Measuring Tire Pressure: How Much Air Do My Tires Need?

Measuring Tire Pressure: How Much Air Do My Tires Need?

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Last updated on March 20th, 2023 at 12:46 pm

Proper tire pressure keeps your car on the road and easy to control. Tires with too much pressure can make for a bouncy, hard-to-control ride.

Tires with too little pressure will cause your car to pull rather than tracking straight.

Low tires are also at risk of sidewall damage and both over and under-inflated tires have a greater risk of blowouts.

Measuring Tire Pressure: How Much Air Do My Tires Need?

Where Do I Start Checking?

If you drive a basic car, SUV or minivan, start with the sticker inside the door. If there’s no sticker, you’ll need to review the owner’s manual.

It’s critical that you start with your car rather than any marking on the tires because tire pressure is closely tied to the weight of the vehicle.

New tires may change the tread depth, but your car will not weigh more or less.

The heavier your car, the higher pressure you will need to maintain. For example,

  • passenger car: 32 psi
  • large SUV, such as a Suburban, 36 psi
  • 1/2 ton pickup: 35 psi
  • 3/4 ton pickup: 50-80 psi

A passenger car spare tire will normally have 60 psi or pounds per square inch.

spare tire on a car

If you own a vehicle with dually tires on the back, it’s a good idea to talk with your vehicle mechanic and your tire sales team.

Very large vehicles will need dually (or double) tires on the back axle to make it easier to manage them on the road, but depending on the weight you’re carrying, your pressure needs will be quite specific.

A word about towing: There are experts on tires who recommend bumping up your tire pressure by 5 psi on a vehicle that you plan to tow with.

While 5 psi is unlikely to put you or your tires at risk, it’s a really good idea to double-check your manual just to be sure.

Towing takes a lot of focus and energy as a driver; you don’t need to also be bouncing around on over-inflated tires.

When Do I Check Them?

It’s a good idea to check your tire pressure once a month. It’s also a good idea not to trust your eyes.

checking tire pressure

A tire that looks low can be almost flat; a tire that looks all right can be dangerously over-inflated. If you have a tire pressure warning light inside the car, heed it.

Check them before you start driving. Never test a hot tire. If you’ve been driving for 30 minutes and your low-pressure light comes on, pull over and let them cool down for at least 2 hours.

Yes, this is a nuisance and may derail your day. However, you won’t get an accurate reading from a warm tire.

The Jeep Grand Cherokee tires should have 36 psi.

You may put in too little air and end up with a low tire again in just a couple of miles.

As you drive, and specifically as you brake and accelerate, the rubber of the tires flexes and warms up.

As your tires get warmer, they’ll read fuller because the air inside the tires expands as it warms up. A tire that is low at home may read fine at the gas station because you drove long enough to warm up the tire.

However, driving on a low tire weakens the structure of the tire and may put destructive pressure on the sidewall, leading to a blowout.

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How Do I Check Them?

You’ll need a tire pressure gauge to check your tires. You can use an analog or digital pressure gauge.

You can also do it with a cordless air compressor with a display field.

Many of these tools also have a locking hose that you can use to fill up the tire and re-check the pressure.

Unscrew the cap on the tire stem, which should be visible and accessible regardless of the wheel cover profile. Press the center of the stem in with the opening on the round head of the tire gauge.

removing valve stem cap from a tire

Be very careful to leave the end of the tire pressure gauge unblocked during this process; if the gauge measuring tool can’t open up unimpeded, you won’t get an accurate reading.

Once you’ve got a reading, put the cap back on the tire stem.

NOTE: If your hubcaps or wheel covers fold over your tire stem, you can damage the tire. Should you need to remove your hubcaps, be very careful when reinstalling them.

How Do I Fill Them?

If you aren’t in a position to fill your tires at home but there’s a space nearby where you can air up, drive slowly and give yourself plenty of time to get there.

The pressure may come up a bit in the driving but air them up to the recommended weight, then check them again tomorrow morning.

The filling tool on the compressor will look a lot like the tire checker gauge. Do your best to get a good seal and air the tire for a count of 10 seconds, then check it again.

If it’s very low, add air for 20 seconds and check one more time. Do your best to avoid over-filling your tires. Be prepared to pay for air.

Many places that offer free air have hose connections that no longer work well.

filling a car tire with air

What Happens If I Drive With Low Tire Pressure?

Tires have two basic edges:

  • the tread, which is what strikes the road, and
  • the sidewall, which is the thinner rubber expanse between the tread and the metal wheel

Driving on a low tire will cause your car to pull, which you will need to correct. As you correct it and the tire continues to lose air, the pressure on the treads will start to stress the sidewall.

While you can get a puncture in your tire tread, it’s the sidewall that will blow out if you put too much stress on it.

Blowouts are dangerous. If you thought you felt a pull before, you will receive quite a jolt when that tire suddenly loses all air.

Your car may be hard to control, especially if the blowout is in one of the front tires.

car tire with low pressure

What Happens If I Drive With High Tire Pressure?

When you consistently drive on over-inflated tires, you’re defeating the purpose of the engineering of the tire.

Tires are supposed to have a specific amount of tread on the road per the weight of the vehicle.

Worn tires with low tread are less safe to handle; for example, they don’t clear water, so you run the risk of hydroplaning.

Over-inflated tires also don’t have the right amount of tread on the road. Your trip will be bouncy, possibly enough for you to lose contact with the road.

They’re less likely to survive a bump against the curb or a pothole. Finally, they’re at greater risk of a blowout.

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