Tire Air-Presure Preparation: timing

[stevenicol]

Silly question:
We are getting ready for a short journey tomorrow afternoon; is it okay to check and fill the air in the trailer tires today; or, should I wait until tomorrow? Does it really matter?

[Harvey51]

Pressure is proportional to temperature in degrees absolute (freezing point is 273, boiling 373).
An increase from 70F (294A) to 80F (300A) causes tire pressure to increase by 6/294x100 = 2%.

[JimK-NY]

I asked a similar question on a different RV forum and did not get an answer. If I understand it the OP is asking about ambient temps for setting tire pressure.

If we do that first thing in the morning before starting a trip the ambient temps might be 60 degrees. If we check later in the day, we do need to make sure the vehicle has not been driven and we need to be sure the tires have not been sitting in the sun. Now the ambient temp might be 85 degrees. Setting pressure at one time versus another can have a very substantial effect. That is what happens within one day's time. Over the course a few days ambient temperature fluctuations can be considerable. I am not sure what makes sense. One thing that does not make sense to me is trying to constantly change and readjust pressures due to daily changes. If the temps are changing when we are setting pressures, they are also changing when we drive at different times of the day.

My rear tires are running at very close to maximum load capacity and I set the pressures at the maximum. I try to error on the side of higher pressure. That means on a cool morning I might be at or just less than the max pressure. On a warm day I might start out several pounds above max.

[jamesroadking]

I check mine first thing in the morning before the sun start heating them up the day before I am leaving.

[DrewE]

As others have said, it doesn't make much difference in terms of pressure changes unless the temperature is changing wildly overnight.

If one (or more) of the tires are quite low, I think it would be a good idea to double-check them before leaving in case there is a slow leak. If they're all relatively close to the correct pressure and all about the same, it's a pretty good guess that none are leaking and that they won't develop a leak sitting parked overnight.

[Devocamper]

you should check your air pressure when the tires are at the current outdoor air temp and not in the sun. If your traveling and do not expect the temps to change much a day before is ok , I check mine the night before when the tires are in the shade and the tire are cool, If you have a TPMS you will see the pressure go up as the tires warm up also the sunny side will have higher pressure than the shady side as you travel. its best to have them cool like the sidewall says xx psi cold

[2oldman]

It only matters if the temperature is expected to be more than 20F greater or less tomorrow.

[ktmrfs]

as long as the trailer has been parked for a few hours it won't matter one bit when you check the pressure. Yes, it can vary slightly as ambient temps change, but really not an issue.