16" wheels/LT tires

[Ag&Au]

Originally Posted by dkottum

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.

Ken .

[CapriRacer]

Originally Posted by Ag&Au

.......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.

Originally Posted by Ag&Au

....... 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.

Originally Posted by Ag&Au

.......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.

Originally Posted by Ag&Au

.......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.

[BoldAdventure]

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.

[paiceman]

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.

[Vlamgat]

Originally Posted by paiceman

. 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.

[Action]

Originally Posted by Vlamgat

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

[Ag&Au]

Originally Posted by CapriRacer

Yes, that is what I am saying.



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.



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.



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.

Thanks for taking the time to explain the origin and the reason for those numbers. It make it much easier to arrive at an informed decision.

The one thing that is obvious from this thread is: There is no way to be absolutely safe from tire failure. If if the engineers do their job and the user is diligent in his selection, a malfunction in a manufacturing or chemical plant, can still produce a substandard tire. As illustrated by the Michelin and other recalls, the user is the ultimate tester. Even if we could make tire manufacturing 100% reliable, there is still the issue of road hazard.

The take away for me is to exercise maimum diligence in selecting your running and towing gear and inspect it often and hope your inspections reveal faults before they cause failure. Keep all this in mind and then find a thought process that allows you to still enjoy the drive,

Ken

[switz]

Seeing that Airstream shipped our 2014 Airstream 31' Classic with four 15" Goodyear Marathons (ST225/75R15D ) rated 2,540 pounds at 65 psi each (four tires equals 10,160 pounds capacity) and the GVW is 10,000 pounds, they do not appear to be following the safety margin concept very closely.

In our specific case, our tongue weight is about 1,345 pounds which would mean the tires could be carrying 8,635 pounds at GVW. The four 15" Michelin LTX (P) 235/75R15 XL tires are derated to 7,940 pounds (side wall load rating would be 8,732 pounds). They would be of inadequate load capacity at GVW.

One tends to overlook the weight loading when parked, but the tires, axles and tongue jack are supporting the GVW then. So the correct tire size helps....

Maybe that is why Airstream is putting the SenDel T03-66655T wheels and Michelin LT225/75R16/E LTX M/S2 tires on the 2015 Classics as standard tires. Four tires are rated 10,720 pounds at 80 psi.

[Action]

Originally Posted by switz

Seeing that Airstream shipped our 2014 Airstream 31' Classic with four 15" Goodyear Marathons (ST225/75R15D ) rated 2,540 pounds at 65 psi each (four tires equals 10,160 pounds capacity) and the GVW is 10,000 pounds, they do not appear to be following the safety margin concept very closely.

While the tongue weight will take some load, I would suggest price is a factor in this example.

>>>>Action

[Gene]

Airstream is very, very slowly converting to Michelins with 16" wheels. When I discussed Michelins with them at least 5 years ago, they were starting to offer them as a barely disclosed option. They did have a display with 16" wheels and tires at the office then. I think they offered a Goodyear LT tire and maybe also Michelin. I ended up trading OEM wheels with them, picking up 16" Michelin LTX tires at Discount Tire in Dayton, and having Airstream install it all. The OEM 15" wheels looked bad as the coating was failing and I got new wheels at a substantial discount. The tire distributer had a one year warranty and wouldn't cover it as I was over the one year.

Over time, Airstream has made the Michelin 16" LTX tires more and more available as either an option or on specific models. Michelins cost about 2 times more than Marathons and larger wheels must cost a little more. But the Goodyear LT option is gone and they have, at least in this instance, listened to customer about Michelins.

Though Michelin had a recall, they didn't stall or try to limit it—they did it on their own and it must be costing a mint. Unfortunately we were out of the recall period as I was hoping for all new tires.

And yes, you have to make the decision yourself based on all available knowledge, trying to sort through the crap to figure out the best thing to do. That is something we have to do with everything, every day. I wish there were easy answers and better research. RV research on many things is weak or nonexistent as there's little money in it.

I am getting close to 5 years on the Michelins and they have lots of tread left. Many here have recommend tires should be replaced at 5 years because of aging (by that standard, I should have been replaced generations ago). Michelin has been quoted as saying 10 years so long as they are regularly inspected. It has been said elsewhere on this Forum that Michelin says 7 years, but I couldn't find anything definite on their website. The 10 year quote comes from Edmunds' website. Regardless of how old they are, regular inspections are a good idea. I don't know where the 5 year rule comes from—it may be "conventional wisdom", thus repeated so often it is believed to be true. I get 65-75,000 miles on Michelins on motor vehicles and that is often more than 5 years, though not by much. Because there are no drive wheels on a trailer, I expect them to last for even more miles.

Gene

[moosetags]

That has been about my experience, Gene. Old Lucy had her 16" Michelins for four years. We put 60,000 miles on these tires. They showed no discernible tread wear.

We have already gotten the Michelins on New Lucy. The tires and wheels cost us $1,600. We were able to sell New Lucy's OEM tires and wheels for $600. Therefore, the upgrade cost us a total $1,000.

I would think that Airstream could offer a Michelin option for $1,000 or less.

Brian

[slowmover]

Tires that do not spend regular time on the road deteriorate more quickly. Exercise redistributes oils within the rubber. This is the problem with trailer tires and why standard manufacturer recommendations may not apply.

Going with premium tires doesn't change TT replacement schedule greatly given differences for local and individual owner conditions.

I'd check Tireman9's blog and ask advice. Whether a Michelin dealer knows exactly what to look for during a dismount would be key.

Michelins have been known to look fine on outside and not on the interior. This happened to the five year old ones on my truck (2007-2012) with only 80k on them. Three out of four failed on a trip back from San Antonio. I was practically given a new set. Had 4/32's total wear and was looking to take them well past the 120k mark that the original set had delivered.

Reading around I believe this was a problem over a few years that has since been rectified.

Three to five years is the usual recommendation due to service. Were I making a few short trips in cooler weather I'd inspect and go on. But extended touring would be something else again.

[CapriRacer]

Originally Posted by BoldAdventure

What if the tire engineers already did that in the design process and have factored in 15% already? Now we're at 30%?.....

Then tires wouldn't be failing and you wouldn't worry about it.

Originally Posted by BoldAdventure

.....This is just based on a personal preference as the 15% seems to be an arbitrary number you came up with correct?.......

No.

When the Ford/Firestone thing was active (winter of 2000/2001), the company I worked for examined all the tire failures they had on record and discovered that most of the tire failures were coming from SUV's and pickup trucks - where there was no reserve tire capacity (unused tire capacity).

Cars, on the other hand, had very few failures. They also generally had about a 15% reserve. What was even more interesting was that SOME SUV's had a 15% reserve capacity and those tires behaved like the ones on cars

So the company I worked for recommended to all the car manufacturers that it was doing business with that all vehicles have a 15% reserve tire capacity - and most followed through, in particular, Ford. (I have to assume, other tire manufacturers did the same sort of analysis and came to the same conclusions as there didn't seem to be any pushback from the OEMs.)

The result was a drop in the rate of tire failures (although it was hard to sort this out as there were changes on the tires taking place at the same time)

So, No, the number is not arbitrary. It is based on personal experience.

[BoldAdventure]

Ok, great to know then.

So the Michelin LTX M/S2 in 225/75R16 rated at 2680 lbs. with 80 psi.

Derated 10% for Trailering = 2420 lbs. and with a safe margin of 15% = 2057 lbs.

2057 lbs. x 4 tires = 8228 lbs rating.

Which means trailers with 10,000 GVWR running these would be way over a safety margin based on above advice. ??

----------------

Unless the math is 15% & 10% from the original rating. At which it becomes 2010 lbs rating x 4 tires = 8040 lbs.

Either way, this all works out for my trailer math wise. But for others????

But this completely kills it on the 15's.

Michelin LTX M/S2 in 235/75R15 at 50 psi. rated at 2183 lbs.

Derated 10% for trailering = 1964 lbs.
Derated 15% safety = 1669 lbs

1669 x 4 tires = 6676lbs rating.

[Al and Missy]

The 10% derating factor is only applied to p-metric tires, and it is an NHTSA and/or MVSS requirement, not just a rule of thumb.

Also, unless I am mistaken, the load limit applies to the weight the tires are carrying, not the GVWR, so subtract off the actual tongue weight.

[SteveSueMac]

Originally Posted by BoldAdventure

Ok, great to know then.

So the Michelin LTX M/S2 in 225/75R16 rated at 2680 lbs. with 80 psi.

Derated 10% for Trailering = 2420 lbs. and with a safe margin of 15% = 2057 lbs.

2057 lbs. x 4 tires = 8228 lbs rating.

Which means trailers with 10,000 GVWR running these would be way over a safety margin based on above advice. ??

----------------

Unless the math is 15% & 10% from the original rating. At which it becomes 2010 lbs rating x 4 tires = 8040 lbs.

Either way, this all works out for my trailer math wise. But for others????

But this completely kills it on the 15's.

Michelin LTX M/S2 in 235/75R15 at 50 psi. rated at 2183 lbs.

Derated 10% for trailering = 1964 lbs.
Derated 15% safety = 1669 lbs

1669 x 4 tires = 6676lbs rating.

Not exactly. The 16s are LT not P tires. No derating required so you're getting over 10700# capacity - then with the 15% safety margin you have over 9100# available.

Next, that's capacity for your weighed trailer. Your max GVWR is just that - a max. When you're on the scales, you'll see what your trailer axles actually see loaded for camping. For example, my GVWR is over 7000# but loaded for camping, the scales show 5800# on the trailer. While it would be great to get each wheel weight individually, I'm happy knowing the 4 tires are sharing 5800#.

If your GVWR is 10,000, your actual towing weight could be 7500ish (weighing it is the only way to know for sure). That's the capacity you need to worry about. Anything under 9100# would work for you with those 16s.

[Rocinante]

Ok, so how about these General Grabber HTS tires for 15" wheels? They seem to have a higher rating than the Michelin 15" tires, which according to the Michelin site are rated for only 1985 pounds. The 109T rated General Grabber HTS in 235/75R15 XL is rated at 2271 pounds with max inflation pressure of 51 pounds. If that's a good tire, it would seem a better choice than the lower-rated Michelin...unless I am misunderstanding, which is entirely possible.

Oh, and the General is a "low rolling resistance" tire, which sounds like it might be helpful for better MPG when towing.

http://www.michelinman.com/tire-sele...ails#techspecs
http://www.generaltire.com/tires/lig...bber-hts#Specs

Thoughts?

[slowmover]

To be thorough trailer tire load need also take into account, when parked, the additional weight of supplies and people aboard. There are those who travel without fresh water, for example.

[BoldAdventure]

I read him wrong on the derating 10%, thought he was applying it to LT tires too. I know the rating is what it's actually carrying, not GVW, but I'm using it as a measure. I know I could use P tires right now, but maybe not when we go full time.

slowmover I've owned General Tires on several vehicles. I like them, good tire. Can't speak to putting them on Airstreams.

[Ag&Au]

Originally Posted by slowmover

To be thorough trailer tire load need also take into account, when parked, the additional weight of supplies and people aboard. There are those who travel without fresh water, for example.

I would have to think about this concept for a while before I accepted it. Tires are rated for moving at their max rated speed and the associated flexing, scuffing and heating involved. When sitting still in a campground or wherever, none of those dynamics are occurring, and a certain amount of the weight is being born by the tongue jack. So my instincts tell me what happens when parked is not a factor. (within reason of course).

If I am misinterpreting what you said, then "never mind" .

Ken