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Topic: Tire Pressure.... what is ambient? (Read 836 times) previous topic - next topic

Tire Pressure.... what is ambient?

I understand how determine the correct "cold" tire pressure from the tire type and coach weight.  But is it necessary to change the "cold" pressure as the minimum outside temperature changes with the season.  For example, we are currently in Anacortes, WA.  The minimum temperature is about 50 degrees.  When we were in Asheville, NC earlier this summer, the minimum was about 70 degrees.  The "cold" pressure I set in Asheville is now too low in Anacortes.  Question....  do I need increase the pressure now that fall has arrived?  If so, how often does this need to be done?  Thanks in advance. 
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George Hatfield

  Never ever use World Line Motors of Nacogdoches for service!

Re: Tire Pressure.... what is ambient?

Reply #1 –
George,

Is it necessary to change the pressure in your tires as the ambient temp goes down?  The answer is YES.  The pressure of a gas falls as the temp of the gas falls.  And, the pressure of a gas rises as the temp of the gas rises.

How often do you need to set the pressure?  Every morning that you are going to drive the coach.  The tire carry capacity is pressure dependent, not temp dependent.

Two examples.

Summer in Houston, set the pressure with the morning temps in low 70s and drive to Nac.  Next morning check pressure in Nac with the temp still in the low 70s, most likely still at correct pressure and can drive to Dallas with no additional air added.

Late fall in Houston, set the pressure with morning temps in high 60s and drive to Nac.  Over night a cold front comes through and check pressure next morning with temps in low 40s, will need to add air to bring pressure back to the pressure set the morning before and then drive to Dallas.
Rudy Legett
2003 U320 4010 ISM 450 hp
2001 U320 4220 ISM 450 hp
1995 U320 M11 400 hp
1990 Granvilla 300 hp 3208T
Aqua Hot Service Houston and Southeast Texas

Re: Tire Pressure.... what is ambient?

Reply #2 –
The bad part of this, when you remove the Pressure Pro sender to. Adjust the psi, your taking a BIG chance the PP will leak and back to why do I tolerate this ?

Considering the above, and k owing the pressure goes up as you drive, WHY mess with a non leaking PP. ?

Just a ?

Dave M

Re: Tire Pressure.... what is ambient?

Reply #3 –
Quote from: Dave M –
The bad part of this, when you remove the Pressure Pro sender to. Adjust the psi, your taking a BIG chance the PP will leak and back to why do I tolerate this ?

Considering the above, and k owing the pressure goes up as you drive, WHY mess with a non leaking PP. ?

Just a ?

Dave M

When my PP tells me my tire is low I fill to proper level.

Roland
1993 U280 4341
2010 Jeep Liberty
The Pied Pipers

Re: Tire Pressure.... what is ambient?

Reply #4 –
Quote from: Rudy –
George,

Late fall in Houston, set the pressure with morning temps in high 60s and drive to Nac.  Over night a cold front comes through and check pressure next morning with temps in low 40s, will need to add air to bring pressure back to the pressure set the morning before and then drive to Dallas.

Begs the question though, if you fill up in low temps 30's then go to high temps 80's do you take air out of the tires?

Roland
1993 U280 4341
2010 Jeep Liberty
The Pied Pipers

Re: Tire Pressure.... what is ambient?

Reply #5 –
Oh yeah !,,  filling the tire with air is not the problem, the experience with LEAKING PP IS, so I assume you never have had an issue with a leaking PP after repeated changes in air pressure and you either added air or let air out ?  :o
Dave M

Re: Tire Pressure.... what is ambient?

Reply #6 –
Quote from: Dave M –
Oh yeah !,,  filling the tire with air is not the problem, the experience with LEAKING PP IS, so I assume you never have had an issue with a leaking PP after repeated changes in air pressure and you either added air or let air out ?  :o
Dave M

Yes I have had to replace some seals, but think I was torquing them up a bit more than I should have. A little less torque and no issues. Having said that I am having a problem with one of my crossfires. Can't get it to hold air with the PP. Going to try buffing the crossfire stem (have tried numerous seals to no avail), when we get to NM. Otherwise no problems.

Roland
1993 U280 4341
2010 Jeep Liberty
The Pied Pipers

Re: Tire Pressure.... what is ambient?

Reply #7 –
George,

My procedures are based on my experience and interpretation of the recommendations of tire manufacturers. The procedures have served us well so far.

I set the cold pressure on my tires when we encounter the lowest ambient temperature in which I expect to operate the coach. I check pressures early in the morning before the sun has shone directly on any of them. I do not let air out of the tires when ambient temperatures rise. When cold (not having been driven for several hours) they never exceed maximum pressure ratings, even when ambient temperatures reach 100F.

I weighed the coach and selected pressures based on axle weights. I took the recommendations for my tires from Michelin data sheets and added five psi. That is the my target pressure for cold tires at the lowest ambient temperature I expect to encounter.

I think the last time I added air to the tires was in Missouri on about December 26. I have checked the tires many times since then. They remain at reasonable and consistent pressures. I expect to start adding air to the tires as ambient temperatures fall.

I frequently check the tires visually, with an infrared thermometer, and with a "thump stick" when we stop to rest while traveling.
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX

Re: Tire Pressure.... what is ambient?

Reply #8 –
Quote from: Roland Begin –
Begs the question though, if you fill up in low temps 30's then go to high temps 80's do you take air out of the tires?

Roland

I read the pressure info on the side to the tire, max 110 psi in my case, bring the pressure up to the maximum indicated in all six and don't touch it no matter what the ambient goes to. They may gain several pounds but will run cooler. Tire manufactures figure in operating temperature fluctuation in their recommendations. A combination of high tire temperatures/low pressures along with bad roads are a tire's worst enemy.
 
Tires flex less at max recommend cold pressures. The more they flex, the warmer they run, wasting fuel doing it along with being more prone to damage. Bottom line is: chasing pressures does more harm than good.

Max cold indicated pressure in the morning is SOP for bus and trucking companies. Excerpt from a truck driving school manual: "Check the tire mounting and air pressure. Inspect the tires every two hours or every 100 miles when driving in very hot weather. Air pressure increases with temperature. Do not let air out or the pressure will be too low when the tires cool off. If a tire is too hot to touch, remain stopped until the tire cools off. Otherwise the tire may blow out or catch fire."

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Tire Pressure.... what is ambient?

Reply #9 –
Right on Pierce, I run the max or more if the tire is getting real warm, my utility trlr has 38psi @ max, i take it to 60, runs cool and very cheerful as I carry some weight on it  :o funny, I never have tire issues  ;D 
As said, "sperience"
Cheers
Dave M

Re: Tire Pressure.... what is ambient?

Reply #10 –
Before everyone bacame bright bulbs, the tire pressure was 10 X ply rating, less one.  The works out to be for a normal 12 ply truck tire, 110 psi (old days), however the 110 seems to still be the magic number. 12 ply -1 = 11 X 10 psi = 110 PSI  :o,  this was in the old days when no one knew anything.
Dave M