Maintaining the correct pressure in car tires is essential to both their performance and safety. When tires are overinflated, they are more likely to blow when you drive over a pot hole, speed bump, or other uneven terrain. When tires are underinflated, however, your car will burn more gas to achieve the same speed. Overinflation is typically caused by human error, with the driver inflating his or her tires beyond the manufacturer's recommended pounds per square inch (PSI). But underinflation is usually caused by something else, such as the following.
One common cause of underinflated tires is temperature changes. When the temperature changes around the tire, so does the temperature inside the tire. Going back to the basics high school physics 101, heat causes things to expand, whereas cold temperatures have the opposite effect by causing things to contract. So, when the temperature drops outside, it may cause the air inside your tires to contract; thus, lowering its air pressure.
Faulty Valve Stem
Another possible cause of underinflation is a faulty valve stem. This otherwise small piece of plastic plays an important role in maintaining the correct pressure in tires. Over time, however, the valve stem may crack, break and deteriorate, at which point the air will leak from the tire. The good news is that valve stems are cheap and readily available at most auto parts shop, with many places selling packs of them for just a few bucks a piece. If you have one or more faulty valve stems, replace them ASAP to prevent air from leaking from your tires.
Of course, the underinflated tires could be attributed to an actual leak. It's not uncommon for drivers to run over nails, screws, glass, pieces of wood, or even sharp rocks, all of which can pierce the sidewall and cause a leak. If the item falls out of the tire, the tire will likely deflate rapidly, forcing the driver to change it. If the item remains stuck inside the tire, however, it will deflate more slowly.
These are just a few of the most common causes of underinflated tires. Regardless of what's causing your PSI problem, you should fix it ASAP. Underinflated tires burn more gas while also affecting handling. Thankfully, it's a problem that's easily fixed if you know what to look for.