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  1. #1
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    Tire pressure at 144psi

    Wondering if this is ok for Cooper RM170 tires to get to 144psi. I fill them cold to the stated pressure on the placard of 125psi. The spec sheet for these tires states max pressure of 125psi. I assume that's cold tho.

    Traveling through the southwest with ambient temps over 100.

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    2020 Ford F-350 Tremor - upgraded with Air Lift 5K bags & S&B 60 gallon tank
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  2. #2
    Seasoned Camper Tgunter5's Avatar
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    Seems like a rather large increase for such a low temperature. I recently installed a factory TMPS and cold pressure is 65 PSI, while traveling they increased to 71 PSI and the temp was up to 135 degrees F. Sorry I can't give any more guidance.
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    Rolling Along OurNewEra's Avatar
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    Quote Originally Posted by steve95628 View Post
    Wondering if this is ok for Cooper RM170 tires to get to 144psi. I fill them cold to the stated pressure on the placard of 125psi. The spec sheet for these tires states max pressure of 125psi. I assume that's cold tho.

    Traveling through the southwest with ambient temps over 100.
    I have tires with max cold pressure of 80 PSI. I see them go up to about 89-91 psi with internal tire temps in the low 100's. This with ambient at about 90 deg. Of course this will vary as ambient temperature varies.

    Here is a web link to an article by Roger Marble.

    https://www.rvtravel.com/rver-concer...sure-increase/

    His Tire Safety site states that ". . . tire pressure will change about 2% for every 10 deg F change in temperature." So basic math says that the higher your cold PSI then your 2% will be a higher number than what I get on a lower cold PSI tire.

    The 'Tire Safety' site has been posted in many other threads on tires and provides very good information. IMHO.

    Of course this all depends on road conditions, trailer weight, and speed. If your trailer is overloaded it would cause an increase in internal tire temperature which would drive up your hot PSI. I do agree with @Tgunter5 that your internal temperature does seem low for the increase in tire pressure.
    Mike & Lisa
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    Quote Originally Posted by steve95628 View Post
    Wondering if this is ok for Cooper RM170 tires to get to 144psi. I fill them cold to the stated pressure on the placard of 125psi. The spec sheet for these tires states max pressure of 125psi. I assume that's cold tho.

    Traveling through the southwest with ambient temps over 100.

    Click image for larger version. 

Name:	Screenshot_20210617-102239.jpg 
Views:	72 
Size:	94.0 KB 
ID:	34997
    What was the air temperature when you last adjusted pressure?
    John & Kathy
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  5. #5
    Setting Up Camp
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    About 70 degrees. The increases make sense, just wondering if that high a pressure is safe.
    2020 Ford F-350 Tremor - upgraded with Air Lift 5K bags & S&B 60 gallon tank
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  6. #6
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    I'm also running Cooper LTs with a max cold pressure of 80psi. I assume the manufacturers allow for expansion
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    Rolling Along OurNewEra's Avatar
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    Quote Originally Posted by steve95628 View Post
    About 70 degrees. The increases make sense, just wondering if that high a pressure is safe.
    Out of curiosity I did the math using the 2% of PSI for every 10 deg F. Using 125 psi at 70 degrees as the starting point, the tire pressure at 120 degrees calculates to 138 psi
    Mike & Lisa
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    Site Sponsor Cannon07's Avatar
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    My G rated start out at 110psi. Most of the time they hit 127, 128. I have seen the hit 130 to 132 on a day when it's in the 90's.
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  9. #9
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    My G-rated Sailuns go from 110 to 120-ish psi and temp from 70F to 105F. This increase to 144 seems with the 125psi tires seems reasonable.
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  10. #10
    Big Traveler geotex1's Avatar
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    Take the cited Marble guide with a grain of salt. His experience is not with heavy carcass tires ala commercial tires or these new ultra-high load range tires. That said, tire inflation pressures are always "cold". Around a 20 psi rise is within expectation, but also note that unless your TPMS sensor is inside the wheel its temperature is inaccurate. Finally, your best advice is advice right from the tire manufacturer, and a phone call should be able to net you good answers and a load-inflation table to boot.
    Rob & Nikki + Cloverfield
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