Mystery Debunk – why do tires lose pressure

It is important to always maintain the correct tire pressure in your car’s wheels. That’s why we recommend checking it regularly to avoid future inconveniences. However, you might notice that your tire loses pressure at certain instances – often, after a month of properly inflating it. Sometimes, you’ll even find a drop of PSI* at a night despite checking it earlier in the afternoon.

The decrease in the PSI, or basically the loss of tire pressure, does not always mean your tires are punctured and that you need to rush to the vulcanizing shop in full-panic mode. In certain cases, it is normal for your tire to deflate over time—or in rare occasions, due to atmospheric conditions—as long as the loss is not that severe. What’s severe and what’s not? Here, we listed a few possible causes that might spare yourself from having panic attack.

Permeation

We know it sounds very scientific but this simply refers to the way how molecules behave. Air can escape from solid material like rubber, and that happens due to permeation, which is actually the diffusion of molecules through a membrane. This is a natural occurrence, and one of the most possible reasons why your tire loses one to three PSIs over the course of a month, depending on the tire model. Note that the recommended tire pressure can be found marked on the walls of the tire.

In tires, rubber blends vary depending on the maker and blends contribute to the tire’s permeability. Permeability is a state of a solid material that causes liquid or gas (permeants) to pass through it. Some tire rubber blends are more permeable than others, meaning air tend to escape easier. So, checking regularly would keep you just fine. Failure to check your tire pressure for a longer period of time poses handling and fuel efficiency changes on your vehicle – in worst cases, danger.

Temperature changes

You might have noticed that there’s a slight PSI difference on sunny and cold days. That’s because temperature is a big factor in air molecule behavior. Exposing your tire under the heat of the sun or driving it for a long period of time will cause the air molecules inside it to expand, increasing the PSI. Accordingly, molecules compressed together in colder weathers, which is why you get lower PSI result whenever you check at night.

It is important that the amount of air inside your tire and pressure aren’t interchangeable. You may have the same amount of air in your tire and inconsistently changing PSI readings all at the same time. A drop in PSI doesn’t mean your tire lost some air, as pressure refers to the force caused by the movement of molecules inside the tire. Because molecules move differently under different temperature, it’s better to check your tires when your they aren’t hot, nor when the weather outside is too cold. This way, you’ll get the normal tire pressure reading.

Altitude

Driving in higher places actually contributes to your tire pressure. The main reason for this is that tire pressure is a direct relationship between the air inside the tire (gas pressure) and the outside air (atmospheric pressure).

Pressure drops when you’re in higher places as there is also less air the higher you go. This is the cause of that uncomfortable feeling in your ear every time you go up on mountains. The thing is, the gas molecules, when trapped inside a volume (which, in our case here, is a tire), constantly move around. In the process, they collide with one another as well as with the volume’s surface (tire wall). While this is all happening, gas molecules outside the tire also exert pressure onto the outside surface of the tire.

So, in essence, the lesser the pressure outside, the harder it is for the molecules inside to hit the inner walls of the tire, since there is not enough outside pressure to balance it out. And, this occurrence actually is the the reason why you perhaps would register a higher PSI reading in Baguio than when you’re in Manila.

Impact breaks

You might also want to take extra care in parking or maneuvering on curves, as carelessness on these spots could result to an instant to gradual drop in tire pressure. How come? In parking your car, make sure you don’t reach to the point where you hit the cement tire stopper. This habit will most likely cause you impact breaks, which are visible bulges on a tire wall.

Impact breaks are caused by hitting curbs, speed bumps, or any object at speed. The impact then stresses the tire wall and damages cords causing them to break. When ignored, this can cause gradual tire problem, including recurring tire pressure and air loss. When this happens, you may want to get a replacement as soon as possible, as this is something you should deal with seriously.

However, should be remembered that, despite these plausible reasons for loss of tire pressure, it is still important to be cautious. So, the moment your tires’ PSI keeps on dropping despite filling to the right PSI over and over, that’s when you seek for professional inspection.

*Pounds per Square Inch - the common measurement unit of pressure