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Old 11-02-2013, 07:35 AM   #561
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Originally Posted by dkottum View Post
This soft ride discussion poses a question.

Do the the 16" Michelin LT tires at 80 psi Airstream uses and recommends have a stiffer sidewall than my Airstream original 15" GYM ST tires at 65 psi?

I've used both on our trailer and see no evidence of damage from either. My understanding is ST tires have a very stiff sidewall, more so than LT tires, but looking for the truth, not opinions.
Inflation pressure has more to do with tire stiffness than the tire itself. A tire's spring rate is almost linear with pressure.

So a tire at 65 psi would be softer than a tire at 80 psi,
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Old 11-02-2013, 08:24 AM   #562
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Just a couple weeks ago I had a discussion with the guy that tours the country giving lectures on corrosion control and prevention of material deterrioration and told him I was using 10 ply LT tires on our AS at 80 PSI.

I told him I had just fell into a set of 3 ton jack stands with ratchet adjustment and that I was planning on jacking AS up, put the jack stands under and set it down with the load off the torsion bar axles and the tires.

Gov't storage at depots require vehicle on stands and tires are removed, deflated and stored in a dark place until the vehicle is reactivated. All the windows are covered with special UV protective wrap. Intakes and exhaust vents are taped, batteries removed etc etc etc.

He went on to say the tires left at full pressure sitting still put stress on them from the inside.
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Old 11-02-2013, 08:35 AM   #563
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Originally Posted by CapriRacer View Post
Inflation pressure has more to do with tire stiffness than the tire itself. A tire's spring rate is almost linear with pressure.

So a tire at 65 psi would be softer than a tire at 80 psi,
Yes, of course, the same tire at these two different pressures would be softer with less tire pressure.

But the question is about two different types of tires. "Do the the 16" Michelin LT tires at 80 psi Airstream uses and recommends have a stiffer sidewall than my Airstream original 15" GYM ST tires at 65 psi?"

Or more simply and less specific, do ST tires have a stiffer sidewall than LT tires?
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Old 11-02-2013, 09:42 AM   #564
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Hi Doug
To answer your question, the Load Range E 225/75R x 16" Michelins have a stiffer ride than the Marathon's. However the Marathons are likely to go out of balance or get a shifted belt which is going to transmit quite a bit of vibration into the trailer.

The 15" Michelin gives you a smoother ride than the Marathon and also stays in balance and I have never seen a shifted belt in one. On your 25' 45 PSI would be the correct tire pressure with the P235/75R x 15" XL Michelin.

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Old 11-02-2013, 11:11 AM   #565
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From Brian's LT tire experience it looks as though the proof is in the pudding! It is really hard to argue with real world results of his LT tire experience.

So Brian, now you have our curiosity up - after 116,000 miles - how did your trailer hold up? Has anything worn out specifically or were you just ready for a change?
Are you going to switch to 16" LT tires, use the Michelin XL 15" tires or roll the dice on the ST tires for awhile?
Of course you must tell us more about the new trailer!
Hi Steve,

Not wanting to through this thread completely off track, I will address your comments and questions over in my thread titled Flying Cloud 23FB.

Brian
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Old 11-02-2013, 11:17 AM   #566
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Hi Doug
To answer your question, the Load Range E 225/75R x 16" Michelins have a stiffer ride than the Marathon's. However the Marathons are likely to go out of balance or get a shifted belt which is going to transmit quite a bit of vibration into the trailer.

The 15" Michelin gives you a smoother ride than the Marathon and also stays in balance and I have never seen a shifted belt in one. On your 25' 45 PSI would be the correct tire pressure with the P235/75R x 15" XL Michelin.

Andrew T
Thanks Andrew T, I was hoping you would come in here.

Wow, 45 psi is quite a departure from the Airstream recommended pressure of 80 psi and even much less than others who have been "playing in safe" at 65 to 75 psi. We'll have to try to get our heads around that, knowing you have more Airstream experience than most here.

I'm also understanding you have noted this recommendation is for a 25' Airstream and is not universal.
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Old 11-02-2013, 12:09 PM   #567
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Originally Posted by dkottum View Post

Thanks Andrew T, I was hoping you would come in here.

Wow, 45 psi is quite a departure from the Airstream recommended pressure of 80 psi and even much less than others who have been "playing in safe" at 65 to 75 psi. We'll have to try to get our heads around that, knowing you have more Airstream experience than most here.

I'm also understanding you have noted this recommendation is for a 25' Airstream and is not universal.
Note that Andrew T's 45 psi reference was for a different tire, the 15" XLT XL rather than the 16" XLT LRE.
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Old 11-02-2013, 01:05 PM   #568
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Note that Andrew T's 45 psi reference was for a different tire, the 15" XLT XL rather than the 16" XLT LRE.
Good grief, just when I finally thought I had an answer . . .poof. I don't think I've got the patience to keep trying, hoping for a definitive answer for all us 16" Michelin users.

Thanks DBK'
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Old 11-02-2013, 02:47 PM   #569
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Good grief, just when I finally thought I had an answer . . .poof. I don't think I've got the patience to keep trying, hoping for a definitive answer for all us 16" Michelin users. Thanks DBK'
On my 85 Sovereign, 25' the tag indicates 700x15 and 45lbs of air pressure.
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Old 11-02-2013, 02:49 PM   #570
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Originally Posted by dkottum View Post

Good grief, just when I finally thought I had an answer . . .poof. I don't think I've got the patience to keep trying, hoping for a definitive answer for all us 16" Michelin users.

Thanks DBK'
Love the new avatar by the way :-). Am calling the factory to schedule something line this for April.

I'm sorry if I'm misunderstanding your issue, but why not just inflate to the max pressure based on the sidewall stamp?
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Old 11-02-2013, 11:06 PM   #571
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Did the 16" upgrade today at Discount Tires. Went with the Sendel T02's to keep the look stock. Had the tires and wheels ordered, shipped, mounted on the rims and balanced in under a week, and they matched the online price including the warranty. Plus knocked off $125 in rebates. That deal, plus the forum member who drove by and bought my 15" rims/tires, made the swap quite easy and slightly less painful in the wallet.

I was able to get the spare to fit. Here's a shot of the GYM 15's on the left, Michelin 16's on the right. It brought the height up about an inch, so I'll need to raise the hitch on the shank another notch.

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Old 11-03-2013, 06:20 AM   #572
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We have the best results carrying the correct tire pressure for the load the tire is carrying. The attachment is the RV load inflation table from Goodyear's website.
Here are the pressures for a 225/75R x 16 LT:

80psi 2680 pounds,
65psi 2335 pounds,
50psi 1940 pounds,
45psi 1790 pounds,
40psi 1650 pounds,
35psi 1500 pounds.

To use this chart you really should weigh your combination connected & loaded for travel on a sectioned scale.

For example the last Eddie Bauer I weighed with a customer was 6700 pounds on the axles (motor cycle inside) or 1675 pounds per tire. Generally I will add 10% to that number for variences in side to side load and the possibility that the scale is out a little so 1850 pounds per tire. Using the chart you could call it at 47 PSI but we went with 50 psi. 50 PSI has several advantages over 80 PSI; a smoother ride for the Airstream, shorter stopping distances espessially when wet and more even tread wear.

Some trailers & fifthwheels with corners are built with 225 Marathons right at their limit just over 10,000 pounds on tandem axles. In those cases we use the 225/75R x 16" LT with 80 psi.

From 1971 - 1984 a factory option on a new Airstream was Michelin 7:00 x 15" load range "C" tires. There were thousands of Airstreams built with these and tire trouble was very rare. I know many would say those trailers were lighter but actually many were not. The brochure weights in those days did not include options and everything was an option. By the time you added awnings, ac, double pane windows 2 door fridge etc. they weighed about the same as the new ones. Generaly 70's units tow a little easier because they are narrower and little more aerodynamic.

Years ago we could buy 225/75 x 16 Michelins in load range C which was a better match for most Airstream's but they are no longer available.

I know this is confusing and it is always easier to assume that bigger and heavier and more pressure has to be better but everthing has its compromizes.

Andrew T
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Old 11-03-2013, 06:27 AM   #573
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Opps I Forgot the attachment

Here is the link as well.
http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
Attached Files
File Type: pdf rv_inflation.pdf (86.7 KB, 29 views)
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Old 11-03-2013, 06:30 AM   #574
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Originally Posted by dkottum View Post
Yes, of course, the same tire at these two different pressures would be softer with less tire pressure.

But the question is about two different types of tires. "Do the the 16" Michelin LT tires at 80 psi Airstream uses and recommends have a stiffer sidewall than my Airstream original 15" GYM ST tires at 65 psi?"

Or more simply and less specific, do ST tires have a stiffer sidewall than LT tires?
No, ST tires do not have a stiffer sidewall than LT tires. Please note that there is some variation in tire make and model within the same size and that does translate into a different ride quality, but compared to the difference inflation pressure makes, that is fairly small.
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