ArchHoagland
Clovis, CA, USA
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Joined: 11/28/2004
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Tire air pressure at various altitudes has been discussed before and I decided to check it on my coach during a three week trip to Arizona.
I measured before we left and when we returned as well as when we were at a higher altitude.
I used an Accutire Oniprog gauge accurate +/- 1% 0 to 99lb. About $18.00
Guage was at room temperature of the coach about 68 degrees.
Measured after coach had not moved for 48 hours.
Michelin XRV 235/ 80R 22.5 tires with about 28,000 miles on them.
DATE . TEMP .. LOCATION .. ALTITUDE....DF.....PF......DRO.....DRI......PRO.....PRI
1/06/08 .. 54 ... CLOVIS CA ... 335' ..........96.4...95.4.....90.0.....90.2......90.6.....90.2
1/19/08 .. 61 ... BENSON AZ . 4,350'.........98.9...EEE....92.6.....93.3......EEE.....93.1
1/26/08 .. 57 ... CLOVIS CA .. 335'............96.0....94.3....88.9.....90.1......89.9.....89.2
EEE SUN WAS ON THE TIRE AND METER WON'T DISPLAY OVER 99 POUNDS
DF ....DRIVER FRONT
PF ....PASSENGER FRONT
DRO ....DRIVER REAR OUTER DUAL
DRI ....DRIVER REAR INNER DUAL
PRO ....PASSENGER REAR OUTER DUAL
PRI ....PASSENGER REAR INNER DUAL
TEMP ....OUTSIDE TEMPERATURE
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jefff929
Pacific wonderland, wet side
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Joined: 05/23/2004
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Hummm... interesting.
I'm glad someone provides this kind of information.
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gusco01
Gallup, NM
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I used to sell tires at high altitude. My town is at 6500 feet. Altitude makes no difference on tire pressure at all. It is the temperature of the tire that changes tire pressures. If your tires are in the sun on one side & shade on the other you will see as much as 10 PSI higher reading in the sun. A tire is a sealed vessel it makes no difference the altitude. Tire loading (weight) & temperature makes the difference. If you fill up in the AM and its 30 degrees & drive to a place that's 50 degrees and let the tires cool it will be higher because the tires are 50 degrees not the 30 that you filled it up at. That's why it says on side of tire not to let air out when tire is hot because they will be under inflated when it gets cold. Cold is were you fill the tires & check them again cold. I was a Goodyear tire store manager for a couple of years. Hope this helps, Dan
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sum1
So-Cal
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Joined: 11/07/2005
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Good stuff...........Thanks
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wallynm
Los Alamos NM
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Joined: 09/27/2000
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Now what am I to do!
ArchHoagland wrote:Tire air pressure at various altitudes has been discussed before and I decided to check it on my coach during a three week trip to Arizona.
I measured before we left and when we returned as well as when we were at a higher altitude.
I used an Accutire Oniprog gauge accurate +/- 1% 0 to 99lb. About $18.00
Guage was at room temperature of the coach about 68 degrees.
Measured after coach had not moved for 48 hours.
Michelin XRV 235/ 80R 22.5 tires with about 28,000 miles on them.
DATE . TEMP .. LOCATION .. ALTITUDE....DF.....PF......DRO.....DRI......PRO.....PRI
1/06/08 .. 54 ... CLOVIS CA ... 335' ..........96.4...95.4.....90.0.....90.2......90.6.....90.2
1/19/08 .. 61 ... BENSON AZ . 4,350'.........98.9...EEE....92.6.....93.3......EEE.....93.1
1/26/08 .. 57 ... CLOVIS CA .. 335'............96.0....94.3....88.9.....90.1......89.9.....89.2
EEE SUN WAS ON THE TIRE AND METER WON'T DISPLAY OVER 99 POUNDS
DF ....DRIVER FRONT
PF ....PASSENGER FRONT
DRO ....DRIVER REAR OUTER DUAL
DRI ....DRIVER REAR INNER DUAL
PRO ....PASSENGER REAR OUTER DUAL
PRI ....PASSENGER REAR INNER DUAL
TEMP ....OUTSIDE TEMPERATURE
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Have a Freightliner Yahoo Group or FCOC Web Page
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newxmar
East Otis, MA
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Joined: 02/04/2004
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The OP's data is very accurate, interesting. The atmospheric pressure is about 1/2 pound less per 1,000 feet of altitude. He went up 4,000 feet and the tire gage read about 2 pounds more. Clue is "tire gage read".
If you want to know the details of reading a "higher tire pressure" at altitude, just goggle "tire pressure at increase in altitude".
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Triker33
Homestead, FL
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Joined: 11/30/2002
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Quote:Altitude makes no difference on tire pressure at all. It is the temperature of the tire that changes tire pressures. If your tires are in the sun on one side & shade on the other you will see as much as 10 PSI higher reading in the sun. A tire is a sealed vessel it makes no difference the altitude.
Goodyear says this. But what do they know?
Atmospheric pressure changes .48 psi for every 1,000 feet change in altitude. If a tire has 100 psi at sea level, your gauge will read .5 psi higher for every 1,000 foot increase in altitude.
You are right about temperature making a difference.
A 10° F air temperature change will: Change inflation pressure 2% in the same direction. That’s an increase of 2 psi on a 100 psi tire when the temperature increases 10° F.
“Working Inflation” increases 5-15 psi when a tire warms up.
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Doug and Cassi Glass
Clifton Forge, VA
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Joined: 02/20/2006
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It all seems pretty insignificant to me. What about airliners that take off at sea level and land at Denver or some of the very high altitude airports in South America. Their wheelwells aren't pressurized.
Temperature and weight are the important factors.
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Bikeboy57
Texas
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Joined: 08/09/2006
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First accept my humble apologies for engineer speak.
When reading pressures, we almost always use a gauge that measures in psig. That stands for pounds per square inch guage. It measures the DIFFERNCE between the vessel and the atmosphere. So if you go up in altitude the pressure in the tire stays the same but the atmospheric pressure drops a little so the gauge reads higher.
There are guages that are marked psia. That stands for pounds per square inch absolute. They measure the pressure inside the vessel regardless of the outside atmospheric pressure. If you have a gauge marked psia it will read 14.7 psia at sea level.
The absolute pressure inside the tire is what supports the weight of the coach. So it is a moot point whether it reads 90 pounds at sea level and 95 pounds at 10,000 feet. The same pressure is in the tire.
Richard, Rhonda, Ty, and Alex
1995 Newell with 470HP Detroit Diesel
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AlanB
Sierra Vista, AZ
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Joined: 11/18/2002
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Tires are inflated to "gauge" pressure. Its the difference between ambient (14.7 psi at sea level) and inside the tire. Altitude does make a difference, although small. As Richard states, a gauge can be absolute or gauge. I have not seen a tire absolute gauge. Example, if a tire at 30 PSI were placed in a pressure tank with 30 PSI, the tire would be flat. There would be no difference between the pressure inside the tire and outside the tire. This is basic HS physics.
AlanB
2002 Holiday Rambler Imperial 40PKDD Cummins ISL
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