Tire pressure and heat

[Jfs999]

Just trying to get some clarification on tire pressure and the affect heat has on them. I currently have an EEZE TPMS and have the current pressures set at 100 in the front and 95 on the rear duals. The high pressure alarm is set at 20 lbs above for each. Coming home from Florida Easter Sunday the outside air temperature started out in low 60's when I departed at 7am with all tire pressures being set to spec. By late afternoon (and being stuck on I95) the outside air temperature on the road had risen to over 90 and the high pressure alarm started going off on one of the rear tires (meaning that pressure had risen up over 115 lbs) and all of the tires were right at the high pressure alert level. The high temperature alarm was not going off and the temperature for all tires was not much over the ambient air temperature. After seeing all the tires with same pressure and temperature - I finally just turned off the monitor Is it normal for tire pressure to increase that much? Do I need to change the high temperature setting or did I just totally miss the boat and was lucky not to have a blow out?

[slickest1]

Temperature rise in tires on a hot day is pretty normal. If you have one that shows way higher than the others then you probably have a low tire. The lower the pressure the more heat it will build.

[Crasher]

If you start the day with a cold pressure at or above the recommended pressure for the load each tire is carrying, you do not need to be concerned about a psi increase of 25-30% or more. My fronts usually go from 115* up to 138-142*. A Michelin tech told me that the cold pressure is the important one. The tires are designed to work with the pressure increase due to OAT and speed. Just set the high pressure alarm 30-35% above the recommended pressure for the tires.

[Dutch Star Don]

You're good.....I would adjust your temp range a little higher.

[TonyDi]

Tire failure can occur between 180 and 220 degrees. My TST set point of the alarm for high temperature is 158 degrees that is their (TST) recommended limit. They feel it gives you enough advance warning to take steps.

[Mr_D]

Originally Posted by TonyDi

Tire failure can occur between 180 and 220 degrees. My TST set point of the alarm for high temperature is 158 degrees that is their (TST) recommended limit. They feel it gives you enough advance warning to take steps.

The TST sensors are usually on the valve stems and don't give a true indication of tire temps.
My SmarTire sensors are interior and they are set for 197°.

[Crasher]

As Mr D said, do not put much faith in the accuracy of the temp reading of the sensors rolling down the road. They will always be tempered by the OAT. Only after sitting in the shade for several minutes will you get a more accurate number. The pressure is a more accurate measure of the tires condition.

[vettenuts]

I set my high pressure value a bit higher for this reason. I left the low value per recommendation since that is of bigger concern.

[jadatis]

Temperature reading of TMPS sensor is pretty accurate, I think, but when screwed on the outside its not the temperature of the inner tire air, so you can trust it less then pressure reading.

Pressure reading of TMPS sensor can be accurate, but depends on the quality of the sensors . If you have TMPS sensors for normal car use they go above their acurate border and give even lower pressure then realy is.
This then already happens at above 60 psi, below that they mostly give a bit to high pressure, wich is never a problem for savety.

Will give a picture of pressure for temperature I made with an Excell spreadsheet, so can make other ranges if wanted.
Then you can compare with your readings and the 158 degrees ( Fahrenheit) someone mentioned to be maximum what the tire inside air is allowed.

Hope it will help you to determine the importance of your alarm settings ( to my opinion not that important).
Its not the temperature of the inner tire air that is important , but the temp of the hottest part of the rubber of tire . They are related, but not in every situation.
If for instance the tire inside gets hot because of the heat of the brakes , transported trough the rimms to the tire inside air, then the pressure rises and with that lesser deflection so lesser heatproduction, so rubber can still stay below a critical temperature , at wich it begins to harden .

[Betr2Trvl]

I don't necessarily worry about the actual temp readouts on my TST TPMS (alarm is set at the default for temp), but watch to ensure that the temps are relatively the consistant on the coach and the toad.

And while the coach tire and toad tire temps are not the same, they do maintain a relatively constant deviation that is not that significantly different. If something would start to look out of whack, either on the RV, the toad, or between toad and RV temps, it's time to stop and see what is going on.

We keep our readout on the dash in front of the passenger seat, so it's something that we actively watch and discuss as we drive.

And the reality is, that while driving we also watch for significant deviations of "hot" front pressures, rear pressures, and toad pressures. If an alarm triggers on either pressures or temp, it's kind of late........ Think about it, my alarm for cold pressure is about 5#s below my "normal" cold pressures, given pressure gain while driving, if the pressure gets anywhere near our cold pressures while we are traveling, we have a problem and hopefully we can spot it before we get to a "critical" alarm setting so we can safely deal with it in a more proactive manner.

And when we start out a day of travel, we pay very close attention to pressures and temps to ensure we see the expected gains as we drive, with particular attention to toad temps in this case which I would expect to show very quickly if we would happen to forget to release the parking brake and are dragging a tire..... .

Regards

[mdvs]

My rear wheels have been at 95lbs per the MH decal. The tire max pressure (cold) is 120lbs. The tires have been run at those values (cold) for over 8 years. I just replaced the tires yesterday and the tire place told me that the min pressure I should have them at is 100. They said that running at a pressure that is greater than 20% below the max cold pressure will cause early side wall damage and void the tire warranty. 20% below the max is actually 96 lbs. I have had the MH for 2 years and never had it weighed. I'm going to have that done next week. Anyone else run their rear duels at 95 cold?

[96 Wideglide]

I run my drive axle tires at 85 psi. Tag axle tires at 80! All recommended by the chassis manufacturer! These are tires that have a max 120 psi.

[Mr_D]

Originally Posted by mdvs

My rear wheels have been at 95lbs per the MH decal. The tire max pressure (cold) is 120lbs. The tires have been run at those values (cold) for over 8 years. I just replaced the tires yesterday and the tire place told me that the min pressure I should have them at is 100. They said that running at a pressure that is greater than 20% below the max cold pressure will cause early side wall damage and void the tire warranty. 20% below the max is actually 96 lbs. I have had the MH for 2 years and never had it weighed. I'm going to have that done next week. Anyone else run their rear duels at 95 cold?

The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire.

From the Michelin RV Tire Guide:

"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."

From page 6 of the GoodYear RV Tire and Care Guide:

"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."

Inflation Pressure Safety Margin
Toyo Tire does not recommend an “inflate-to-the-load” policy for RV tires. Tires that are inflated to accommodate the vehicle’s actual loads do not have any inflation safety margin. Consequently, even a minor loss of air pressure will cause the tires to be under-inflated and overloaded. Toyo Tire’s policy is to observe (as a minimum) the tire pressure established by the vehicle manufacturer as indicated on the tire information placard. There are multiple reasons why a safety margin
(by inflation) makes sense:
• All tires lose about 1-1.5 PSI per month due to natural permeation of the tire’s internal air pressure through the tire’s rubber membrane.
• In the event of slow air leaks from punctures, an inflation “reserve” may allow detection and repair of the leak prior to reaching a dangerously low inflation level.
• A safety margin is prudent for users who are apathetic regarding tire inflation maintenance.
[/QUOTE]
But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:

The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.

[mdvs]

Mr. D. Great information.
I forgot to mention that the tires had 40K miles on them and looked great due to covering and proper maintenance. I use a TPMS but like the idea of putting an extra 5lbs as a buffer margin. I still plan on weighing the coach to better understand the weight distribution.