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Old 09-11-2012, 05:42 AM   #1
JeffS
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Tire Pressure - Altitude Effect

Should I adjust tire pressure for altitude increase?

Our tires were all at the correct PSI when we left Michigan (about 700 feet above sea level assumed air pressure about 14.7psi). We are now in Colorado and at 6,000 feet (air pressure about 11.7psi) soon to go to 8,800 feet. Will be at 6,000 - 7,000 feet for about 3 weeks.
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Old 09-11-2012, 06:13 AM   #2
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I never really thought much about it but this is what Tire Rack has to say about it. Bottom line is that it appears temp affects more than altitude so adjust cold inflation pressure each morning and you should be good to go. Thanks for bringing it to my attention, Hank

Now you have me thinking what effect altitude has on TPM systems???
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Old 09-11-2012, 06:21 AM   #3
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Well if you go any higher the FAA will reqiure the pilot to be on oxegyn after a 1/2 hour but what hank just posted is the rule of thumb!!
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Old 09-11-2012, 06:29 AM   #4
Bob Landry
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Altitude would have a negligible effect if any at all(unlikely) You're dealing with air pressurized in a mostly rigid container(tire), not a fuel/oxygen mix. It would have more of an effect on non-fuel injected motors.
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Old 09-11-2012, 07:15 AM   #5
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hankpage, Howdy;

Quote:
Originally Posted by hankpage View Post
I never really thought much about it but this is what Tire Rack has to say about it. Bottom line is that it appears temp affects more than altitude so adjust cold inflation pressure each morning and you should be good to go. Thanks for bringing it to my attention, Hank

Now you have me thinking what effect altitude has on TPM systems???
Why would altitude have any effect on a pressure reading devise ???
When flying Pilots don't re-calibrate their cockpit gauges, cabin pressure at
altitude is kept at or near 8,000' ASL (Above Sea Level).

hankaye
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Old 09-11-2012, 07:45 AM   #6
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over 10,000 ft in a non pressurized aircraft ie Cessna, piper, you would get light headed and do something dumb like pass out. the gauges will work fine you just won'rt be coherant enough to read them. and Chevy ford and dodge don't have pressurizes cockpits lol
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Old 09-11-2012, 07:52 AM   #7
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Quote:
Originally Posted by hankaye View Post
hankpage, Howdy;



Why would altitude have any effect on a pressure reading devise ???
When flying Pilots don't re-calibrate their cockpit gauges, cabin pressure at
altitude is kept at or near 8,000' ASL (Above Sea Level).

hankaye
From the Tire rack article : 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.
With that in mind, OEM TPMs are mounted inside the rim and not exposed to ambient pressure. So, will a measurement taken from an external gauge differ in reading??? This is also just me thinking out loud. Sometimes it is kind of hard to get things through to me.
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Old 09-11-2012, 08:48 AM   #8
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THE PRESSURE INSIDE THE TIRE WILL STAY RELIVILY CLOSE AT HIGHER ALT THAT AT SEA LEVEL. THE OUTSIDE OR AMBIANT PRESSURE WILL BE LOWER SO THE TIRE WILL EXPAND. BUT NOW WE ARE SPLITTING HAIRS HERE YOU CAN SEE THIS WITH A BALLOON. LOW PRESSURE DAYS THE BALLON GETS BIGGER HIGH PRESSURE IT GETS SMALLER. FOR OUR CAMPER USE WE ARE OK OUR TIRES ARE GOOD JUST DON'T TAKE IT UP TO 40,000FT NOW YOU GOT ME RUNNING IMAGES IN MY MIND HUM!!!
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Old 09-11-2012, 12:56 PM   #9
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WOW, am I ever glad I ask about this LOL. However, I do know that the new bag of potato chips we brought from Michigan is blown-up tight! Now how's that for a technical observation?

We are going to run Engineer Pass (12,800) and Imogene Pass (13,114) in the San Juan's and I am going to air-down for those but not because of altitude.
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Old 09-11-2012, 01:39 PM   #10
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I have been travelling from high altitudes to low and you can definitely see a difference on a tire pressure gauge. Just a couple of pounds so not all that significant in the real world, but noticeable. To answer the original question, you do not need to make any allowances when adjusting pressure. The gauge reads pressure above ambient, and that is what you want in the tire. For example if you are setting to 80 psi at sea level with your tire pressure gauge, do the same at altitude.
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Old 09-11-2012, 04:47 PM   #11
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Quote:
Originally Posted by JeffS View Post
WOW, am I ever glad I ask about this LOL. However, I do know that the new bag of potato chips we brought from Michigan is blown-up tight! Now how's that for a technical observation?

We are going to run Engineer Pass (12,800) and Imogene Pass (13,114) in the San Juan's and I am going to air-down for those but not because of altitude.
FWIW, when I hauled potato chips out of our now defunct local "Eagle Snacks" plant, shipments destined to or passing through higher elevations were filled using a different gas mixture (think it was nitrogen) to prevent the bags from rupturing
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Old 09-11-2012, 05:53 PM   #12
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Pressure

Hankpage got pretty close. Most pressure gauges measure PSIG which is relative to ambient pressure. There are specialized gauges which measure PSIA which is absolute pressure. They are certainly not in use for tires, however.

My feeling is that temperature is the major factor in variation and moisture content in the air in the tire has a major effect on the temperature effect. This is why dry nitrogen has less variation vs temperature. Dry air would do as well but you would not get dry air from a run of the mill air compressor.

IMHO,
John
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Old 09-24-2012, 07:58 PM   #13
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We just went to Yellowstone and Glacier Nat'l Park and hit passes of 8,000 feet. I checked my tires each morning and set to 80 psi. Seems the colder temps affected the psi more than the altitude.

Going to a higher altitude is not an issue as the pressure in the tire will increase. The danger is going downhill where the tire pressure will decrease and that's where you'll have issues with an under-inflated tire.
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