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Old 10-11-2022, 02:22 PM   #1
Island Eddie
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Pressure and temp ?

Just got back from #2 in our new trailer, great trip, so great we booked it again only longer for next year.

I had to pump up my tires after I brought the trailer home from the lot I purchased it at.
They called out 65 pounds cold.

Before setting out I hooked up my T&P sensor, the pressure was 4 pounds less on all four tires however the cold temperature was cooler than when I pumped them up last time.

I am thinking this is normal, right?
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Old 10-11-2022, 02:28 PM   #2
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Yes, pressure changes with temp. (PV=NRT). I don't trust the TPMS sensors for accurate pressure but for pressure and temperature trends. I use a round, bourdon tube type gauge for accurate pressure readings on truck and trailer and adjust about 4 times per year, but do check before each trip.
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Old 10-11-2022, 08:04 PM   #3
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Quote:
Originally Posted by Gkri View Post
Yes, pressure changes with temp. (PV=NRT). I don't trust the TPMS sensors for accurate pressure but for pressure and temperature trends. I use a round, bourdon tube type gauge for accurate pressure readings on truck and trailer and adjust about 4 times per year, but do check before each trip.
OK, last trip after I pumped them up, using a handheld digital gauge, the TPMS read 65lbs on all four, as well when I started out.

I did nothing to them, and I don't recall if I took a reading on each tire first, this last trip....

I do know the first time the outside temperature was about 15 degrees warmer at that time, which I'm guessing means I hit 65lbs sooner than if it was say 50 degrees outside, yes?
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Old 10-11-2022, 08:36 PM   #4
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Outside temps have an effect on tire temps. Hotter = higher, lower = lower temps. Air them up when they are cool, haven't been on the road, to the indicated pressure. From there realize that as the day gets hot so do the tires. Hot pavement makes it even moreso. When things start cooling down, or you stop driving, the tires cool off. With those increased temps you will see some increase in tire pressure, same with cooler temps. Air them up when they are cool using a good temp gauge. For reference you can then look at your tpms to see where it stands vs a good gauge and just log it in memory. From there just watch the tire temps/pressures, they will vary up and down. You just watch for variances that aren't normal, particularly one tire hotter, lower/higher than the others. From there just cruise on down the road....
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Old 10-11-2022, 08:54 PM   #5
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Thanks..... I was leaning that way, just asking for some affirmation
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Old 10-12-2022, 05:43 AM   #6
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Thanks..... I was leaning that way, just asking for some affirmation
using a few rough assumptions for volume of air, a 20 degree temp swing calculates to about 3 psi difference. With some room for error, I'd say what you saw is reasonable.
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Old 10-12-2022, 06:38 AM   #7
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This may not be the "scientifically approved and engineering tested" method, but it's what I do and my reasoning:

I always check my tire pressure in the morning before we tow. I adjust the tire pressure to the maximum sidewall pressure, which I've found is where my trailer tows best and I get the best performance from my tires. I do not check them again until the next morning, again, before we tow.

During the day, every time we stop I "shoot the tires, hubs and spindle" for temperature with a HF digital thermometer. What I'm looking for is any "wide variance in temperature between the wheels ON THE SAME SIDE. As an example, if one tire ON THE SAME SIDE is 95F and the other is 98F, that's OK. I'd expect to see a similar temperature span on the hubs on that side and on the spindle on that side. As long as they're similar, I move to the other side and repeat.

I expect that the "sunny side" will be several degrees hotter than the "shady side" when towing. I've seen anywhere from 10F to 25F warmer on the sunny side. So, that's not a problem and I'd expect a similar variance as on the shady side between the tires, hubs and spindles.

Expect that if you're towing at 70MPH on the interstate and use the brakes to slow to a stop at the rest area truck parking, when you pull in, get out and "shoot the tires" the rubber may be close to the last check, but the hubs may well be significantly hotter because of the "hard braking you just did in slowing down". So the "temperature difference on the hubs when compared to the last check" may be significantly different, but again, as long as both hubs on that side are similar, it shouldn't be a concern and again, the "sunny side" will be warmer than the "shady side"....

The objective, at least for me, is to identify any significant (25 to 50 or more degree) difference between the tires, hubs or spindle ON THE SAME SIDE. If I see that happen, then I investigate to find a reason.

Otherwise, I'll start tomorrow with the same pressure check, tires set to sidewall pressure before towing and begin the temperature checks at every stop along the route.
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Old 10-12-2022, 07:14 AM   #8
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Originally Posted by JRTJH View Post
This may not be the "scientifically approved and engineering tested" method, but it's what I do and my reasoning:

I always check my tire pressure in the morning before we tow. I adjust the tire pressure to the maximum sidewall pressure, which I've found is where my trailer tows best and I get the best performance from my tires. I do not check them again until the next morning, again, before we tow.

During the day, every time we stop I "shoot the tires, hubs and spindle" for temperature with a HF digital thermometer. What I'm looking for is any "wide variance in temperature between the wheels ON THE SAME SIDE. As an example, if one tire ON THE SAME SIDE is 95F and the other is 98F, that's OK. I'd expect to see a similar temperature span on the hubs on that side and on the spindle on that side. As long as they're similar, I move to the other side and repeat.

I expect that the "sunny side" will be several degrees hotter than the "shady side" when towing. I've seen anywhere from 10F to 25F warmer on the sunny side. So, that's not a problem and I'd expect a similar variance as on the shady side between the tires, hubs and spindles.

Expect that if you're towing at 70MPH on the interstate and use the brakes to slow to a stop at the rest area truck parking, when you pull in, get out and "shoot the tires" the rubber may be close to the last check, but the hubs may well be significantly hotter because of the "hard braking you just did in slowing down". So the "temperature difference on the hubs when compared to the last check" may be significantly different, but again, as long as both hubs on that side are similar, it shouldn't be a concern and again, the "sunny side" will be warmer than the "shady side"....

The objective, at least for me, is to identify any significant (25 to 50 or more degree) difference between the tires, hubs or spindle ON THE SAME SIDE. If I see that happen, then I investigate to find a reason.

Otherwise, I'll start tomorrow with the same pressure check, tires set to sidewall pressure before towing and begin the temperature checks at every stop along the route.
the engineering thing is an "occupational hazard", sometimes i just can't help myself. maybe next year when i retire i can turn that side of my brain off - maybe. i also see the difference on the TPMS for tires sitting in the sun vs. the shady side of the truck and trailer. What HF digital thermometer do you use, i think that should be my next purchase
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Old 10-12-2022, 07:21 AM   #9
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On cooler days (ambient temp), our tires are typically 6-8psi below a "normal" ambient temp day; call that a 45 degree night vs a 75 degree day. I've also observed a similar pressure difference from the tires on the side of the trailer that are in direct sun light vs the shaded side. Once I've driven a few miles the pressures balance back out again. From stationary to driving at highway speeds, I usually see a 6-8psi increase as well. With that in mind, if my trailer tires start at 74psi and can be reasonably sure they're going to hit 82psi on the highway. At 80psi cold I'll usually see them at 86-88psi on the highway (think I've seen as high as 93).
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Old 10-12-2022, 02:03 PM   #10
Island Eddie
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Seeing all four tires react the same, I pretty much felt all was good and caused by ambient static temperature prior to use.

Now how much of an issue might one expect if they pump up in a freezing climate, then drive to 85 degrees in a few hours like in California?
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Old 10-12-2022, 02:34 PM   #11
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Suggestion. Many threads along this line; even some recently. Fill tire to MAX PSI indicated on sidewall when cold. Temps rise from both turning on the road and ambient temps and I suspect this was taken into account by the tire engineers. Sometimes temps go from about 80 PSI (LRE) to 90-95F and this is normal. Don't overthink it.
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Old 10-12-2022, 04:35 PM   #12
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Quote:
Originally Posted by Gkri View Post
the engineering thing is an "occupational hazard", sometimes i just can't help myself. maybe next year when i retire i can turn that side of my brain off - maybe. i also see the difference on the TPMS for tires sitting in the sun vs. the shady side of the truck and trailer. What HF digital thermometer do you use, i think that should be my next purchase
This is an updated version of the HF thermometer I use. It's got the standard HF 90 day warranty and costs about $25. https://www.harborfreight.com/121-in...ter-63985.html

Amazon has a similar version for $15 with a 1 year warranty. https://www.amazon.com/Thermometer-E...s%2C102&sr=8-5

If I were buying a new one today, I'd probably opt for saving the few bucks as well as the gas to drive to HF. IMO, Amazon wins another one...
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Old 10-12-2022, 04:42 PM   #13
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Quote:
Originally Posted by Island Eddie View Post
Seeing all four tires react the same, I pretty much felt all was good and caused by ambient static temperature prior to use.

Now how much of an issue might one expect if they pump up in a freezing climate, then drive to 85 degrees in a few hours like in California?
I grew up at an elevation of almost exactly a mile high (supposedly my parents garage was exactly 5280'). We would leave the snow (sub 30 degree temps) and be down in the San Bernardino valley in 20 minutes where it could be 80 degrees. Like mentioned, this is all factored in when the tires were produced and engineered.
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Old 10-13-2022, 08:19 AM   #14
Gkri
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Originally Posted by JRTJH View Post
This is an updated version of the HF thermometer I use. It's got the standard HF 90 day warranty and costs about $25. https://www.harborfreight.com/121-in...ter-63985.html

Amazon has a similar version for $15 with a 1 year warranty. https://www.amazon.com/Thermometer-E...s%2C102&sr=8-5

If I were buying a new one today, I'd probably opt for saving the few bucks as well as the gas to drive to HF. IMO, Amazon wins another one...
Thanks John. We are Amazon Prime so shipping will be free. it will be on order today.
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