How do you know what air pressure to fill your tires? What pressure should they be in winter or summer? What happens if the pressure is too high or too low? What is TPMS?
When it comes to regular tire maintenance, knowing the recommended tire pressure is important. The recommended tire pressure is different for every car, truck, and SUV. Most newer vehicles will have the recommended tire pressure on a label in the door jam. This is the pressure they should be at when the tires are cold before they’re driven on and gotten heated up.
Many tend to overcomplicate what tire pressure should be. It’s understandable. There are some aspects that can be a little confusing as well as some myths.
Let’s review some of the questions that people have that can be confusing.
Recommended Tire Pressure
The manufacturers’ recommended tire pressure for your car, truck, or SUV is found on a label in your driver’s door jam.
If for some reason it isn’t there check your owner’s manual.
Recommended tire pressure is generally between 30 and 40 psi is very common.
The maximum recommended tire pressure is listed on the tire itself. Never inflate tires beyond this amount.
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What Should My Tire Pressure Be?
In general, passenger vehicle tires have air pressures between 30 and 40 psi. 35 psi is a very common recommended tire pressure. The recommended tire pressure for your car, truck, or SUV will vary but not likely by much.
You should always follow the recommended tire pressure for your specific vehicle. This ensures that you get the best tread wear life from your tires and most grip.
Modern cars have the suggested tire pressures listed on a label in the door jam. Older cars may have it on the fuel door, glove box door, or even the trunk lid. Manufacturers have standardized around one location.
Do I Use The Tire Pressure On The Tire Or Door Jam?
Do not use the pressure listed on the tire. This is the maximum pressure the tire can hold and should not exceed.
The recommended tire pressure for your vehicle is inside the driver’s door jam. It is usually located near the door latch. Sometimes the recommended tire pressure label will is on the edge of the door itself.
Sometimes these labels will get painted over or removed somehow. This can happen because of an accident repair or other events that occur over the life of the vehicle. If the sticker for your car, truck, or SUV is missing you may need to refer to the owner’s manual.
If you don’t have the owner’s manual then you may need to do a Google search. Search for your make, model, and year. This should give you the correct tire pressure for your vehicle.
How To Read A Tire Pressure Sticker
The tire pressure sticker on your door jam will look like the image below.
Tire pressures are for the front tires and rear tires. Usually, the front tires and rear tires have the same pressure. For some vehicles, pressures can be different front and rear. Tire pressures from side to side should always be the same.
Tire pressures are usually listed in “psi” or “kPa” units but you may come across units listed as “BAR” or “ATM”. You’ll need to make sure you’re using a pressure gauge that includes the units on your label. If you don’t have one you’ll need to do the conversion.
Besides the recommended pressures, you’ll also see the original tire size. This is good information to know when it’s time to replace your tires.
How Important Is Tire Pressure?
Proper air pressure in your tires is key to ensuring your tires grip their best and last as long as possible. Over or under-inflating tires can shorten tire life. It can also reduce gas mileage, and tire grip.
What Is The Maximum Tire Pressure?
The maximum tire pressure will vary from tire to tire but it is on the sidewall of the tire itself. Manufacturers don’t usually list a maximum pressure for specific vehicles. The maximum pressure listed on the sidewall is the maximum safe tire pressure. This is true even if your tires are not the kind that came with your vehicle.
What Tire Pressure Is Too High?
The maximum pressure shown on the tire sidewall is too high. But how much above the recommended air pressure for your tire is too high?
TPMS (Tire Pressure Monitoring Systems) trigger a warning if air pressure is off by 25%. This is still pretty drastic. When your TPMS goes off you should treat this as a time to take immediate action but not a time to panic.
If the air pressure is 10% more than the recommended amount you should release a little air to bring it back down. For instance, if the proper tire pressure for your tire is 40 psi then 4 psi is 10%.
If you’re checking your tires after driving for a period of time they’ll be pretty hot. Air pressure inside the tires will have increased from the heat. Recommended tire pressure is for when a tire is cold. The air pressure will reduce as they cool back down.
What Happens If Tire Pressure Is Too High?
Tires act like a balloon and expand when inflating them. The contact patch normally extends across the entire width of the tread evenly.
If your tires overinflated they will stretch. This means they will not be the shape the tire manufacturer intended. This will reduce the width of the contact patch. It will shrink toward the center of the tread more and more as it’s overinflated.
This will reduce the tire’s ability to grip the road and can be very dangerous. This is because the contact patch is smaller and only a small amount of the tire treads will be able to do their job.
Not only will the tires not be able to grip the road as well but the tires will begin to wear down more quickly. A much smaller area of the tire tread is being asked to do the work that a much larger area is designed to do.
What Tire Pressure Is Too Low?
When tires are underinflated by more than 10% they are too low. This isn’t an emergency situation. You should add air to your tires as soon as possible though. This will make sure your tires are working their best and last as long as they can.
TPMS sensors will warn you when your tires are underinflated by 25%. This amount is not a reason for panic but should be fixed immediately.
Anything beyond 25% shouldn’t be driven on for any distance or you will risk damage to your tire. It is also dangerous since the tires are not going to work as they are intended. They won’t be able to grip as well as they should.
What Happens If Tire Pressure Is Too Low?
Tires have a reduced contact patch when overinflated. The same is true when they’re underinflated.
When air pressure is too low the center of the tire loses contact with the road. The tire begins to ride on its outer edges. It becomes supported more by the sidewalls than the air pressure. The contact patch becomes 2 separate patches on the edges of the tire tread.
Underinflation is as dangerous or more so than overinflation. The reduced contact patch means the tire has a lot less rubber available to grip the road. Also, the tire is putting more strain on the sidewalls the tire. The more underinflated a tire is the more strain there is on the sidewalls. This puts a lot of heat into the sidewall and can lead to a catastrophic blowout.
Underinflation also causes premature wear on the outer edges of the tire tread. Given how expensive quality tires are, this is an expensive mistake to make.
What Is The Lowest Tire Pressure You Can Drive On?
No one wants to be stranded on the side of the road with a flat tire. Many cars now unfortunately don’t come with a spare tire. Even if it does, you may find that the spare tire has failed and no longer holds air.
If your tire isn’t “completely” flat you may entertain driving on it. It’s safer and wiser to not risk it and wait for AAAor for a tow truck. We have busy lives and often don’t feel like we can wait. Sometimes our situation may be dangerous and waiting could be unsafe.
If there is 20 psi in the tire, it is possible to drive on a passenger tire. You should stay below 25 miles per hour and only drive a short distance. This could be enough to get you to a tire shop or to your destination where you can safely deal with the flat.
Driving on a tire with less than 20 psi will ruin the tire quickly. This is not only going to ensure the tire can’t be patched but it’s very dangerous. If the tire separates it could damage the wheel, bodywork, and suspension components.
How Does Temperature Affect Tire Pressure?
For every 10 degrees Fahrenheit, your tires will typically rise or fall by 1 psi. 1 psi isn’t enough of a difference to significantly change the performance of your tires. But as the seasons change temperatures will swing a lot farther up and down and have more of an effect.
If your car was made after 2008 it will have a tire pressure monitoring system. It will alert you when your tire pressure has dropped 25% or more. Ideally, you would be checking your tires regularly so this never happens.
At 25% lower than recommended your tires won’t be performing as well as they could. This will affect tire wear and have an adverse effect on your fuel economy.
Checking your tire pressures regularly will extend the life of your tires. It’s also smart for your safety.
You should also pay extra attention to tire pressure during Spring and Fall. As temperatures rise and fall you’ll need to adjust air pressure.
What Is The Best Temperature To Check Tire Pressure?
You should check your tire pressures when the tires are cold, but what temperature is cold? Cold in summer is very different from cold in winter.
Manufacturers say to inflate tires to a certain temperature “when cold”. They don’t mean the current outdoor temperature. What they mean is the temperature of the tire. Cold is before you drive on them and hot is after you drive on them.
As you drive around your tires will become hot. This is from the forces the weight of the car, truck, or SUV exerts on the sidewalls and rubber. You should make sure your tires are at the right pressure before you drive. If you check or adjust pressures after driving the air in the tire will be hot and the pressures wrong.
The outside temperature doesn’t matter. The point is that as temperatures change you’re maintaining consistent pressure.
Tire Pressure When Cold
As fall and winter come the temperature drops. It’s common to get a warning from a tire pressure monitoring system when this happens.
The reason is that as temperatures drop air shrinks. The air inside your tires will drop in pressure. If your tires are already a little low on pressure then this will trigger the TPMS warning. This will let you know your tires are low and need attention.
The amount of pressure required for your tires to grip well and last as long as possible is still the same. You’ll need to top them up with a little more air to get them back up to the right pressure.
What Should Tire Pressure Be In Winter?
If you have winter tires you should run them at the air pressure listed on the door jam of your vehicle. Most people dealing with ice and snow during winter should have winter tires. Winter tires are designed to deal with more extreme winter weather.
Those of us a little further south don’t often deal with snow and ice. We still deal with colder temperatures and we will likely have all-season tires. Some of us will even have summer tires. Some manufacturers recommend adding 3 to 5 psi to your tires during the winter months if you are driving on all-season or summer tires. This will help counteract the effects of the cold on your all-season or summer tires.
Tire Pressure When Hot
As you drive your tires will become hotter and so does the air inside the tires. It’s common for tires to increase in pressure 1 psi every 5 minutes for the first 15 to 20 minutes of normal driving.
If you are driving to a gas station to check your air pressure the tires won’t be cold. You’ll need your own air pump and pressure gauge so you can check and adjust the pressure at home.
The tire pressures recommended on your door jam are for when your tires are cold. Setting the pressure when the tires are warm means that you’ll be setting them too high. This could cause the tires to not grip well or wear out quicker.
If your tires are hot, it’s recommended that you wait 3 hours. This allows them to cool down to ambient temperature before checking air pressures.
What Should Tire Pressure Be In Summer?
Tire pressure in summer shouldn’t be different than the manufacturers’ recommendation. There is more emphasis on tire pressure during the summers. This is because people often travel more during the warmer months. It’s important that you check your tire pressure before trips for safety reasons.
Air pressure is higher when air is warmer but the recommended tire pressure is still the same. If you’re about to set off on a road trip be sure and check your tires before you hit the road.
How To Check Tire Pressure?
Once you know what pressure to inflate your tires you can check to see if they are within spec. You’ll need to have access to a tire pressure gauge. One that reads in the units that match the recommended pressure is most convenient.
It’s important to note that recommended tire pressures are for “Cold Tires”. Cold tires are tires that haven’t been used for 3 hours or more. You should not check tire pressure after having recently driven.
When you drive your vehicle the tires become warmer. Heat causes air to expand and this causes the pressure inside the tires to increase.
This is normal and safe. Air pressure recommendations are for Cold Air Pressure. You’ll not be able to get the pressures accurate if you’ve been driving within 3 hours.
Tire Pressure Measurement Units
- psi – Pounds per square inch is the most common unit of measurement used for air pressure in the United States.
- 1 psi = 6.89476 kPa
- 1 psi = 0.068947 bar
- 1 psi = 0.068045 ATM
- kPa – Kilopascals is the metric unit of measurement for air pressure. It is often included as an alternative unit in the United States.
- 1 kPa = 0.145038 psi
- 1 kPa = 0.01 bar
- 1 kPa = 0.00986923 ATM
- bar – Bar is a unit of pressure measurement that is also somewhat common. 1 bar equals a little less than the pressure of the Earth’s atmosphere at sea level. 1 bar is also equal to 100 kPa.
- 1 bar = 14.5038 psi
- 1 bar = 100 kPa
- 1 bar = 0.986923 ATM
- ATM – Like bar, ATM is approximately equal to the Earth’s atmosphere at sea level, but it is not the same as bar. It is short for “atmosphere” and is sometimes called “standard atmosphere”.
- 1 ATM = 14.6959 psi
- 1 ATM = 101.325 kPa
- 1 ATM = 1.01325 bar
What Is TPMS (Tire Pressure Monitoring System)
Tire pressure monitoring systems measure the air pressure in your tires. They will let you know when the air pressure drops past a certain amount. The system works with wireless sensors in each tire. The sensor can measure the air pressure in the tire. If the pressure drops below a certain amount it will alert you to the problem.
Tire pressure monitoring systems are required for vehicles in the United States. This has been law since 2008. It has been a huge safety improvement. It’s especially important for low profile and run-flat tires.
Low profile tires have a very short sidewall and don’t flex much when flat. The same is true for run-flat tires. It can be very difficult to notice when a low profile or run-flat tire is low. It is very unsafe to drive at speed with tires that are underinflated.
I can vouch for this myself. I had a pre-2008 car with low-profile tires and got a flat in the rear without knowing it. The tire separated and the rear end began swerving back and forth. Thankfully, I was able to keep it from spinning around. I pulled over to the side of the road without any damage other than the blown tire.
TPMS is a great safety addition. But it shouldn’t replace checking tire pressures every month. TPMS alerts when tires are beyond the recommended tire pressure by 25% or more.
This is very low and risks wearing your tires out quicker. It will also reduce tire grip.
Checking your air pressure often will extend the life of your tires. It will also make sure you get the most performance possible out of them.
How To Check Tire Pressure With A Gauge
There are 3 main types of tire pressure gauges – Stick/pencil, Dial, and Digital. All 3 will get the job done but they all work differently.
Digital gauges are better than the other 2 types. Digital gauges are more accurate, inexpensive, and easiest to use.
Let’s review each type of gauge.
Stick/Pencil Tire Pressure Gauges
Stick pressure gauges are inexpensive. They can be a little more difficult to use than the other types of gauges. They can work well and are quite accurate. If you’re looking to buy a tire gauge to keep on hand this isn’t my first pick. If cost is the most important factor then a stick pressure gauge will do the job.
How To Use A Stick/Pencil Tire Pressure Gauge
- Remove the valve stem cap and firmly place the open end of the gauge on the valve stem.
- Try to align the open end of the gauge so that you don’t hear loud hissing air. You may hear a little air releasing but it should be very slight.
- The pressure of the air will force the stick out of the gauge and where it stops is the pressure of your tire.
- To read the pressure, look at the edge of the stick where it exits the gauge body. The writing on the stick at the edge of the gauge body is the pressure of your tire.
- I recommend taking a few measurements to ensure you’re getting a reliable reading.
Dial Tire Pressure Gauges
Dial gauges vary widely in accuracy, quality, and cost. They’re easier to use than stick gauges but not as user-friendly as a digital gauge. Accurate dial gauges tend to be relatively expensive. For these reasons they’re not my first choice but a quality dial gauge is nice to use.
How To Use A Dial Tire Pressure Gauge
- Remove the valve stem cap and firmly place the open end of the gauge on the valve stem.
- Try to align the open end of the gauge so that you don’t hear loud hissing air. You may hear a little air releasing but it should be very slight.
- The needle on the gauge will or show the current air pressure in the tire.
- I recommend taking a few measurements to ensure you’re getting a reliable reading.
Digital Tire Pressure Gauges
Digital tire pressure gauges are the most accurate gauges you can use. They are also the easiest to use and nearly as inexpensive as stick gauges. The display of the best digital gauges are large, backlit, and easy to read. I highly recommend picking up a good quality digital tire pressure gauge.
How To Use A Digital Tire Pressure Gauge
- Remove the valve stem cap and firmly place the open end of the gauge on the valve stem.
- Try to align the open end of the gauge so that you don’t hear loud hissing air. You may hear a little air releasing but it should be very slight.
- The digital readout should lock and or show the pressure that it has read.
I recommend taking a few measurements to ensure you’re getting a reliable reading.
How To Check Your Tire Pressure At A Gas Station
Most gas stations will have an air pump available for customers to add air to their tires. These pumps usually cost a little to use but occasionally they are free. The pumps usually have a gauge built into the tip of the hose. The gauge that is usually included is a metal version of a typical stick gauge. These are reasonably accurate although a little finicky to use.
- Locate the air pump at your nearest gas station. Pull up so that you can easily pull a hose from the pump to either side of your vehicle.
- Pay the amount required to get it working.
- Remove the valve step cap and firmly place the open end of the air hose on the valve stem.
- Try to align the open end of the air hose so that you don’t hear loud hissing air. You may hear a little air releasing but it should be very slight.
- The pressure of the air will force the stick out of the gauge and where it stops is the pressure of your tire.
- You can add air by pulling the trigger on the hose.
- The gauge stick will withdraw back into the gauge housing while you are adding air to the tire.
- When you release the trigger and stop adding air the gauge stick will slick back out of the gauge housing. It will show the new tire pressure.
Here are a few helpful tips when dealing with gas station air pumps:
- Don’t be surprised if the first gas station you visit has an air pump that isn’t working. Air pumps are a courtesy at most gas stations and don’t generate income so they tend to get neglected. Try to treat it well while you use it so that it will be available for the next person in need. You may have to visit several gas stations to find one that is functioning.
- Be prepared to pay more than once. I’ve found that there isn’t usually enough time allotted for me to check pressures and top up all the tires up. If the air pump takes quarters you’ll want to have a stack handy.
- Often, the hose is under tension to retract back into the air pump housing. You can step on the hose to help keep it extended. There is more than enough pressure to keep your foot from pinching off the hose. Also, the hose is very durable and this shouldn’t damage it within reason.
- Try not to extend the hose across the hood or other parts of your car, truck, or SUV as it will scratch the finish.
How To Check Air Pressure Without A Gauge
Checking air pressure without a gauge isn’t accurate enough to be of much help. But it can give you a sign of whether the tire pressure is very low or not.
- Place your hand on the shoulder of the tire and push on it with all your weight.
- It should only give a small amount and bounce you back.
- If you can get the tire to give anything more than this it is too low. This is not very safe to drive on.
Where Can I Get My Tire Pressure Checked For Free?
Most auto repair or tire shops will be able to check to see if your tires are properly inflated. Most will do this for free as a courtesy. A great place to go is Discount Tire. They offer many services for tires for free, including checking tire pressures. One impressive free service they offer is patching tires. If you have a tire that needs patching you’ll already be at the right place to get it repaired for free. It’s amazing you can get anything free these days. Especially with no strings attached!
How Often Should I Check My Tire Pressure?
It’s suggested that you check your tire pressure every month. You should do this whether you have a tire pressure monitoring system or not. This will make sure your tire’s performance will be at its best and you’ll get the most life out of them.
How To Adjust Tire Pressure
Adjusting tire pressure is pretty straightforward. Each tire has a valve stem that protrudes from the tire, usually within the wheel so that it is protected.
The valve is called a Schrader valve and this design has a small pin in the center. This pin is what keeps air in the tire. This pin must be depressed to allow air to flow in or out of the tire.
Let’s go over how to raise and lower air pressure.
How To Raise Tire Pressure
If you want to increase tire pressure you’ll need a powerful pump to do so. A bicycle pump isn’t going to get the job done. An electric pump is going to be what’s required to get the pressure high enough.
Your local gas station may have a pump on their property that you can use. Often these are not in the best working condition. A better solution is to buy a portal air compressor. You can keep it in your car, truck, or SUV to use when you need it. This way you won’t have to worry about finding a gas station with a working air pump.
Most air pumps will have a pressure gauge built-in. But if the one you’re using doesn’t happen to have one you’ll need to check the pressure with a gauge of your own. My suggestion is to use a good digital gauge. They’re inexpensive, easy to use, and more accurate than stick or dial pressure gauges.
My recommendation is the Craftsman V20 Inflator. It’s a high-quality product. It can be plugged into a 12v outlet in your car, a standard wall outlet, or run off a lithium-ion battery pack. It has an auto-set feature and an easy-to-read large digital gauge. It also comes highly recommended by Consumer Reports as well.
How To Lower Tire Pressure
Lowering tire pressure is very easy. Press the pin in the center of the Schrader valve to release some air and lower your air pressure. Since you’re likely trying to hit a specific tire pressure I find that using my tire pressure gauge is best.
If you don’t seat your gauge all the way on the valve stem you can release air. You can then alternate between seating the gauge all the way and releasing air. You can read the pressure occasionally as you’re dropping it.
Once you hit the desired tire pressure you can stop. You’re done!
Resources
Below are some links you may find helpful when learning about tires
