2nd Gen Non-Engine/Transmission Tire pressure at altitude

[rjrkihap]

Just got back from Wyoming (to Portland, OR) and noticed something weird with my tire pressure. Before leaving I set the fronts at 52 and the rears at 48. Before leaving Wyoming I checked them again. Fronts were at 61 and rears 55. The temp. in Wyoming was around 30 degrees (20 degrees colder than in Oregon).



So, the altitude must have affected the reading somehow. Does the lower altitude pressure make the gauge read higher? Any thoughts?

 

[nps]

Yes. Next time you take the trip, open an empty 2 liter plastic soda bottle in OR then reseal it. Take it with you and open it in WY - will sound like a bottle full of soda when you open it. Reseal it and take it back to OR. It will be collapsed when you arrive.

 

[RustyJC]

The tire pressure gauge reads the difference between the air pressure in the tire and atmospheric pressure - this is why the reading is expressed as PSIG (pounds per square inch gauge). Barring a leak, the air pressure in the tire (expressed in PSIA - pounds per square inch absolute) will not change as altitude increases, but atmospheric pressure decreases. For example, sea level barometric pressure of 14. 7 PSIA will drop to something like 11. 7 PSIA at 7000 ft elevation. Since the tire gauge reading is absolute pressure minus atmospheric pressure, as atmospheric pressure drops (as altitude increases), the tire gauge reading will increase since absolute pressure in the tire remained constant.



Rusty

 

[rjrkihap]

Thanks Guys for the info. Makes total sense.



Here's a follow-up question. To have your tires properly inflated (ie 50 PSI) you should check and adjust the tire pressure based on your gauge as you travel up and down in elevation. In Wyoming I would let some air out to bring my tire pressure back to 50PSI and then as I drove back to Portland, I would re-inflate my tires to bring them to the 50PSI mark. Is this correct???



Thanks



Ron

 

[MChildress]

Just for grins, we had left south Texas and taken our 4 wheelers up into northern New Mexico around Red River running around 10000 to 12000 ft. I always run 4 lbs in the 4 wheeler tires. I have tie downs that use the trailer ball on the back of the 4 wheelers that plug into a 2" receiver square tubing on a 4 wheeler rack I had made to put two in the back of the truck. After the first day and loaded back up I could not get my trailer ball tie downs latched. The 4 wheelers were setting almost an inch higher than normal. I set back and scatched my head and finally checked the tire preasure 8 lbs. I let them back down to 4 lbs and every thing worked fine. The truck tires changed about 10 lbs but I run 10lbs under max and this was not a concern. When we got home with the 4 wheelers the tires looked like marshmellows 2lbs. The patato chip bags we took up with us blew up like baloons. We road in snow on Wheeler Peak,pretty awsome being July.