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Old 03-06-2016, 11:17 AM   #29
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Tire inflation

Are you interested in trying them at 50 PSI cold and seeing what happens? Or are you concerned that will be too much pressure on the Airstream? If you've had them at 50 and that wasn't good for the trailer I understand. If you've never tried them at 50, you now have a baseline at 44 - compare notes and see what happens! My unofficial $0.02 - free advice worth everything you paid for it! 😃
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Old 03-07-2016, 08:51 AM   #30
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I was going to bump them up to 46 and see what happens on the next trip in early April. It will be much "warmer" then in Arizona.

On a side note, I really looked at the Mercedes and trailer and realized the trailer was level but the rear wheel well of the car was farther off the ground than the front wheel well. The car has the Mercedes air suspension. I had started driving this combination when I picked up the trailer with 3" on the Hensley Arrow jacks like I had used when towing the 25FB.

The front axle was 50 pounds or so overloaded on a recent trip with the rig completely loaded for camping and I thought maybe there was too much downward weight distribution torque going to the front of the TV when lightly loaded in the TV.

At 4" the car was level with a trace of gentle vertical movement going down the gentle undulations highway. The next outing I will cross the scales and see what has transpired.
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Old 03-07-2016, 01:36 PM   #31
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Thanks all. This is an excellent discussion on inflation parameters. Really appreciate the explanation that discounts pressure rise from a change in ambient air temperature when checking for an out of boundary pressure increase. Is solar heating a consideration or insignificant in comparison? Pat

Edit - maybe the question should be, is there any consideration for pressure adjustment/setting other than load and speed. Understand that tire condition will have an impact on pressure increase and associated replacement, but would ideal cold pressure not remain the same for a given load and travel speed?
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Old 03-10-2016, 01:10 AM   #32
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Over inflating?

I don't understand why everyone wants to max out their tire inflations.

I have a 28' 2013 International, which is dual axle, with the stock Goodyear ST225/75R15s. I had my trailer weighed at a truck stop when we were loaded up on a 6-month trip. It came in just under 7,000 lbs.

If you divide 7000/4, you come up with each tire being loaded with 1750lbs. If you look at Goodyear's inflation guide for those tires, it recommends 35lbs of pressure for 1760lbs of weight, cold—even thought the tire can take 65lbs of pressure, for a max rating of 2540lbs. Airstream says the trailer's loaded weight is 7500lbs. Divide that by 4, and you get 1875, which would be 40lbs cold. So, I should be running between 35 and 40 lbs cold, if I want to error on the cautious side. Why are people jacking them up to 65lbs?

Is there something I'm missing?

I have a link to a screenshot of the tire ratings from good year, but it's not working for some reason...
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Old 03-10-2016, 12:26 PM   #33
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I also don't understand the need to run at max pressure. I have ST tires on both of my trailers. ST max pressure is 65#. I run 55# and have zero tire problems running in ambient temps of +7F to 128F. I never exceed the speed limit of the tires, 65mph.
Why beat the trailer up with rock hard tires?
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Old 03-10-2016, 05:19 PM   #34
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Originally Posted by swan View Post
I don't understand why everyone wants to max out their tire inflations.

I have a 28' 2013 International, which is dual axle, with the stock Goodyear ST225/75R15s. I had my trailer weighed at a truck stop when we were loaded up on a 6-month trip. It came in just under 7,000 lbs.

If you divide 7000/4, you come up with each tire being loaded with 1750lbs. If you look at Goodyear's inflation guide for those tires, it recommends 35lbs of pressure for 1760lbs of weight, cold—even thought the tire can take 65lbs of pressure, for a max rating of 2540lbs. Airstream says the trailer's loaded weight is 7500lbs. Divide that by 4, and you get 1875, which would be 40lbs cold. So, I should be running between 35 and 40 lbs cold, if I want to error on the cautious side. Why are people jacking them up to 65lbs?

Is there something I'm missing?

I have a link to a screenshot of the tire ratings from good year, but it's not working for some reason...
In the above calculation there is no room for reserve load capacity. Increased inflation pressure increases load capacity. If the tire is inflated close to actual load there is no room for reserve. I would recommend multiplying actual load by 110% or 115% and then get tires inflated to that load.

And tires do not load evenly so a reserve capacity is needed.

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Old 03-10-2016, 09:24 PM   #35
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A Q&A PDF for the Michelin lovers.

http://www.michelinman.com/US/en/help/faq.html
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Old 03-11-2016, 07:05 AM   #36
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Check out your low air pressure tires when turning a tight corner....the tire will be twisting and that is not good...
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Old 03-11-2016, 07:25 AM   #37
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Quote:
Originally Posted by CapriRacer View Post
Rule of Thumb: For every 10 degrees F change in ambient temperature, the pressure in a tires changes 3%.


.
So if a tire had nitrogen in it what would the change be?
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Old 03-11-2016, 07:27 AM   #38
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Check out your low air pressure tires when turning a tight corner....the tire will be twisting and that is not good...
Then go with bias ply or LT tires.
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Old 03-11-2016, 08:49 AM   #39
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Check out your low air pressure tires when turning a tight corner....the tire will be twisting and that is not good...
I have heard this when parking the trailer, the sideways scrubbing. Using LTX M/S Michelin tires on our Airstream and truck, it seems to me similar sideways scrubbing happens when we steer our truck around a curve or corner at speed. Surely the LTX M/S must be designed to handle that? Maybe the ST trailer tires are not?
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Old 03-12-2016, 06:32 AM   #40
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Quote:
Originally Posted by CapriRacer View Post
Rule of Thumb: For every 10 degrees F change in ambient temperature, the pressure in a tires changes 3%.
So if a tire had nitrogen in it what would the change be?
No change. N2 reacts the same - as does pretty much EVERY gas.
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Old 03-12-2016, 06:59 AM   #41
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Quote:
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Snip...

Rule of Thumb: For every 10 degrees F change in ambient temperature, the pressure in a tires changes 3%.

So far a passenger car tire, 3% is about equal to 1 psi for every 10 degrees.

- AND -

A tire measured at 65 psi at 55 degrees would measure at 115 degrees, 3% times 6 (60 degrees) = 18% more or 12 psi. That needs to be accounted for when doing pressure build up.

So a tire operating at those conditions could run as high as 85 psi.

Snip...

Let me see if I understand this concept correctly. My p-rated 15" Michelins have a max of 50 PSI. So let's say it's 70 degrees outside at 8:00 am and the trailer has been sitting overnight. I ensure the tires are at 50 PSI and start a long road trip.

By noon, it's 100 degrees outside so the ambient temp is +30. So I should expect about 3% of 50 PSI increase for each 10 degree rise in ambient - or a total of 4.5 PSI increase just due to the rise in ambient temperature, correct?

And what then should I expect for the 4 hours of 65 mph towing? Is that where your 10% window comes in to play - and if so, is that on top of the increase for ambient? In other words - if the PSI was 59.5 in this scenario where 4.5# was due to rise in ambient temp and 5# (or 10%) was due to travel friction - is that 19% total increase in PSI acceptable? Or is it dangerous because it's more than a total of 15% increase in PSI?

I ask because I've set my TPMS alarm to go off at 57 PSI thinking if I get over that 12-15% range I'm in trouble. Wondering if it's safe to set the alarm at 60 instead to account for both factors?

I've usually seen almost exactly 10% increase in PSI and 30 degree temp above ambient no matter how cold or warm ambient actually is and no matter how many miles I drive - though maybe once or twice to 56 PSI on triple digit days....
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Old 03-12-2016, 08:47 AM   #42
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Quote:
Originally Posted by dkottum View Post
I have heard this when parking the trailer, the sideways scrubbing. Using LTX M/S Michelin tires on our Airstream and truck, it seems to me similar sideways scrubbing happens when we steer our truck around a curve or corner at speed. Surely the LTX M/S must be designed to handle that? Maybe the ST trailer tires are not?

Tandem axle trailers are subject to much more scrubbing due to the fact that in sharp turns, the tires based on their position on the trailer aren't rolling as much as a motorized vehicle. This causes some tremendous forces as the tire sidewall attempts to pull from the wheel.
ST tires are built with stiffer sidewalls that resists collapsing under that torque. Since LT tires are truck tires, their construction also provides additional rigidity over passenger car tires.

Inflation pressures also play a big part in giving those side walls support. At a campground I once watched a SOB tandem owner attempt a back in to a site. His tires on the trailer seemed to be a little low and as he made the pivot, a tire on the inside of the turn collapsed as the tire bead separated from the wheel. He promptly put on the spare and continued the back in. That spare was also under inflated and that tire also separated from the wheel. My last view of him was leaving the trailer in the campground road as he took one wheel and tire to get it inflated it properly.

Jack
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