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Old 10-23-2015, 01:36 PM   #85
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Originally Posted by martian View Post
Back in 2012, I jumped at the opportunity to upgrade my trailer tires from 15" Goodyear Marathons to 16" Michelin LT tires. You see, two years earlier I took my SOB trailer with Marathon tires from Wisconsin to Glacier National Park. I had the distinct displeasure of fixing a flat tire in Western Minnesota and another in Eastern Montana on the way out. Fixing involved buying replacement Marathon tires. On the way back, I had to replace the other two Marathon tires before I got out of Montana. Swapping out tires on the side of a narrow highway is not my idea of a good time. I swore I'd never have another trailer with Marathon tires. A little research on my part lead me to going to the light truck tire with more rubber on the road and higher weight capacity. Now I'm a happy camper!

Similar situation-
After 2 ST tire failures there will not be a third-
I've never had that trouble with p-rated or LT tires- just run 'em till the tread is gone or they dry rot- no tread separation- no coming apart-


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Old 10-23-2015, 01:53 PM   #86
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Originally Posted by Tireman9 View Post
One reason for tires on trailers seem to fail early is that the suspension design of tandem contributes to significant increase in "Interply Shear" forces that are internal forces in the tire structure that are trying to tear the tire apart from the inside.

If you think about it, a tire needs to rotate with the center of rotation pointing toward the center of the radius but this is not possible with two fixed axles on a trailer. This results in shear forces being over 20% higher than experienced by tires when used on a motorized vehicle where all tires do rotate about a center line that does point to the center of the turn radius.

The fact that most tires used on multi axle trailers happen to be ST type has an impact or the belief that the fault is simply because the tires are ST .

Bottom line is if the issue causing the failure is interplay sheer, then ST tires aren't up to the job. So in my situation the fact that ST tires are present says changing out to an LT is better than sticking to ST's. So far based on the reports coming from those who have replaced with LT's, we aren't hearing reports of early failures due to belt separation. Many of the earlier adopters of using LT's are now reaching the 4-5 year timeframe since their change. The longer we go with continued good reports of moving to LT's, the more evidence it will give us that the ST is not the best tire structurally for the many conditions imposed by those of us with heavy trailers.

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Old 10-23-2015, 02:01 PM   #87
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I hope next year to purchase a Flying Cloud 25FB Twin and have been following this thread with great interest. This week I contacted the Airstream factory to inquire if they have any plans to equip the 2017 Flying Cloud with 16” wheels and Michelin LT tires. A member of their Customer Relations department by the name of Gretchen responded to my request. Clearly, they have no plans to replace the Goodyear Marathon 15” tires (ST 225/75R 15 load range D) on any Flying Cloud trailer or any of the International trailers.
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Old 10-23-2015, 02:11 PM   #88
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Originally Posted by Tireman9 View Post
One reason for tires on trailers seem to fail early is that the suspension design of tandem contributes to significant increase in "Interply Shear" forces that are internal forces in the tire structure that are trying to tear the tire apart from the inside.

If you think about it, a tire needs to rotate with the center of rotation pointing toward the center of the radius but this is not possible with two fixed axles on a trailer. This results in shear forces being over 20% higher than experienced by tires when used on a motorized vehicle where all tires do rotate about a center line that does point to the center of the turn radius.

The fact that most tires used on multi axle trailers happen to be ST type has an impact or the belief that the fault is simply because the tires are ST type.

Correlation is not the same as Causation.

If you want to learn more about Interply Shear I suggest you Google the term and include RV tires in your search. You will find some technical papers on the topic along with other information on these forces.
So are you saying the more rigid and thicker sidewall ST tire makes it a better choice on a travel trailer than the more flexible, thinner sidewall LT tire? Just looking for clarification
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Old 10-23-2015, 02:48 PM   #89
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So are you saying the more rigid and thicker sidewall ST tire makes it a better choice on a travel trailer than the more flexible, thinner sidewall LT tire? Just looking for clarification
Nope
The sidewall stiffness is not a major contributor either plus or minus to the Interply Shear forces which occur in the belt edge area.

Switch to LT tire in itself is not really the reason for apparent improved durability. Don't forget that it is basically the volume of air at pressure that supports the load so increasing the pressure or increasing the volume provides increased capacity.
If you look at the load capacity of an ST and LT tire that have the same Load Range (pressure) you will see that the LT is rated to carry less load so when a switch in type is done properly i.e. ensuring the rated load capacity is equal or greater than the tire being replaced you do end up with an increase in volume of air in the LT type tire.

All too often people do not consider all the variables when trying to understand why one tire seems to perform better than another and almost never do people make a nice "apples to apples" comparison.
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Old 10-23-2015, 02:54 PM   #90
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Bottom line is if the issue causing the failure is interplay sheer, then ST tires aren't up to the job. So in my situation the fact that ST tires are present says changing out to an LT is better than sticking to ST's. So far based on the reports coming from those who have replaced with LT's, we aren't hearing reports of early failures due to belt separation. Many of the earlier adopters of using LT's are now reaching the 4-5 year timeframe since their change. The longer we go with continued good reports of moving to LT's, the more evidence it will give us that the ST is not the best tire structurally for the many conditions imposed by those of us with heavy trailers.

Jack
have you considered what might happen if you changed from a LR-D to LR-E of same size ST type tire and compared the durability of the two different tires when they are run at the inflation molded on the tire sidewall? Do you think you would get better durability if you had a greater margin of capacity vs actual loading?

or

Have you considered what would happen if you first found the size of an LT type tire that is rated to carry the load of your ST type and then gone with an ST type tire in a size with the same dimensions you learned about needing in the LT type? The larger ST tire would have a greater load capacity. Do you think you would get better durability if you had a greater margin of capacity vs actual loading?
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Old 10-23-2015, 03:01 PM   #91
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Interesting discussion at the link below on Interply Shear from 2012. It's a very helpful, fully illustrated, thread on one person's experience with that issue.

ST Tire Failure Analysis (Lots of Pics) - Sunline Coach Owner's Club

Safe travels!
Yes John took a solid engineers approach to problem solving. He did a reasonable job of inspecting his tires and also a good job of preparing the samples for my further inspection.
You will note that his lack of experience in doing a tire autopsy resulted in his missing the location of the actual failure.
We worked together and now he has a much better understanding of how and why any tire can fail if run at or above the load capacity and operational limits for the expected usage.

ST tires use a load calculation formula that in my opinion is 30 to 40 years out of date. If you ran a single axle trailer at never exceeded 60 mph (when most highway speed limits were 10 to 25 mph slower than they are today) you would have a good chance of seeing 50 to 100% improvement in durability.
That was the expected usage when the load formula was last changed for ST type tires
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Old 10-23-2015, 04:20 PM   #92
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15" rim vs. 16" rim ?

Quote:
Originally Posted by Tireman9 View Post
have you considered what might happen if you changed from a LR-D to LR-E of same size ST type tire and compared the durability of the two different tires when they are run at the inflation molded on the tire sidewall? Do you think you would get better durability if you had a greater margin of capacity vs actual loading?

or

Have you considered what would happen if you first found the size of an LT type tire that is rated to carry the load of your ST type and then gone with an ST type tire in a size with the same dimensions you learned about needing in the LT type? The larger ST tire would have a greater load capacity. Do you think you would get better durability if you had a greater margin of capacity vs actual loading?
As far as your first alternative, I did that. The Maxxis tires I used were load rated E. I ran those at 80 PSI. Had belt separation on two tires that occurred sometime during the drive home on the 1st trip of year 4 of usage. So for all intents from a calendar year usage I got 6 months more out of them than D rated Marathons.

Quite honestly I talked to Airstream and my local dealership. Both recommended going to 16" wheels and the Michelin tire. My dealer pointed out that some of the heavier 5th wheels on his lot were starting to come with LT tires as standard equipment. The person I talked to from Airstream was a long term employee who was down here for the local RV show. He said he was quite aware of difficulties with the ST tires and said I should get better performance out of the LT's and recommended the 16" wheel and LT tire solution.

I also sat down and thought about costs. The Maxxis tires were not available in the local St. Louis area from anyone. I had gotten mine from a dealership about 140 miles away. My neighbor who was in that area picked those up for me. As it ended up the Michelin's were $200 each from Discounttiredirect.com with free shipping. They also provided a $100 Visa cash card rebate also. The Michelin's were about $20 each less in cost rather than going after another set of E rated Maxis ST's via the Internet.

Truly after two failures of two different ST tire manufacturers, I was unwilling to sink any more money into the ST line of tires, especially since in both cases I caught the failures at home without having a catastrophic failure on the road. I really didn't want to press my luck.

Getting an entirely larger tire was a possibility but after recommendations from both Airstream and my dealer, and not wanting to deal with potential clearance issues along with other factors, the LT's seemed to be the best option at this point.

Again there are folks with a lot of good experiences with the ST's so I really believe that that it's not a defect that we are dealing with, but in some cases once you take away issues like over loading, insufficient air pressure, and damage caused by pot holes, hitting curbs etc., the % of load vs the maximum load capacity of the tires and time, limits the useful life of an ST tire.

Before ST tires I would do a complete replacement after 5 seasons of use. With my Classic three years seems to be the limit of ST tires. That 3 year limit would only be viable to me if I stuck with E rated ST's. The economics of tire costs just don't justify that line of thinking if I can get 5 seasons out of the LT's.

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Old 10-23-2015, 04:50 PM   #93
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It would help if you could provide the OE tire size, the size of the Maxxis and the size of LT tires you are considering. Be sure to include the LR and speed rating for each of the three tires.
Also knowing the actual load on each of the 4 tires would help as just going by advertised GAWR and dividing by 2 or GVWR and dividing by 4 will not give us your actual tire loading.
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Old 10-23-2015, 07:51 PM   #94
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ST and LT; Apples and Oranges

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Originally Posted by Tireman9 View Post
......

ST tires use a load calculation formula that in my opinion is 30 to 40 years out of date. If you ran a single axle trailer at never exceeded 60 mph (when most highway speed limits were 10 to 25 mph slower than they are today) you would have a good chance of seeing 50 to 100% improvement in durability.
That was the expected usage when the load formula was last changed for ST type tires
This seems like a major point: I think you are saying, an ST tire rated for a load capacity of X has less real-world load capacity than an LT tire rated for X.

Tireman, is there any rule of thumb or SWAG that would say what percentage difference it would be? Or is it two much apples and oranges? And would the same be true for comparing an ST tire rating to a P tire rating?
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Old 10-23-2015, 11:00 PM   #95
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I surrender Tireman9, this discussion has become too technical for my weak brain to comprehend. I would like your recommendation. When the time comes to replace my LT tires on the trailer, should I go to ST tires? What would be the best configuration (load rating & other specs) for a 27 to 31 ft Classic? Please don't respond with "It depends." I'd blow a fuse.
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Old 10-24-2015, 09:55 AM   #96
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My 30 plus years of anecdotal evidence plainly says LT tires are superior to ST tires in wear, reliability, and overall cost.

Pretty much, in my experience, people who need reliable tires to make a living are not using trailer tires.


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Old 10-24-2015, 10:37 AM   #97
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Quote:
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I surrender Tireman9, this discussion has become too technical for my weak brain to comprehend. I would like your recommendation. When the time comes to replace my LT tires on the trailer, should I go to ST tires? What would be the best configuration (load rating & other specs) for a 27 to 31 ft Classic? Please don't respond with "It depends." I'd blow a fuse.

Not quite sure if you want to do that. If you find that in your usage that the LT's give you good service, going back to ST tires might yield you a serous case of regret. I think many of us who made the jump to LT's haven't second guessed making the change. In the years I've been monitoring this topic, I've not seen anyone who made the 16" wheel, LT tire jump, come back here with regrets for doing so. As I noted earlier we are now approaching 4-5 years with member experience using LT's and we haven't seen them coming back with the issues we have seen with ST users.

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Old 10-24-2015, 03:52 PM   #98
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Bottom line is if the issue causing the failure is interplay sheer, then ST tires aren't up to the job. So in my situation the fact that ST tires are present says changing out to an LT is better than sticking to ST's. So far based on the reports coming from those who have replaced with LT's, we aren't hearing reports of early failures due to belt separation. Many of the earlier adopters of using LT's are now reaching the 4-5 year timeframe since their change. The longer we go with continued good reports of moving to LT's, the more evidence it will give us that the ST is not the best tire structurally for the many conditions imposed by those of us with heavy trailers.

Jack
Ur right Jack. Switching to a larger, speed rated tire is a good way to get increased tire life. Do you by any chance have the comparison of safety margin of load capacity from when you were doing the calculations do learn what size & LR of LT type tire you needed?
I have seen a number of TT with OE ST type tires with margin of about 1% which is a long way from the suggested 15% minimum margin.
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