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Old 07-14-2016, 09:25 PM   #15
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Originally Posted by SteveSueMac View Post
Canyonduck- have you weighed your trailer loaded for camping? You may find you're not at the GVWR or GAWR for your trailer but something less than that. You may have the space to do it, but if not, you might want to check out the Pirelli LT 15" here:

https://m.tirerack.com/tires/TireDet...=375SR5SCORATR

2335# each at 65 PSI or 4670 per axle (4400 if you use the 94% rule mentioned earlier).

Good luck!
The pirelli's look nice.

Consider bumping up your wheels to 16" for more load on the michelins.
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Old 07-14-2016, 09:36 PM   #16
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Isn't the reason for the derating because of the weaker sidewall on these tires compared to an ST tire? It helps to accept the derating if you know why.

Tire threads are addictive.

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Old 07-15-2016, 04:28 AM   #17
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Isn't the reason for the derating because of the weaker sidewall on these tires compared to an ST tire? It helps to accept the derating if you know why.

Tire threads are addictive.

Gene

You want to understand the "why" behind a US federal regulation? 😂

No seriously, I honestly agree with you. It would be great to know why. And when. I'm not sure when these regs were written and whether newer processes and materials would change the regulation (government moves a bit slower than industry). I even question whether the authors screwed up the math - like they wanted a 10% reduction and mistakenly applied dividing by 1.10 as the opposite of adding 10% by multiplying by 1.10. But what do I know? 😀

I've seen some tire talk suggesting the bead on a P is weaker than the bead on an LT and the sidewall argument is usually that STs have thicker/stiffer sidewalls than LTs or Ps. It could be due to load and application. There are many 1/2 ton trucks that come from the factory with P tires presumably because, even at 91% of their stamped capacity, they are sufficient to handle the max load of the truck and give a smoother ride.

I do wish I knew more. What I do know is that anyone can do the math and determine whether their tire usage does/n't comply with these regs. But - like eating kale - whether or not one wants to or fully understands why is a different concept. 😀
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Old 07-15-2016, 08:04 AM   #18
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Since the popular Michelin LTX MS/2 is a passenger rated tire (and not an LT) does it need to be derated 10% for trailer use? I was under the impression it did not and I need to know if I will be safe with my intended use of this tire. I have a single axle 19' (2004 international) and I need to replace the stock GY Marathons after less than two years. My trailer GVWR is 4500 and the axle rating is 4300. I was going to go with a set of these Michelins that are rated at 2183 per tire or 4366 for the axle. This doesn't seem to provide much margin, but would at least be greater (by 66 pounds) than the axle rating. The new Michelin Defender LTX M/S is another options and those are rated slightly higher - 2271 per tire or 4552 for the axle. Am I thinking this through properly? I wanted to make sure the tires I get are going to be properly rated for our single axle application. Thx
First off according to the Michelin web site the new Defender 235/75/R15 109T is not a (P) car passenger rated tire & that's why I recently swapped my 15" Marathons on my 2016 22' Sport Bambi which has a GVWR 4500# also to the latest New Michelin LTX M&S XL 109T which just came available. The new Michelin's have a load capacity of 2271 per tire or 4542# single axle capacity. They are a light truck tire and are designated on the Michelin web site as a light truck tire not a car passenger tire. They do sell Defender car passenger/mini van tires under the car passenger tire category but not the LTX M&S XL 109t. They are not advertised as a Passenger car tire anywhere on its website or indicate anywhere on the tire itself that it is a (P) rated tire. Now if you still are nervous because of all the is or not opinions voiced here, you have a single axle not a tandem which has deferent stress issues. My opinion base on what Michelin states on their web site combined having a single axle trailer .... no de rating needed.
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Old 07-15-2016, 08:41 AM   #19
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Originally Posted by Gene View Post
Isn't the reason for the derating because of the weaker sidewall on these tires compared to an ST tire? It helps to accept the derating if you know why.

Tire threads are addictive.

Gene

While I wasn't around when this was put in place (late 1960's), perhaps I can give you some insight into the why.

Oh, and the first reference I found to derating passenger car tires for use on trucks and trailers appeared in the 1968 Tire and Rim Association Yearbook - and that predates the government regulations by a couple of years. The way I interpret that is that the tire industry itself is the source.

So why derate passenger car tires? - and be aware, this is just my opinion - It has to do with the service application.

The load carrying capacity of tires is a function of many things. We all know about size and inflation pressure, but it is also a function of speed, road roughness, and - I suspect - the stiffness of the suspension. I'm not going to spend this thread explaining why each of those affects the load carrying capacity. I hope you will accept that it does.

Compared to a car, a truck (and trailers, too!) have stiffer suspensions, ride on slightly rougher roads, and while they travel at slightly slower speeds, the net effect is lower load carrying capacity. This is reflected in the published load tables for the type of service.

And a brief discussion on tire type. When someone says *Passenger Car Tires*, what they are really referring to is the load tables that are published by the tire standardizing organizations, such as The Tire and Rim Association (TRA, the US based tire standardizing organization). Those tables describe a service that a tire was intended for.

So there are load tables for Passenger car tires, Light Truck tires, Medium Trucks tires, Off Road Tires (and by that, they mean earthmovers and the like, not Monster trucks!), Fork Lift tires, etc. These tables are all published in yearbooks published annually by the tire standardizing organizations. The books are over an inch thick - hundreds of pages of load tables for the many types of tires being made.

But note that there are no special tables for SUV's, or mini-pickups, both of which can use Passenger Car tires that have to be derated that 10% we are discussing.

And some of the tables are just versions of existing tables. For example, the table for Mobile Cranes is simply a note referring to other various other tables.

ST tires appear to be a special case of speed restricted LT tires. There are few common sizes (meaning dimensions) with LT tires, and many appear to be old passenger car sizes with higher Load Ranges.

I hope that explains things a bit. It's an obscure and complicated area and sorting it out can be confusing - even for those well versed in the technology. And - editorial comment - you won't find a guy at a tire shop who knows how this works. It isn't needed to do what he needs to do.
I have many copies of TRA yearbooks as well as some from Europe and Japan.
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Old 07-15-2016, 09:00 AM   #20
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Originally Posted by jcole View Post
First off according to the Michelin web site the new Defender 235/75/R15 109T is not a (P) car passenger rated tire & that's why I recently swapped my 15" Marathons on my 2016 22' Sport Bambi which has a GVWR 4500# also to the latest New Michelin LTX M&S XL 109T which just came available. The new Michelin's have a load capacity of 2271 per tire or 4542# single axle capacity. They are a light truck tire and are designated on the Michelin web site as a light truck tire not a car passenger tire. They do sell Defender car passenger/mini van tires under the car passenger tire category but not the LTX M&S XL 109t. They are not advertised as a Passenger car tire anywhere on its website or indicate anywhere on the tire itself that it is a (P) rated tire. Now if you still are nervous because of all the is or not opinions voiced here, you have a single axle not a tandem which has deferent stress issues. My opinion base on what Michelin states on their web site combined having a single axle trailer .... no de rating needed.

Response from Michelin to my question of whether this is a P or LT:

Thank you very much, Steve. The Defender LTX M/S in this size is considered a European metric tire, and as such, does not have a P or LT rating. However, Euro metric and P-metric tires are used interchangeably, and as such, the tire can be considered a P for practical purposes.
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Old 07-15-2016, 09:18 AM   #21
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I am not sure whether or not this is the appropriate place to ask this question or not? I have 16 inch Michelin Tires on my 28 ft. 2015 Flying Cloud. My question is do trailer tires need to be rotated like car tires? If they do; how do you rotate them, and how often do they need to be rotated?
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Old 07-15-2016, 10:19 AM   #22
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Isn't the reason for the derating because of the weaker sidewall on these tires compared to an ST tire? It helps to accept the derating if you know why.

Tire threads are addictive.

Gene

That's just it, the misscomprehension is that the ST tire is stronger due to its stiffer sidewalls. In fact non ST tires have far stronger sidewalls. Just consider the flexing of those sidewalls without failure over 70,000 miles.
ST tires are prone to tread separation due to their very construction and thus in my opinion less safe and reliable. Not to mention the rivet popping ride and the constant worry about pressure and speed. I and thousands of others are enjoying the benefits of using the LTX tires yet every time someone starts a tread about this subject the fear mongering begins. Oh you better reconsider, or go to 16" wheels! The DOT hasn't changed or rewritten these regulations for decades. The tire industry is light years ahead of them. The EPA has lots and lots of regulations as well. How are those working out for us ?
I remember getting 30,000 miles out of a set tires as being awesome. Today we routinely expect 60,000 plus.
Recently I spent 3 days at Jackson Center. One morning I decided to check out tires on the dozen or so Airstreams at their campground and better than half the units were sporting 15" wheels and Michelin LTX tires. I was glad to see other folks out there with common sense as well.
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Old 07-15-2016, 12:03 PM   #23
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Frankly, franklyfrank, you seem pretty riled up by this topic and I can't understand why.

If your profile is up to date, you have a 2013 30' Int'l with a dry weight of 6300 and GVWR of over 8000. Have you ever weighed it fully loaded for camping?

If you come in at 7425# or less, you're fully compliant with the regs (both the de-rating of 9.1% and not using more than 94% of that capacity).

Where's the fear mongering in that? It's just a factual observation.
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Old 07-15-2016, 03:13 PM   #24
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Response from Michelin to my question of whether this is a P or LT:

Thank you very much, Steve. The Defender LTX M/S in this size is considered a European metric tire, and as such, does not have a P or LT rating. However, Euro metric and P-metric tires are used interchangeably, and as such, the tire can be considered a P for practical purposes.
Or just consider it to be a Lt truck tire as Michelin states on their web site to be used within its load rating & don't worry about de -rating it.
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Old 07-15-2016, 03:29 PM   #25
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From FMVSS, aka 49CFR571.110

"S4.2.2.2When passenger car tires are installed on an MPV, truck, bus, or trailer, each tire's load rating is reduced by dividing it by 1.10 before determining, under S4.2.2.1, the sum of the maximum load ratings of the tires fitted to an axle."

This is where the previously derided 10% number comes from.

See:
https://www.law.cornell.edu/cfr/text/49/571.110


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Old 07-15-2016, 04:05 PM   #26
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Or just consider it to be a Lt truck tire as Michelin states on their web site to be used within its load rating & don't worry about de -rating it.

Do what makes you happy 😀

They don't state LT or P - but you can see in the response to my question, the Euro and P rating (which applies to this tire) are interchangeable.

Happy camping everyone!
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Old 07-15-2016, 04:05 PM   #27
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Or just consider it to be a Lt truck tire as Michelin states on their web site to be used within its load rating & don't worry about de -rating it.
On the Canadian Michelin web site the 'T' after the 109 in the model number denotes that this tire is considered to be for family sedans and vans and is not a light truck tire. Perhaps in the USA car, truck and trailer tires can be used interchangeably without regard for intended use?
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Old 07-15-2016, 04:49 PM   #28
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On the Canadian Michelin web site the 'T' after the 109 in the model number denotes that this tire is considered to be for family sedans and vans and is not a light truck tire. Perhaps in the USA car, truck and trailer tires can be used interchangeably without regard for intended use?
The " T " is the speed rating & no more. You are wrong, Michelin web sites do not use this code to designate whether it is a passenger or truck tire.
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