Most motorists have this if-it-seems-inflated-it's-probably-OK mentality.
That is wrong and must be rectified not only to make sure that you get to use the tire for the duration of its lifespan (which is somewhere between 6-10 years) but also to prevent accidents.
Inflation pressure is one of the biggest determining factors for tire longevity. But first, the units. Pressure -be it air or water- is often expressed in a variety of units. Depending on where you are, it could be measured in psi (pounds per square inch), kPa (kilopascals), or bar (barometric pressure).
Whatever the proper number is can be found in the owner’s manual, but you can also find it on the vehicle’s doorframe (driver side). For conventional sedans, SUVs, and even pickup trucks, it is usually between 32-35 psi or 220-241 kPa or 2.2-2.4 bar.
More importantly, you need to know that the number indicated in the cold inflation pressure. Just make sure that you take a reading with a properly calibrated gauge while the tire is cold, preferably before it’s driven or if it’s been parked for at least 3 hours. Sometimes vehicles have a TPMS or tire pressure monitoring system built-in which uses readouts from a sensor in the tire valves.
If you don’t have a gauge, make sure you don’t drive more than a kilometer before checking the PSI and putting air in or taking some out. As mentioned above, tire temperature rises due to the ambient heat and the rolling motion. Any miscalculation will lead to your tires being overinflated.
Overinflated tires make like a balloon and round themselves out. This reduces the contact surface on the road, which in turn decreases traction and braking performance. The harder the tires, the rougher the ride too. That’s bad for the suspension as it will wear components out more quickly.
Underinflated tires, even by as little as 6%, will increase your fuel consumption by 5%. This is because the tire surface that makes road contact flattens too much due to lack of air pressure. This leads to higher rolling resistance and emissions. That’ll be an extra Php 250 a week for gas (assuming you spend PHP 5k weekly). Low tire pressure also forces the sidewall to flex too much, which lowers steering precision and cornering stability while also building up internal heat. All that action will eventually decrease tire lifespan by 25% or approximately two years.
As for the spare tire, check its pressure on a monthly basis as some sources indicated that it loses about 1 PSI a month. If you're thinking about filling her up with nitrogen, that's a great option but we'll air that one out later on. No pun intended.
So, while it may seem innocuous, the amount of air (or lack of it) has a direct effect – short and long term - on your tires, major components of the vehicle, and fuel efficiency. Know these pointers on pressure so you get the best performance out of your tires.