Elevation TPMS Reading

Arrived here in Breckenridge Colorado Sunday from Illinois. I have a 22 4R. Ever since I have arrived the tire pressure reading on the car vs a tire gauge is totally different. For example, car says 30 psi vs a tire gauge and pump reading 37. Never ever had any issues. The reading on car and gauge always were the same. Is it by chance the altitude? I’m totally stumped.

 

tire pressure will increase slightly at elevation but gauges should agree. If they don't pick one you trust and just go with that as a reference.

 

Buy a decent tire gauge and go with that.

 

Here's a good read:

Significant changes in altitude affects tire pressures when traveling from one elevation to another. Fortunately, this influence is relatively small and can be easily accommodated.

Atmospheric pressure is the force exerted on objects by the weight of the air molecules above them. While air molecules are invisible, they have mass and occupy space.

However, as altitude increases, atmospheric pressure decreases. For example, atmospheric pressure pushes against the earth at 14.7 pounds per square inch (1 kilogram per square centimeter) at sea level, yet drops to only 10.1 pounds per square inch at 10,000 feet as indicated in the following chart.

Altitude (ft.) Air Pressure (psi)
Sea Level 14.7
1,000 14.2
2,000 13.7
3,000 13.2
4,000 12.7
5,000 12.2
6,000 11.7
7,000 11.3
8,000 10.9
9,000 10.5
10,000 10.1

When it comes to measuring tire inflation pressure, it is important to realize there is a difference between atmospheric pressure and gauge pressure. Most pressure gauges (including all tire pressure gauges) are designed to measure the amount of pressure above the ambient atmospheric pressure.

Imagine removing the core from a tire valve and allowing the air to escape. Even after the air has completely stopped rushing out of the valve, the tire is still experiencing 14.7 pounds per square inch of atmospheric pressure. However, a tire pressure gauge would read zero pounds per square inch of tire inflation pressure because the pressure outside the tire is equal to the pressure inside.

Since a tire mounted on a wheel essentially establishes a flexible airtight (at least in the short term) pressure chamber in which the tire is shaped and reinforced by internal cords, it retains the same volume of air molecules regardless of its elevation above sea level. However, if tire inflation were set with a tire pressure gauge at sea level (where the atmospheric pressure of 14.7 pounds per square inch is used as ambient atmospheric pressure by the gauge), the same tire pressure gauge would indicate the pressure has increased at higher elevations where the ambient atmospheric pressure is lower. Those measured at the 5,000-foot level (where an atmospheric pressure of only 12.2 pounds per square inch is the ambient pressure) would indicate about 2-3 psi higher than at sea level. On the other hand, traveling from a high altitude location to sea level would result in an apparent loss of pressure of about 2-3 psi.

However, the differences indicated above assume that the tire pressures are measured at the same ambient temperatures. Since tire pressures change about 1 psi for every 10° Fahrenheit change in ambient temperature, the tire pressure measured in the relatively moderate climate typically experienced at sea level will change when exposed to the colder temperatures associated with higher elevations.

This means that in many cases differences in ambient temperature may come close to offsetting the differences due to the change in altitude. Depending on the length of their stay at different altitudes, drivers may want to simply set their cold tire pressures the morning after arriving at their destination, as well as reset them the morning after they return home.

https://www.tirerack.com/upgrade-ga...yfdzsqnO5puGRL_qX2mWofaj9CetrrhoTyJ0AFwHcSY-Q

 

if tire gauge says 37 at 10k ft, your actual pressure at sea level is roughly 33 psi (37-4)

 

You could have just posted the link.

 

Thanks everyone. What baffles me is that the tire gauge says 37 on every tire but the truck is showing 32 on all tires. Happened right after I aired down. I aired down to 20 psi but the car read 15. It seems like the car is off 5 psi. I’m confident the gauge is correct

 

Sometimes tpms doesn't update immediately. Frequency can vary based on a number of factors (motion, battery life, and also rapid pressure changes). For example, a sudden decrease in one tire could result in more frequent updates being broadcasted from the sensor.

If the batteries are low, or low enough that cold weather would reduce capacity meaninfully, an update may not broadcast until enough motion occurs to energize the internal batteries.

If you read the raw tpms data, it will usually publish temperature as well.

Interesting thought experiment.

 

How big a guy are you? Guess if a large enough person sits in the vehicle, the internal gauge might read a higher number than if said large person exits the vehicle and measures the pressure manually

 

I think you nailed it. You mentioned a sudden decrease in tire pressure. We noticed it reading off immediately after we used an air down valve to rapidly decrease the tire pressure prior to doing some off roading. I think you nailed it. Thank you so much.

 

Interesting post... I just came back from 8000 ft+ for 2 weeks and had the same issue.. TPMS showed 29/30 all week and kept giving me low tire warnings.. but true gauge pressure was 36+. I'd assume TPMS doesn't take more than 2 weeks at altitude to calibrate.. anyway it was annoying enough that I actually half-assedly (SP?) looked up how to calibrate the TPMS .. thought maybe that was an option.. I struck out on that spelunking exercises and just ignored the warning light until I got back to sea level.

 

This is exactly what I’m experiencing. I’m the OP and sitting in Breckenridge CO right now. Driving me nuts. I’m so glad you responded to my post. It made me feel better. Did yours eventually fix itself?

 

yeah.. .. I could watch it slowly return to semi-accurate on the 6 hr drive home.. gradually decreasing elevation the whole way..

 

Thank you so much. You literally saved me money as well. Was about to take it in and have it looked at. Thank you again. Really appreciate it

 

My car TPMS was accurate, but found that my ARB pressure gauge was reading higher at altitude. Contacted ARB and they said it needed to be reset(batteries taken out for 5 minutes). Both car and gauge matched afterwards.

 

it is normal that the tpms will read a lower number and the tire gauge will read a high number than the actual pressure inside the tire.

As the link I posted above explains, atmospheric pressure decreases with altitude.
To make it easy, let’s say atm at sea level= 15 and atm at 10k ft= 10.

Let’s assume your tire was inflated to 32 psi at sea level.That means the absolute pressure inside the tire is 47 psi (32+15).

Now go at 10k ft, there’s less pressure exerting force on the tire (10 psi instead of 15). So the tire expends slightly in volume, which means the actual pressure in the tire slightly decreases (maybe 2 psi?). So our new pressure inside the tire is 45 psi.

Measure with the tire gauge and it reads 35 psi because the tire gauge accounts for the atmospheric pressure at 10k ft (45-10=37).
On the other hand, TPMS still thinks sea level atm of 15 psi, so the car will read 30 psi (45-15)

 

Figured it would be easier to read than going on a different website