Skip the auto shop - Our mechanics make house calls

Q: tire pressure

asked by on

Yesterday the psi in my car tires read 35 psi in all 4 tires..i checked them again the next day and they all read 44 psi or higher! I have owned over 40 cars in my life and never ever once had i had to let air out!..what gives?

My car has 27454 miles.
My car has an automatic transmission.

Car manufacturers require that tire pressure be set to the required psi before the vehicle is driven on the roadway. Tire pressure has to be measured and set before the car has operated on the roadway because friction from operation raises the internal temperature of the tire and hence the air pressure within. This manufacturer specification is referred to as cold tire pressure and is the required pressure documented on the vehicle information placard on the door pillar. However, cold tire pressure tire, once set at a specific temperature, will go on to vary up and down as ambient temperature goes up and down. Furthermore, if the sun is shining on a black tire, the internal temperature within the tire will increase significantly above what you measure as ambient, increasing the pressure. To illustrate, let’s say that yesterday it was 25 degrees out and the car was parked in the shade. The cold tire pressure was set at, or observed as, 35 psi. Today it is 70 degrees and the tires are in direct sunlight. Inasmuch as tire pressure increases 1 PSI for every 10 degree increase in ambient temperature, you will have a 4.5 psi increase today just due to the change in weather. You report a pressure of 44 and it will be easy to reach that in our illustration if you assume that the tires sat in direct sunlight (increasing the temperature well above the ambient measure of 70 degrees, WITHIN the tire) and/or the vehicle was actually driven on roadways, further increasing the pressure. Please let us know if you have further concerns or questions as we are always here to help you.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: What Happens if I Overinflate My Tires?

Inflating tires to the correct pressure is one of the most important factors when inflating a tire. Both under and, over-inflating a tire can actually be detrimental to the performance of a vehicle and to the life of a tire....

Q: I replaced the clutch but the pedal sticks to the ground and won't go into gear

Hi. It sounds like the clutch master cylinder and the slave cylinder has gone bad. Both of these components aid in shifting the the car and effect the clutch pedal effectiveness. There could also be the possibility that the throw...

Q: How do you use the push button start system?

Your car is equipped with a push button start/stop system. While this is definitely more convenient than using a conventional key, there are a few things that might take some getting used to. Here’s what you should know about using...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...