Tire Pressure

[mypopslou]

I had my coach weighed and determined I wanted to run my tires with 110 lbs all the way around. With temperature around 50 degrees TPMS shows I have 110 all the way around. This was in the afternoon of a cloudy day before I moved my coach. The next morning with the temperature in the 40's and sunny, I started my coach to take it to Cummins for annual state inspection and oil change. As the tires warmed up, averaged about 50 degrees the pressure in the tire on my TPMS showed 117 in 4 of the tires, 113 in one inside dual and 114 in the other inside dual. My question is this increase iin tire pressure normal and if so how high would it have to go before I should worry. Planning a trip to Florida tomorrow and wondering if I am good to go.

Tires are Michelin 295 x 80r x 22.5

Appreciate any help or thoughts on this issue.

[wildebill308]

Sounds normal. The tire engineers allow for the increase in preshure because of heating. Have a great trip.

Bill

[wolfe10]

Yup, pressure rise with temperature rise is taken into consideration by the tire engineers. 

All normal.

[kaypsmith]

Only way that I know for it not to change, is to fill with nitrogen, but you will need a fat pocket book when you leave home.

[wolfe10]

2 minutes ago, kaypsmith said:

Only way that I know for it not to change, is to fill with nitrogen, but you will need a fat pocket book when you leave home.

Sorry, that is a myth spread by those wanting to sell Nitrogen.

Nitrogen like all gases follow the Ideal Gas Law: PV=nRT.  When temperature rises, pressure WILL rise. Basic high school chemistry/physics.

Now, if one fills from one of those coin op with lots of water in it, THAT is a different matter.  Ya, water is NOT an ideal gas, so pressure goes up more than with DRY AIR or Nitrogen.  Said another way, very little difference in pressure change for a given temperature rise for either dry air or Nitrogen.

[wayne77590]

Earth's atmosphere is 78% nitrogen, 21% oxygen, 0.9% argon, and 0.03% carbon dioxide with very small percentages of other elements.

Must just be the other than nitrogen that is heating up.

As stated, the rise is normal and anticipated by the engineers.

Do not inflate to minimum temperature for your weight. Instead find a medium between minimum and maximum. Always check when tires are cold,  by 2 to 3 hours. When inflated between min and max it give a fudge factor so you don't have to keep inflating and deflating to maintain a safe pressure for your weight.

[mypopslou]

Thanks for all your help, I picked my coach up from Cummins and the temperature outside is now in the 60's and the side of the coach facing the sun is now reading 122 and the tire temperature was in the upper 70's. I need one more bit of information to ease my mind. The max pressure on the side of the wheels is 120 at what point/pressure reading on my TPMS should I consider lowering the air pressure in my tires.

[wolfe10]

24 minutes ago, Mypopslou said:

..... at what point/pressure reading on my TPMS should I consider lowering the air pressure in my tires.

You should NOT ever reduce PSI because of a rise caused by a rise in temperature.

Absolutely, the tire engineers understand physics.  All their recommendations including those on the sidewall of the tire are for COLD (read that as before driving).   They KNOW that PSI will rise with temperature rise due to rise in ambient temperature, sun exposure, friction with the road. ...........

[mypopslou]

Brett, OK thank you, at what pressure would it be considered unsafe?

[wolfe10]

Reasonable question.

I have forwarded it to a retired Tire Engineer on FMCA's Technical Advisory Committee for a reply-- past my pay grade.

Brett

[tireman9]

11 hours ago, Mypopslou said:

I had my coach weighed and determined I wanted to run my tires with 110 lbs all the way around. With temperature around 50 degrees TPMS shows I have 110 all the way around. This was in the afternoon of a cloudy day before I moved my coach. The next morning with the temperature in the 40's and sunny, I started my coach to take it to Cummins for annual state inspection and oil change. As the tires warmed up, averaged about 50 degrees the pressure in the tire on my TPMS showed 117 in 4 of the tires, 113 in one inside dual and 114 in the other inside dual. My question is this increase iin tire pressure normal and if so how high would it have to go before I should worry. Planning a trip to Florida tomorrow and wondering if I am good to go.

Tires are Michelin 295 x 80r x 22.5

Appreciate any help or thoughts on this issue.

First off I would not be concerned with the numbers you have. Tires normally change temperature pressure by about 2% for each change in temperature of 10F. The only pressure I am concerned with is the CIP or Cold Inflation Pressure. If you have that correct for your load the increase can easily be tolerated by your tires.

You can see the Science for the pressure change in my blog. I covered the temperature effect in three posts HERE.

Gotta run the DW just called me to dinner. Will post a bit more in about an hour.

Edited May 1, 2018 by tireman9
change "temperature" to "pressure"

[tireman9]

3 hours ago, Mypopslou said:

Thanks for all your help, I picked my coach up from Cummins and the temperature outside is now in the 60's and the side of the coach facing the sun is now reading 122 and the tire temperature was in the upper 70's. I need one more bit of information to ease my mind. The max pressure on the side of the wheels is 120 at what point/pressure reading on my TPMS should I consider lowering the air pressure in my tires.

NO 

Wheel pressure is CIP Not the hot pressure. Basically, the 120 would match up with the tires that would be applied to the Rv using those wheels. Might be a couple different sizes but in each case, the tire is rated for its max load  AT 120psi. Wheels like tires are designed to tolerate normal pressure increase.

Side comment on your TPM readings. I recently did an evaluation of TPM pressure accuracy. Results HERE.

TPMS are designed to warn of pressure drop.    If you did a test with your system and could let out an identical amount of air I bet you would find that all 6 of your sensors would give a warning when they lost the same number of pounds (+/- 1 or 2 psi)

 

Bottom line. All this variation might be "Measurable" but the differences in the numbers are not really "Meaningful" You can get a better understanding of these two terms HERE.

 

Hope I was able to answer your questions.  I may not always be available for quick answers but I bet that just about all the questions folks might have on tires in RV use have been covered in my blog which is available 24/7

[mypopslou]

Thank you for this information, in traveling last night my TPMS registered up to 130 PSI with the tire temperature in the low 70's. I have not checked them today yet ans we are getting a late start. However we are heading to Florida where the temperatures will be higher than the 60's we have experienced so far. What should I do?

[wildebill308]

1 hour ago, Mypopslou said:

However we are heading to Florida where the temperatures will be higher than the 60's we have experienced so far. What should I do?

Drive to Florida, get set up, drink a cold beverage and don't sweat it. If you want to be obsessive check your CIP while there. 

Your tires have been doing this all along you just became aware of it. Did you know your Jeep tires do the same thing?

Bill

[mypopslou]

Thanks to everyone for your help and suggestions, we arrived in Florida with the TPMS showing pressure as high as 135 but coach ran fine and we had no issues. I have decided that I do not believe my TPMS anymore and will only use it for alarms for fast loss of pressure or overheating. It has never had readings like this before so maybe the cold winter we had in Pa damaged it in some way.

We are here and it is nice, thanks again for your help and suggestions...time or a strong cold beverage

[wolfe10]

Yes, probably worth checking against a good/calibrated tire gauge.

[mypopslou]

Brett, good suggestion and that is my plan. My daughters boyfriend is a mechanic and I bought a gauge from him that I attached to my air compression and clips onto valve stem to fill tires and it is guaranteed to be accurate within .002 of a pound. I will use it before we head back so I don't have to worry the entire time back

[hermanmullins]

Hay Pops, is there a part number?

Herman

[manholt]

Pops.

From my experience, prior to the invention off TPMS & remote monitors, we had no concern!  TPMS to me, is another warning tool, if I have a sudden air loss in a tire, I can get off the road and stop the coach, before I have structural damage!  How hot is too hot?  IMHO I'm not Paranoiac enough to care.  Don't over react to the exact science, leave that to the Racing Pros!

Enjoy your travels, don't forget that an air gauge, like a leveler, is only as good as the last time it was calibrated.... 

[richard5933]

I think having a warning for low air pressure is a good thing. But, am I the only one who thinks that some of the TPMS simply provide too much information?
 

I check pressure in the morning before driving. If necessary, I add air using a Milton inflation gauge. I never check pressure when tires are hot since there's little use. The tire shop told me that the engineers figure the higher pressure encountered during operation when they set the inflation charts. I do, however, use a heat gun to check that the hubs/brakes/etc. are heating equally and that I don't have a problem (like a dragging brake or frozen bearing.)

 

[manholt]

Richard.

Yes, TMI can be and normally is, a bad thing!  Also got a heat gun for your reason & it does double duty at the Grill...

[mypopslou]

Herman, the gauge that I bought from my daughters boyfriend is made by Matco Tools, DT4B 3.5 digital Tire Inflator with hose, and I was wrong it is accurate to 0.1PSI, which is what it says on the box, however inside the box I have a Accuracy Certificate which says at Air Pressure 0-58 accuracy is +/- 1.2 psi and Air Pressure 59-174 psi accuracy is +/- 2.0.

He used this at his shop and after struggling with cheap gauges and compressors I decided it was worth the money to get something that filled my tires quickly and accurately. I am totally pleased with this purchase and would recommend it to anyone

[hermanmullins]

Thanks, I will look into one.

Herman

[wolfe10]

A quick look for that gauge did not show it as a dual foot gauge.  Assume you added that for checking rear duals.

[jleamont]

I have one of these that sits in the pocket next to the drivers seat. Before EEZTire TPMS I used it often, I took the batteries out of it now.