Tire pressure increase

[TXiceman]

I put Goodyear G614 LT235/85R16 tires on the trailer last year.  HitchHiker Champagne 38RLRSB (3 axles)  and we are loaded to a bit over 19,000 lb on the road with 14,700 lb on the axles.  I had Escapees Smart Weigh and all is good on the tire loads.  We start out with 110 PSIG on a 75 degF morning.  After being on the road a couple of hours, the tire pressure is approaching 130 PSIG, especially the side that the sun is on.

When we found the trailer in Chanute, it had load range E Chinese tires and we immediately changed them to Hankook load range G tires.  The Hankook tires would increase 10 to 15 PSIG for the most part starting out at 105 PSIG.

Has anyone else seen such a large increase in tire pressures while on the road?  I have checked tire and hub temperatures and see nothing out of the ordinary.

Ken
 

[remoandiris]

3 hours ago, TXiceman said:

Has anyone else seen such a large increase in tire pressures while on the road? 

Yes.  My coach has 2 stickers, each with a different PSI ratings;  one says 115 and the other says 125.  So, I split the difference and run 120 in my Saliun tires.  I also ran 120 in the OEM tires.  I do not remember the make.

The TST sensors have read over 140 on some days.  I have yet to find a reliable source that says those pressures are too high.  As long as all 4 tires are similar pressure, I call it good.  If one was a lot higher than the rest, I would worry about a problem.

[Chad Heiser]

2 hours ago, remoandiris said:

Yes.  My coach has 2 stickers, each with a different PSI ratings;  one says 115 and the other says 125.  So, I split the difference and run 120 in my Saliun tires.  I also ran 120 in the OEM tires.  I do not remember the make.

The TST sensors have read over 140 on some days.  I have yet to find a reliable source that says those pressures are too high.  As long as all 4 tires are similar pressure, I call it good.  If one was a lot higher than the rest, I would worry about a problem.

Very similar results with the tires on my 5er.

[lockmup68]

That is why it says COLD MAX PRESSURE on the tires. Heat increases the pressure. If you want to keep static tire pressures, you have to fill with nitrogen, but the minute you add air, the pressures will fluxuate with temperature. So then you have to haula nitrogen tank around with you.

 

[durangodon]

All gases expand at the same rate when subjected to heat.  Nitrogen does also.  Here's a website with some helpful information.  https://powertank.com/pages/nitrogen-truths-and-myths

Excerpt:

Nitrogen doesn't expand with heat like air because it is drier.  Your tire pressure stays more constant through tire temperature changes.

Here's a claim that we've heard more times than we'd like to admit. Bottled nitrogen is dry, drier than typical air, and it is said that a drier gas will exhibit less pressure change to temperature changes. This would mean that as my nitrogen filled tires heat up, the pressure will not go up as much as if they were filled with air. The dryness of CO2 is also put into question since it is a "liquid" gas under pressure. CO2 vapor is very dry. Don't forget that nitrogen is also a liquid gas under certain pressure and temperature. The truth is, the differences in thermal expansion values (TEV) between nitrogen, air, and CO2 at automotive tire pressures is virtually undetectable to a driver. In our own tests we compared the pressure changes of nitrogen, air, and CO2 through a wide temperature range and found that they all expanded (increased in pressure) at virtually the same rate (see Gas Test below).

 

[Ray,IN]

7 hours ago, durangodon said:

All gases expand at the same rate when subjected to heat.  Nitrogen does also.  Here's a website with some helpful information.  https://powertank.com/pages/nitrogen-truths-and-myths

Excerpt:

Nitrogen doesn't expand with heat like air because it is drier.  Your tire pressure stays more constant through tire temperature changes.

Here's a claim that we've heard more times than we'd like to admit. Bottled nitrogen is dry, drier than typical air, and it is said that a drier gas will exhibit less pressure change to temperature changes. This would mean that as my nitrogen filled tires heat up, the pressure will not go up as much as if they were filled with air. The dryness of CO2 is also put into question since it is a "liquid" gas under pressure. CO2 vapor is very dry. Don't forget that nitrogen is also a liquid gas under certain pressure and temperature. The truth is, the differences in thermal expansion values (TEV) between nitrogen, air, and CO2 at automotive tire pressures is virtually undetectable to a driver. In our own tests we compared the pressure changes of nitrogen, air, and CO2 through a wide temperature range and found that they all expanded (increased in pressure) at virtually the same rate (see Gas Test below).

 

Exactly! The only thing that causes wide temperature changes is water/moisture turning to a vapor when heated.That expansion rate is vastly different. https://inspectapedia.com/plumbing/Hot_Water_Expansion.php

[griffinmike]

If it bothers you why dont you check  with the tire dealer/manufacturer and find out what the increase should be instead of stirring up the tire expert wannabes>

[chief916]

On 8/29/2020 at 6:22 PM, Chad Heiser said:

Very similar results with the tires on my 5er.

Same same....Sailen 637's across the USA and back....110 psi and carrying a smart car in the garage.

 

[remoandiris]

Meh.  Regular air is nearly 80% nitrogen already, so...

[TXiceman]

5 hours ago, griffinmike said:

If it bothers you why dont you check  with the tire dealer/manufacturer and find out what the increase should be instead of stirring up the tire expert wannabes>

I called Goodyear and they were useless.  They did not have a clue.

The nitrogen gimmick is exactly that...a gimmick unless you are running a race car or an airplane.  air is 78% nitrogen. and 21% oxygen.  The remainder is water vapor (which is hydrogen and oxygen) and a mixture of other gases.  The amount of water vapor normally introduced into a tire is minimal and will have a very small effect of pressure as temperature increases.

[bobsallyh]

TXiceman, you are 100% correct. Race cars and airplanes!

[RoamingRanger]

I agree largely with the sentiment regarding using Nitrogen as opposed to air but something else to consider is that Nitrogen from a tank will be "dry" compared to air from a compressor without a properly functioning dryer which would be filling your tires with moist air. I've never really given it much thought but perhaps this is the main benefit of N2. 

[rickeieio]

The amount of moisture in a tire filled with regular air, even in a humid climate, is insignificant.  And the expansion of said moisture doesn't become a problem until you reach boiling point, but the tire has likely failed long before that.

A racing friend told me that the whole nitrogen thing started because race haulers used nitrogen bottles to run air tools and anywhere else compressed air was needed.  It was easier to store on the hauler truck than a compressor.  Of course the mind games of racer types took over and a myth was born.

I have well over 100 tires on this place and have yet to find moisture in one when changing,  And yes, I change my own tires, even the 7' tall tractor tires.

[bobsallyh]

The reason we used nitrogen in race tires on the circuit where I worked the tires was to keep the tires from "growing" and to keep the psi build up down. Crew chiefs wanted to keep the "stagger" as close as possible from the start unless something else dictated a pressure change. A quick example, a right front tire could measure 93 1/2 inches around. You wanted to keep it from getting bigger round and upsetting the chassis. Goodyear would put air in them when they mounted the tires, we would bring them back to the garage stall or pit, remove the Schrader valve to let the air that Goodyear put in and refill with nitrogen. With brake rotors getting extreme high temperatures at certain tracks and just the "planting" of putting the right front tire into a turn is why the nitrogen. Do I use nitrogen in our rigs tires, heck no.

Edited September 8, 2020 by bobsallyh

[rickeieio]

Doesn't Boyle's Law apply to all gases equally?  I think it does, but perhaps I was mis-informed.  I'll go check.........

Well, I went searching and found myself wrong, again..........  I looked up Boyle's Law, which is all about "ideal gases".  It seems most elemental gasses are "ideal", but the introduction of water vapor skews it a bit.  https://en.wikipedia.org/wiki/Ideal_gas

In short, for racing at the highest levels, having a dry gas, whether nitrogen or not, can have benefits.  In real life, I agree with Bob.

[Ray,IN]

Auto/truck tires are designed to withstand high temperatures. For more information visit rvtiresafety.net. I think my TST 507 TPMS has a minimum temperature setting of 158°F, well below the danger zone for tire temperature.

The rise is of little concern to ordinary drivers, what is important is the difference in temperature readings between tires on the same axle..

Airplanes use nitrogen because it is not flammable, nor will it support combustion; these tires go from a standstill to airplane landing speed within a second. A blown tire can catch fire, oxygen in air is an accelerant.

Edited September 8, 2020 by Ray,IN

[rdickinson]

On ‎9‎/‎3‎/‎2020 at 3:46 AM, griffinmike said:

If it bothers you why dont you check  with the tire dealer/manufacturer and find out what the increase should be instead of stirring up the tire expert wannabes>

It doesn't matter if he does.  Years ago there were 2 expert contributors from major tire firms.  One I met in Calgary, the other I contacted by e-mail.  When they posted information, members here told them they were F.O.S., so both left.  Who needs it?

So here is what the experts told me 10 yrs ago.  In my case, I'm running Hankook 17.5's with a 4800 lb rating.  Run them full pressure and you shake the heck out of the trailer.  So by the time you take the trailer gross, subtract the pin wt and divide by 6, I'm running at about 75% of the capacity so the tires run at 90 psi not 110.  Same with the Volvo.  Rear and front tires run at 90 psi.  The rear duals are connected by a connector called 'Crossover' as I recall.  It's a braided hose going from 1 tire to the other.

The whole system is monitored by a TPMS.  All sensors are set for 90 psi. 1 sensor on the pair of duals 'cus they are connected.  I set high and low pressure limits along with high temp limit.

Yes running E>W, temps will be higher on the South side or side facing the sun.

Years ago there was a woman with a dark or black RV.  She couldn't open the door to get in or out, can't remember.  Dark side was facing the sun and expanded causing it to jam.  I told her to hang a white sheet over the door.  It worked, that's all it took.

This is what I do and it's worked for about 10 years.  I ask the experts.

[TireHobby]

Nitrogen Information.

 

https://www.ustires.org/sites/default/files/TISB_44_USTMA.pdf 

[griffinmike]

What did the tire mfg/dealer tell you????????

[TXiceman]

1 hour ago, griffinmike said:

What did the tire mfg/dealer tell you????????

Goodyear was of little help.  All they would say was they THOUGHT it was excessive pressure rise.  

No need to tell me about Boyle's Law or Ideal Gas Laws.  I am a retired mechanical engineer and my career was spent in Applied Thermodynamics and Heat Transfer.

Ken

[griffinmike]

Sounds like you talked to the wrong person.

"Tire air pressure increases as the temperature goes up. Scientists have figured out that for every 10 degrees (Fahrenheit) that the temperature rises the tire pressure will increase by one pound per square inch (PSI)."

What is the tire heat rating?

Is the tire hotter than it is rated for?

So what causes the temperature to go up?

- pavement temp

- tires rolling down the road

- wheel bearings

Good place to start searching:"https://www.bing.com/search?q=tire+pressure+increase&form=PRUSEN&mkt=en-us&httpsmsn=1&msnews=1&rec_search=1&refig=d21efc7f0137423f920955b65328644f&sp=-1&ghc=1&pq=tire+pressure+increase&sc=7-22&qs=n&sk=&cvid=d21efc7f0137423f920955b65328644f"

 

[Ray,IN]

On 9/10/2020 at 1:06 AM, rdickinson said:

It doesn't matter if he does.  Years ago there were 2 expert contributors from major tire firms.  One I met in Calgary, the other I contacted by e-mail.  When they posted information, members here told them they were F.O.S., so both left.  Who needs it?

So here is what the experts told me 10 yrs ago.  In my case, I'm running Hankook 17.5's with a 4800 lb rating.  Run them full pressure and you shake the heck out of the trailer.  So by the time you take the trailer gross, subtract the pin wt and divide by 6, I'm running at about 75% of the capacity so the tires run at 90 psi not 110.  Same with the Volvo.  Rear and front tires run at 90 psi.  The rear duals are connected by a connector called 'Crossover' as I recall.  It's a braided hose going from 1 tire to the other.

The whole system is monitored by a TPMS.  All sensors are set for 90 psi. 1 sensor on the pair of duals 'cus they are connected.  I set high and low pressure limits along with high temp limit.

Yes running E>W, temps will be higher on the South side or side facing the sun.

Years ago there was a woman with a dark or black RV.  She couldn't open the door to get in or out, can't remember.  Dark side was facing the sun and expanded causing it to jam.  I told her to hang a white sheet over the door.  It worked, that's all it took.

This is what I do and it's worked for about 10 years.  I ask the experts.

Yep, Tireman9 is a retired tire design engineer, yet some tell him he is  wrong.  rvtiresafety.net

You do tire pressures as he recommends. Some think the load/inflation charts are a bible. Guess they don't realize that is operating a tire at 100% of its capacity.