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Old 03-20-2015, 10:21 PM   #43
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Gavin, all tires have flats or blowouts. Good luck with your decision.
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Old 03-21-2015, 09:15 AM   #44
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Not even in the same league

A question I always have in my mind is how much weight would an LT tire be rated for if its speed were limited to 65MPH?.
Two tires that I often compare (in my mind)
GoodYear Marathon ST225/75/15 LRD #2,540 max 65MPH
Pirelli Scorpion STR LT235/75/15 LRD #2,335 max 112 MPH

To me, a tire capable of carrying #2,335 at 112MPH would be a better choice than one that can carry 205 pounds more but is limited to 65 MPH.
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Old 03-21-2015, 10:08 AM   #45
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Quote:
Originally Posted by Top View Post
A question I always have in my mind is how much weight would an LT tire be rated for if its speed were limited to 65MPH?.
Two tires that I often compare (in my mind)
GoodYear Marathon ST225/75/15 LRD #2,540 max 65MPH
Pirelli Scorpion STR LT235/75/15 LRD #2,335 max 112 MPH

To me, a tire capable of carrying #2,335 at 112MPH would be a better choice than one that can carry 205 pounds more but is limited to 65 MPH.
Lance, I would have to agree with your thinking.

And in addition, I have read that ST tires have the weight rating they do because they are restricted to 65 mph, and from steering and drive wheel locations, i.e. to trailers.

However, the tire "guru's" say if you use any other tire on a trailer, it must be derated in weight capacity, even though that tire is designed for higher speed, steering and drive axle locations.

Makes no sense to me. I often have the thought that it's a conspiracy by the tire manufacturers to make more money selling an inferior product at a high price, but that's the way my suspicious mind leans.
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Old 03-22-2015, 08:36 AM   #46
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....... However, the tire "guru's" say if you use any other tire on a trailer, it must be derated in weight capacity, even though that tire is designed for higher speed, steering and drive axle locations. .......
That only applies to P metric tires - and the difference is the softness of the suspension. A trailer (or a truck) has a much stiffer suspension, so the tire has to absorb more of the pavement irregularities, so in order to get the same level of durability, the load on the tire has to be reduced.
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Old 03-22-2015, 10:32 AM   #47
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A question I always have in my mind is how much weight would an LT tire be rated for if its speed were limited to 65MPH?.
Two tires that I often compare (in my mind)
GoodYear Marathon ST225/75/15 LRD #2,540 max 65MPH
Pirelli Scorpion STR LT235/75/15 LRD #2,335 max 112 MPH

To me, a tire capable of carrying #2,335 at 112MPH would be a better choice than one that can carry 205 pounds more but is limited to 65 MPH.
One thing to check is the speed limit for RV application as published in the tire companies literature. For many that have actually bothered to put together a guide 9like Goodyear & Michelin but not "Cheep-O" tires as sold by Billy-Jo-Bob low cost tire and bait store) I think you will see 75 mph max even for tires with Speed rating Symbols that are faster.

Tire ratings are based on normal application conditions which include the expected % of time a tire is asked to carry 90+% of its rated load etc.

If you try and "game" the system you can expect problems.

Taken to the extreme maybe a 15" NASCAR tire rated at 200 mph with 3,000 load would be a good choice. Of course it isn't designed to retain air for more than a few hours or ever hit a pot hole or curb but maybe you could test out a set and let us know how well they worked in trailer application..
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Old 03-22-2015, 10:39 AM   #48
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How much faster than 65 do folks typically want to go with your trailer in tow anyway? Even with the Michelins on mine, I rarely go above 62-65, often less than 60 and rarely above that for brief stretches.

Lots can go wrong pretty fast and having a few extra tons on your back complicates matters exponentially.

Those Pirelli's have more load capacity than the Michelins and appear to be the same size/aspect ratio. I almost picked up some 15" Goodyear Cargo tires with 2450# capacity at 65psi but the aspect ratio would have required a hitch adjustment I wasn't prepared to make. The belly pan is already pretty low to the ground...
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Old 03-22-2015, 11:01 AM   #49
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Originally Posted by Phoenix View Post
Quote: "It is a fact that of the 30,000 or so RVs that have been weighed with individual tire position scales over half have one or more tires in an overload condition. In any population of products if over half are being used beyond their design intent (max load based on measured inflation) why would we be surprised if there is a relatively high failure rate?"
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248 AirForums members completed the Tire Failure Poll. 118 Airstreams had 173 tires that failed. Most of these were OEM GYMs or ST tires in a size and inflation pressure specified by the Airstream factory.

While similar data for 16" wheels and LT tires are not available, it looks like only five LT tire failures have been reported by AirForums members who switched.

In my opinion, unless those 30,000 RVs are Airstreams and the tire models, sizes and inflation pressures are available, I don't see how this data is pertinent. Could you please cite your source

RV Safety & Education Foundation
and provide a data extract of only Airstreams with OEM-spec tires and inflation pressures? Without comparable data, this comparison is of apples and oranges. Sorry you will have to ask them or go to one of their seminars.

If this information is unavailable, I don't know why AirForums members should accept the blame for tire failures, when the personal experiences of many indicate that ST tires have not been well-suited for use on their Airstreams.
==========
Quote: "It is important to remember that if you do not properly identify the real reason for a product failure simply changing the brand or painting your RV a different color will probably not prevent a recurrence of a future failure."
----------

In my opinion, this statement is untrue.

As non-tire-engineers, we do NOT need to know the exact cause of tire failures. By trial and error, many of us have determined for ourselves that (at least on our own Airstreams) LT tires are more reliable than ST tires; and switching to 16" wheels and LT tires WILL greatly reduce the chances of future failures.
Interesting interpretation on the validity of using Science to try and learn something.

If as you believe it is not important to understand the real reason why something failed I have to wonder if you have ever gone to a Doctor. After all if they prescribe medicine for you it is based on studies done on other people, maybe its of no value to believe that you will probably react the same way. Got a headache? Try some cyanide. Who knows it may work on you for just because cyanide kills others that doesn't mean it will kill you. Right?

See the problem with using your approach to problem solving?

Correlation is not proof of Causation

Do you actually believe the tires know the type TT they are on and they only fail on silver ones? Does being an Airstream somehow protect a tire from ever getting a puncture? For following your logic we can blame the tire for ever being punctures or for that matter we can blame the tire if the valve leaks.

You are entitled to your opinion but as an engineer who uses the "Scientific Method" to solve problems just as Doctors do or Airline Pilots do or Race Car drivers do, it has been shown that facts learned through detailed observation of the natural world can most likely be applied to other objects in the natural world and failures can be reduced.

Good luck with your system of just buying new products till you no longer have any problems and never listening to others who spent their lives trying to make product improvements based on facts.

We will have to agree to disagree that facts matter.
Safe travels.
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Old 03-22-2015, 11:04 AM   #50
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How much faster than 65 do folks typically want to go with your trailer in tow anyway? Even with the Michelins on mine, I rarely go above 62-65, often less than 60 and rarely above that for brief stretches.

Lots can go wrong pretty fast and having a few extra tons on your back complicates matters exponentially.

Those Pirelli's have more load capacity than the Michelins and appear to be the same size/aspect ratio. I almost picked up some 15" Goodyear Cargo tires with 2450# capacity at 65psi but the aspect ratio would have required a hitch adjustment I wasn't prepared to make. The belly pan is already pretty low to the ground...
So how is 2,335# greater than 2,540#? or was that a typo or do you have data to support your idea?
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Old 03-22-2015, 11:24 AM   #51
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Speaking for Steve

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Originally Posted by Tireman9 View Post
So how is 2,335# greater than 2,540#? or was that a typo or do you have data to support your idea?
Sometimes when we feel offended we get a bit touchy, eh?

Steve is talking about the Michelin LTX MS2 P235/75/15XL and the Pirelli Scorpion LT235/75/15 LRD that I linked.
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Old 03-22-2015, 12:22 PM   #52
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Thumbs up

"For us, increased tire reliability and reduction in downtime on the side of the road are worth any additional expense."
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For us and for you do not need be the same.

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Old 03-22-2015, 01:05 PM   #53
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So how is 2,335# greater than 2,540#? or was that a typo or do you have data to support your idea?

Sorry - should have specified I have the 15" Pmetric Michelins which derated come in around 1900#...
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Old 03-22-2015, 02:26 PM   #54
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"How much faster than 65 do folks typically want to go with your trailer in tow anyway?"

The issue to me is more how the load ratings are determined rather than how fast we want to drive. Even though the Goodiyear Marathan Tires are speed rated at 65 it is, according to Goodyear, okay to drive them at 75 mph if you put in more air than it says on the sidewall max. Confusing and fustrating.

But the question for some of us is how much load would the P235 XL tires be rated for if they were tested the same as the ST tire. I suspect it would be a lot more than they are rated for now. In other words, I suspect that comparing load ratings between ST and P tires is a sort of apple/oranges thing. So if I need la load capacity of 1800 lbs am I better off with a p235 XL derated to 1985 lbs or a ST tire with a 2500 lb max load. I suspect the extra "safety margin" from the ST tire is an illusion born from different testing and rating methods.
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Old 03-22-2015, 03:31 PM   #55
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....snip.....

Even though the Goodiyear Marathan Tires are speed rated at 65 it is, according to Goodyear, okay to drive them at 75 mph if you put in more air than it says on the sidewall max. Confusing and fustrating.
First of all, I'm not trying to pick a fight here. Second, I have no dog in this fight anyway because I don't buy ST tires. Having thrown those disclaimers out there, I think the key word in the above quote is "confusing".

Here is the quote from the goodyear product service bulletin issued to dealers:

"Goodyear Marathon Special Trailer tires, with the “ST” size designation, are speed rated at 65 MPH (105 km/h) under normal inflation and load conditions."

....it then goes on to say:

"If Goodyear tires, with the ST designation, are used at speeds between 66 and 75 mph (106 km/h and 120 km/h), we recommend the cold inflation pressure be increased by 10 psi (70 kPa) above the recommended pressure based on the trailer placard for normal inflation and load conditions."
===============
Now then, to me, the confusing part of this is that the "implication" is the consumer could increase the inflation to 75psi. I suspect that is NOT what goodyear is trying to say however. What they "are" saying is the inflation can be increased 10 psi "above the recommended pressure based on the trailer placard for normal inflation and load conditions".

In other words, they may be saying you could literally increase the inflation pressure 10 psi above what the load/inflation table states is the acceptable minimum.

So for instance, if the load/inflation table says that you could run 55 psi for the given specific load, then you could run 65 mph at 55 psi. To increase your speed to 75 mph, you could increase the pressure to 65 psi. Further, you cannot assume an increase in load capacity by this pressure increase, only a speed capacity increase.

Hopefully Roger or Barry will weigh in on this, but I personally have not seen a tire manufacturer that "allows" for tires to be inflated beyond the psi stated on the tire sidewall. I will stand corrected on that however if one of the tire engineers say that I am in error on that.

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Old 03-22-2015, 04:00 PM   #56
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Does it make me bad if I towed my ST tires in excess of 75 MPH frequently when crossing Texas?






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