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Overinflation and underinflation
Incorrect tire pressure can harm you and your car in many ways, from premature wear and tear to the risk of losing control of your vehicle in more extreme cases.
What you should keep in mind is that both underinflation and overinflation have their disadvantages.
When there's not enough air pressure, the tire changes its shape, and the contact surface becomes flatter. Besides the chance of failure, the tire's life is reduced by up to 25%, fuel economy can go up by 5%, and you will experience a loss in steering precision and stability. Luckily, new cars have a tire pressure sensor and a warning light on the dashboard, so there's not need to regularly check the pressure.
Put too much air in your tires and you get a stiffer ride as well as a reduced contact patch with the asphalt. Overinflated tires can't correctly absorb bumps in the road which can cause them severe damage over time. There's also an upside to overinflation, in the sense that both handling cornering stability increase to some extent.
Tricks and tips
The most self-explanatory piece of advice we can give is to have a look in the owners' manual for the standard cold tire inflation pressure.
As a rule of the thumb, carmakers usually recommend a PSI (pounds per square inch) value situated in the 27-32 units interval (sometimes even around 40 units) for sedans, MPVs, and hatchbacks.
As far as SUVs and pickup trucks are concerned, these might require tire pressure of 45 PSI or higher, depending on the type and weight of the load they carry. Also, keep in mind that the producer might recommend different tire pressures for front and back tires.
Also, don't take the lazy approach and try to estimate the amount of air in a tire by simply looking at it. It just doesn't work like that. Instead, let a mechanic check your car's tire pressure or do it yourself with an air pressure gauge.
However, avoid using the commonly-used pencil-type gauge as it is notorious for its lack of accuracy. For a more accurate alternative, consider choosing analog or digital gauges. In addition, remember that tire pressure should be checked as the seasons come and go. Cold weather makes tire pressure drop while hot or warm weather will make it go up.
Last but not least, forget about the myth saying that the max pressure value offered by the manufacturer is the top value which a tire can handle before exploding and whatnot. In fact, this value presents an insight on the pressure at which tires can carry the maximum amount of weight.