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Old 09-26-2020, 08:15 PM   #1
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Tire Pressure and Ambient Temperature

Tire pressure is affected by temperature, whether ambient or by heat generated from rolling down the road.

How do you adjust/compensate as the outside temperature changes? This time of year in particular depending on where you are, the temps could be in the 40s in the morning and in the 70s or 80s in the afternoon. That's a pretty big swing! If I inflate all my tires to the PSI I like to roll with in the afternoon, when I start out in the morning the PSI is much, much lower because it is cold or cool. Also as the season heats up or cools down the tire pressure changes, so do you adjust your pressure?

Just wondering what folks do to deal with this or should I worry about it?

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Old 09-26-2020, 08:50 PM   #2
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Baseline "cold" tire pressure is generally considered to be 68F. Pressure increases or decreases approximately 2% for every 10 degrees of temperature so if the ambient temperature in the morning when you check your tires is 40F and you want to be more precise you could adjust your cold pressure downward by about 6%. That assumes you know that it's going to warm up significantly during the day.

That said, it can get pretty complicated trying to juggle the effects of ambient temperature in the morning, temps while you're on the road in the heat of the day, changing weather conditions, as well as altitude. I usually make minor tweaks in my cold pressure based on the temp when I inflate the tires and my best guess for later conditions and then keep an eye on the TPMS readout for the trailer while I'm travelling. If things get too far out of whack I can make an adjustment, but usually I don't find it necessary to make changes. In general, I think with a TT it's better to have tire pressure set a little high than to be underinflated.
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Old 09-27-2020, 08:46 AM   #3
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A good buddy of mine has spent his entire career selling tires & services to the trucking and hauling industries. Based on his advice, I set my pressures based on the starting conditions in the morning and don't worry about what happens to pressure as temperature may rise. The 2 or 3 PSI that may change pales in comparison to the 20-30 PSI when they're in motion.

You've asked a good question, but there is nothing to get excited about here.
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Old 09-27-2020, 09:34 AM   #4
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Quote:
Originally Posted by stevejones View Post
Tire pressure is affected by temperature, whether ambient or by heat generated from rolling down the road.

How do you adjust/compensate as the outside temperature changes?
I don't.
The highest temp I've seen on the TST was a 95 degree day and I stopped for gas and the driver's side tires were in the Sun. It went to 110 deg. As I drove, it went back down. No ill effects.
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Old 09-27-2020, 09:47 AM   #5
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I use the 2% per 10 degrees method and set them for the mean expected while driving ambient. But it is correct that the practical difference in safety and handling is not a great amount.

Keep in mind the temperatures recorded by the monitoring systems does not accurately reflect tire ply temperatures. A typical tire will gain about 6-10% pressure or 30-50 degrees over ambient at highway speeds. So you can figure at 90 ambient the tires will have an internal temperature of 120-140 degrees when properly inflated.
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Old 09-27-2020, 10:15 AM   #6
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Do not worry about trying to adjust for temp variation. Tire manufactures and there engineers have designed our tires to work fine with no adjusting for temp. They wont explode or melt as the day gets hotter. The biggest concern for me before we leave is starting the trip with the pressure at the max cold sidewall pressure 80 PSI in my case. This keeps the tires cooler than at a lower pressure and helps mitigate sidewall shear on tandem axles. Some folks will argue and say it is too stiff and bouncy. That's there choice. I like my E rated tires. Regardless of your tires rating "D" or "E" I would start with the max sidewall pressure and roll on down the road. My $0.02

By the way there are two Tire engineers here on the forum. Tireguy9 and Capri racer. Find there blogs and get some real advise.

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Old 09-27-2020, 10:33 AM   #7
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I don't compensate? TP is set COLD👍


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Old 09-28-2020, 06:21 AM   #8
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Yup, "cold" pressures are defined by the ambient temperature - and as the ambient temperature changes, so should the pressure - about 3% per 10F.

So if you start the morning at 40F and you set your tire pressure at 60 psi, by the midafternoon when it is 70F, your "cold" pressure would be 9% higher = 65F. If you are measuring the pressure when the tire is still in service, then the pressure buildup is on top of that - and that buildup shouldn't exceed 10% (In our example: ~72 psi)

And, Yes!, the max pressure on the sidewall is "cold", but the burst pressure is several times that value, so it is OK to exceed that value when the tire is operating!
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Old 09-28-2020, 12:04 PM   #9
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A question I hope someone can shed light on. I monitor my tire pressure closely and use TPMS on both my truck and trailer. Last year Ideparted in the morning with TT rears set at 80 psi per GM recommendation. During day air temperature rose significantly and I went from 3000 ft to over 10,000 ft. Pressure rose to 94 psi. I run Michelin truck tires on everything. I was uncomfortable with 94 and lowered them to 90. What would you have done? Recommendations welcome.
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Old 09-28-2020, 02:46 PM   #10
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I was uncomfortable with 94 and lowered them to 90. What would you have done?
If it were my choice on my trailer.

Nothing

Assuming the tires were set correctly before the vehicle was moved. It is that type of action that could lead to over loading the tires.
The tire pressure will increase when on the road.
The tire pressure will increase as ambient temp increases.
Decreasing inflation pressures on hot tires reduces the tires load capacity.

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Old 09-28-2020, 04:04 PM   #11
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A question I hope someone can shed light on. I monitor my tire pressure closely and use TPMS on both my truck and trailer. Last year Ideparted in the morning with TT rears set at 80 psi per GM recommendation. During day air temperature rose significantly and I went from 3000 ft to over 10,000 ft. Pressure rose to 94 psi. I run Michelin truck tires on everything. I was uncomfortable with 94 and lowered them to 90. What would you have done? Recommendations welcome.
First off, as Capri Racer indicated tire burst pressure is quite high. Tires fail from being overheated, generally not from being over pressured, so don't sweat it from a safety standpoint. Traction performance is a different matter and here you did the right thing. The rise from 80 to 94 psi indicates the tire internal temperature rose by nearly 90 degrees. You did not say how much of that was ambient. If your system is not overloaded tire flex should account for 30-50 of that and no more. So if ambient rose by 40 degrees then releasing 4 psi was a good choice.

Edit: A bit more on tire pressure and traction. If you are pulling a trailer near the tow vehicle limit, you will want the trailer tires near the pressure required to manage the actual load. 15% over minimum for load is a good choice. This way the trailer will slip wide a bit and reduce force on the tow vehicle rear axle in an emergency.

You want the rear tow vehicle axle 5-7 lbs over recommended to increase cornering but not so much the footprint is compromised. You want the front 2-3 psi under so the front will also slip wide and reduce oversteer and jackknife.
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Old 09-28-2020, 08:35 PM   #12
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My mistake, tires at 80 were on the rear of tow vehicle, not trailer. Run trailer at 55. My knowledge level is zero about the impact of reducing pressure on hot tires. That is why I asked. I was just uncomfortable with that large of an increase. The tow vehicle had significant unused payload. It had about 2800 lb of payload, that includes tongue weight. It was rated for a bit over 3800.
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