What is the "cold" temperature for tire inflation?

"cold" is the temperature before the trailer has been going down the road.

It's also ambient air temp, whatever that happens to be.

I have 225/75/17.5 tires, put in 120psi at 65 degrees after 300 miles with air temp at 80 degrees pressure went to 140 psi and temp was 90s; after a night a 7500 ft air temp was 45 degrees pressure was 116 psi drove 400 miles cruising at 70 mph outside air was 95 degrees, tire temp was 106 degrees and air pressure was 146 psi that is with my TST TPMS

That sounds like an extreme pressure change!
I would double check with a quality pressure gauge.

Down loaded from the web

The calculations for this change are based on the Ideal Gas Law. A good rule of thumb is this: For every 10 F degree change in temperature, the pressure will change by 1.9%. If a tire is filled to 32 psi at a temperature of 75 F degrees and the temperature drops 10 degrees, the tire pressure will drop to 31.4 psi; a difference of .6 psi. If a 100 psi tire is filled at 75 F degrees and the temperature drops 10 degrees, the tire pressure will drop to 98.1 psi; a difference of .9 psi.

nineoaks2004 wrote:
That means, before the tire has moved more than a few miles, does not mean ambient outside temp., as tires roll the temp inside rises, so if you over air the tires they can burst when the air heats and expands in a tire, (just like over inflating a balloon)

Stop. A tire is not going to burst if you fill it when hot. It's just not. Will it be overfilled when hot? Yep, sure will.

I have taken thousands of tire temps and hundreds if not thousands of tire pressures over the years at the race track. They just don't increase that much unless you have a WHOLE bunch of water in the tire. If this is the case one should refill with "dry" air or nitrogen.

That means, before the tire has moved more than a few miles, does not mean ambient outside temp., as tires roll the temp inside rises, so if you over air the tires they can burst when the air heats and expands in a tire, (just like over inflating a balloon)

I have checked tires at -35C. Yep they were frozen. If you disregard tire OEM load and inflation tables which factor design traction and consider tires part of the suspension, and use rv.net instructions and always inflate to MAX you won't have that trouble.

wsc7050 wrote:
Hello quick question. My trailer tires instruct me to use 65 psi when cold. Well some days I start in the 30's and some days in the 70's. And for argument sake, let's say both of those days end in the 90's. I know from using my tire temp and pressure monitor that if I put 65 psi in at 30 degrees and ran it to 90 degrees it would be different than if I put it in at 70 degrees and then ran it to 90 degrees. So should I be aiming for 65 psi for the temp I would spend most of the day towing at, or?
Thanks in advance!

I have 225/75/17.5 tires, put in 120psi at 65 degrees after 300 miles with air temp at 80 degrees pressure went to 140 psi and temp was 90s; after a night a 7500 ft air temp was 45 degrees pressure was 116 psi drove 400 miles cruising at 70 mph outside air was 95 degrees, tire temp was 106 degrees and air pressure was 146 psi that is with my TST TPMS

Always, always, always use cold temperature stated on the side of your tire, Check an inflate the tires when they are cold, never, never deflate a hot tire to a cold temperature.

If you think a tire is going flat and you check it an it reads low, then inflate the tire to match the already warm/hot other tires, then check that tire again the next time you stop again, if it's low again then seek out a tire shop to get tire repaired or change to your spare if you have one ...

Only add air if the tire is going flat, temps will very on different road surfaces, cement, asphalt, hot and cold ambient temperatures. They will always gain air when hot and loose when cold unless they a filled with nitrogen an then they will still gain some or loose some but the temperature of the tire will however run cooler overall ...

I always check my tire pressure 1st thing in the morning before starting out, i check the temperatures of the tires and axle hubs during the day when I stop to make sure they are not overly hot to the touch, some people use lazier gauges to do this same thing.

Safe travels

Simple answer.......
On travel day in the morning before you drive on them

The tire pressure recommended in your vehicle's owner's manual or tire information placard is the vehicle's recommended cold tire inflation pressure. This means that it should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun's radiant heat affects it.

Cold is the morning before you roll and before the sun hits them.

Ambient air temperature in the shade. Unless you have issues with your brakes, bearing, or alignment, your tires will only heat up 5-10 degrees above the air temp when driving and the pressure will usually increase less than 5 psi. Tire manufacturers account for this when they determine the "cold pressure". However, tires facing the sun will get warmer than those in the shade. If you're parked on asphalt the tires, in the sun, will get hot and cool down when driving so don't rely on that "hot" temp.