View Full Version : Tire pressure gain from heat etc.

07-23-2016, 01:34 PM
Just curious if anyone out knows the science about this. I notice that when I am driving my Viper with 30 psi, it climbs to about 35 psi when fully warmed up, so it climbs 17% of the original cold temp. So my new RAM 3500 with tpms starts at 75 psi in front and 65 in rear unloaded, and driving around today in 80 degree weather at 6,800 feet altitude, the pressures rose to 87 psi in front, and 73 in rear. So the fronts rose 16% and the rears about 13%. Is the rise in pressure a percentage thing, rather than a constant? So if I were towing my Monty around today starting at 105 psi, would it have risen 13-16% so it would get to around 119 - 122 psi? Just want to know what you typically see as far as pressure rise form cold 105 psi to driving around in 80 degree temps. Thanks

07-23-2016, 02:09 PM
Can't give you the scientific answer but today driving 250miles I saw a gain from 100 to 113psi with the ambient temperature in the upper 80s to low 90s. These were on G614s

07-23-2016, 02:12 PM
I have H rated tires at 125 PSI and after a few hours of running the 85 to 90 temps, I generally see approx 140 PSI, but I'm running quite a bit heavier than Montanas.

07-23-2016, 02:16 PM
G614's set to 105PSI air temps 100 degrees plus.Tire PSIs as per the TST 115/117.

07-23-2016, 04:05 PM
Just drove back from the Central States Rally. Started with pressure at 106 temp at 68. Outside temp rose to 90 by the time we hit Kansas and the tires averaged 122# by the time we got home the outside temp was 101 and pressures averaged 126#.

07-23-2016, 04:22 PM
My guess (and purely a guess) would be less temp rise on rears due to less weight on them.

Former StClairSailor
07-24-2016, 03:01 AM
Cooler temperatures have the opposite effect. I had my dealer fill the G614's to 100 psi. The ambient temperature was in the upper 40s. A couple of weeks later, on our way south in IN, the temperature was -1F, tire psi's were in the upper 80s. Took it easy on the road until tire temps got into the mid 90s.

07-24-2016, 05:23 AM
I noticed low temps and altitude, I'm at 6,800 feet, plays a big role also. So I'm wondering if there is a base line that people should be using. So if you are starting at 7,000 feet and it is 45 degrees out, and you will be traveling down to 500-1,000 feet, and temps of 80's plus,I'm guessing you should start out with something like 90 psi in the tires. I guess this is a good reason to have a good TPMS system active while traveling? I also have a good compressor i will be taking with me to adjust if necessary.

07-24-2016, 05:30 AM
If your tires are supposed to have 100 psi in them then that is what they should be set at when cold. DON'T set them lower just because temps will be going up

07-24-2016, 07:27 AM
The newer Rams must be set different. Ours are 60 in front and 80 on the rear for towing. But, it isn't just temp that affects the pressure. Crown of the road, sunshine, load distribution, and overall weight all play a role in tire pressure gain. Altitude change will also affect it. For that reason, there is no formula for pressure gain. One could do a DOE, select 3 factors, and then run the experiment but it would be difficult, time consuming and may lead to other factors. You could do a simple regression based on starting temp/pressure and then driving temp/pressure. If you can do sum of squares, you could actually determine how much of the variability is explained by the change in temp. Myself, I make sure my cold pressure is around 105 and watch my TPMS.

07-24-2016, 07:53 AM
Yikes you guys have far to much time on your hands. Set the psi to the recamended level for the tires and load and just keep an eye on the TPMS. JMHO

07-24-2016, 10:30 AM
quote:Originally posted by 8.1al

If your tires are supposed to have 100 psi in them then that is what they should be set at when cold. DON'T set them lower just because temps will be going up

Yes, you guys are making this way to complicated. Set them in the AM prior to moving, get in and drive.

07-24-2016, 07:41 PM
Yup, that's my take.... measure things in the AM before getting on the road then unless you have a problem don't worry about it.

For the original post, I hope you typed in the numbers backwards and that you have the higher PSI in the rear, not the ftont.

07-25-2016, 03:54 AM
My unscientific study, so take with a grain of salt. For the last 4,000 miles, I have only driven in hot weather, and I watch my pressure and temp. way more than I should. I have noticed that my pressure rises about 10% as I drive and the temperature rises about 10% above the outside air temp (95 deg outside my tires run about 104 deg +-2). I have also noted (again, not scientific) that type of road makes a slight difference. I would have thought concrete light colored roadways would be cooler, but I have found the opposite. The new darker road materials seem to run a few degree's cooler than the concrete roadways.

07-31-2016, 02:18 PM
Art, No everyone on this site that has a RAM 3500 dually and the placard on the side of the truck says when towing your Monty, put 80 psi in the front tires, and 75 in the rears, because you have 4 tires in the rear, since it is a dually.

08-04-2016, 07:35 AM
Check out Boyle's Law and Charles' Law



Everything you need to know about tire temp and pressure in its raw form.

08-04-2016, 10:16 AM
Although I own a TST system mainly to alert me of pressure loss ... remember the good ole days with limited data to tax the brain. Check air in the tires before a trip ... never have a thought of what the temps and pressure rises were ... and make it all the way to your desination sucessfully. Can you tell I'm typing with a lisp as my tongue is stuck to my cheek?