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Old 04-29-2013, 01:47 PM   #1
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Rivet Great ST tire information

Here is the most informative post I have ever seen on ST tires,
Thank You Shaowcatche of irv2.com for this information.

As many of you have figured out I am a bit obsessive about information and with reported problems with trailer tires and about a 30% failure rate including a couple of folks on this forum who have had catastrophic failures.

Portion of a post by Mike Mitchell, NuWa (HitchHiker) CEO in a discussion regarding trailer tires on the NuWa Owner's Forum.

As we banter about regarding tire types and loading, I believe that we are finally starting to understand a few important things.
I have asked many times for someone to explain how a ST tire can be rated to carry more weight than a LT tire in a similar size, without a good answer.
The answer lies in what is called reserve capacity. To quote from Trailer Parts Superstore and this same statement exist on just about every tire site:

HEAVY DUTY 'LT' TRUCK / TRAILER TIRES
'LT' signifies the tire is a "Light Truck/Trailer" series that can be used on trailers that are capable of carrying heavy cargo such as equipment trailers.

If a tire size begins with 'LT' it signifies the tire is a "Light Truck-metric" size that was designed to be used on trailers that are capable of carrying heavy cargo or tow vehicles. Tires branded with the "LT" designation are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo.

So what is reserve capacity? It is capacity beyond the rating of the tire, capacity that is held in reserve. This reserve capacity comes from the heavy-duty sidewall of the LT type tires. LT's rank at the top of the list when we look at P, ST and LT tires.

Now I finally have an answer to how a ST tire can be rated to carry more weight than a LT tire of similar size.

The ratings of ST tires infringe into the reserve capacity of the tire. This is double bad, because the design of the ST gives us a tire with less reserve capacity to start with as it has a lighter sidewall to start with as most ST tires are much lighter than their LT counterparts.

To quote one tire site:
"Put a different way, the load carrying capacity of an ST tire is 20% greater than an LT tire. Since durability is strictly a long term issue - and the results of a tire failure on a trailer are much less life threatening than on a truck - the folks that set up these load / inflation pressure relationships allow a greater......ah......let's call it load intensity."

There it is in print to be read. They make a calculated decision to give the ST tire a higher load rating because a failure is less life threatening.

I have on a number of occasions pointed out the weight difference between the different tires and have been told that does not matter. Well it does matter. The rubber in the average tire only makes up around 40 some percent of its weight, the rest is in the steel belts, gum strips, steel beads, and the carcass plies. The remaining 60 or so percent of the stuff in a tire is what builds in the reserve capacity.

So to review again, here are some weights:
1. Michelin XPS RIB LT235/85R16 LRE (rated to 3042lbs) Weight 55.41
2. Goodyear G614 LT235/85R16 LRG (rated to 3750lbs) Weight 57.5
3. Bridgestone Duravis R250 LT235/85R16 LRE(rated to 3042lbs) Weight 60
4. BFG Commercial TA LT235/85R16 LRE(rated to 3042lbs) Weight 44.44
5. Uniroyal Laredo HD/H LT235/85R16 LRE(rated to 3042lbs) Weight 44.44
6. GY Marathon ST235/80R16 LRE(rated to 3420lbs) Weight 35.4

So which tires on the list have the most reserve capacity? Well that is not a completely simple answer, as one of the tires is a G rate 110 lb tire and the rest are LRE at 80lb inflation. So if we disregard the G614, then the Michelin XPS RIB and the Bridgestone Duravis R250 due to their all-steel ply construction will have the most reserve capacity inherent in their construction. The twin Commercial TA and Laredo will be next and the Marathon would have little or no reserve capacity available because it was used up in its higher load rating, AND because of it's much lighter construction it had much less inherent reserve capacity to start with.

So what have we learn from this?

I think that the first thing that we learned was that a LT tire can be used at or near it max rated loading without having issues, as they built with "substantial reserve capacity to accept the additional stresses of carrying heavy cargo".

The second thing we may have learned is why ST tires are failing on mid to larger 5th wheels, in that they do not have inherent reserve capacity beyond that rated max loading. Again this is because they have less reserve capacity to start with and their greater "load intensity" used up any reserve capacity that might have been available.

Now, here is an interesting bit of information. I just called Maxxis Tech Line and asked the weights for two tires.

ST235/80R16 LRD 3000 lb rating at 65 lbs of air weights 38.58
ST235/80R16 LRE 3420 lb rating at 80 lbs of air weights 43.43

What??? The Maxxis load range E tire weights almost the same as the Commercial TA?? This is a ST tire that has heavier construction than the GY Marathon at 35.4 lbs. So it has more inherent reserve capacity due to its heavier construction.

Those that claimed its virtues maybe did not know why it was a better ST tire than some of the others, but there it is! It is a heavier built tire with more reserve capacity.

So as one chooses a replacement tire or is asking for an upgrade on a new trailer please get educated on where the reserve capacity exist. Is it inherent in the tire you choose or do you have to factor it into the weight rating of the tire you choose.

The thread Tire blow out - cause unknown
and the survey http://blog.goodsamclub.com/wp-conte...ireSurvey4.pdf
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Old 04-29-2013, 03:12 PM   #2
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dannydimit, that is a fine bit of sleuthing there!

What that poster says makes a lot of sense. It sure does answer a lot of vexing questions.

I happen to own a set of faultless Maxxis tires. They have been great.

Now, let's hope the Maxxis accountants aren't reading your report. If they are like the others' beancounters, they may tell their engineers to quit designing their tires so well. They last too long, which cuts profit margins ... Unless, of course, their growing reputation adds to their sales, which in the long run can award them for their wonderful approach to engineering safety margins.
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Old 04-29-2013, 03:17 PM   #3
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Evan though the specs quoted were all for 16 inch tires, the numbers on the specs for 15 inch L T verses S T tires should be right in line with the 16's
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Old 04-30-2013, 05:48 AM   #4
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Dannydimitt,

I think you will find people who disagree with some of the things reported as "facts" in Mr. Mitchell's post. I know I do. Here is but one:

Quote:
......I have asked many times for someone to explain how a ST tire can be rated to carry more weight than a LT tire in a similar size, without a good answer......
Ask me. I know the answer.

Quote:
......The answer lies in what is called reserve capacity.......
Sadly, no, that is not the answer.

Quote:
.......Tires branded with the "LT" designation are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo..........
Uh.......Mmmmmmm...... No, but let's see where this is going.

Quote:
.........So what is reserve capacity? It is capacity beyond the rating of the tire, capacity that is held in reserve......
I was afraid that this was where this was going - and it's wrong. The way the term is used in the tire industry is that reserve capacity is the difference between the maximum load at the pressure being used and the actual load on the tire.

Quote:
........This reserve capacity comes from the heavy-duty sidewall of the LT type tires.........
Nope. Totally wrong.

Quote:
.....Now I finally have an answer to how a ST tire can be rated to carry more weight than a LT tire of similar size.......
Sorry, but you don't.

- and at this point I will start filling in the gaps.

ST tires are rated at a higher load carrying capacity than LT tires because 1) they are restricted to 65 mph, 2) because they are free rolling, not driven or steered, and 3) because they are not on passenger carrying vehicles.

Mr. Mitchell also quotes ME on the "passenger carrying" issue, but gets the conclusion wrong. The OTHER factors are much more important in determining the load carrying capacity.

Then he completely misses a particularly important point. ST tires are generally used at their maximum load carrying capacity - while LT tires are rarely used at their maximum load carrying capacity (when adjusted for speed).

There are other issues why LT tires seem to perform better - major manufacturers, larger sizing, etc.

- and that is why there are so many tire debates. Lots of ill formed, but strongly held opinions.
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Old 04-30-2013, 07:35 AM   #5
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I am still going to put my money on a good man rated tire as opposed to an ST tire. I will stick to my 235/75-R15 XL (Airstream) tires over the 225/75-15 ST (dump tailer) tire. On my garbage trailer ST tires are ok because the dump is only a mile from my house.

Perry
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Old 04-30-2013, 07:46 AM   #6
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Quote:
Originally Posted by Airstreamer67 View Post
dannydimit, that is a fine bit of sleuthing there!


I happen to own a set of faultless Maxxis tires. They have been great.

Now, let's hope the Maxxis accountants aren't reading your report. If they are like the others' beancounters, they may tell their engineers to quit designing their tires so well. They last too long, which cuts profit margins ... Unless, of course, their growing reputation adds to their sales, which in the long run can award them for their wonderful approach to engineering safety margins.
Thought you should know this: http://www.airforums.com/forums/f438...ml#post1292385

Not a Marathon, but a club member/friend had a Maxxis "ST" tire come apart on the way back from our Rockport rally yesterday, and we stopped to help change the tire.

It was the typical "ST" tire failure, it was four years old, the remainder of the tread we found stuck between the brake backing plate and the axle had more than sufficient tread depth. Other than that small portion of tread, all that remained of the tire was the beads, and small portions of the side wall. He was fortunate the only damage to the trailer was the wheel well molding and the area of the belly pan and banana wrap directly behind the curb side tire.

Interesting observation was the remaining tire on that side of the trailer also showed some tread separation starting, and the spare had even more. He decided to continue on at 50 MPH since it was Sunday, and he made it home (100 miles) with no additional failures. This tells me that if a close inspection is done frequently of the tread on these tires, potential failures might be caught before doing so much damage.


So, the Maxxis are not without failures.

And, Danny, your link to the survey does not work.
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Old 04-30-2013, 07:56 AM   #7
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Everytime I stop, I inspect the tires and feel how hot they are running.

Perry
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Old 04-30-2013, 08:00 AM   #8
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Originally Posted by perryg114 View Post
Everytime I stop, I inspect the tires and feel how hot they are running.

Perry
Perry, I think you missed the key point I was trying to make. The bulges in the tread area are the beginnings of tread separation, which will lead to throwing the tread, and then a blowout.

The beginnings of tread separation is what the tires needs to be checked for.
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Old 04-30-2013, 08:01 AM   #9
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SteveH, thanks for the info.

In my note above, I meant the tires have been "faultless" for ME since I got them. I can't speak for anyone else. I'm sure that others have had problems. But, gauging from the info I have read on a number of forums through the years, the Maxxis brand seems to be rated up there with the best.
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Old 04-30-2013, 08:03 AM   #10
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Yes, I too have run the Maxxis in the past without incident. Just didn't want you to think they are infalable.
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Old 04-30-2013, 08:08 AM   #11
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Well you can see tread separation when the tires are on the ground, especially side wall bulges.

Perry

Quote:
Originally Posted by SteveH View Post
Perry, I think you missed the key point I was trying to make. The bulges in the tread area are the beginnings of tread separation, which will lead to throwing the tread, and then a blowout.

The beginnings of tread separation is what the tires needs to be checked for.
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Old 04-30-2013, 08:12 AM   #12
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Actually, it has been my observation that tread separation starts as a bulge in the tread area, and usually not all the way around the tire.

So, it depends on where on the tread the bulge is located vs where the tire stops if you can see it or not.

To accurately check for the beginnings of tread separation, the tire needs to be lifted off the ground and rotated while watching for bulges in the tread.
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Old 04-30-2013, 09:45 AM   #13
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How about just a good old 7.00x15 LT bias-ply tire?

Good stiff sidewalls to lower trailer sway, been around for years, when they blowout, they don't become a chainsaw down the side of your trailer. Had my first one in 12 years of towing let go its tread a few months ago, but did not blowout. Even rode on the nylon cords for a few miles!

Just an old school kinda guy I guess. They are the only thing I put on my Airstreams.

Enjoy,
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Old 04-30-2013, 09:54 AM   #14
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How about just a good old 7.00x15 LT bias-ply tire?

Good stiff sidewalls to lower trailer sway, been around for years, when they blowout, they don't become a chainsaw down the side of your trailer. Had my first one in 12 years of towing let go its tread a few months ago, but did not blowout. Even rode on the nylon cords for a few miles!

Just an old school kinda guy I guess. They are the only thing I put on my Airstreams.

Enjoy,
Have a friend in our unit that uses them with good success. He says the same thing about the lack of a steel belt to do all the damage to the trailer.

Only problem is they are hard to find. He buys his at a farmer's CO-OP.
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