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Old 11-25-2014, 07:09 PM   #813
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Bold - you'd have 7,936 with those Michelins because using a P rated tire on a trailer requires you to derate the load capacity by 10%.

I use them on my 27FB which loaded for camping on the scales sees 5800# on the trailer axles. That's literally more than a ton of headroom on the de-rated capacity of the tires.

Good luck!
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Old 11-26-2014, 06:49 AM   #814
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We have installed the 15" Michelins on hundreds of Airstreams with virtually zero failures. Many of these are 30' models including older Classics with axle weights of 7500 pounds. Even at those weight ranges the tires run cool and are completely reliable.

The big advantage with them is that they are much easier on the Airstream and the items you carry inside it.

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Old 11-26-2014, 06:56 AM   #815
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Andrew, Which specific Michelin tires would you install on a 2004 25' Safari SS? Thanks for you reply.
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Old 11-26-2014, 07:43 AM   #816
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Originally Posted by Ag&Au View Post
I'm not going to try to figure out all the numbers you guys are using. However just want to be sure you know that a user on these forums "CapriRacer" who is a tire engineer and seems to know what he is talking about has said that LT tires used in a trailer application should have their load ratings decreased by 15%. Perhaps that is in the numbers you are using. In that case never mind?

Ken
Ah ..... Mmmm ..... Not exactly.

I think tires should never be loaded to more than 85% of their rated capacity (which includes the adjustment if you are using a lower inflation pressure.)

This applies to ALL tires, not just LT tires.

Also, those who are doing the 10% reduction in P type tires should be aware that the 15% mentioned above is NOT included in that 10% - you need to do both.
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Old 11-26-2014, 09:03 AM   #817
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On the issue of load rating vs wheel size: I think the thread has moved a little off center over it 59 odd pages. The issue is not whether 15" wheels and tires can carry the load per the tire specs. Rather that the 15" tire production is almost universally made in China and because they are "trailer" tires, are not built to any standard. Yes there are numbers and letters on the sidewalls but there is significant doubt as to whether any of those numbers are true or accurate. Even rolling circumference differs between manufacturers. Whereas the 16" light truck tires at the D or E load ratings are subject to to the risk/reward of the wider consumer market of truck owners and tend (but not always as we were taught by Michelin) to be more robust, reliable and able to meet an operating environment at 80% of capacity on a predictable basis. This has been my experience (3 years) and seemingly that of other A/S owners.
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Old 11-26-2014, 10:22 AM   #818
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Originally Posted by CapriRacer View Post
Ah ..... Mmmm ..... Not exactly.

I think tires should never be loaded to more than 85% of their rated capacity (which includes the adjustment if you are using a lower inflation pressure.)

This applies to ALL tires, not just LT tires.

Also, those who are doing the 10% reduction in P type tires should be aware that the 15% mentioned above is NOT included in that 10% - you need to do both.
OK, obviously you know what you are saying better than I do, but now I am confused.

Are you saying ALL tires, even when used in their intended service should never be loaded more than (their rated load-15%)? If that is the case why don't they publish the rated loads as 15% less, and eliminate the confusion? If that's not what you are saying, please clarify in what situations you recommend the 15% reduction. I though that was correction for P and LT tires on a trailer. Apparently that is what the 10% is. Correct?

I have spent my entire life with the belief that any system is designed with a safety margin above the max specs if used as intended. (I even applied this belief to my diapers when I was a baby) And if used as intended, the max specs are a safe and intended use. Is my bubble (or diaper) burst?



Ken
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Old 11-26-2014, 10:42 AM   #819
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Noting that it is tire engineers who developed the Good Year Marathon we love so dearly, I am am skeptical of their advice.
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Old 11-26-2014, 10:56 AM   #820
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Quote:
Originally Posted by CapriRacer View Post

Ah ..... Mmmm ..... Not exactly.

I think tires should never be loaded to more than 85% of their rated capacity (which includes the adjustment if you are using a lower inflation pressure.)

This applies to ALL tires, not

Also, those who are doing the 10% reduction in P type tires should be aware that the 15% mentioned above is NOT included in that 10% - you need to do both.
Yes, I remember that, Capri. 85% of the derated capacity is 6745 for the set of 4 and I'm still almost 1000# under that limit according to scale tickets. I inflate to 50 PSI cold and my internal TPMS sensors tell me I never exceed about 30 degree F temp rise or 10% (really closer to 5-6%) pressure rise while traveling.

I almost switched out to a D-rated Goodyear Cargo LT (I want to say G26 or something like that?) but the profile would have dropped the trailer more than an inch and I didn't want to futz with the level hitch alignment I've got now. I may go that route in the future but for now am very happy with the Michelins.
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Old 11-26-2014, 11:25 AM   #821
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Noting that it is tire engineers who developed the Good Year Marathon we love so dearly, I am am skeptical of their advice.
I tend to believe that politicians and/or bureaucrats and company executives are more responsible for the ST tires in general and Marathons in particular. I see no reason to assume the engineering is the problem. These are the biggest problems in my mind:

Regulators deciding that trailer tires need not have the same design standards because they don't carry people, in total disregard for the fact that trailers are towed by vehicles that are all carrying people.

Company executives deciding to make big bucks by manufacturing these already substandard tires in overseas sweatshops with substandard factory practices and regulation and then selling them for the same price as decent tires are sold for, thereby making users believe they are not junk.

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Old 11-27-2014, 06:38 AM   #822
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Quote:
Originally Posted by Ag&Au View Post
.......Are you saying ALL tires, even when used in their intended service should never be loaded more than (their rated load-15%)?....
Yes, that is what I am saying.

Quote:
Originally Posted by Ag&Au View Post
....... If that is the case why don't they publish the rated loads as 15% less, and eliminate the confusion?.......
Because:

1) That is MY recommendation

2) The confusion would not be eliminated because there would now be 2 charts with different loads on them.

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.......I thought that was correction for P and LT tires on a trailer. Apparently that is what the 10% is. Correct?....
No, that 10% is NOT part of my recommendation. It is a separate issue - the standard way of dealing with P type tires used in LT and trailer service.

To put it distinctly, the load carrying capacity of a P type tire has to be reduced by 10% to get the load carrying capacity when the tire is used on Pickups, vans, and trailers - and then another 15% reduction per my recommendation.

Quote:
Originally Posted by Ag&Au View Post
.......I have spent my entire life with the belief that any system is designed with a safety margin above the max specs if used as intended. (I even applied this belief to my diapers when I was a baby) And if used as intended, the max specs are a safe and intended use. Is my bubble (or diaper) burst?....
Not exactly.

When I was in college, I had a professor who said "Overdesign, underutilize". What he meant was that products need to be overdesigned to accommodate those things we engineers don't know about when we design stuff - and when those products are used, they should be used at a lower level to also accommodate those things we don't know about the intended usage.

What reducing the published load from the tables by 15% does is part of the "underutilize" part of the equation.
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Old 11-27-2014, 07:47 AM   #823
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What if the tire engineers already did that in the design process and have factored in 15% already? Now we're at 30%?

This is just based on a personal preference as the 15% seems to be an arbitrary number you came up with correct? Or is there some math to the 15% rule of personal preference? Trying to understand this. Because by the numbers some folks shouldn't even be using 16 LT's.
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Old 11-27-2014, 08:02 AM   #824
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I am no longer taking into consideration what others say, engineers, tire experts, or users. I read all the posts some time ago, did my own research on tires, ST vs LT. Checked as many websites as I could find on failures or supposed tire failures and opted for 16" Wheels by Sendel and Michelins 16" LT Tires. On our new trailer had them installed at the AS factory as an unadvertised option they offer. EAch of us needs to make as informed a decision as we can taking into consideration cost and safety. We could not be more satisfied with Michelins, to the point I specifically ordered them on the F350, could have been two other brands if not specifically noted on the order.
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Old 11-27-2014, 08:54 AM   #825
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. EAch of us needs to make as informed a decision as we can taking into consideration cost and safety. We could not be more satisfied with Michelins, to the point I specifically ordered them on the F350, could have been two other brands if not specifically noted on the order.
So how do you make an "informed decision" when there is no information? No documentation or regulatory process exists in the public domain that demonstrates how load ratings are determined let alone tested; the Tire Manufacturers Association publications are vague, contradictory; severely dated; and do not apply to ST or specific to LT designated tires. In fact the whole concept of trailers vs. tractors. vs trucks is a confusing and without definition by weight or usage. But where I agree is that the combination of personal experience and internet holistic posting provides some level of relative experience that IMO is far more "informed" than reading an owners manual written with half an eye on economics and another on liability experience.

Also BTW the so called derating of tires for trailer use is written in very dated publications without reference to trailer type or usage. However its also a sensible approach given the lack of quality control over all trailer tire specs and manufacturing. Personally I think the same applies to any tire in any application. I too race sports cars (important definition) and have had some remarkable experiences with tire failures at Daytona vs. Road America that left the Hoosier and Pirelli techs scratching their heads and eventually advising that the cars be withdrawn if that specific tire size continued to be used. Its not an exact science and in the trailer context is probably not a science at all. Look at the Michelin recall of the last 2 years to see how variable the process can be. For a year preceding that recall, Michelin and its dealers denied, ducked and avoided the issue to my personal loss. It was not until the NTSB got involved that they withdrew their LTX 16" tires. I blew through 4 before that happened and not even the Ford Truck forum was commenting.

So being informed at this level of technology is very hard, if not impossible.
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Old 11-27-2014, 09:56 AM   #826
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So how do you make an "informed decision" when there is no information? No documentation or regulatory process exists in the public domain that demonstrates how load ratings are determined let alone tested; the Tire Manufacturers Association publications are vague, contradictory; severely dated; and do not apply to ST or specific to LT designated tires.

So being informed at this level of technology is very hard, if not impossible.
Part of the issue is your question seeks an answer of 1 design that works in a variable environment.
Application designs are passenger cars, light trucks and trailers (There are other applications) When the load is light the tire's job isn't as difficult. Add lots of weight and the stakes go up. Add variable weigh over the tire life, changing road conditions, changing weather, different tire pressures or the leakage in tire pressure and different road speeds. Then the manufacturer has to compete in price to get the tire sold, because price is a factor.

A P tire was not designed for trailer usage. To adopt a P tire for trailer usage would require adaption of the specs so one doesn't experience a less than desirable event.

Having a margin of safety so one doesn't experience the above said event would seem to be prudent. As an example (non-AS) I bought a boat that weighed in excess of 7000 pounds. The design of the trailer is to get it as low to the ground as possible so 14" rims were supplied. The greatest trailer (ST) tire load available wad only about 150# greater than the actual load. The boat was on a show room in CA and going to be delivered to me in Phoenix. Before I took possession the trailer had 2 blowouts on that trip. And the load was NOT greater than the capacity of the tires. I can not speak to the inflation or speed as I was not towing. I did not think about that event, until a 2years later and I got 2 blow outs in the same year.

My conclusion, the tires even though they were NOT over loaded based on numbers, in actual application they didn't work.

I use a 10 percent rule that the trailer tires have to be rated for 10% over the max possible load. I haven't towed much in the recent past and that 10% rule has serves me. And I never use P tires on a trailer.

>>>>>>Action
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