TPMS - How accurate?
Team Owner
Joined: Feb 2000
Posts: 45,538
Likes: 892
From: Texas
CI 1-4-5-8-9-10 Vet
St. Jude Donor '03 thru '10, '17
ALL gases change volume, or pressure if constrained in a constant volume vessel such as a tire.
Nitrogen is a gas, therefore it complies with ideal gas law and the laws of physics and thermodynamics.
However, commercially available nitrogen has been processed so that when bottled it is virtually completely dry.
Atmospheric air is 78% nitrogen, but there is also water vapor in humid air that probably affects the pressure change due to variations in temperature to a greater extent than when the tire is filled with dry nitrogen, or any other dry gas.
So....a tire filled with nitrogen will experience pressure changes due to changes in temperature, or ambient atmospheric pressure, just like any other gas.
Bob
Nitrogen is a gas, therefore it complies with ideal gas law and the laws of physics and thermodynamics.
However, commercially available nitrogen has been processed so that when bottled it is virtually completely dry.
Atmospheric air is 78% nitrogen, but there is also water vapor in humid air that probably affects the pressure change due to variations in temperature to a greater extent than when the tire is filled with dry nitrogen, or any other dry gas.
So....a tire filled with nitrogen will experience pressure changes due to changes in temperature, or ambient atmospheric pressure, just like any other gas.
Bob
PV = nRT ?
Race Director
Joined: Jan 2005
Posts: 10,924
Likes: 854
From: Daytona Beach FL
However, on a 95 degree day the density altitude can be 2,700 to more than 3,000 feet, depending on the humidity and barometric pressure setting.
That means that the ambient atmosphere you're driving around in is exactly the same as if you were at around 3,000 feet in elevation on a standard day.
So.....in the summer time in Conroe you're going to see DIC pressures a couple psi lower than your handheld gauge reads.
Butt.....maybe there's a hint of fall in the air down in Conroe, so soon the temps should be down, which will lower the DA, and your DIC should get closer to your gauge pressures as your temps get down to a standard SL temp of 59*.
Bob
Race Director
Joined: Dec 2007
Posts: 19,574
Likes: 167
From: Frederick, MD
ALL gases change volume, or pressure if constrained in a constant volume vessel such as a tire.
Nitrogen is a gas, therefore it complies with ideal gas law and the laws of physics and thermodynamics.
However, commercially available nitrogen has been processed so that when bottled it is virtually completely dry.
Atmospheric air is 78% nitrogen, but there is also water vapor in humid air that probably affects the pressure change due to variations in temperature to a greater extent than when the tire is filled with dry nitrogen, or any other dry gas.
So....a tire filled with nitrogen will experience pressure changes due to changes in temperature, or ambient atmospheric pressure, just like any other gas.
Bob
Nitrogen is a gas, therefore it complies with ideal gas law and the laws of physics and thermodynamics.
However, commercially available nitrogen has been processed so that when bottled it is virtually completely dry.
Atmospheric air is 78% nitrogen, but there is also water vapor in humid air that probably affects the pressure change due to variations in temperature to a greater extent than when the tire is filled with dry nitrogen, or any other dry gas.
So....a tire filled with nitrogen will experience pressure changes due to changes in temperature, or ambient atmospheric pressure, just like any other gas.
Bob
Team Owner
Joined: Feb 2000
Posts: 45,538
Likes: 892
From: Texas
CI 1-4-5-8-9-10 Vet
St. Jude Donor '03 thru '10, '17
Conroe is about 200 feet above sea level.
However, on a 95 degree day the density altitude can be 2,700 to more than 3,000 feet, depending on the humidity and barometric pressure setting.
That means that the ambient atmosphere you're driving around in is exactly the same as if you were at around 3,000 feet in elevation on a standard day.
So.....in the summer time in Conroe you're going to see DIC pressures a couple psi lower than your handheld gauge reads.
Butt.....maybe there's a hint of fall in the air down in Conroe, so soon the temps should be down, which will lower the DA, and your DIC should get closer to your gauge pressures as your temps get down to a standard SL temp of 59*.
Bob
However, on a 95 degree day the density altitude can be 2,700 to more than 3,000 feet, depending on the humidity and barometric pressure setting.
That means that the ambient atmosphere you're driving around in is exactly the same as if you were at around 3,000 feet in elevation on a standard day.
So.....in the summer time in Conroe you're going to see DIC pressures a couple psi lower than your handheld gauge reads.
Butt.....maybe there's a hint of fall in the air down in Conroe, so soon the temps should be down, which will lower the DA, and your DIC should get closer to your gauge pressures as your temps get down to a standard SL temp of 59*.
Bob
Team Owner
Joined: Feb 2000
Posts: 45,538
Likes: 892
From: Texas
CI 1-4-5-8-9-10 Vet
St. Jude Donor '03 thru '10, '17
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Burning Brakes
Joined: Apr 2011
Posts: 968
Likes: 2
From: Indio (near Palm Springs) Ca
I am 13 feet below sea level, no I don't live in a hole, mines, yes I said mines, is 2 psi high compared to my professional digital handheld. I set mines at 28 psi to read 30 on the DIC...
Burning Brakes
Joined: Apr 2011
Posts: 968
Likes: 2
From: Indio (near Palm Springs) Ca
Team Owner
Joined: Feb 2000
Posts: 45,538
Likes: 892
From: Texas
CI 1-4-5-8-9-10 Vet
St. Jude Donor '03 thru '10, '17
Team Owner
Joined: Mar 2008
Posts: 21,502
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From: Southern Utah
Burning Brakes
Joined: Apr 2011
Posts: 968
Likes: 2
From: Indio (near Palm Springs) Ca
i've done that a few times, and found this was the best "compromise" for summer driving.
I ran into a hi pressure warning when i did 32, DIC 34, in the summer the tires increase 6-7 PSI as im driving around. tires shot up to 40+ PSI and triggered it. so i left it a bit on the low side just incase..
and Nitrogen would be good but the aftermarket 3 piece wheel leak a bit so they need to be topped off a few PSI every few weeks...
I ran into a hi pressure warning when i did 32, DIC 34, in the summer the tires increase 6-7 PSI as im driving around. tires shot up to 40+ PSI and triggered it. so i left it a bit on the low side just incase..
and Nitrogen would be good but the aftermarket 3 piece wheel leak a bit so they need to be topped off a few PSI every few weeks...
Burning Brakes
Joined: Apr 2011
Posts: 968
Likes: 2
From: Indio (near Palm Springs) Ca
Team Owner
Joined: Mar 2008
Posts: 21,502
Likes: 465
From: Southern Utah
To clarify a bit....the reason that tire pressure is important is mainly to make for good, even tire wear. For this purpose, the important pressure is the relative pressure, not the absolute. So the handheld tire gauge is the more important of the two. The inflated shape of the tire is what is important and this is determined by the relative pressure, not the absolute pressure. 