rehoppe
Denver
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Joined: 01/30/2009
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skimask wrote:patinlouisiana wrote:You know what would be "cool"?
Liquid Nitrogen!
Actually I think it would be quite cold ;-)
And a hard ride...for awhile anyway.
Anybody know what the expansion rate is when it warms up?
Could turn 'May Pops' into 'Did Pops', in a hurry? And would that void the warranty? 
Hoppe
2011 Dodge 1500 C'boy Caddy
2000 Jayco C 28' Ford chassis w V-10
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rjstractor
Auburn, WA
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Joined: 01/20/2003
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patinlouisiana wrote:Let me see if I have this straight in my head?
Atmospheric pressure at sea level is about 14.7 psi
Atmospheric pressure at 10,000 feet is about 10.1 psi
The difference is 4.6 psi.
If I have 40 psi in my tires at the beach the go up in the mountains to 10,000 feet my tire ppressure would increase to 44.6.
Correct or not?
Sounds about right. I think you see much more pressure variation due to temperature as opposed to elevation. Tires are designed to survive the pressure changes without any issues. They typically post a "cold" inflation pressure. If set my rear tire pressure at 80 psi and leave my house on a 60 degree July morning and check my pressure that afternoon in Wenatchee where it's 95 degrees or more, I will see pressures of 95-100 psi. I don't adjust the pressure because when the tire cools down the pressure would be well below the recommended 80 psi.
1998 Gulfstream Ultra B/H Ford E450 V10
2005 Chevy 2500HD 6.0 w/ Maxidump insert
2006 Ford Escape Hybrid
1998 Saturn SL2 toad
2012 VW Jetta S
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skimask
ND
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Joined: 04/06/2010
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Another small point to be made...
Those cheap little 99 cent tire pressure gauges (and most of the more expensive ones) are calibrated against a spring, not ambient air pressure. So they actually do read absolute pressure at a known temperature, assuming the spring doesn't go out of calibration.
Change the temp of the spring, change the outside pressure, change anything, and the calibration goes out of spec.
But, we've been using them for years, and close enough is 99.99999% of the time, close enough. No sense in buying a thousand dollar piece of equipment for this.
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rehoppe
Denver
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skimask
What you say,,,, is very true. Perhaps even the understatement of the year.
Several years ago I had access to some 'precision gauges, for the Right price. I made up a TP gauge complete with an oil filled gauge that was about $150 new. Had been using it for some time when I found I needed new tires. Got tires. They weren't round (bumpy), took it back to the tire store. I had checked inflation with my gauge and leveled to within 1#. The tire shop said they took out 6#s of air. I rechecked the pressures. Not only did they take air out but they had a 3# spread between 4 tires.
Appeared to me that their inline gauges weren't as close as mine. When asked why they lowered the TP and didn't get the even? They blamed MY gauge as being faulty!
I decided at that point the TP was a moving target. I keep a spring loaded gauge in the glove box of each vehicle, so at least that's now a constant. Truth of the matter, and the reason for retiring the expensive gauge? It is oil filled (anti vibration), and takes a bit to get a reading when the oil is cold.
Of course 2 of the three vehicles now have TPI, so don't check TP physically very much now.
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Tireman9
Akron, OH
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Joined: 08/16/2002
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Couple of posts respond to questions here.
"Inflate with Nitrogen and there will be MAGIC"
Altitude (elevation) effect on Tire Pressure
Hope these answer the questions.
Check out my Blog www.RVTireSafety.com
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skimask
ND
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rehoppe wrote:Perhaps even the understatement of the year.
I like playing the part of Captain Obvious 
(kinda like that bit on the Bob&Tom show on the morning radio)
I've got access to precision cal stuff at local PMEL lab (used to work at an AFB, so got to know the guys). So, took my nice little digital tire pressure gauge up a few years ago and checked it against their "master" machine. Dead nuts on!...well, within the .1psi indicated on the gauge itself! Not bad for a cheap gauge. Took it back in right before I retired last year. Same results, dead on.
AND, the digital gauge is an actual differential pressure gauge vs. the absolute type you get with a cheapy spring loaded type.
But same rule still applies as above, cheap spring type = good enough for me.
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