Tire Pressure Vs. Ambient
I recently found that adjusting our tires to the cold inflation temperature base on the local ambient may not be the correct way to do this. Based on this info, the ambient temp for setting tire pres...
Forum Discussion
OK, I got an answer from Roger Marble. Note that the short answer is that one should just add 10% to the minimum cold inflation pressure for the loading on that axle, which avoids the necessity of "chasing your tail" on the temperature-pressure curve. Hope this helps.
Skip
-----Response-----
"The concept of "Standard Temperature" comes from laboratory experiments "Since temperature and air pressure vary from place to place it is necessary with a standard reference condition to compare testing and documentation of chemical and physical processes."
Tire inflation guides are not a chem lab experiment guide but are guides for proper inflation needed to carry a specific load in the real world. Tire manufacturers do not say to set tire pressure to "Standard" conditions but to set the pressure when the tire is at "Ambient" temperature i.e. not artificially increased due to running or exposure to a direct heat source. The term "cold inflation pressure" should be synonymous with being at ambient temperature and not warmed up from running. Note it also does not mean you have to place your tires in a refrigerator to get them "cold"
RE the need to "correct" the cold pressure. Since cold pressure means at ambient there is no correction needed.
While it is always possible for some to come up with travel plans such as leaving Pike's Peak at -10°F and driving to Death Valley where it is 120°F that night so they want to know if they should set the pressure for some future ambient temperature and elevation. I would suggest that this is not necessary as even this extreme change would only result in a theoretical pressure increase of about 14 psi which the tire can tolerate. If you still feel the need to compensate then take a 2 hour lunch and adjust your pressures at that time.
For more normal travel I suggest simply adjusting your "cold" inflation when you haven't driven on them for two to three hours and they are not in direct sunlight. Morning before travel usually meets these guidelines.
I will fall back to earlier posts and info on my blog where I tried to summarize inflation guidelines.
1. Using your actual tire loads know the minimum inflation needed when the tires are at ambient temperature by consulting tire mfg Load/Infl charts. Lets call this the Minimum Cold Inflation Pressure or MCIP.
2. All tires on an axle should be run at the same inflation so this means you use the heaviest loaded tire to learn the MCIP for the tires on that axle.
3. Always run your tires at or above the MCIP.
4. To avoid chasing your tail when the temperature drops which means you need to add 1 or 2 psi I suggest adding 10% to MCIP and as long as you are within the range of 100%MCIP to 110% MCIP all is OK.
Hope this helps.
Roger
Skip
-----Response-----
"The concept of "Standard Temperature" comes from laboratory experiments "Since temperature and air pressure vary from place to place it is necessary with a standard reference condition to compare testing and documentation of chemical and physical processes."
Tire inflation guides are not a chem lab experiment guide but are guides for proper inflation needed to carry a specific load in the real world. Tire manufacturers do not say to set tire pressure to "Standard" conditions but to set the pressure when the tire is at "Ambient" temperature i.e. not artificially increased due to running or exposure to a direct heat source. The term "cold inflation pressure" should be synonymous with being at ambient temperature and not warmed up from running. Note it also does not mean you have to place your tires in a refrigerator to get them "cold"
RE the need to "correct" the cold pressure. Since cold pressure means at ambient there is no correction needed.
While it is always possible for some to come up with travel plans such as leaving Pike's Peak at -10°F and driving to Death Valley where it is 120°F that night so they want to know if they should set the pressure for some future ambient temperature and elevation. I would suggest that this is not necessary as even this extreme change would only result in a theoretical pressure increase of about 14 psi which the tire can tolerate. If you still feel the need to compensate then take a 2 hour lunch and adjust your pressures at that time.
For more normal travel I suggest simply adjusting your "cold" inflation when you haven't driven on them for two to three hours and they are not in direct sunlight. Morning before travel usually meets these guidelines.
I will fall back to earlier posts and info on my blog where I tried to summarize inflation guidelines.
1. Using your actual tire loads know the minimum inflation needed when the tires are at ambient temperature by consulting tire mfg Load/Infl charts. Lets call this the Minimum Cold Inflation Pressure or MCIP.
2. All tires on an axle should be run at the same inflation so this means you use the heaviest loaded tire to learn the MCIP for the tires on that axle.
3. Always run your tires at or above the MCIP.
4. To avoid chasing your tail when the temperature drops which means you need to add 1 or 2 psi I suggest adding 10% to MCIP and as long as you are within the range of 100%MCIP to 110% MCIP all is OK.
Hope this helps.
Roger
