Originally Posted by rgarner
I have a 2004 FR Sunseeker 3100 Class C. After having a blow out last year in Colorado (I live in Texas), I was directed to a Tire store where they installed new Goodrich Commercial T/A LT225/75R16 115/112P Load Rate E tires on the rear duals. Recently I bought a TPMS and installed it before a 4 hour drive to a state park here in Texas. The tires were inflated to 80 in the rear and 65 in front as per the instructions. Additionally the TPMS suggested an alarm setting of 20% high---or 96 for the rear duals.
After about 2 hours on the road (and it was warm) the tire pressure alarm went off as 2 of the tires reached that threshold of 96 psi. Actually, all of the tires were within 3-4 psi of each other. I noted that the tire temperature (also monitored) did not even come close to the pre-set number. So, the magic question is at what temp should I be worried? On the way home I reset the alarm to 98 and one tire hit that--the others hovered around 94-96. I called the tire shop--no one had a clue as to what the manufactured maximum pressure might be---only that max cold was 80 (I knew that). I even called Goodrich...they took down a lot of marketing information, but ultimately told be to start out with 75 psi on hot days. Of course, others say that is a bad idea due to loading issues. So...does anyone have any guidance or help to offer on this? By the way, the rig has been weighed and is well below the weight limit--including corner weights. Obviously, the tires have likely always run this hot since they were installed a year ago...but I only now have a monitoring system that shows the info. Any help is appreciated.
You need to remember that TPMS sensors are being cooled by outside air if they are screw on the end of the valve stem type. Also if you use extender hoses the sensor is further from the heat source. I understand that most TPMS come from the factory with a high Temperature warning set to 70C or 158F. I would leave it there.
Pressure increases by about 2% for each change in temperature of 10F. BUT the temperature we are talking about is the temperature of the internal air which is going to be hotter than the temperature at the sensor.
Air is a good insulator and so is rubber so heat flow is not so great. The hot spot on a tire is burried deep in the shoulder at the belt edges so there is no way for the air to reach the critical rubber temperature.
If you are seeing a 20 - 25% increase in pressure that is indicating a possible 100F increase which is a lot. Are you sure your tires are not overloaded, even at 80 psi?
Were the 2 hot tires the inner dual? They are normally hotter than the outer dual due to less cooling air reaching the wheels and tires.
Double check your pressure gauge too. I find about 10 to 15% of gauges are off by 5 psi or more.