How To Check Tire Pressure

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How To Check Tire Pressure - Featured Image

Do you rely on your car’s tire pressure monitoring system to maintain tire inflation? If so, you are probably used to wasting money on more fuel than you need, poor steering and braking response, premature tire replacements, and last but not least, an uncomfortable ride. No it’s not because of cheap tires, it’s because you’re improperly inflating them  .

TPMS systems are notoriously inaccurate, and your tires could be under inflated by as much as 25% or more before the system will alert you to a problem. (Which is another reason why you should never buy used tires – you never know what the guy owning them did). Fortunately though, all of these issues can be resolved simply by checking your tire pressures once a week or so- here is how to do it.

Check the tread wear

Tread Penny Test

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The image above tells the story of these tires’ unhappy inflation history, and what you can (and should) do to keep your tires wearing evenly across the whole tread width. However, once tires have worn to the extent shown here they are beyond saving, so avoid this happening to you simply by following the steps below.

Get a digital tire pressure gauge

Any digital tire pressure gauge is several orders of magnitude more accurate than any other type of gauge, and besides, a good quality digital gauge can be had from any auto parts store for well under $20. With a digital gauge you are always sure that the displayed reading corresponds to the actual pressure in the tires, which is not the case with other types of gauges.

Only check the tire pressure on cold tires

Tires are said to be “cold” when the vehicle had been stationary for more than three hours, or if the vehicle had been driven for no more than 1 mile (1.6 km). This is an important consideration, because as tires heat up during driving, the air inside them expands, which can increase the pressure by as much as 10% under some conditions.

Thus, if you check the pressure when the tires are hot and you find a high reading, do NOT deflate the tires to get to the “correct” pressure. Doing this will mean that as the tires cool down, the pressure could drop to an unsafe level as the air inside the tires contract, which means that you could have dangerously under inflated tires when you resume your journey.

Do NOT inflate tires to the maximum indicated pressure

All tires have their maximum design inflation pressure molded into the sidewalls. This value indicates the MAXIMUM pressure a tire can be inflated to when that tire is carrying its maximum allowable weight, and NOT the tire’s safe working pressure.

Tires are designed to flex and deform by certain amounts during normal operation. Over inflation prevents a tire from doing this, which reduces traction, steering response, braking response, and eliminates a tire’s ability to absorb some of the unevenness of modern road surfaces.

Only inflate tires to their recommended inflation pressures

All tires only perform best when they are inflated correctly, which is why car and tire manufacturers are very specific when they recommend that a tire on any given application be inflated to a certain value. This information could save your life, so be sure to find it in the user manual, or on a sticker that is usually stuck inside the driver’s door jamb.

Inflation pressures are usually given in PSI (Pounds per Square Inch), but it might be given in metric units on some imported vehicles. Common metric units could be Bar, Kpa (Kilopascal), or Mpa (Megapascal), although the most commonly used unit in the world remains PSI, even in markets that use the metric system for everything else.

If you need to convert PSI to other pressure units, make sure that the pressure gauge is calibrated to display the tire pressure in the correct (desired) unit. The difference between units of pressure is profound, so make sure you know what your pressure gauge is telling you.

Check tire pressures at least once a week

While most authorities recommend a period of two weeks or so between pressure checks, anything can happen to a tire at any time, meaning that a tire could be partially deflated by the time the next pressure check rolls around, or the TPMS system notices that something is wrong.

Long experience in the car repair industry has taught me that checking tire pressures at least once a week is a better way to maintain tire pressures, and especially in climates where huge temperature swings occur over short periods. As a rule of thumb, and assuming that there are no pressure losses due to slow leaks, the pressure in a tire changes by 1 PSI for every 10oF change in ambient temperature, both up and down.

Thus, if the difference between two ambient temperatures is say, 500F, the pressure in a vehicle’s tires will change by about 5 PSI, which is more than enough to seriously affect traction, handling, and tire life. Of course, we get that adjusting tire pressures twice a day is a pain in the behind, and we don’t recommend that you do so, but what you could do is maintain the tire pressure at a mean level that does not over-, or under inflate your tires by more than two or three percent at either end of the temperature scale.

Arriving at the ideal tire pressure when night and day temperatures swing from one extreme to the other is a challenge, but getting it right means longer tire life, better handling and fuel economy, no matter if you’re using best all-season tires or best snow tires.