Tire pressure being refilledThat low tire-pressure alert isn't for nothing. It's the one thing that affects nearly every part of how your car performs. From tread wear to fuel economy to handling to heat management, the wrong PSI could be a headache waiting to happen. One of the most commonly used methods for determining if your tire pressure is in the right place is known as the "4 PSI rule." With a simple bit of mental math and some highway speeds, it can help you tell whether your tires are operating within a safe temperature range. What it means if your tires don't pass the 4 PSI ruleTire PSI checker on tireIf you're seeing a pressure increase beyond 4 pounds per square inch, your tires might be underinflated. Underinflated tires flex more as they rotate. That generates more friction, which, in turn, generates more heat. Eventually, that heat can build faster than the tire can disperse it through the tread. When that happens, you run the risk of structural damage or tread separation. If you're seeing a number under 4 PSI, then the opposite is true: Your initial pressure might be too high. The higher the pressure, the more the tire concentrates wear at the center of the tread. That's not good, either.Of course, the 4 PSI rule is not a universal formula for every terrain. It really only works at steady highway speeds on sealed roads. Rough gravel or dirt won't give you the same pressure readings, and the same is true for wet or snowy roads. No matter the terrain, routine pressure checks are still the best way to extend the life of your tires. Tires naturally lose air over time, so pressure should be checked often (and with an accurate gauge, not just with a quick once-over with your eyes or a tap of the foot). Want the latest in tech and auto trends? Subscribe to our free newsletter for the latest headlines, expert guides, and how-to tips, one email at a time. You can also add us as a preferred search source on Google.