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Old 05-23-2015, 05:01 AM   #15
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The Good Year Tire web site does a good job. I know I am "out voted" on truck v/s trailer tires for an airstream, but at least read what Good Year has to say. I would never put truck tires on a trailer any more than I would put airplane tires on. Good Year know tires after over a 100 years of making them.
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Old 05-23-2015, 07:28 AM   #16
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[QUOTE=larryglarson;1625597]The Good Year Tire web site does a good job. I know I am "out voted" on truck v/s trailer tires for an airstream, but at least read what Good Year has to say. I would never put truck tires on a trailer any more than I would put airplane tires on. Good Year know tires after over a 100 years of making them.[/QUOTE]

If this were true, a person would think the GYM's would have a much lower failure rate.
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Old 05-24-2015, 07:35 AM   #17
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I have Good Year Marathon Tires on my 30' classic and I do not have any trouble. They wear well, the air does not leak out of them, just no trouble. I hear all kinds of stories about trouble so I guess there must be some. I am 72 and have driven over 3 million miles. I have had bad tires and rigs that "ate" tires, but in the last 30 years I have not had any trouble with Good Year tires. I know there are other good tires out there, but for cost and quality, I think Good Year's are OK.
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Old 05-24-2015, 08:37 AM   #18
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Originally Posted by CapriRacer View Post


That's why you need the load tables.
I would suggest the load table of the tire size you are using from the manufacturer of the tire you have.


Using a ST tire table on your LT tire may get you into some shortened tire life.

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Old 05-24-2015, 02:58 PM   #19
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Originally Posted by Hophead View Post
Any reputable and knowledgeable tire dealer (like Les Schwab) can explain how it works and what tires are right for your load and trailer/driving conditions.

Monitor tire wear and adjust pressure accordingly. Over inflated tire on an Airstream rides rougher and may shake out the rivets (per my dealer). So I called Airstream (Ohio) and they have no real justification on what tires are installed, other than that is how we have always done it.

Attachment 238946
Many reputable tire dealers I have talked to in my locale will only recommend and sell ST tires for trailer use. (That liability issue pops back into the picture). As a matter of fact, some even refuse to mount anything other than ST's on a trailer. To keep things clean I ordered from the Internet and took the tires and wheels to a dealer to get my LT's mounted. No questions asked and no issues.

As far as matching pressure to load, make sure to add enough pressure to give you at least 15% reserve load capacity over what your maximum weight of the trailer would be.

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Old 05-26-2015, 12:15 PM   #20
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PSI is really dictated by the load the vehicle will have to carry. There should be no issues with having the psi lower than the maximum rating as long as it is sufficient to carry the load of the vehicle, and you would want to consider the full load with water, luggage etc.. when factoring total weight of loaded vehicle and appropriate PSI required for the load.

Load and PSI works as you assumed. Attached is an industry standard for trailer tire loads and comparable PSI.

Any reputable and knowledgeable tire dealer (like Les Schwab) can explain how it works and what tires are right for your load and trailer/driving conditions.

Monitor tire wear and adjust pressure accordingly. Over inflated tire on an Airstream rides rougher and may shake out the rivets (per my dealer). So I called Airstream (Ohio) and they have no real justification on what tires are installed, other than that is how we have always done it.

Attachment 238946
I would strongly advice, not to use the ST part of that document of Goodyear.
The loadcapacity's are calculated with the formula for diagonal tires.
this is the formula that was first introduced in 1928 , and later adjusted ( about 1970 ) in its power for radial tires.
EUR all kind of tires to 0.8 power.
USA P-tires H/W div down to 50 power 0.5
P-tires lower H/W div then 50% power 0.65
LT tires up to truck tires power 0.7.
I already warned Goodyear a year ago about it but they wont see my point.
But who would believe this gus from Holland Europe , where they put Gremlins in all the stuff the sent to America .
As late as 2006 USA TRA swiched over for P-tires and XL to the power of EUR
of 0.8 but left LT at 0.7 power.
The higher the power the lower loadcapacity it calculates for a pressure.
Power 1 is the same as no power and is the logical calculation.

I made my own pressure/loadcapacity lists and you can find them here.
https://onedrive.live.com/?cid=A526E...e092e6dc%21904
Set the formula that tight that sooner to low loadcapacity then to high, wich is always saver, but think its verry close to the ever to be ideal formula to laws of nature.

In this first go to the USA map and then choose if you want it given per tire, axle single or axle dual. Ten you dont have to devide by 2 or 4 anymore.
Open the PDF for your AT-pressure and search the loadindex/maximum load of the tire, then find the loadcapacity yust above the tire or axle load you want to know it for, and read below or above the needed pressure.
Best is to add 10% to the weighed load you use before looking back the pressure.
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Old 05-26-2015, 06:39 PM   #21
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Tire load inflation charts/tables should have TRA approval.

Most of the current GY charts used on the WWW have a 2005 date. It's on the bottom of the PDF pages. That date is before the last tire rule change approval of 2007.

When tires of the same size are manufactured with differing materials in their construction the inflation charts will not even come close to pressures needed at each increment to achieve the desired load capacity.

The ST235/85R16E has a maximum load capacity of 3640# at 80 psi.
The LT235/85R16E has a maximum load capacity of 3042# at 80 psi.

Airing your trailer tires to coincide with the load being carried requires you to go to the scales every time you make a significant change in your cargo load. Airing your tires to the trailer manufacturers recommendations will normally provide a reserve load carrying capacity providing your load is balanced.

In any event, overloading and under inflation MUST be avoided.

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Old 05-27-2015, 06:46 AM   #22
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Originally Posted by jadatis View Post
I would strongly advice, not to use the ST part of that document of Goodyear...........
I strongly disagree with that. The rationale that follows is faulty in that EVERY load table derives from the same set of formulae.

While we are aware of the issues with ST tires, we can NOT completely assign those issues to strictly the load table. There are many other possible causes.
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Old 05-27-2015, 09:50 AM   #23
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With a little over 16000 miles on original gym's ,I marked them and took them to tire shop and rebalanced them, one wanted 4 oz, rotated the tire on the rim and it took 2 oz, when replacing they got Xed, all have even wear at 65-70 lbs, they are being watched very closely .
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Old 05-27-2015, 10:55 AM   #24
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they are being watched very closely .
If they are over three years old, I suggest you watch very closely in your rear view mirrors because that's where you are most likely to see them when they come apart and leave the trailer.
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Old 05-27-2015, 01:37 PM   #25
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Quote:
Originally Posted by CapriRacer View Post
No.

Long Version: Barry's Tire Tech

Short Version: The load curve is a curve. (I think I just made a funny.) While it is close to linear, it is indeed a curve.

And in the region we use, inflation pressure is not linearly proportional to the load carrying capacity. Put another way, a 10% reduction in inflation pressure does not result in a 10% reduction in load carrying capacity - it is less.

That's why you need the load tables.

BTW, this applies to ALL tires - passenger car, truck, trailer, aircraft, lawn and garden, bicycle, motorcycle, etc.

Thanks for the link to Barry's site. Very informative.
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Old 06-03-2015, 05:13 AM   #26
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I strongly disagree with that. The rationale that follows is faulty in that EVERY load table derives from the same set of formulae.

While we are aware of the issues with ST tires, we can NOT completely assign those issues to strictly the load table. There are many other possible causes.
But fact is that ST tires are calculated in their maximum load for more deflection allowed. This brings the loadcapacity to the edges of what is wise to laws of Nature.
If you then calculate it for lower pressure with a formula that gives even more deflection in the lower pressures , the tire deflects to much and produces more heat , more then it can cool down , so spots of tire get to hot and harden and tire damage begins.

Fact also is that these pressure/loadcapacity lists are made using a formula.
I will give picture I used in my warning mail to Goodyear.



compare calculation 1 and their list copied at the bottom.
In exeption to 35 psi and 60 and 65 psi all the given loadcapacity's are rounded from the calculation for Diagonal tires in list 1 I gave with power 0.585.
Explanations for the exptions is 35 and 65 are AT-pressures for B-load and D-load. What they did is calculating with power 0.585 for C-load and replaced 35 and 65 psi by the maximum load belonging to B-load and D-load. The 60 psi I think is because of roundings and conversion from KG/kPa to lbs/psi.
For me this prooves that they used this formula to determine this P/LC-list.

I see no yustification to calculate P/LC lists for Radial ST tires with the old formula for diagonal tires.

I will try to explain the effect of this by an example.
If you would asume the american LT calculation with power 0.7 to be sufficiŽnt, and probably it even is not, and calculate for 30 psi , it gives in picture calculation 2 =1504 lbs loadcapacity, and for calculation 1 =1595 lbs loadcapacity ( for diagonal tires).
This will give aproximately 1595/1504=1.0605 times more surface on the ground so service length ( because surface with stays the same).
I determined that this gives about squaire 1.0605=1.1246 times as much deflection , so as much heatproduction . That to the already to the edges calculated deflection for the speed of 65m/h of ST gives significant more heatproduction and more then it can cool down , so tire-damage in the long or shorter run.
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Old 06-05-2015, 02:57 PM   #27
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To the OP and others
Simple question but complex answer. There are two actual tire engineers on this thread plus some who just play tire engineer on TV

There is a formula used to generate most of the numbers in the published tables. In general the formula gives
Load Capacity = Air Pressure to a power x tire air volume x K

Now the K factor is generally based on expected usage based on the type of tire covered. I think we can all understand that passenger tire usage (laod, speed, type of surface etc) is clearly different than say a mining tire of identical dimensions.

The power valus on the inflation pressure also varies based on general shape of a tire. An ultra low aspect tire like a 235/35R18 has a different factor than a 235/75R15 as the deflection characteristics are different. (this comment will make our tire engineer hobbyist happy to know)

With regard to ST type and trailer application. I strongly recommend you use the inflation associated with the max load capability molded on the sidewall of the tire as this will lower the "Interply Shear' that is unique to multu axle trailers. This is because the trailer tires, unlike the tires on your TV are not rotating around the center of the turning radius but are being dragged around the curve which increases the shear force that is trying to detach the belts from the rest of the tire.
If you want to know more you can simply Google "Interply Shear" to see both tire blog posts and technical papers on the topic.

Finally there is the reality that some tire sizes needed to be "grandfathered" as their load capacity was developed many years ago and the load/infl table was based on actual service results not some formula developed later to fit the curve of the individual points in the table. There is simply no single formula that will fit all sizes and type of tires.

The above is why you need to use the table your your specific type & size tire as published by the manufacturer of your tire. While the vast majority of tires of the same type and size have the same capacity there are some that vary a bit so you should not use a Michelin table for a Goodyear tire even if both were the same size and type.

Now as to the suggestion from our tire engineer wanna-be. I would warn that the suggestions he offers have not been adopted by any tire company or regulatory agency in the world. But you are of course free to decide if you want to go with his idea or follow what all the rest of the tire engineers in the world do.

Tires are designed to pass certain well defined durability and strength tests that specifically point to the published load & inflation numbers for that specific tire. If you decide to ignore the industry tables and invent your own personal guide please don't come back here and complain about hving a tire failures "for no apparent reason"

PS I do like the suggestion to have at least 15% "head room" between the tire capacity at the inflation you are running and your measured individual tire load.
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Old 06-05-2015, 03:38 PM   #28
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Now I am confused... The attached Maxxis table shows anything but max pressure according to the weight.
Max load on my axles is 3800 per axle (per Airstream) , I figure 2000 per tire (rounding up) , + 10% for uneven load , + 10% to go over 65mph puts me at about 2400 lbs. puts me at 60-65 lbs pressure. All good with a ST 225/75/15 LRD tire.
I have the tire shop recommended LRE tires with max pressure of 80 psi which I now know will beat the rivets out of our Airstream.
What pressure should I run?

http://ecx.images-amazon.com/images/I/71x0iLT9jAS.pdf


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