Interply Shear Question - 15" XL vs 16" LT

[billtrev]

It's time to get new shoes....


Trailer is a 2006 Safari 25' FB. In 2013 we purchased the trailer and replaced the 2006 GYM"s with Michelin LT225/75/16 LTX's and Sendel T-03 wheels. These tires are due for replacement due to age.

Still have the OEM 15 inch wheels.


I have read Tireman9's recommendation to inflate to max sidewall pressure to help mitigate the Interply Shear forces on tires in tandem axle service.


My question is which tire is less likely to be damaged by Interply Shear- a 16" LT225/75/16-E @ 65psi (which is 15 psi below max sidewall pressure) or a 235/75/15-XL @ 50 psi (which is at max listed sidewall pressure)?













lt

[r carl]

You don't need to worry about that with Michelins.

[OTRA15]

Why would Michelin tires be immune from interply shear [IPS] on a 25' AS with two axles? IPS is not as pronounced on a single-axle trailer, but what is unique about Michelins that permits them to avoid the laws of physics?



IPS search results FYI: https://www.google.com/search?q=inte...=airforums.com

Click on the orange arrows in quotes to go to the posts:

Originally Posted by Tireman9

The Interply Shear is a function of the tires being dragged around every turn and not rotating about a center-line that points to the center of the turn radius so any tire will get these extra forces.
. . .

Originally Posted by Tireman9

Yes, the Interply Shear forces will be higher on multi-axle trailers than single axle trailers.

r carl --what is unique about Michelins?



Thanks,

Peter

[r carl]

r carl --what is unique about Michelins?

Thanks,
Peter

What is unique is the plies are set in at a different angle than other brands.

[OTRA15]

Thanks.

Maybe Tireman9 will chime in here because he was quoted yesterday. Here is another quote which continues my confusion about whether Michelin tires are immune from IPS, or just hold up better because of the different configuration of their tire plies.

Originally Posted by Tireman9

All radials have interply shear.
. . .

Thanks,

Peter

[r carl]

I think a tire not properly vulcanized, or designed can fail from interply shear.

[Action]

Any tire "not properly designed" will fail including tires made by Michelin.

All tires of all brands experience the shear forces or tire slip IF the trailer makes a turn. That happens on very turn, every time. And many non-Michelin tires do well on a trailer. In fact Michelin does not recommend their tire for use on any trailers. Even though many trailer owners use Michelins.

>>>>>>>>>>Action

[SailorSam205]

To directly answer the OP. My non-expert opinion...

The larger tire will hold up better. Due to more area on the surface of the tire. I expect damage due to shear is cumulative. On a smaller tire, each point on the tire will accumulate the shear forces at a higher rate. I have no idea how much of a difference 1" makes though.

I'd suspect increasing the load range on a same size tire makes more of a difference than increasing the size and staying at the same load range.

My question to the OP, if the rule is to run TT tires at max cold inflation value, why are you inflating to 15psi below the max?

[r carl]

Originally Posted by Action

Any tire "not properly designed" will fail including tires made by Michelin.

All tires of all brands experience the shear forces or tire slip IF the trailer makes a turn. That happens on very turn, every time. And many non-Michelin tires do well on a trailer. In fact Michelin does not recommend their tire for use on any trailers. Even though many trailer owners use Michelins.

>>>>>>>>>>Action

I don't think Michelin makes a tire not properly designed.
Michelin must have told Airstream it was OK to put on their LT tires on new Airstreams.....

[Action]

Originally Posted by r carl

I don't think Michelin makes a tire not properly designed.
Michelin must have told Airstream it was OK to put on their LT tires on new Airstreams.....

I did not state Michelin tires are not properly designed. Except the ones that have been recalled.

Michelin designs and makes tires. The designed use for those tires are stated in lots of publications and their website. Michelin will sell tires to any user, including Airstream.

However in all of Michelin's publications, the website and in verbal conversations from customer service there is NO trailer use recommended. Michelin does NOT make a ST tire either. Michelin's stated use for their tires is for passenger vehicles and light trucks. They do not recommend usage for trailer of any type.

Airstream installs Michelin tires because the buyers of their trailers WANT Michelin tires. Airstream is in the business of doing business to sell trailers as their buyers want them equipped. If you want a brand new Airstream and want Michelin tires. That Airstream will have Michelin tires.

And Michelin still does not recommend their tires for trailer usage. Don't take my word for it. I am just a guy on a keyboard. Contact the Michelin company directly. (Not the tire dealer)

>>>>>>>>>>>>>>>>>>>>>>Action

[Commish]

I'm not exactly super sharp when it comes to interply shear, but the question that continues to elude an answer is simply, "why are you using LT (Light Truck) tires on a trailer? I understand Michelin will not warranty an LT tire on a trailer. Maybe there's a reason for this. Yet, I saw LT Michelins on a new AS on a lot. An LT tire likely has sidewalls engineered for the stresses on a vehicle, not a trailer.

Color me confused...

[thewarden]

Originally Posted by SailorSam205

To directly answer the OP. My non-expert opinion...

The larger tire will hold up better. Due to more area on the surface of the tire. I expect damage due to shear is cumulative. On a smaller tire, each point on the tire will accumulate the shear forces at a higher rate. I have no idea how much of a difference 1" makes though.

I'd suspect increasing the load range on a same size tire makes more of a difference than increasing the size and staying at the same load range.

My question to the OP, if the rule is to run TT tires at max cold inflation value, why are you inflating to 15psi below the max?

I do not believe there is a "rule" to run TT tires at max cold inflation. Tire manufacturers publish inflation/load tables with their tires to allow the user to choose an inflation rate to meet their particular load. At 65 psi, the Michelin 16" tire safely exceed the loads that a typically loaded 25-28' AS would be. Inflating to the max should only be done if max load carrying capacity is needed. Higher air pressures will certainly contribute to a rougher ride for the trailer, not a good thing. Lower pressures soften the ride, so it is always best to run tire pressures appropriate to the load you are carrying. It is always advisable to add 8-10 % as insurance.

[Action]

Originally Posted by Commish

I'm not exactly super sharp when it comes to interply shear, but the question that continues to elude an answer is simply, "why are you using LT (Light Truck) tires on a trailer? I understand Michelin will not warranty an LT tire on a trailer. Maybe there's a reason for this. Yet, I saw LT Michelins on a new AS on a lot. An LT tire likely has sidewalls engineered for the stresses on a vehicle, not a trailer.

Color me confused...

Your statement is mostly true. Michelin does not recommend their LT tires on any trailer. As to warranty coverage I am not sure about. It may depend on how the tire failed as to if there would be warranty coverage.

Back to the LT question - Many users use a LT tire because it works. In the past and some applications now the trailer industry has installed tires that JUST barely hit the load needed. This was in an effort to keep the total retail price down. The rational was a travel trailer isn't used on a daily basis for the most part. So the parts of a trailer won't see that kind of use. So why build in that kind of product if it isn't going to be used that way? Therefor cheap tires to get to the market cheaply and make a sale. LT tires tend to be bigger, heavier, carry more load and are more expensive.

An example (Not real numbers) A 4000 pound trailer gets four 1000 pound rated tires. To hit the 1000 pound load per tire that same tire HAS to be inflated to max pressure. Anything less than max and the tire may suffer a failure. Unlike a passenger car tire that may be rated for up to twice the load it may see in service. Trailer tires are usually always loaded close to their max limit. And this assumes the end user does not exceed the load rating of the trailer. Another thing, a trailer tire especially a multi-axle trailer the tire get pulled or pushed around a curve. This is because the axis of the trailer axle does not hit the turning center of a curve. This puts a lot of strain on the side wall of a trailer tire. (inter-ply shear) So trailer tires have to be beefy enough to handle that stress as well.

For those reasons, moving to a much higher load rating for a tire solves some of the above issues. Tires should be inflated to the recommended pressures to handle the loan and the tires should be rated at least the max load possible plus a margin. TO achieve that result many have moved to a larger rim diameter or to a LT tire that may be larger. (Some do this because everyone else did it and they thought it was a good idea not knowing exactly what is happening)

>>>>>>>>>>>>>>>>>Action

[GammaDog]

I happened to talk to Michelin US corporate customer support this morning (no fooling). I had questions about their LTX M/S2 tires which were standard on my 2014 Eddie Bauer and may be nearing time for replacement. We've put about 30,000 miles on these tires. They've held up well. I would gladly replace them with another set of Michelins (and add TPMS at the same time). I asked two questions: 1. Are these tires warranted when used on trailers? 2. If I was to put new Michelins on, what is their preferred tire for this application. The answers: 1. The Michelin warranty applies to tires specified by vehicle manufactures including LTX M/S2 on this Airstream 2. Their preferred tire for trailers of this size (our GVW max is 7,300 on two axles with 225/75R16 tire size) is the XPS RIB. Just thought I'd toss that news into the soup...

[Action]

This isn't a new thing

http://www.airforums.com/forums/f438...ty-181219.html

http://www.airforums.com/forums/f438...ire-71294.html

In my search I did not find the thread with a cut and paste of a chat session between a forum users and a Michelin customer service person. It exists on this forum somewhere. The Michelin customer service person was asked about trailer application for Michelin tires. The reply was Michelin doesn't make a tire for RV trailer application.

Not knocking Michelin tires. I think they are a fine tire and I use them. Just reporting what Michelin has stated.

>>>>>>>>>>>>>>Action

[OTRA15]

. . . and another thread heads off to the tire races . . .



The new search function, in the blue box above, works great! Searches for "Michelin trailer use" and "Michelin RIB" will find many threads and posts on those topics, without this thread having to re-hash the same old stuff IMO.

The OP here asked:

Originally Posted by billtrev

. . .
. . . which tire is less likely to be damaged by Interply Shear . . .
. . .

. . . and the discussion then broadened a bit to include the possibility that Michelins might be less vulnerable to Interply shear than other tires.

Any chance we could stay focused on these narrow issues?

Thanks,

Peter

[SailorSam205]

Originally Posted by thewarden

I do not believe there is a "rule" to run TT tires at max cold inflation. Tire manufacturers publish inflation/load tables with their tires to allow the user to choose an inflation rate to meet their particular load. At 65 psi, the Michelin 16" tire safely exceed the loads that a typically loaded 25-28' AS would be. Inflating to the max should only be done if max load carrying capacity is needed. Higher air pressures will certainly contribute to a rougher ride for the trailer, not a good thing. Lower pressures soften the ride, so it is always best to run tire pressures appropriate to the load you are carrying. It is always advisable to add 8-10 % as insurance.

I've gotten that rule from several people who have experience as tire designer or have other extensive industry experience. Here are a couple of very recent quotes from someone I consider credible.

Roger Marble, listed as an RV tire expert posted in his blog dated Friday, June 15, 2018 titled "What should Airstream and similar type trailer owners do?" states:

"Finally, with a multi-axles trailer, you should use the tire sidewall pressure number as your "Cold Tire Inflation" to try and lower the Interply Shear forces that are trying to tear the tire belts off the carcass."

In his June 21,2018 blog on filing a claim with NHTSA he states on tire failure:

"Always run the tire pressure on the tire sidewall for your CIP (cold inflation pressure) if you are pulling a trailer."

Sounds pretty unequivocal to me. On motor homes and other non-trailer vehicles matching load to inflation is the appropriate course of action. If you are more worried about shaking what is in your rig than damage caused by a blow out - you are free to lower your tire pressure. For me, I'm more concerned about blow outs and damage cause by tread separation.

[CapriRacer]

Originally Posted by billtrev

....... My question is which tire is less likely to be damaged by Interply Shear- a 16" LT225/75/16-E @ 65psi (which is 15 psi below max sidewall pressure) or a 235/75/15-XL @ 50 psi (which is at max listed sidewall pressure)?

The LT225/75R16 at 65 psi has a load carrying capacity of 2335#. The 235/75R15 XL at 50 psi has a load carrying capacity of 1985# or 2065# depending on the exact tire in question (after factoring in the 10% derating for trailer service)

So I'm going with the LT tire at the conditions stated as having less IPS.

And regarding Michelin's comments about their LT tires on trailers: You have to be very careful how the question is asked. Officially Michelin (and all tire manufacturers for that matter!) can not be in a position to recommend any tire for trailer service that doesn't match what is stated on the vehicle tire placard. If it doesn't say "LT", then the can't 'approve", "recommend", or any other wording you chose to make. One way to state this is to say the warranty doesn't cover such an application.

HOWEVER, LT tires can be used in trailer service, and the warranty MIGHT be in force. It will depend on how the warranty is actually worded and how it is interpreted.

But I think the bigger question is: Would it be better to use a 15" ST tire that is called for on the vehicle tire placard, or a 16" LT tire that may or may not be officially covered by a warranty - and I vote for the larger LT tire, simply because it will have more load carrying capacity at the conditions used (and this load carrying capacity issue to a bit complicated to explain.).

[billtrev]

Originally Posted by CapriRacer

The LT225/75R16 at 65 psi has a load carrying capacity of 2335#. The 235/75R15 XL at 50 psi has a load carrying capacity of 1985# or 2065# depending on the exact tire in question (after factoring in the 10% derating for trailer service)

So I'm going with the LT tire at the conditions stated as having less IPS.


........


But I think the bigger question is: Would it be better to use a 15" ST tire that is called for on the vehicle tire placard, or a 16" LT tire that may or may not be officially covered by a warranty - and I vote for the larger LT tire, simply because it will have more load carrying capacity at the conditions used (and this load carrying capacity issue to a bit complicated to explain.).

Thanks for all the replies. I wasn't sure that this question would generate much interest....


CapriRacer thanks for your insight.

[OTRA15]

Originally Posted by CapriRacer

. . .
So I'm going with the LT tire at the conditions stated as having less IPS.
. . .

Thanks for the input. Is there something special about Michelin tires which makes them less subject to IPS than other brands, as was suggested in these early posts?

Originally Posted by r carl

You don't need to worry about that with Michelins.

Originally Posted by r carl

. . .
What is unique is the plies are set in at a different angle than other brands.

In your opinion, CapriRacer, is this last statement correct?

Thanks,

Peter