Proper Tire Pressure

[Rick4570]

I drive on the highway a lot, and currently on my JL Sport I have the Michelins. Proper tire pressure in 36 psi. I live in the Appalachian Mountains, but work in Tennessee. It is common for the temperatures to be 22 degrees in the morning (2am when I am heading to work) and then be in the low 70's when I am off work. If I put 36 psi in the tires in the morning, by the time I am on the highway heading home in the late afternoon my tire pressures are reading 46 plus pounds! Think I should back down the psi a bit?

Sponsored

 

[conFUcius]

Assuming they’re the OEM tires, go by the OEM specs. If they’re aftermarket, that’s where you’ve got to ‘experiment’ or do a chalk test to see what you should go with.

 

[BaconFury]

Nitrogen fill the tires, a whole lot less sway in pressures in extreme temperature differences.

 

[IllinoisChris]

IMO always set pressure when tires are cold. Regardless of the temp swing cold setting is, as far as I know, the accepted method.

 

[Sidewalk]

I live in an area that has that kind of dramatic temperature swing, and I don't experience that kind of pressure change. I will have to remember to look next time I drive, but maybe a couple PSI difference?

Nitrogen fill the tires, a whole lot less sway in pressures in extreme temperature differences.

They are already 78% nitrogen, adding in another 20ish percent won't make THAT much of a difference.

 

[jaymz]

As long as you don't exceed the tire manufacturers recommended max cold inflation, you'll be fine. They account for pressure fluctuations due to temperature when they engineer a tire and specify the cold inflation specs accordingly.

 

[notacon]

I run 315/70 R17 patagonia M/T tires and set the pressure at 36 psi cold (about 60 deg. for so. ca.)
This brings them up to about 38 to 40 on the freeway. I set my pressure at the amount needed to have an even tire wear across the width of the tread based on depth micrometer readings. Don't know if this is correct but it works for me.

 

[roaniecowpony]

I drive on the highway a lot, and currently on my JL Sport I have the Michelins. Proper tire pressure in 36 psi. I live in the Appalachian Mountains, but work in Tennessee. It is common for the temperatures to be 22 degrees in the morning (2am when I am heading to work) and then be in the low 70's when I am off work. If I put 36 psi in the tires in the morning, by the time I am on the highway heading home in the late afternoon my tire pressures are reading 46 plus pounds! Think I should back down the psi a bit?

Since it's impractical to air up in the cold morning or down in the warm afternoon on your daily commute, you should just bracket it. My opinion is you should err on the higher side of pressures. I would stick with your 36 "cold" at the start of your day.

Pressures will change about 2% for every 10F of change.

However, that is not for ambient temperature change, but for actual tire air temperature change. That has to be considered, since the tire is black, going from night/dark garage to direct sunlight will change the tire air temperature significantly, just setting still. Add in the temperature increases due to driving.

Manufacturers of vehicles provide "cold" tire pressure recommendations based on their testing of pressures in tires that are at operating temperatures. The "cold" pressure recommendations are calculated to approximate pressures the manufacturer established for operational pressures. It's really a way of "dumbing down" a tire pressure recommendation to something people can use without consternation, because tire pressures vary all over the place in different phases of daily use, let alone a trip where the environment changes.

This can be exemplified in the extreme in racing car applications. On a race car, the tires run very hot, because they are scrubbing and flexing to extremes. F1 tires can run from 212 to 280F at track temps. The only pressure that matters is the pressure at which the tire is being used.

So, for a daily driver, IMO, your priority for knowing your ideal operating pressure should be for safe handling first and other things like fuel economy, tire wear, etc as secondary considerations.

But frankly, since TPMS gives us real-time pressures, it's about time the manufacturers provide recommended operating pressure ranges for cold to running temperatures.

 

[Rick4570]

As long as you don't exceed the tire manufacturers recommended max cold inflation, you'll be fine. They account for pressure fluctuations due to temperature when they engineer a tire and specify the cold inflation specs accordingly.

Since it's impractical to air up in the cold morning or down in the warm afternoon on your daily commute, you should just bracket it. My opinion is you should err on the higher side of pressures. I would stick with your 36 "cold" at the start of your day.

Pressures will change about 2% for every 10F of change.

However, that is not for ambient temperature change, but for actual tire air temperature change. That has to be considered, since the tire is black, going from night/dark garage to direct sunlight will change the tire air temperature significantly, just setting still. Add in the temperature increases due to driving.

Manufacturers of vehicles provide "cold" tire pressure recommendations based on their testing of pressures in tires that are at operating temperatures. The "cold" pressure recommendations are calculated to approximate pressures the manufacturer established for operational pressures. It's really a way of "dumbing down" a tire pressure recommendation to something people can use without consternation, because tire pressures vary all over the place in different phases of daily use, let alone a trip where the environment changes.

This can be exemplified in the extreme in racing car applications. On a race car, the tires run very hot, because they are scrubbing and flexing to extremes. F1 tires can run from 212 to 280F at track temps. The only pressure that matters is the pressure at which the tire is being used.

So, for a daily driver, IMO, your priority for knowing your ideal operating pressure should be for safe handling first and other things like fuel economy, tire wear, etc as secondary considerations.

But frankly, since TPMS gives us real-time pressures, it's about time the manufacturers provide recommended operating pressure ranges for cold to running temperatures.

Thanks for such a well-informed answer! Much appreciated!

Sponsored