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Old 11-29-2019, 06:24 PM   #61
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Originally Posted by SailorSam20500 View Post

Simply increasing the load range on the tires does NOTHING to alleviate the reason Roger recommends running multi axle trailers at max sidewall pressure: interply shear caused during turns. On my trailer, the OEM tires have a +30% margin over my actual static weight. So, possibly, I could go down a load range and still have sufficient capacity. I run the tires at max inflation.
Interply shear (also referred to by several other terms in the industry" exists All the time the tire is turning, just driving down the road, not while making those lawn gouging, asphalt scraping turns in an RV park or parking lot. It occurs when the "tread package" is deflected and that happens to every square millimeter of the tire's structure but is most problematic in the tread sue to the angle of tread cord angle (usually ~20-22 degrees). Yes, it's called a "Radial Tire" but tread cord is laid on the carcass on bias angles in relationship to the circumferential center line. Interlaminar stress has a limit. It's equal to the limit of traction of the tire on whatever it's rolling on. The difference between the stress caused while driving and the stress while making our slow speed turns (usually about 1/4 mph or less) is the heat generated at highway speed.

Tires are also imperfect and while moving in a straight line they generate "Plysteer" which also creates laminar stress.

Tire manufacturers spend a lot of time measuring these stresses and by using different compounds, various layup strategies, and inserting tread edge wedges or edge cap plies (perhaps even full nylon cap plies) do a lot to minimize the effects of laminar stress.

Another strategy to reduce such stress, and also rolling resistance, is to build a tire in it's naturally inflated profile (called NIP by one manufacturer). When they do so they have a stated cold inflation pressure for various loads that produce predicted deflection in the tire. Running below this pressure with a higher load increases the stress in the tread package. Conversely, over inflating can have the same effect as it concentrates any flex over a smaller tread contact patch and bring on other stress related failures.

Want to be a tire expert in your spare time?

Read this:

http://www.safetyresearch.net/Librar..._Pneu_Tire.pdf

FWIW, you'll find the term "Inter-ply Shear" only once near the beginning.

If you want to skip to reading about it just go the index and look for "interlaminar shear.

While reading note the numerous references to heat, load, and speed and the role all play. Solving the problem is not as simple as just inflating a tire to the max. If it was tire companies could save a ton of $$$ on research and development.
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Old 11-29-2019, 07:06 PM   #62
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Originally Posted by Chuck_S View Post
ST tires can and should be run at max cold sidewall pressure. In your case that's 65 pounds.

Underinflated tires are the primary cause of tire blow outs (other than old tires). Sidewall flex = internal friction = increased tire pressure = blow out.

-- Chuck

Not quite. Sidewall Flex failures result from running at highway speed while significantly low on air. This is what TPMS are for. To warn the driver that the tire is leaking air. If properly loaded and not loosing air the heat from sidewall flex will not result in a sidewall "blowout".
As pointed out in the post on Why Tires Fail. Belt separations come from long term operation at excess load and speed which heats the belt rubber which ultimately weakens it so the Interply Shear literally tears the belts apart from the inside (of the structure) out.



In your "Sidewall flex = internal friction = increased tire pressure = blow out" example what really happens is Air Pressure Loss > Excess sidewall bending > Excess body ply heat > loss of body ply strength > Sidewall Flex failure.



Bottom Line. Tires just don't "Blowout" from the increased operating pressure
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Old 11-29-2019, 07:33 PM   #63
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Originally Posted by TitanMike View Post
Interply shear (also referred to by several other terms in the industry" exists All the time the tire is turning, just driving down the road, not while making those lawn gouging, asphalt scraping turns in an RV park or parking lot. It occurs when the "tread package" is deflected and that happens to every square millimeter of the tire's structure but is most problematic in the tread sue to the angle of tread cord angle (usually ~20-22 degrees). Yes, it's called a "Radial Tire" but tread cord is laid on the carcass on bias angles in relationship to the circumferential center line. Interlaminar stress has a limit. It's equal to the limit of traction of the tire on whatever it's rolling on. The difference between the stress caused while driving and the stress while making our slow speed turns (usually about 1/4 mph or less) is the heat generated at highway speed.

Tires are also imperfect and while moving in a straight line they generate "Plysteer" which also creates laminar stress.

Tire manufacturers spend a lot of time measuring these stresses and by using different compounds, various layup strategies, and inserting tread edge wedges or edge cap plies (perhaps even full nylon cap plies) do a lot to minimize the effects of laminar stress.

Another strategy to reduce such stress, and also rolling resistance, is to build a tire in it's naturally inflated profile (called NIP by one manufacturer). When they do so they have a stated cold inflation pressure for various loads that produce predicted deflection in the tire. Running below this pressure with a higher load increases the stress in the tread package. Conversely, over inflating can have the same effect as it concentrates any flex over a smaller tread contact patch and bring on other stress related failures.

Want to be a tire expert in your spare time?

Read this:

http://www.safetyresearch.net/Librar..._Pneu_Tire.pdf

FWIW, you'll find the term "Inter-ply Shear" only once near the beginning.

If you want to skip to reading about it just go the index and look for "interlaminar shear.

While reading note the numerous references to heat, load, and speed and the role all play. Solving the problem is not as simple as just inflating a tire to the max. If it was tire companies could save a ton of $$$ on research and development.

Yup. What the NHTSA paper was talking about was the forces in a tire when used on a motor vehicle. You will note that they did not mention the forces the belts experience when a tire is applied to a multi-axle trailer that is dragged , not driver around curves.


You might want to consider a more focused paper, that I cited in my Feb 7 2018 blog post, titled "Interply Shear Stresses and Coupled Deformations of a Folded Belt Structure Under Extension". IMO the NHTSA paper was not written for the Tire design Engineer but for the lawmakers who were trying to decide what to do in response to the Ford Explorer roll-over situation. As far as I can see there is nothing wrong with the NHTSA paper EXCEPT it does not address the issue of ST tires as it was focused primarily on LT and P type tire applications.


THIS post has a graphic that makes it clear that tires on motor vehicles, as address in the NHTSA paper are not experiencing interply (or interlaminar if you prefer that term) shear forces.


When you look at trailer operation you will learn that the belt Interply Shear can run 24% higher in towing application than if the identical tire with identical load and inflation is driven around the same turn but on a motorized vehicle. The video in THIS post shows the tire distortion in trailer application. You will never see this in a motor vehicle.


While the extra components in some modern ST tires can improve their resistance to Interply Shear forces. It is true that increasing the inflation of St tires will lower the slip angle in operation which will lower the interply shear forces. Possibly enough to allow 5 to 7 years use without suffering a belt separation.
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Old 11-29-2019, 07:56 PM   #64
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Originally Posted by Tireman9 View Post
Yup. What the NHTSA paper was talking about was the forces in a tire when used on a motor vehicle. You will note that they did not mention the forces the belts experience when a tire is applied to a multi-axle trailer that is dragged , not driver around curves.


When you look at trailer operation you will learn that the belt Interply Shear can run 24% higher in towing application than if the identical tire with identical load and inflation is driven around the same turn but on a motorized vehicle. The video in THIS post shows the tire distortion in trailer application. You will never see this in a motorvehicle.


-- Note am having problems with on-line pictures. hope to fix later tonight 11/29
No dispute here but how much have engineers been able to mitigate the effects of this increased force in ST trailer tires in recent years? Through better compounding and reinforcement of the critical belt edge area.

Perhaps the lower end Chinese tires don't have much work done in this area but how about Goodyear.

I know at the Co I retired from ST trailer tires were a very small portion of the market and were pretty much orphans as far as our manufacturer's were considered. Market was pretty much ceded to the Chinese but as more and more Towables hit the road more interest has been generated.

I know that the GY Endurance tires I put on my TT are light years ahead of what came off and also those I've encountered before I retired.
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Old 12-01-2019, 04:34 PM   #65
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Originally Posted by JVS04 View Post
I got rid of the Castle Rocks and purchased Goodyear Endurance load D ST205/75R15 for my Salem 26DBLE. I was running 65psi per the side of the tires. THEN

I weighed the axles separately at the CAT scale.

TT Front Axle. 3060
TT Rear Axle. 2620

Per the Goodyear Load/Inflation chart states inflation for the following weights per tire should be

Front +- 1530 per tire @ 35 to 40psi
Rear +- 1310 per tire @ 30 to 35psi

the Max rating is 2150 @ 65psi

SO if I run the 65psi per the tire am I seriously overinflated?
OR if I run the load/inflation rates am I seriously under inflated?
Confused to the point of inaction.

Another question: has anyone with a similar layout (slide w/ dinette & couch one side and sink, stove, fridge, pantry opposite side) been able to weigh the left and right side of the axles separately?

All opinions are greatly appreciated! Thanks

Having read the massive and extended debate, I feel really good about my method...I pay a tire professional to inspect, recommend, and advise me on my RV tires and he's never led me wrong. Of course I pay a little more but I have a tire guy's business on the line to make sure he gets it right. And, he services my passenger vehicles too.
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Old 12-02-2019, 07:29 PM   #66
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Is your hitch at the proper level for the receiver hitch? Makes me wonder why so much difference from one axel to the next!!!
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Old 12-02-2019, 07:40 PM   #67
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Is your hitch at the proper level for the receiver hitch? Makes me wonder why so much difference from one axel to the next!!!
If axles are torsion, it's possible to have differences front to rear even with a level trailer. It's going to depend on whether the axles have the same "drop".

From looking at mine I believe it is possible to "shim" the axle support frame where it attaches to the TT frame. If rear axles for example are carrying less load, and TT is not nose down, adding shim material to the rear of the frame will add load to the rear axle. This of course will depend on whether or not attachment holes on vertical part of axle "frame" are slotted for adjustment.

I have a slight mismatch in axle loading even though frame to ground measurement when loaded and hitched is almost dead even all around. Have considered doing what I described above.
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Old 12-02-2019, 08:26 PM   #68
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Originally Posted by babock View Post
From Tireman9's website.
RV Tire Safety: Inflation
Naturally, he didn't address my situation. Same size tire but bumped up a load range. From Castle Rock ST205/75R14C To GY Endurance ST205/75R14D.
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Old 12-02-2019, 08:43 PM   #69
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Naturally, he didn't address my situation. Same size tire but bumped up a load range. From Castle Rock ST205/75R14C To GY Endurance ST205/75R14D.

Well, since you have a multi-axle trailer, it comes down to which issue you are most concerned about.
Run using the load table data plus at least 10% PSI based on actual load weight if you are worried about a somewhat rougher ride.
If you think the inter-ply shear (or inter-laminar stress) causing tire failure is more important, run at the sidewall pressure listed on the tire...
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Old 12-02-2019, 10:20 PM   #70
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Naturally, he didn't address my situation. Same size tire but bumped up a load range. From Castle Rock ST205/75R14C To GY Endurance ST205/75R14D.
You didn't read the article titled "What inflation to run when changing Ply Rating or size"?
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Old 12-02-2019, 11:25 PM   #71
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Having owned and hauled lots of heavy equipment we always ran the tires at max sidewall pressure loaded and empty. Examples, empty trailer 10,500 loaded 78,000, small roller trailer 1100 empty, 6500 loaded single axle. The point here is the higher pressure won’t hurt you, lower might or sometimes definitely will.
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Old 12-03-2019, 12:09 AM   #72
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You didn't read the article titled "What inflation to run when changing Ply Rating or size"?
It's very difficult to give inflation pressure information to a party that does not respect the vehicle manufactures basic recommendations for OE tires.

In the tire world the correct nomenclature for a tire size is ďdesignated sizeĒ

This is a designated size; ST205/75R14. It has optional load ranges; they do not affect the designated size. The designated size uses the same load inflation chart, regardless of load range or brand. In short, a LRC and LRD will provide identical load capacities at 50 PSI. So, adding a load range does nothing to affect the vehicle manufacturerís owner manual recommendation, vehicle certification recommendation or tire load and inflation recommendation. However, the LRD option does allow the owner the option of increased load capacity reserves via increased inflation pressures, up to and including tire sidewall max. Verification of wheels and valve stems psi ratings to 65 PSI is recommended.
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Old 12-03-2019, 06:28 AM   #73
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Originally Posted by JVS04 View Post
I got rid of the Castle Rocks and purchased Goodyear Endurance load D ST205/75R15 for my Salem 26DBLE. I was running 65psi per the side of the tires. THEN

I weighed the axles separately at the CAT scale.

TT Front Axle. 3060
TT Rear Axle. 2620

Per the Goodyear Load/Inflation chart states inflation for the following weights per tire should be

Front +- 1530 per tire @ 35 to 40psi
Rear +- 1310 per tire @ 30 to 35psi

the Max rating is 2150 @ 65psi

SO if I run the 65psi per the tire am I seriously overinflated?
OR if I run the load/inflation rates am I seriously under inflated?
Confused to the point of inaction.

Another question: has anyone with a similar layout (slide w/ dinette & couch one side and sink, stove, fridge, pantry opposite side) been able to weigh the left and right side of the axles separately?

All opinions are greatly appreciated! Thanks
My calculation comes to F 61pai, R52 psi , and this is max pressure at wich no bumping, and gives max reserves and livetime of tires( if protected against UV and Ozon.

For this I lowered the loadindex by 6 steps from 107 to 101, becauseyour ST is calculated in maxload for 65mph , even if Endurance.



I have not read all the 4 pages written in the week since you started the topic.

Did someone already protested against the different pressure between the axles? Comon use is to give all 4 trailertires of a tandemaxle, the same pressure. If you weighed with 65 psi filled, rear has lesser deflection, so giving pressure based on list or calculation , shifts a bit more weight to front axle . Compare with a tag- axle.
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Old 12-03-2019, 06:55 AM   #74
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I often wonder how TT owners pull these trailers ... I have to say it is not without effort ... is the trailer loaded properly??? read sidewall inflate to max cold and have some fun .... WOW just WOW
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Old 12-03-2019, 07:35 AM   #75
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Why not go to the place you bought the tires from and ask them, if thats not enough then go to the dealer you purchased the trailer from and between them you will most likely get a more informed decision based upon a lot of experience with many variables and industry recommendations.
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Old 12-03-2019, 07:51 AM   #76
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I recently upgraded to the Goodyear Endurance, load range E tires, they didnít offer load range D on their website at Discount Tire. I noticed a discussion going on at the wheel balancer. It was a Ďsafety inspectorí telling the techs that my rims were not rated for the 80 psi max the tire were rated for. I told them that is ok, 55psi will do the job with plenty of margin. I had already looked over the Goodyear inflation charts. FWIW.
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Old 12-03-2019, 09:33 AM   #77
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I have a single axle TT that weighs 3400lbs loaded, and I opted to go to E rated tire with 80psi max pressure . I run 60-65psi and it rolls down the road beautifully w/just a touch of sidewall flex. They are speed rated to 81mph which is another reason I switched, I usually drive 70mph on open hwy with no worries.
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Old 12-03-2019, 03:13 PM   #78
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I have tried to weigh only one side of my trailer several times to no avail. Couldn't find a scale that would allow it. Either had physical barriers on each entrance side or was prohibited by the weigh master.
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Old 12-03-2019, 07:24 PM   #79
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I have tried to weigh only one side of my trailer several times to no avail. Couldn't find a scale that would allow it. Either had physical barriers on each entrance side or was prohibited by the weigh master.
I don't know where you live but here in WA State the scales used to monitor commercial traffic are often closed, only open at times designed to surprise truckers.

I have one near my house i use that's closed most of the time, only opened at random intervals to catch gravel haulers and log trucks by surprise.

I can weigh each side as there are no barriers and the weight readout is turned towards the window so I can see it. Always left on.

If you ever pass a scale-house in your travels that is signed "Closed", check it out.

Also check your local trucking companies (moving and storage) to see if their scale will allow you to weigh with one set of wheels off the platform.

If you know any local Race Teams, many of them often have individual wheel scales used for chassis setup.
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Old 12-06-2019, 10:12 AM   #80
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Originally Posted by Tony K View Post
I have a single axle TT that weighs 3400lbs loaded, and I opted to go to E rated tire with 80psi max pressure . I run 60-65psi and it rolls down the road beautifully w/just a touch of sidewall flex. They are speed rated to 81mph which is another reason I switched, I usually drive 70mph on open hwy with no worries.



Two things to remember.
The Load Formula for St type tires is based on an assumed max operating speed of 65 mph. Higher speeds are possible but require adjustments in Load (decrease) and/or inflation (increase).


Also the SAE speed test (where the "rating" letters come from is a test designed for passenger car application and only requires a tire be capable of running 10 minuets at the max speed.


If you ever plan on towing faster than 65 I suggest you get something in writing from your tire supplier that approved continued non-stop operation at the tire max rated load at the stated speed. I would be interested to hear from anyone that gets a reply in writing.
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