when warm).