How Much Does Driving Up a Mountain Change Tire Pressure?

Here we take a look at not only how much the tire pressure will change in your car as you drive up in elevation, we also look into why the tires in a car will build pressure when driving up the side of a mountain.
A typical tire pressure measurement does not measure the amount of pressure in the tire (Absolute Pressure) instead it measures the pressure difference between the atmosphere and the tire (Gauge Pressure).
As you go up in altitude the air pressure (aka. atmospheric pressure) decreases. Meaning going up in altitude produces a theoretical change in measured tire pressure.
This change in tire pressure has a somewhat counterintuitive influence on the performance of vehicle tires. The pressure 'in' a tire is not exclusively determined by how much air is in the tire, it is also influenced by the atmospheric pressure acting on the outside of the tire.
I will be the first to admit, having been to the top of Pikes Peak many times I knew theoretically what was going to happen but when I saw the digital gauge read a negative value (@4:15s) the physics hit on a level that was much more visceral than any equation.
I measured tire pressure using a calibrate-able digital gauge as well as a standard pen gauge. Additionally tire temperature as well as tire contact patch areas were measured to see if a change in tire pressure would actually produce tangible results in the tire contact patch.
Additionally, many a TPMS or Tire Pressure Monitoring Systems work much like the digital gauge used in this video. They measure absolute pressure then display a reading that is offset by atmospheric pressure, usually a constant 15psi.
Nerd Note In order to keep temperature in the tires from messing up the results, the car sat for an hour at altitude before measurements were taken.

[@manishmessi6423]

excellent

[@INTEGRALPHYSICS]

thanks

[@Cadu12345]

In your opinion, do you think you could have just used ideal gas law ?

[@INTEGRALPHYSICS]

PV=nRT is based on Absolute Pressure, which was nearly constant in this scenario (because temperature had very little change, luckily). The decrease in atmospheric pressure caused the increase in gauge pressure and decrease in contact patch even though, according to the ideal gas law, nothing changed inside the tire.

[@donlindell1994]

I lost this bet once, tire pressure and patch pressure are close, but not the same because of the added structural rigidity from steel belts, tread & forming structure, and material compounds. The tire doesn’t flex like a latex balloon, so the patch doesn’t quite equal the internal pressure.

[@INTEGRALPHYSICS]

True. I've seen guys run zero psi on dirtbikes trying to increase traction. The sidewall is all that holds the tire up in those cases.

[@Freezeation]

Is this function completely linear?

[@INTEGRALPHYSICS]

I assume you are asking about the function relating atmospheric pressure to altitude; Nope, its not linear.

[@danksourav]

can you explain what exactly is sea level difference in relative to different heights and what does it signifies in a new video

[@verbalsawdust]

Was always curious about this. Now I know. You couldn’t resist the puns …? Where’s the math?!

[@INTEGRALPHYSICS]

I tried to keep the math out of this one... Just wanted to look at data and results.

[@invertedpolarity6890]

Still interesting and an excellent validation of the relation between temperature, pressure, and volume of gases.

[@INTEGRALPHYSICS]

Thanks. This one was fun.