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Old 08-01-2019, 03:55 PM   #1
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Tire Pressure Increase

I've had a TPMS since my first (and only) blowout over 10 years ago on my previous FW. Our Excel 31IKE has the factory option 17.5" wheels with Goodyear tires, we also have MORryde IS. The recommended cold inflation pressure is 110psi. I check these with a hand held gauge too, it's pretty close to the TPMS pressure readings.

In hot weather I've had the indicated pressure on the TPMS increase to 131 or even 132psi. The TPMS alarms at +20psi so I've cut back my cold inflation a couple pounds but I wondered if any one had thoughts on +20 psi increase from cold TP.

The date code on the tires tells me I'm just past 5 years so I'll be replacing them pretty soon but I've seen these +20psi increases since they were new.
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Old 08-01-2019, 04:07 PM   #2
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Yes to the increase on pressure. Our tpms recommended between 20 and 30% above the normal for high alarm. I tried 20% and got alarms so I am at 25% for the high alarm now.

Depending on your weight compared to recommended inflation pressure and the tires you may not want to start lower as that causes overheating.
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Old 08-01-2019, 07:28 PM   #3
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Brad,
I just put some new tires on the truck and the trailer. I went with Continental on both. The Continentals were OEM on the truck and are a good tire though pricey. I got a great deal from the Continental BestDrive Tire store in Grand Prairie, TX.

I don't know where you got the recommended tire pressure from, but if it was from the VIN sticker by the pinbox, the tire cold inflation pressure may have been overstated. For my 2013 L36GKE, the VIN sticker stated the cold inflation pressure was 120 psi. According to the Michelin XTA load/inflation chart, 120 psi was the max cold inflation pressure for the tire as well as for an axle weight of 9,610#. My trailer has 7,500# axles. The recommended tire pressure for a 7,500# axle was between 85 - 90 psi. I put 90 psi in my XTA's and didn't have any problems with them. I talked to a couple of tire engineers from Continental and Michelin about the recommended tire pressure and they stated to follow the tire charts. They stated over-inflated tires are just as bad as under-inflated tires. Over-inflation can cause vibration damage to an RV as well as premature tire wear. The Michelin engineer asked me what I had the tires on. He asked me the trailer's axle weight and what the tire inflation pressure I was using, he stated that the 90# was "good".
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Old 08-02-2019, 12:57 PM   #4
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Brad, sounds normal but you may want to weigh your rig to get your axle weight. Then check the load inflation chart for the tires to see where it falls. Just stating the obvious but if you wind up lowering your cold inflation the hot weather running pressures will fall also.

We replaced the load range J Michelin's that came with ours a couple of years ago with a set of Hankook regional haul trailer tires in load range H. Still at max inflation of 125 psi each tire will carry 4805 pounds. That is 19,220 pounds for 4 and we weigh 13,300 on our axles. The inflation chart for our tires shows we could run the minimum 80 psi which would give 13,500 capacity. I started at 110 but felt the ride was a little solid, dropped to 100 and may drop to 90. Even at 90 I still would have 14,780 in load capacity.
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Old 08-10-2019, 09:21 PM   #5
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Tandem axle trailers are different from other RVs. When turning the tires undergo potentially significant sidewall loading as the tires twist. Tighter the turn the greater the sidewall stress. Most of the heat in a tire is generated in the sidewalls and this sidewall interplay can be significant.

Many people with tandem axles inflate the tire's max cold inflation value as shown on the sidewall. The RV's factory card can not count for different types tires owners use. In my experience tire inflation charts include numbers for single and dual tire applications, but do not have entires for tandem axle configurations with the sidewall interplay issue.

I run my tandems at the max cold inflation on the tire of 110 PSI. I check them with a quality digital pressure gauge early in the morning before the trailer is moved or the sun has been on the tires. I trust the digital gauge and make a mental note of the difference with the TPMS values. The TPMS is close but never right on. Typically I see the TPMS pressure values rise to about 120-124 PSI at 65mph and typical road conditions. I see sun angle, cross winds, etc all effect running pressure. I set the TPMS alarm at +20% or 132PSI. Never seen it sound off for high pressure. I live at 7,000 ft and sometimes will be camping at 10,000 ft. In the morning the air temperature may drop enough to cause enough of a pressure reduction to trigger the low pressure alarm. I don't adjust if all tires are down by a similar amount.
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Old 08-11-2019, 05:21 AM   #6
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The OP apparently is loaded very heavily

Dont lower psig due to the increased psig

As someone noted increase the alarm unless you want to replace the over heated tires sooner instead of later
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Old 08-11-2019, 03:28 PM   #7
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Thanks for all the great information in your replies. I'm glad to hear that the increase to 131 or 132 PSI from 110 cold inflation is not unusual at 20%. My TPMS default sets it's limit at +20 PSI not +20% so I'm going to adjust my limit a little higher and keep my cold inflation at the recommended 110 PSI. We are not loaded really heavy with the trailer weighing in at 15800# under the 17500# GVWR of our Excel. Our TPMS shows temperature too and I've never seen alarm level temp increase.
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Old 08-11-2019, 05:49 PM   #8
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I don't put very much importance on the temperature side of a TPMS monitor. If the sensor was inside the tire it might be useful. The sensor is on the end of the valve stem spinning in open air and only has a very small air exchange with the interior of the tire. So I do not believe its reading can be very useful. The tire's pressure increases with increased temperature so the pressure value provides some idea that the temperature is within reason.

Perhaps someone has information of comparing temperatures from an external sensor vs an internally mounted sensor. Even then the important temperature is the sidewall not on the wheel where many internal sensors are mounted.
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Old 08-21-2019, 01:23 PM   #9
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Quote:
Originally Posted by BRS50 View Post
I've had a TPMS since my first (and only) blowout over 10 years ago on my previous FW. Our Excel 31IKE has the factory option 17.5" wheels with Goodyear tires, we also have MORryde IS. The recommended cold inflation pressure is 110psi. I check these with a hand held gauge too, it's pretty close to the TPMS pressure readings.

In hot weather I've had the indicated pressure on the TPMS increase to 131 or even 132psi. The TPMS alarms at +20psi so I've cut back my cold inflation a couple pounds but I wondered if any one had thoughts on +20 psi increase from cold TP.

The date code on the tires tells me I'm just past 5 years so I'll be replacing them pretty soon but I've seen these +20psi increases since they were new.

If you have the correct cold inflation based on your measured "4 corner weights" then the problem is the High-Pressure setting of your TPMS.


I suggest you increase your High Pressure alarm level to 135 or so.
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