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Old 04-16-2016, 05:52 PM   #15
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The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire.

From the Michelin RV Tire Guide:
Quote:
"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."
From page 6 of the GoodYear RV Tire and Care Guide:
Quote:
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."
From TOYO:
Quote:
Q: What are the consequences of inflating the tires to accommodate the actual loads?
A: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.
But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:
Quote:
The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.
From our owners manual:
Quote:
Federal law requires that the tire’s maximum load rating be molded into the sidewall of the tire.
If you look there, you will see the maximum load allowed and the cold air inflation pressure required to carry that stated maximum load. Less air pressure restricts the tire to carry a lighter load.
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Old 04-16-2016, 06:42 PM   #16
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I'm assuming this is what to use for my tires
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Old 04-16-2016, 09:37 PM   #17
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Dave
I'm not a tire wizard but a couple of things got my attention re: your initial post and then the second with the tire pressure chart. Some things to consider:
- Are your inflation pressures based on actual axle weights?
- Are all your tires the exact same size and load rating?
- Recommend you talk with Michelin about using pressures less than the chart minimum?
Safe travels ...
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Old 04-16-2016, 10:27 PM   #18
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As a new guy with a tag I found this very interesting. I'm going to do some experimenting.

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Old 04-16-2016, 11:24 PM   #19
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One thing I did do when the XZE*'s 12R's were installed, and the coach was new to me, is get out and walk the coach with the infrared heat gun to check the temps. Factoring for the long runs on the sun side of the coach the best I could, they wall seemed to be within a few PSI of each other. With the inside duals usually being a bit higher, even on the sun side of the coach, then the outside tire. (I noted that the temps were almost equal, minus sun exposure, when adding Crossfires to the mix!.

Will do this same thing with he new and different size tires, until I get a good feel for things.

And as seen in this post, sure lots of different ways to approach PSI in general. And that to me is all good, as long as no one is really under PSI for the safe loads the tires are carrying.

Sure appreciate the dialog, and best to all,
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Old 04-17-2016, 03:05 PM   #20
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Tag's tire PSI vs Drive

Quote:
Originally Posted by Lv2Roam2 View Post
Dave

I'm not a tire wizard but a couple of things got my attention re: your initial post and then the second with the tire pressure chart. Some things to consider:

- Are your inflation pressures based on actual axle weights?

- Are all your tires the exact same size and load rating?

- Recommend you talk with Michelin about using pressures less than the chart minimum?

Safe travels ...

Yes, actual weights and all are 295/80R22.5. The Michelin chart I used 3 years ago included 75 psi per the weight of my tag axle. At that setting the tag tire foot prints are slightly smaller than the drive tires.
Regarding other posts...
If I were to inflate the tag tires to max cold psi, the tire would ride on the center of the tread and would not provide as effect a braking capability due to less tire footprint on the road. I don't think the tag can "assist" the drive axle in carrying weight in event of a tire failure. To depend on it would be folly. I have TPMS to provide tire status.
Like I said, all temps are near even while running.


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Old 04-17-2016, 03:33 PM   #21
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It isn't valid to apply trucking practice to RV tyre inflation practice. Trucks have other considerations to worry about - tyre life, loaded and empty running, KISS and comfort due to tyre pressure doesn't even appear on their list which leads to them having vibration mountings on their cabs and air suspension seats to try and avoid their spines from disintegrating.
RVs are essentially constant load vehicles that are relatively flimsily constructed, and it doesn't make sense to totally destroy a tyre's ability to contribute positively to the vehicle suspension characteristics by pumping them up to rated sidewall pressures for no good reason.
Why reduce braking efficiency and handling by overinflating tyres.
Why take notice of the manufacturer's generic tyre placard and ignore the tyre manufacturers vast testing programs and real world experience.

BTW reason why the tyre fitters recommend 100 psi for 22.5" tyres is because it is a nice round number and easy to remember.
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Old 04-17-2016, 03:42 PM   #22
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Quote:
Originally Posted by CampDaven View Post
I'm assuming this is what to use for my tires
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You're using a chart for 275/ 70's, and your tires are 295/ 80's!


I run the pressures posted on the sticker by the drivers seat. Thats 5psi less pressure in the tag tires, than is in the drive tires.

This is what Toyo wants RV owners to do.

I've run across a scale a couple of times. According to the charts ( for my tires), I could lower the pressures some, but like I said.... This is where Toyo wants you to run your pressures !
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Old 04-17-2016, 04:38 PM   #23
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Tag's tire PSI vs Drive

Quote:
Originally Posted by 96 Wideglide View Post
You're using a chart for 275/ 70's, and your tires are 295/ 80's!


I run the pressures posted on the sticker by the drivers seat. Thats 5psi less pressure in the tag tires, than is in the drive tires.

This is what Toyo wants RV owners to do.

I've run across a scale a couple of times. According to the charts ( for my tires), I could lower the pressures some, but like I said.... This is where Toyo wants you to run your pressures !

My bad. Took pic of the wrong chart.
I used the 295/80 Michelin chart.
When I bought this rig all of the old tires were at 110. If I put 115 in my drive and tag (up from 85 and 75) it would ride real harsher and leave too small of a tire footprint for braking. Not as safe.
My Monaco sticker says 115/85/80, but weighing and adjusting accordingly is what my Michelin dealer and tech both recommended. I'm not as loaded as some rigs may be: only 37,500 out of 44,600. 120 in front is due to 14,100 of 14,600 max.
I feel that I have properly optimized my pressures for the best ride, wear, and MPG. No idea why Newmar and Toyo suggest all must be the same.
No tire wear. Even temps. And the RR10S chassis simply can't be beat.


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Old 04-17-2016, 04:55 PM   #24
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I'm exactly the same weight as you, and run the suggested 115/ 85/ 80.

115psi will be fine for your front axle weight.
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