The 5 Steps to Checking Tire Air Pressure (PSI)

The air pressure in your tires can vary from day to day. This doesn’t mean you have a leak or a bad valve stem; it’s just science. Temperature is the biggest factor in changing tire pressure. As the temperature increases, the air pressure builds in the tire. Conversely, when it gets colder, the pressure decreases and your tire can even look flat. This is why you need to check your tire pressure and air up your tires on a regular basis.

Of course, it could be that you have a leaky tire or a faulty valve stem. That doesn’t necessarily mean you need a new tire. Valve stems can be replaced for almost nothing, and a lot of tires can be patched or sealed. The best thing to do if you think you have a leak is to have a professional evaluate your tires. But first, make sure your pressure is correct and check the weather. If you have a leak, the pressure will go down even if the temperatures don’t.

 

How to Check Your Tire Pressure:

1. Locate the Factory Required PSI Values
2. Remove the Valve Stem Cap
3. Use the Air Pressure Gauge to Check PSI
4. Inspect the Air Pressure Gauge and Re-Test
5. Re-Install the Valve Stem Cap

 

#1 – Locate the Factory Required PSI Values

The optimal pressure for factory tires is located in both the owner’s manual and inside the car. On the driver’s door, there should be a sticker located about halfway down. Look at the part of the door that is covered when it’s closed (the edge).

You can also look at the tire itself. If you have installed after-market wheels or new tires, you definitely want to check the value on the tires, in addition to the owner’s manual. The PSI value can be located on the tire’s sidewall in very small print.

The number provided on the inside of the door will mostly likely differ from the number on the tire. That’s because the PSI on the inside of your door represents the ideal ride based on the car’s suspension and handling. The value on the tire sidewall is the maximum PSI value that the tire can hold. Anything more and you run the risk of a blowout on the street.

It’s always best to use the manufacturer’s recommended PSI when filling stock tires. However, some adjustment can be made for temperature. In cold weather, the pressure inside the tire drops a bit, and during hot weather, it increases. Because of this, you do need to check your pressure regularly.

Use the tire’s maximum pressure rating on the sidewall as a guideline during weather adjustments and also as a way to judge the correct pressure in custom wheels. The tires on most passenger vehicles range from 27 to 32 PSI while SUVs and trucks usually require 31 to 40 PSI.

 

A “Word of Caution” About Recommended PSI

The PSI values from the manufacturer are recommendations only. These values are not the maximum or minimum value for the tire pressure. Going with a lower PSI than recommended can provide traction on sand or snow while adding PSI can increase fuel efficiency.

However, you need to be careful if don’t follow the manufacturer’s recommendation. Lowering the tire pressure below the recommendation may decrease braking distances. Raising the tire pressure could cause uneven tire wear and increase braking distances.

EuroDrift recommends following the car and tire manufacturer values for PSI. The car manufacturer’s numbers are optimal for car handling. Never go above the tire manufacturer’s PSI numbers, or you might suffer a blowout. Keeping your pressure between the two for safety.

 

#2 – Remove the Valve Stem Cap

To remove the valve stem cap, simply unscrew it from the valve stem. The valve stem cap covers the valve stem to ensure there is no debris buildup in the stem. It is highly recommended that you have a valve stem cap on each tire as well as on your spare tire. If someone steals your valve stem cap, you can easily locate a replacement at any automotive retailer (i.e. Pep Boys).

 

#3 – Use the Air Pressure Gauge to Check PSI

To use the air pressure gauge, align the opening on the gauge over the valve stem. Press down firmly and evenly. This pushes the valve stem pin inward causing air to leak out through the stem and exert pressure on the gauge. You might hear a slight hissing noise as you engage the valve stem pin. However, if you have aligned the gauge correctly and pressed evenly, the noise should all but disappear.

If the reading is taken while air is leaking from the connection of the gauge and the stem, then it will not be correct. Realign the two if necessary and try again.

Depending on whether you have an electrical or mechanical air pressure gauge, the result could be different. An electrical pressure gauge provides you with a digital reading on the air pressure. The electrical pressure gauge is also more reliable than a mechanical gauge if it is calibrated correctly.

The mechanical gauge is more common and has been around for decades. A mechanical gauge uses the air pressure to move a rectangular prism within a cylinder at a distance that equates to PSI. For example, if there is 32 PSI in the tire then the air pressure will move the prism to the 32 PSI marker on the display.

 

#4 – Inspect the Air Pressure Gauge and Re-Test

To inspect the air pressure gauge value, simply read the display on an electronic gauge or inspect the line value on the mechanical gauge. The reading on the air gauge should make sense, and it is always a great idea to check multiple times. There is always the chance that the air pressure reading of the tire will be off due to human error. Simply not angling the gauge properly can cause the reading to be incorrect.

To make sure the tire PSI value is correct, test the PSI of the tire until the same reading is obtained two or three times. This way you can spot an erroneous reading. Differences in pressure readings could be due to human error, or it could be your gauge. Some tools are more accurate than others, and it could be that your air gauge is not working properly.

Consistent readings should indicate that you are measuring correctly and your equipment is working.

 

#5 – Re-Install the Valve Stem Cap

To reinstall the valve stem cap, simply screw the cap back onto the valve stem. Make sure that the cap isn’t loose but be careful not to overtighten the cap. Over-tightening the cap may strip the threads inside and possibly damage the stem.

You should check your tire pressure each time you fill the gas tank, before trips, or if you even think there might be a problem. You will know there is a problem when the car isn’t handling correctly. Look for bulging sidewalls or uneven wear on the treads. All of these are indicators that your pressure is not quite right.

It only takes a minute to check and adjust the tire pressure. Doing so just might save you from a blowout or an accident. Oh – and don’t forget to check the spare! It’s important to keep it aired up along with the other tires.

 

References
http://www.wikihow.com/Check-Air-Pressure-in-Tires
http://www.dmv.org/how-to-guides/check-tire-pressure.php

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