Max tire pressure and daily temperature changes

The manufacturers take temperature fluctuations into account. That's why the tire max pressure is for cold tires.

Tire manufacturers state to check tires when cold. I read that to say that they are designed to accommodate any increase in pressure due to heat. I fill mine to the specified PSI when cold

And cold is 70 degrees. This is the listed temperature on most all tire manufacturer websites.

I only check/adjust tire pressures (truck/trailer) in the AM when they are 'cold' (haven't been driven on).
I run MAX PSI on trailer tires (110#) and MAX PSI on truck rear tires (80#) as I run at/close to max load ratings. Truck front tires are at 55# always as the weight doesn't change whether towing or not. Truck rear tires are at 45# when not towing.

The rule of thumb that I follow is that the tire's pressure increases by one psi for every ten degrees F. As was said, the mfg's do take temperatures into consideration when building the tire. I always try to check my tires in the morning just after I read all my newspapers. Air temps here rarely get into the extremes, because why? Because its S. CA.




Outside of a dog, a book is man's best friend. Inside a dog, its too dark to read. Mark Twain.

As Gonzo42 states, 1 psi per 10 degrees ambient temperature change. With a 40 deg change we are only looking at 4psi increase / decrease in the tire pressure. I am very particular about tire pressures, so I generally check pressures first thing in the morning at the coolest time of day. I started doing this when I noticed a substantial difference in left / right tire pressures from the sun beating on one side of the vehicle. A couple of psi difference left and right IS a big deal (to me).

I have a pressure pro system. I have set my pressures at 65 on my class D tires. Here is what I have noticed. If the trailer is not in tow the pressure will rise with temperature (only a couple psi if tires are not in the sun). But when under tow for 10 miles or so I find my pressures do not very much (maybe 5 psi)from towing at 60 degrees ambient and 90 degrees ambient.
I have also noticed when under tow for at least 10 miles the tires on the sunny side will run about 1-2 psi greater than the tires on the shade side.
After under tow for 5-10 miles I watch for any tire pressure change.
I had a tire down a couple psi (still several psi from alarm) from the others. I stopped at the first chance where I could pullover safely and found I had picked up a 3/8 by two inch bolt in one of my 5th wheel tires. The TPMS saved me some grief that day.

We are prepping for a 50 day trip and I will set my 5er tires at 80, my truck rear tires at 80, my truck fronts at 70 and not worry the rest of the time. Been setting my tires that way since '05 and have never had an issue. Just lucky I guess.

Thanks, will keep doing that early in the morning. A TPMS seems nice but I had bad experience with wireless stuff (I tried a camera and it sucked). I wonder how reliable they are.