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 > Max Pressure Cold vs Hot Pressures - How Much Is Too Much

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Rollochrome

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Posted: 11/18/21 11:46am Link  |  Quote  |  Print  |  Notify Moderator

way2roll wrote:

Curious why you are setting to max. Your FW should have a recommended psi .


It does. It came with F rated tires that had a max psi of 100

I replaced them with G rated tires that have a max psi of 110 so I went with the tires max psi rather than what the trailer sticker specified based on the factory equipped tires


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Cummins12V98

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Posted: 11/18/21 02:02pm Link  |  Quote  |  Print  |  Notify Moderator

Rollochrome wrote:

Cummins12V98 wrote:

You are well under temps that would be of concern.

Does your axle weights require the MAX of 110# ?


gawr 7,000 LB each axle

gvwr 15,500


You need to know your actual loaded axle weights. One you do compare to the load/inflation chart specifically for your tire size and load range.

I am betting you are running too much air.


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Crespro

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Posted: 11/18/21 02:59pm Link  |  Quote  |  Print  |  Notify Moderator

I run 108 PSI cold (usually about 65 degrees in CA) and 120 to 124 PSI warm. Temp increases by about 16 to 20 degrees over ambient. In three decades of DPs, most inflate about 5 to 8 PSI over the recommended. i think trailers should be at or close to the max rating.


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Michelle.S

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Posted: 11/18/21 03:09pm Link  |  Quote  |  Print  |  Notify Moderator

I know I read it on one of the Tire MFR's sites, but don't remember which, but what I remember was trying to set the tire pressure at an ambient temp of 70 degrees. When temps are in the mid 50s the pressure will be approx 10 to 15 Lbs below the set pressure, but within a few miles rolling down the road they will be at the set temp and continue rising as the continue heating up.


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CapriRacer

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Posted: 11/19/21 05:49am Link  |  Quote  |  Print  |  Notify Moderator

Rollochrome wrote:

My Carlisle CSL 16's have a cold max pressure of 110.

I installed a TPMS the same day I bought them.

I read up on these tires and there was nothing about a hot max pressure from Carlisle. I contacted Carlisle and they said there was no "hot max" specified.

So on the maiden voyage with them, I watched the temps rise and rise above 110 to just under 120.

The tires on the sunny side were uniformly higher than the ones in the shade side understandably too.

I read elsewhere that a different manufacturer emphatically states on their website regarding trailer tires to NEVER bleed down HOT tires.

So it begs the question, how much hot pressure is too much? The TPMS system instructs to set alert levels that are pretty high.

What do you think is an acceptable pressure level hot relative to the cold max?


First, the burst pressure of tires is many times the max pressure listed on the sidewall. In this case we are talking over 300 psi! Yes, you read that right! (Be aware that a road hazard is NOT bursting the tire! It is damaging it! So that can occur at ANY pressure!)

Second, Rule of Thumb is that the increase in pressure from cold to hot shouldn't be over 10% (excluding ambient temperature effects.) In this case a 110 psi tire shouldn't exceed 121 psi (excluding ambient temperature effects!)

If you exceed 10%, then you need to do something about increasing the load carrying capacity of the tire = more pressure, larger tire, slowing down! If you exceed 15%, you need to do this IMMEDIATELY as that tire is going to fail fairly soon!

Ambient Temperature Effects = 2% increase for every 10°F increase in ambient temperature. So a 110 psi tire set in the morning when it is 50°F, in the afternoon at 90°F will be at 115 psi, just due to the outside temperature.

Michelle.S wrote:

I know I read it on one of the Tire MFR's sites, but don't remember which, but what I remember was trying to set the tire pressure at an ambient temp of 70 degrees. When temps are in the mid 50s the pressure will be approx 10 to 15 Lbs below the set pressure, but within a few miles rolling down the road they will be at the set temp and continue rising as the continue heating up.


No!! That is wrong! You set the pressures to the ambient conditions, whatever they happen to be. The only exception to this is in winter where the ambient temperature is going to be LOWER than when you set it, and you use the "2% for every 10°F" rule while estimating how cold it is going to get.

*****************************************

An important thing to remember is that UNDERINFLATION is bad, where over inflation only causes minor issues! In other words, pay attention that you have ENOUGH pressure in your tires, but don't be paranoid about having too much.


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way2roll

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Posted: 11/19/21 06:56am Link  |  Quote  |  Print  |  Notify Moderator

"An important thing to remember is that UNDERINFLATION is bad, where over inflation only causes minor issues! In other words, pay attention that you have ENOUGH pressure in your tires, but don't be paranoid about having too much."

I think this is so/so advice for trailer tires, but over inflation can affect traction, ride quality, and stability. A FW or TT with a limited contact patch can get squirrely, skid while breaking, bounce out of control etc. Over inflation on a MH or PV could be very dangerous.

The proper way to set tire PSI is to follow the tire manufacturers instructions. Weigh the rig loaded for travel and set the PSI accordingly. While I agree that when in doubt set to max, it still isn't the proper or safest way to set PSI.

The max on the sidewall of my FW tires is significantly higher than what the recommended psi is loaded for travel.


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Posted: 11/19/21 07:10am Link  |  Quote  |  Print  |  Notify Moderator

For decades I set cold tire pressure at 110% of max sidewall pressure. Just like flipping a switch, that 10% change stopped throwing caps. I believe that it was because of less heat buildup, but have no way to prove it.

fj12ryder

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Posted: 11/19/21 07:28am Link  |  Quote  |  Print  |  Notify Moderator

Why pay any attention to the sidewall pressure at all, when you arbitrarily decide to determine your own max pressure? MAX means MAXIMUM, not a suggestion by some guy named Max.


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Michelle.S

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Posted: 11/19/21 07:56am Link  |  Quote  |  Print  |  Notify Moderator

I have to disagree with the 10% increase when running. I'm running 17.5" "H" tires at 125 PSI and see normal temps running at 65 of 140 to 150 depending on ambient temps. So that's closer to 20% increase. Currently running Sailun which replaced my GY G114s after one exploded. And the GYs ran the same temps as the Sailuns.

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Posted: 11/19/21 08:20am Link  |  Quote  |  Print  |  Notify Moderator

fj12ryder wrote:

Why pay any attention to the sidewall pressure at all, when you arbitrarily decide to determine your own max pressure? MAX means MAXIMUM, not a suggestion by some guy named Max.


Throw caps off about half your tires before tread wears out. Buy new tires, the failure rate does not change, would you think about a solution to the problem?
Out of the next 3 sets of new drive tires I bought (24 tires) I had 5 carcasses that could not be recapped the 3rd time because of road hazard. No tires failed by dropping a alligator on the highway.
I'm not telling anybody they should air their RV tires that tight. Sometimes to make production, I had to run hard. Much more often, I had to run fat. What I am saying that it is much safer to run 10% over than 10% under.

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