Tire pressure

CapriRacer wrote:

Dave H M wrote:
Just got my TST system cranked up and also just came off the road from a 920 mile run. Have 16's on the fifth wheel so I always start at 80 psi cold. It was generally around 56 degrees or cooler outside. One morning it was 40 outside and I noticed the tires generally had dropped from 80 to 78. The highest pressure indicated was 92 psi. Temp ran about 12 degrees higher than ambient.

I been wondering on this subject also so this was a good read.

I did not time it but sure was surprised how the tire temp and pressure quickly climbed close to the final running numbers when initially starting out.

The rule of thumb is that you'd like no more than a 10% pressure build up - and if you get 15% or more, you need to take action.

You are AT 15%, so you need to take some action to improve the load carrying capacity of the tires - which means a larger size or more inflation pressure.

You said you were using 16" tires at 80 psi, but you didn't say what size. If they are ST235/80R16 Load Range E's, I'd recommend you move up to the larger LT235/85R16's Load Range E's.

Could be that the 92 psi read by Dave H was after some severe braking.
The normal warm pressure could be in the 80 somewhere .
Then the pressure rising is pretty normal.
So to determine if the cold pressure needs to be higher or tires with higher maximum load should be used, he should yust do 4 point weighing and calculate the pressure with a comfortable reserve.
So Dave, was this 92 incidental or constant when driving?
You also write that temps ran about 12 degrees higher then ambiënt.
So this is the inside tire temperature read from your TPMS?
Then this is way lower then the about 30 degrees I assumed for RV tires of these sises and so not that bad.
If you would have read the temperature when the pressure was 92 psi , it would prove to be higher. Filled 50degrF cold and 80psi cold in in my spreadsheet I mentioned , and at 92 psi it gave an inside tire temperature of 115 degrees, wich is 65 degrees hotter so not even that bad. Still think that 92 was exeptional and short time.

Played a little further with my spreadsheet and and when temperature goes from 56 to 40 degr , pressure lowers from 80 to 77.1psi, yust about what was measured, becouse the 78 can be a inacuracy of the device or rounding to 1 degree the TPMS mayby does.