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Old 07-01-2014, 09:57 AM   #1
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Multi Axle Tire Pressure Requirement

Okay, I switched to the "Airstream Option" of 16" wheels and LT tires. I am hard pressed to put more than 1800 pounds per tire on my triple axle Limited.

Is it correct to run max tire pressures of 80 psi in these new tires? I have read that this is a must for multi axle trailers as the side loads are higher since you are "dragging" the tires around corners. I have read in these Forums multi axle trailer tires need to be at max pressure.

David
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Old 07-01-2014, 11:58 AM   #2
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Several times, this question has been asked. Each time I recommend 70 PSI for the load range E 16 tires. Inevitably, there are then about 300 posts with all manner of equations and opinions, and, so far, at the end of each thread the consensus seems to be to run about 70PSI in them.
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Old 07-01-2014, 07:00 PM   #3
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Thanks Overlander63. This is my first experience with 16" E rated truck tires on my Airstream. I was "under tired" with 15" C rated ST that I ran at 50 psi. I just wanted some advice from folks who run 16" E rated truck tires on their multi axle Airstreams. I was thinking I would run 65 psi and pretend they were D rated tires for a slightly better ride. But I don't want to run the risk of bead separation due to side loads.

I understand tires and pressures are hot discussion topics. Maybe even more than the "best tow vehicle". Maybe even more than politics!

David
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Old 07-01-2014, 07:05 PM   #4
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David,

Don't forget hitches in that "special topics" category.

Safe travels and Terry speaks from lots of experience.

Gary
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Old 07-02-2014, 03:38 AM   #5
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the high advice is mostly because TT's have ST tires.
Those tires are calculated in their maximum load for lower speed, and so have more maximum load then a LT tire for 160km/99m/h.
Best for those tires is to give them the same deflection as a LT of same sises would have so substract 15% of maximum load.
Taking that into account the advice pressure mostly ends up at pressure needed for the maximum load, wich is called Reference pressure ( Pr ) in the formula I once got hold of and went running with, because most TT's have tires with yust enaugh loadcapacity for the Gross axle weight rating.

But Airstream TT's sometimes have oversised tires so with maximum load that have more reserve. This allows lower pressure.

I can calculate a save pressure with some reserve with my TT tirepressure-calculator in wich I use an even saver formula then European ETRTO does , and to my opinion takes care that the deflection of tire stays the same as when maxload and Pr on tire

for that I need GVWR, GAWR's ( Gross vehicle/axle weight rating) of your airstream, and howmany axles and tires on the road. From new tires maximum load and Pr and speedcode or if ST tires.
Extra info like sises would be fine, also if you ever weighed those axle of seperate wheel(pair) weight.

Then I will give in my answer a picture of filled in calculator and info how I came to it.
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Old 07-02-2014, 04:30 AM   #6
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First, I think giving advice about tire inflation pressure without knowing what tire size is being discussion is just plain wrong. You can't make any valid statement unless you know what the load carrying capacity of the tire is - and to know that, you need to know the tire size.

Second, the discussions I have seen generally end up with 80 psi as the inflation pressure for Load Range E tires - once we establish that the tire size is the usual.

But the question I have to ask the OP is: How do you know that 1800# is the max loading? If you didn't weigh each tire separately, you're guessing.
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Old 07-02-2014, 06:59 AM   #7
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Thanks for reviewing my thread asking for tire pressure advice on 16" E rated LT tires that I mounted on my Airstream. I'm concerned about my upgrades with these stiff truck tires, ProPride hitch, and Super Duty tow vehicle. I may shake my Airstream apart with everything so stiff!

Tires are 225 75 R 16. My 34' Limited has a GVRW of 8000# and a GAWR of 2800#. CAT scale weight of hitched and loaded trailer, WD bars at my settings is 7620#. I don't have weights under each tire, and I don't need them. All I wanted was advice on running lower than max air pressure in my new LT tires. People often do this on the tow vehicle to gain a smoother ride with more side wall flex. My new trailer tires have 40% more load carrying capacity than my old ones. I pull at 62mph with occasional spurts to 70mph while passing slow vehicles.

In a perfect world I have 1400# max per tire since the gross axle weight rating is 2800#. That's why I guessed that I would be hard pressed to get 1800# on a tire. I do know I leave big black marks on my driveway when I jackknife the trailer into its parking position. I know there is a lot of side load on the tires while turning sharp.

I'm going to run my new tires at 70psi. I'll let everyone know if I have a tire failure.

David
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Old 07-02-2014, 07:21 AM   #8
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Quote:
Originally Posted by dbj216 View Post
I'm concerned about my upgrades with these stiff truck tires, ProPride hitch, and Super Duty tow vehicle. I may shake my Airstream apart with everything so stiff!
Tires are 225 75 R 16. My 34' Limited has a GVRW of 8000# and a GAWR of 2800#. CAT scale weight of hitched and loaded trailer, WD bars at my settings is 7620#. I don't have weights under each tire, and I don't need them. All I wanted was advice on running lower than max air pressure in my new LT tires.
I do know I leave big black marks on my driveway when I jackknife the trailer into its parking position. I know there is a lot of side load on the tires while turning sharp.

David
David,
I made the same upgrade, and also worry about too stiff of a ride for the AS due to my F250, and HaHa hitch. I am going camping this weekend, and a stop at a truck scale is in our plan. I am hoping to find a scale that can weigh each axle.
I also get the big black marks on the driveway... So I make that jackknife turn very slowly, to save the tires.
I have been running at 70psi for a while now, but want to lower it down to 60 or 65, if the truck scale reading allow me too.

I also plan to change the HaHa to a Airsafe hitch.

Mike
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Old 07-02-2014, 09:49 AM   #9
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Hi Air Texas. A 34' triple axle with slide out. Wow, that is the very top end Airstream. You could rent out rooms in it at the campground! I have never seen one like yours.

I've not seen a truck scale that would do each axle independently. I guess you could pull up or back up so just one axle is on the weigh scale pad and take a reading, and then back up some more and weigh two axles, and so forth. Don't do this if there is a line of impatient truckers waiting for the scale! They may have a little session with you behind the truck stop!

Will 60 psi weaken the side wall stiffness to the point of heat build up or popping a bead off the rim during turns?

David
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Old 07-02-2014, 10:19 AM   #10
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Quote:
Originally Posted by dbj216 View Post
Will 60 psi weaken the side wall stiffness to the point of heat build up or popping a bead off the rim during turns?

David
This is what I am hoping to learn...through research (once I get true weights), not through practical application!
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Old 07-02-2014, 05:10 PM   #11
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Quote:
Originally Posted by dbj216 View Post
Thanks for reviewing my thread asking for tire pressure advice on 16" E rated LT tires that I mounted on my Airstream. I'm concerned about my upgrades with these stiff truck tires, ProPride hitch, and Super Duty tow vehicle. I may shake my Airstream apart with everything so stiff!

Tires are 225 75 R 16. My 34' Limited has a GVRW of 8000# and a GAWR of 2800#. CAT scale weight of hitched and loaded trailer, WD bars at my settings is 7620#. I don't have weights under each tire, and I don't need them. All I wanted was advice on running lower than max air pressure in my new LT tires. People often do this on the tow vehicle to gain a smoother ride with more side wall flex. My new trailer tires have 40% more load carrying capacity than my old ones. I pull at 62mph with occasional spurts to 70mph while passing slow vehicles.

In a perfect world I have 1400# max per tire since the gross axle weight rating is 2800#. That's why I guessed that I would be hard pressed to get 1800# on a tire. I do know I leave big black marks on my driveway when I jackknife the trailer into its parking position. I know there is a lot of side load on the tires while turning sharp.

I'm going to run my new tires at 70psi. I'll let everyone know if I have a tire failure.

David
I the tire manufacturer says 80# for max load, I'd carry 80 pounds. You bought the 16" tires, Load rating "E" for a reason, so why not used it? You would probably be OK at 70, but I wouldn't go less.
For whatever it's worth.
Larry
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Old 07-02-2014, 06:27 PM   #12
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I read somewhere DOT regulations say that when a different size tire is placed on a vehicle (is a trailer a vehicle?) that the new tire should be inflated to a pressure that gives it the same load carrying capacity as the original tire at the manufacturers recommended pressure. Tire dealers are required to place a supplementary sticker near the original sticker with the new tire size and inflation pressure.

For my original ST225/75-15 tires at 65 psi, replacing with LT225/75-16 MS/2, that worked out to 74 psi. I run at 75, but that's not far from the maximum of 80. This results in a load carrying capacity that is 200% of the weight on the axles, but no change from the original tires. I'm thinking this gross excess must be related to the increased sidewall stress. I've only been about 500 miles on the new tires, but so far no issues.

Al
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