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That 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.
It's all about how much your tire pressure increases as your tires warm up during normal driving. First, fill your tires to the PSI recommended for your vehicle. Then, travel at highway speeds for about 20 to 30 minutes. After that, check the pressure again. If the reading's gone up by 4 PSI from where you started, your pressure's right where it should be. Some heavier-duty 4WD and light-truck tires may see a rise closer to 6 PSI, which is perfectly fine.
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What it means if your tires don't pass the 4 PSI rule
If 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).
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Read the original article on SlashGear.
