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Old 02-21-2012, 10:43 PM   #1
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02/12: New Tire Discussion on Woodalls: LT versus ST and more.

There's a new discussion on WOODALLS in re LT versus ST (and a great deal more depth besides). Three threads and about 30-pages. As one put it, (roughly) "first new data in over three years of roundy-round threads."

Those of you who read on other vehicle sites may recognize the screen name CapriRacer as the nom de plume of Barry Smith, tire engineer and owner of the invaluable tire information site

Barry's Tire Tech

who, along with a retired tire engineer TireMan9 (and some fairly well informed amateurs) have breathed new life into this subject (link below).

I gathered a few quotes for my own notes, starting with the opening post of this thread by CapriRacer, with other quotes below it (in a revisit of an earlier thread):


OK, I'll try this again but with a different tack.

I am of the opinion that ST tires should have a 15% reserve capacity (85% of the load at a given pressure) in order to be reasonably sure they won't fail. There are a couple of ways of estimating what the actual load is on a given tire of a trailer, but the best way is to actually measure each tire. The RMA has a procedure to follow:

RMA: Tire Service Professionals

I am of the opinion that this 15% reserve capacity is likely to require higher load ranges and larger sized ST tires - or both. And maybe even a step into LT type tires - and here is where it gets tricky.

While I feel uncomfortable recommending that LT tires be loaded to their maximum load, that is in essence the result. I feel uncomfortable with that because I don't have enough experience to say it with confidence. However, I have no hesitation in recommending replacing ST tires with LT tires if it can be done with enough clearances around the tire.

A couple of other points:

ST tires can be inflated 10 psi over the maximum pressure listed on the sidewall of the tire - and I'd recommend that if you can't get to a 15% reserve capacity.

Recent bulletins from the tire industry indicate that tires degrade simply due to time. The age of a tire is important even if the tire is unused.

There is some disagreement over how to best express this age limitation,
but my take is:

If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years. If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years. States in between are ..... ah ........ in between.


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


A rule of thumb for estimating if you need more load carrying capacity:

Check the cold (ambient temperature) tire pressure before starting off. Measure the inflation pressure after an hour of driving.

If the tire pressure build up is less than 10%, it's OK. If the pressure build up is between 10% and 15%, then continue to monitor until you are sure it is not above 15%. If the pressure buildup is 15% or greater, add load carrying capacity (and one of the ways to do that is to add pressure). For ST and LT tires, NEVER use more than 10 psi over the sidewall pressure.


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


the 40% rule:

If the rim you want to put a tire on is wider (or narrower) than the rim width specified, then the tire's section width is wider (or narrower) by 0.20" for every 1/2" change in rim width.


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


ausie607 wrote:

......What criteria would you use when/if you were shopping for new 'ST" tires.......

I'd be modifying my trailer to make sure I was not exceeding 85% of the rated load.


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


. . I will jump on that bandwagon, too! I think going up in tire size will pay more benefits than anything else.


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


. . For the same "size" and Load Range, an ST tire carries between 9% and 15% more load than a comparable LT. For the purposes of simplicity, I am going to call this 12%. This is close enough for our purposes.


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


Woodalls Open Roads Forum: Revived Trailer Tire Thread (formerly on the 5th Wheel Forum


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


FastEagle RV Tire Blog
RV Trailer Tires


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


TireMan9 Blog
www.RVTireSafety.com


TM9: trailer tires need to run the max sidewall inflation all the time. Increased inflation will decrease the slip angle needed to generate the cornering force so increasing the inflation will also decrease the shear internal to the tire at the interface between the belt edges and should also decrease the tendancy to peel the belts off the carcass.


.
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Old 02-24-2012, 12:22 PM   #2
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A few more notes:

[Tire engineer] TM9:

Two significant differences: Tread depth is less with ST tires. That allows them to run cooler at same speed, load & inflation

ST have a speed restriction of 65 vs 85, 99 or faster for LT tires.

It is fact that max operating temperature is the main controller of a tire's durability.

[Contributor] ERS will probably agree that if you say you need to hold max operating temperature constant when you vary speed, load and tread depth, so when you increase one or more of these three the others must be lowered.

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

I believe [tire engineer] CapriRacer explained this much earlier. My understanding is that a different K factor is used for ST's than for LT's. The LT load rating displayed on the tire is calculated with a greater safety factor and it is possible that an LT marked 3042# could be stronger than an ST marked 3640#.

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

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Old 02-24-2012, 01:19 PM   #3
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After reading all these different tire threads I have decided to just go buy a couple of blocks of solid rubber and carve my own tires. So much he said vs. he said in all of them. Who knows what to believe. Seriously, I just ordered a pair of Marathons and I think that they will work just fine for my little Bambi II on the origional 14 inch wheels.
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Old 02-24-2012, 08:52 PM   #4
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Sir, you do a disservice to your RV fellows and to men who've spent their professional careers in the tire industry with that.

Lighter trailers, lightly used, and in more temperate climates are the least likely to have problems.

Those of us without your luxury -- full-timing, often in the hottest parts of the US, and who may also be unable/unwilling to suffer tire failure on heavy trailers -- with potential, consequent damage upwards of $5,000 per incident (and on trailers not so easily serviced as an Airstream) find the subject, now, to finally have some controls on it.

Numbers that can be made to work. Hallelujah!! Tires neither too little nor too much in ability, but just right.

.
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Old 02-25-2012, 08:27 AM   #5
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Apparently I have offended you in some way. That was certainly not my intention. For me it is a matter of information overload. I have found that if you place 10 so called “experts” in a room together, you will get 10 different opinions on the same subject. That is exactly what I see in all these different threads discussing tires.
"Lighter trailers, lightly used, and in more temperate climates are the least likely to have problems.” If that is indeed true then I should have very little to worry about with my tire choice.
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Old 02-25-2012, 09:17 AM   #6
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It is true that people have different viewpoints and if you get 10 "so called 'experts'" you will probably get different opinions though probably not 10 of them. Maybe with real experts you will get fewer differences. The process of coming to agreement is sloppy and difficult. We are trying to find answers by comparing experiences and what we can find out in a variety of ways. There are some pretty smart people looking for answers. The proper tires for trailers are especially difficult to understand and the tire industry has not been much help.

I also find the tire threads (and other threads at times) frustrating and sometimes I need a rest from the fray. I avoided this thread for a couple of days, but have failed to stay away. But I want to put the best tires for the purpose on our vehicles and not punt to a tire that appears from many accounts to be substandard. It may be the best choice for your very light and small trailer; I haven't spent time thinking about Bambi's since I don't have one. But my only thought is with a single axle I'd want to the best damn tire I could find because a blowout could be a really bad experience; maybe that block of carved rubber would be the best solution.

I did find the block of rubber comment funny and perhaps wood would work better. If wooden wheels were good enough for the pioneers, maybe they're good enough for us.

Now, everyone step back from the keyboard, take a deep breath and praise aluminitis.

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Old 02-25-2012, 10:16 AM   #7
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Quote:
Originally Posted by AWCHIEF View Post
Apparently I have offended you in some way. That was certainly not my intention. For me it is a matter of information overload. I have found that if you place 10 so called “experts” in a room together, you will get 10 different opinions on the same subject. That is exactly what I see in all these different threads discussing tires.
But if you ask 10 experts if china st tires are junk you will get the same answer from them.
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Old 02-25-2012, 10:43 AM   #8
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Quote:
Originally Posted by AWCHIEF View Post
Apparently I have offended you in some way. That was certainly not my intention. For me it is a matter of information overload. I have found that if you place 10 so called “experts” in a room together, you will get 10 different opinions on the same subject. That is exactly what I see in all these different threads discussing tires.
"Lighter trailers, lightly used, and in more temperate climates are the least likely to have problems.” If that is indeed true then I should have very little to worry about with my tire choice.
Not offensive. Dismissive. (And forget it, I'll look forward to your posts on other subjects. No doubt I've been adamantly in opposition to someone on some good-better-best debate, and the next morning been writing them a Thank You for a post on another subject altogether).

And if we can find [10] authorities disagreeing on a subject where numbers are used to determine validity, I'd like to see it. Differences in interpretation, maybe, disagreement, no. That's the power of numbers.

The Woodalls thread pulls back the curtain on some of the numbers.

.

.
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Old 02-27-2012, 06:29 AM   #9
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I read through the entire thread and took away a number of things I consider useful that appear to be grounded in facts insofar as there are a couple of people inside the industry on the thread who can vouch for them. I also read through the blog linked from the thread. It was about four hours of reading overall and well worth it.

1) ST and LT tires have similar internal construction and differ little. The minor differences mentioned were that STs tend to be made in lower-volume facilities that may lack the sophistication of the larger plants that make LT tires, the tread is thinner which reduces the heat buildup somewhat, and the sidewall markings are different. The speed restriction and the higher max load are due to anticipated use not due to tire construction. There was some speculation that the tires are tested slightly differently.

2) The tire engineer guy thinks that the failures of ST tires is mainly due to overloading and insufficient pressure for load and speed. Many travel trailers are loaded beyond GVWR, and even those that are not will inevitably have some difference in weight distribution from side to side and among axles. He that ST tires, if run at speeds over 65 MPH, should be inflated 10 PSI beyond the load and inflation tables, and there was spirited discussion of whether it was safe and sensible to do this if the tires were already at max load and therefore max pressure.

3) The perceived improvement in longevity with LT tires is due to the fact that people who install LT tires choose bigger ones than the ST tires they replace. Replacing the existing ST tire with a larger ST tire (or one in a higher load range and then inflated to a higher pressure) would accomplish the same thing.

4) Tire engineer guy said that the deterioration of tires over time is affected by temperature and suggested a six year life for areas with hot weather and a ten year life for areas with cold weather. However in the ensuing discussion of failures there was never an example brought up of a tire that failed just because it was old.

5) No reason to use nitrogen rather than air

6) There was some brief discussion of the XPS Rib and other "all steel" tires with the tire engineer guy saying that these were designed primarily to be able to be retreaded or regrooved, and unless you were going to do that, there was no reason to run these tires. While they may be great tires there are other great tires that are cheaper and have a better ride but aren't retreadable.

7) There was some discussion that the RV industry as a whole is specifying and installing tires that are too small, that car manufacturers by and large don't install tires that run constantly at maximum load, and trailer manufacturers probably shoudn't either. Talked at length about the vehicle manufacturer having a responsibility to select suitable tires and about the testing and selection process car manufacturers use, and how it differs from the approach RV makers use.

8) There was some discussion of pressures and the affect on ride. Tire engineer guy likes higher pressures, says if you reduce pressures because the tires aren't at max load you adversely affect tire life, says impact on ride is minimal and should be compensated for by vehicle suspension. Said if you want a softer ride keep the pressures low and move to a larger tire, ride will be the same and capacity will increase

9) Though not relevant to trailer tires there was some discussion of the four-way tradeoff between traction, treadwear, and rolling resistance, and how treadwear is poor on most OEM new car tires because they are optimized for traction and rolling resistance.

In my situation I've been airing down to 50 PSI (from 65 max) because I run below max load. I'm going to stop doing that and keep the tires at 65. Going to be more careful about daily pressure checks, I do them but occasionally have been sloppy in the past.

I think in most cases, given all the above, most people switching to 16" rims and LT tires could get the same benefit by upgrading size or load range on the existing rims.
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Old 02-27-2012, 11:29 AM   #10
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We had tire failures on both OEM Goodyear Marathons (load range D) and on one Maxxis (load range E). There is no other 15-inch ST tire with a higher load rating, and 225/75x15 is the only size available (for 15-inch wheels) that will fit in our wheel wells. Carlisle reviews seem no better than Marathons; and Tow Master, Green Ball and other brands are not widely distributed and have mixed reviews.

On the otherhand, 16-inch Michelin LT tires have excellent reviews, although mostly for installations on light trucks. However, there are recent reviews from SOB and boat trailer owners that made the switch to LT tires because of Marathon failures. So, Airstream owners are not alone in the quest for better tires.

I view the purchase of Michelin XPS Ribs and other LT tires like travel insurance. I'd rather spend the money on better tires, than on roadside assistance, towing charges, wheel well repairs, and time spent on roadsides and in tire shops.
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Old 02-27-2012, 12:56 PM   #11
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Nice job, Jammer. I've had a few mails with one participant, and I'm going to go back and re-read to nail some things down.

The questions raised -- floated -- are the most important part of the thread.

Max sidewall pressure, with the tire tread width matching the rim width, on a tire having a 12-15% reserve capacity. Closed shoulder tread design of modest tread depth. But not in ST.

Changing to LT is a no-brainer. Yet an "exact match" for a particular ST rating is not.

Seems direct enough. Made "simpler" by sorting out heavy wheel positions from lighter ones via individual wheel position weights, not just axle averaging. Some interior re-arrangement might bring to light some needed info, and FF vs RR axle discrepancies need investigation (for those so inclined).

Simple, until one needs to inflate past sidewall maximum to ensure reserve capacity . . or some of the other "unusual" surmises present.

Added to that that IR temp guns and some TPMS systems measuring "methods" are still a matter of luck due to tire construction and actual internal temperatures. Good to use, but not as good as some of us had hoped.

And so forth.
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Old 02-27-2012, 01:06 PM   #12
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Quote:
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We had tire failures on both OEM Goodyear Marathons (load range D) and on one Maxxis (load range E).
Was the Maxxis inflated to the maximum load range E sidewall pressure or to the lower load range D pressure indicated on the trailer sticker when it failed?

Quote:
I view the purchase of Michelin XPS Ribs and other LT tires like travel insurance. I'd rather spend the money on better tires, than on roadside assistance, towing charges, wheel well repairs, and time spent on roadsides and in tire shops.
I think the point is that the Michelin XPS Rib, at roughly $300 in 245/75R16, is no more reliable than (say) the Michelin A/T2, at roughly $200 in the same size. The only advantage is that it can be recapped, which isn't a benefit unless you're putting 20,000 miles a year on the tires. For everyone else they'll age out before they are ready to be recapped.
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Old 02-27-2012, 01:22 PM   #13
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Quote:
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Was the Maxxis inflated to the maximum load range E sidewall pressure or to the lower load range D pressure indicated on the trailer sticker when it failed?



I think the point is that the Michelin XPS Rib, at roughly $300 in 245/75R16, is no more reliable than (say) the Michelin A/T2, at roughly $200 in the same size. The only advantage is that it can be recapped, which isn't a benefit unless you're putting 20,000 miles a year on the tires. For everyone else they'll age out before they are ready to be recapped.
Just a FYI for everyone. The M/S2's and the A/T2's cost the tire dealer about $88. I have several friends that can sell me the tires at $100 each so be aware that above this price point the dealer is just padding his/her pocket. This price does not including mounting and balancing as I do it myself.

Above that I agree with Jammer on all other points.
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Old 02-27-2012, 01:43 PM   #14
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Nice job, Jammer.
Jammer,

If you pass Rednax testing for a summary I'm sure you'd pass mine. I'm glad not to have to read the thread.

One thing not considered is the frequency of tread separation with Marathons and possibly with other ST tires vs. the LT tires— is it caused by low manufacturing standards for ST tires? It is suggested, but not explicit. I think ST tire manufacturers may think people only tow trailers short distances every year and the ST's don't have to have standards for heavy use. It appears to me (just guessing) that a lot of us here do travel a lot and may have worse experiences than the average RV owner—speculation city of course.

Next is whether specific brands are better, all other things being equal. I realize all things are never equal, but I will continue. My experience with Michelins is they have good traction right up to the time tread wear indicates replacement. They also ride smooth and last a long, long time. That alone is a good reason to choose them.

I determine air pressure by calling the tire manufacturer and asking them. They do not recommend maximum pressure but pick pressure by asking about the weight they support. I also see what others are doing on the Forum. I check tread wear after that—it serves two purposes: to see when to rotate tires and it will tell me whether the tires are over- or underinflated. For the Michelin 16" LT's, I started with 68 psi. After about 20,000 miles I saw a little more wear on the outer tread indicating more pressure was needed. Note that it took 20,000 miles for this to show up, so I decided the difference to optimal pressure wasn't very much. I now inflate the tires to 72 psi just like Moosetags. Maybe I should have believed him right away.

It is interesting that it was said ST and LT tires are not constructed too differently. But maybe manufacturers make them differently. Michelin does not make ST tires. Maybe the comparison was between Goodyear LT's and ST's.

Gene
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