Colorado B.S. Thread

Damn that place must have been hopping

 

For those of you with TPMS or a way to see your tire pressure, what kind of variation do you get between your pressure gauge when airing up and the numbers the truck says? Which number do you go off of?

Was reading this article about how variation is common. My gauge reads 5 PSI higher than my truck TPMS, so I figured it's better to go with the lower reading to be at 30PSI cold, 32 ish warm.

https://www.minderresearch.com/accuracy-of-pressure-gauges-and-tpms/

 

Every gauge I have ever used is 4 psi high than my truck display.

 

My TPMS reads 5 or so PSI higher seemingly at all pressures. I've checked with multiple gauges.

 

I think we both have the AstroAI gauge? I know on Josh's gauge, it reads 4 higher.

So your TPMS would display 35PSI when the gauge says 30? Exact opposite of John and I lol

 

Yeah. I started airing down using the tpms readings in the dash. Got it to 15psi and when I checked with a gauge I barely had 10 in there. It's off the same amount at 30psi too.

I really only trust it to tell me if im losing air at this point.

 

anyone interested in doing a meet up near Colorado Springs August 23/24th or near Ouray August 24-27? I will be out there with a group of about 25 rigs but I want to grow the friendships with everyone so Id be interested in meeting anyone interested.

 

My astro AI reads 3 psi higher and mechanical gauges read around 5 higher.

 

Interesting. I know my ARB deflator(Mechanical) is only 2 PSI off from my TPMS. Reads 2 PSI high than TPMS.

 

Your tire pressure gauge has a reference pressure of actual atmospheric pressure where the TPMS is completely inside the tire with no chance for reference air pressure of "zero". With tire pressure sensors being assembled at sea level, getting there reference air pressure down there causes the difference. If you deflate your tires to zero the computer actually shows negative numbers.

 

Makes sense. So the pressure on the gauge is theoretically the one to trust then?

 

That is how I took it from the Toyota engineers. Though, that could cause false warning lights as you near threshold pressure for illumination.

One stated that it is a very imperfect system that can't account for barometric and temperature changes and it is best to just set to 5psi over.

 

Makes a lot of sense.

 

Yeah, I would rather have the PSI a few high so I don't have to drive around with my tire pressure light on all day.

Since barometric pressure and temperature can't be accounted for, I'd guess that volume(Larger tire size) can't be account for either?

Part of me would think that it is still reading pressure within the tire, yes the larger tire is capable of holding a larger volume of air, that would just mean that it would take more air to change the PSI?

 

I always air up by the gauge and air down by what I know the TMPSes will read when I am done.

 

Pressure is pressure. The volume has nothing to do with it other than, yes, it does take more air to increase that pressure.
30psi in a 33” is the same 30psi in a mountain bike tire.

 

That would be the same at higher altitudes as well correct? Where atmospheric pressure is lower, so it would take longer to air up at lets say 14,000ft compared to Denver at 5,400ft

 

It's the opposite because the air pressure we measure with our gauges & TPMS are measuring relative. Since the atmospheric pressure is less at 14k, you'll need less air to get to a higher pressure.

Atmospheric pressure at 14k is less than Denver is less than sea level.

So if everything were constant in the Pv=nRT equation (Pressure * Volume = constant * another_constant * Temperature), the measured PSI (or bars if you're a weirdo) will be increased at higher elevations.

Keep in mind that temperature is the likely variable when you measure air pressure, which is why you should be consistent about it. Don't compare your pressure you measure in the morning, parked in the shade after the truck has been sitting all night to the pressure after a highway burn to Moab at the gas station when you arrive.