Don’t judge tire inflation just by looking at it, unless it is visually flat. Always use a tire pressure gauge to get accurate pressure readings, make sure you check them when cold before driving. Temperature play an important role on tire pressure. Cold temperatures can cause tire pressure to vary by as much as 1 psi per every 10 degrees; higher temperatures mean higher tire pressure readings.
In addition to safety, environmental and economic benefits having your tires properly inflated could save up to 3% in gas mileage.
Always refer to the owner’s manual for the correct tire pressure, the door jamb sticker is another place where you’ll find tire information, including pressure and tire size.