# Tire Pressure



## azthroop (Jun 16, 2007)

Okay, I got the five new Maxxis tires put on the trailer yesterday. The rims are good to hold the pressure (80psi), but the question is do I put 80 psi in them cold or do I put something less in knowing that they will heat up (the tires are rated at 80psi)? Also, I have Michelins on the Suburban. They also say 80 psi when cold. Same question for the 'burb: what is the optimal pressure?









I didn't get to drive to far on the new trailer tires, and it may all be in my head, but the new radials seem to ride much better than the original Duros that came on the trailer.

Lastly, I got the tires on the internet at the Discount Tire Direct and they came with a a fairly good DOT date. It was the 42 week of 2009, so that puts it around November-ish. Great price and then it was $19.95/each to have them mounted/balanced/metal valve stems and then put on the trailer.

We will be testing them out in just a little more than a week with a 14 hour drive to Mexico.









Any suggestions on the psi, please let me know.

Jim


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## swanny (Oct 31, 2007)

when towing I run max psi "cold rating". for me that's 80 psi. If I'm not towing for awhile I'll drop the psi to about 60#. Just make sure tire are not warm when checking. the sun will send the psi up a little. I have a TPMS and the tires in the sun are always a little higher psi than the others.

kevin


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## battalionchief3 (Jun 27, 2006)

The tire PSI should be checked when cold, like stated, not in the sun. As far as 80 psi max psi cold is for the max weight carried by the tires, so unless your running heavy at the max GVWR of the TT then you should run 80psi. I have D load range tires on 14" rims and mine states 60psi cold. Since I'm not at the max weight I run them at 55 and they heat up to about 65. Now that summer is close by I will run them at 50 and they will probably heat up to 60-65 on a long run. I have a burb too with Michelin's too and they say psi cold, I run them at 75 since I have a lot of junk I carry and the hitch weight. I run 60 in the front all year long. When I got new tires, Kumho's, I thought they felt better. May be in my head too. It has to ride better since I put in an EZ flex system with a flip kit. Thats my theory. Make sure you re-torque those lugs too. My 2 cents....


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## azthroop (Jun 16, 2007)

battalionchief3 said:


> The tire PSI should be checked when cold, like stated, not in the sun. As far as 80 psi max psi cold is for the max weight carried by the tires, so unless your running heavy at the max GVWR of the TT then you should run 80psi. I have D load range tires on 14" rims and mine states 60psi cold. Since I'm not at the max weight I run them at 55 and they heat up to about 65. Now that summer is close by I will run them at 50 and they will probably heat up to 60-65 on a long run. I have a burb too with Michelin's too and they say psi cold, I run them at 75 since I have a lot of junk I carry and the hitch weight. I run 60 in the front all year long. When I got new tires, Kumho's, I thought they felt better. May be in my head too. It has to ride better since I put in an EZ flex system with a flip kit. Thats my theory. Make sure you re-torque those lugs too. My 2 cents....


Both replies have been 80psi, so that's what I will do! Should I check it on the way? If so, what if it is showing 90 psi or something like that? I just have not put any tire up to that high of a pressure before, but I guess that's why I bought the tires!!


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## battalionchief3 (Jun 27, 2006)

Nope, tires actually get bigger when they get hot. If your crossing death valley at noon on a summer day you might want to drop the pressure in the tires if they climb up to 100psi. They tell you to check pressure cold cause the tire and air expand when heated, they can handle it. At least a good tire can I wont bank on a cheap one. I have been to Fla in the summer, towing and stuck in traffic ( thanks Ga DOT for a decade long project ) and never had a problem. My trans heated up to 175 and the fan kicked on and the rear end cooled down 140. Even the AC still cooled. Just re-torque the lugs so you don't loose a wheel.


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## swanny (Oct 31, 2007)

As Battalionchief3 said, Make sure you check your lug nut torque. Don't just over tighten. I can tell you from experience the pressure will go up. My psi starts at 80 and on hot days will go to 95. I could be wrong but, putting less air in because your worried about how high the psi might go is not too good. tire will heat faster and sidewall will probably have more flex. Max pressure will carry max load for that tire. If you have time start hereTire stuff


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## SouthLa26RS (Jul 10, 2006)

Best to run the stated manufacturer side wall cold psi.


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## raynardo (Jun 8, 2007)

SouthLa26RS said:


> Best to run the stated manufacturer side wall cold psi.


DITTO!

Inflate them to 80 PSI when cold, and don't worry about when they get hot, as long as you've purchased good tires they should be able to handle it. ALWAYS visually check ALL your tires at EVERY fuel fill up. I know because it probably saved me big time - even though some damage had already been done. I've related that tale here previously at least once with photos.


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## azthroop (Jun 16, 2007)

Thanks again. I will be putting in the 80 psi. We'll be going through the desert all day, but at least it is not the heat of summer. I will keep checking the psi and lugs. I bought a torque wrench to leave in the trailer.


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## funtownrv (Feb 13, 2010)

I dont know if it can be done after the fact but many of the new model coaches are copming with nitrogen filled tires..If you fill them with nitrogen then you will have absolutely NO variation in pressure regardless of the temperature change..Just a thought..They say it can be done at any Firestone shop...


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## funtownrv (Feb 13, 2010)

I dont know if it can be done after the fact but many of the new model coaches are copming with nitrogen filled tires..If you fill them with nitrogen then you will have absolutely NO variation in pressure regardless of the temperature change..Just a thought..They say it can be done at any Firestone shop...


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## Nathan (Jan 2, 2007)

funtimerv said:


> I dont know if it can be done after the fact but many of the new model coaches are copming with nitrogen filled tires..If you fill them with nitrogen then you will have absolutely NO variation in pressure regardless of the temperature change..Just a thought..They say it can be done at any Firestone shop...


HUH?!?!









It's been 15 years since I took Thermodynamics, but that's not exactly how I remember it.....


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## Joe/GA (Aug 14, 2009)

You're right, Nathan. Temperature and pressure in a closed container (tire) are directly proportional!


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## VacaRick (Jul 23, 2009)

The "Ideal Gas Law" hasn't chnanged in the 45 years since I took Thermo. The N[sub][/sub]2 molecule is larger and takes longer to permiate the tire. The compressed air is ~78% N[sub][/sub]2, ~18% O[sub][/sub]2 + stuff. I doubt that you would ever see the improvement in a trailer tire. Since filling with N[sub][/sub]2 would perform near an "ideal gas", it is more predictable as far as temperature variations go. I don't know that that translates to a safer tire, still check your pressure frequently.


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## Joe/GA (Aug 14, 2009)

VacaRick said:


> The "Ideal Gas Law" hasn't chnanged in the 45 years since I took Thermo. The N[sub][/sub]2 molecule is larger and takes longer to permiate the tire. The compressed air is ~78% N[sub][/sub]2, ~18% O[sub][/sub]2 + stuff. I doubt that you would ever see the improvement in a trailer tire. Since filling with N[sub][/sub]2 would perform near an "ideal gas", it is more predictable as far as temperature variations go. I don't know that that translates to a safer tire, still check your pressure frequently.


I heard an interesting theory that, since the "O2 and stuff" would permiate the tire, that leaves the N2 molecules behind. As you add more compressed air, you add more N2 and the other stuff, but the other stuff leaks out again. After a while, you end up with nearly pure N2 in your tires!


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## swanny (Oct 31, 2007)

holy cow. I'm glad the monitor in the truck only show psi and temp. IIRC, I read a tech report about tire pressure. Now, the psi in your tire really isn't the pressure in the tire. It was so sort of ratio of the internal pressure and the atmospheric pressure.


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## Nathan (Jan 2, 2007)

swanny said:


> holy cow. I'm glad the monitor in the truck only show psi and temp. IIRC, I read a tech report about tire pressure. Now, the psi in your tire really isn't the pressure in the tire. It was so sort of ratio of the internal pressure and the atmospheric pressure.


Sure, but atmospheric pressure doesn't change much. A swing from 28 inHg to 32 inHg is only a 2psi change in atmospheric pressure (typical atm pressure is 14.7psi). Even at 10,000 ft, you'll likely have an atmospheric pressure of ~11 psi, so it's likely your gauge has more inaccuracies than the atmosphere variablilty.


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## CamperAndy (Aug 26, 2004)

Nathan said:


> I dont know if it can be done after the fact but many of the new model coaches are copming with nitrogen filled tires..If you fill them with nitrogen then you will have absolutely NO variation in pressure regardless of the temperature change..Just a thought..They say it can be done at any Firestone shop...


HUH?!?!









It's been 15 years since I took Thermodynamics, but that's not exactly how I remember it.....
[/quote]

Its good to hear you still remember.









I think what chris should have been told was that an N2 purge and fill removes most of the moisture and creates a very dry fill that provides a more consistant pressure over a wider range of tire temperatures. The problem is most tire jocks use a ton of soapy water to get the tires on the rim and this is almost impossible to purge out. This water has a significantly greater expansion rate then any inert gas that could be put into the tire.

If a N2 fill is free then sure why not, if they want to charge you for it tell them no thanks. Don't need to go out of your way for it.


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