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Old 04-04-2014, 12:46 PM   #99
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RE Load & Infl tables.
I left a message with the importer of Gladiator tires. Will let you know what I learn.
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Old 04-04-2014, 03:18 PM   #100
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Originally Posted by Tireman9 View Post
Trailers are different than motorhomes. The close spacing of multi-axle trailers places about 24% more force into the belts trying to tear them apart. You can lower, but not eliminate, this increase with increased inflation, that is why I advocate trailers run the tire sidewall inflation. Most tire placards also spec the tire sidewall inflation.
I think this is new information, at least to me. The importance of this recommendation is that it eliminates the use of inflation charts to determine which tire pressure to use on our Airstreams. Just air them to maximum sidewall pressure. And maybe that's why Airstream also recommends doing so on the trailer placards and at their factory service center in Jackson Center.
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Old 04-04-2014, 03:32 PM   #101
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Originally Posted by Tireman9 View Post
Getting individual weights at least once will tell you how unbalanced your TT is both side to side and axle to axle.
Lacking actual numbers I suggest you use 45/55 when dividing the load on the two axles and further assume 45/55 side to side. This means you should assume 31% of the trailer load is on one tire (but you don't know which one) so you would need a MINIMUM inflation rated for that load.

If your tire sidewall pressure would not result in matching the 31% load figure you have a problem that must be fixed.

Once you know you are not in the 57% of RV owners with an overloaded tire you can keep an eye on the load by a simple CAT scale check and comparison to the numbers of the individual calculations.
So our Michelin LT245/75R16 are each rated to support 3042# at their maximum 80 psi. Using the 31% load figure, and considering a significant portion of the load is supported by the tow vehicle through it's receiver, even the heaviest of Airstreams are not likely to overload a tire. Well, that is if the owner has some common sense.

Note: The heaviest current Airstream model is 10,000# with maximum load.
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Old 04-04-2014, 06:24 PM   #102
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Yes, if the 31' Classic models are loaded to the maximum GVW of 10,000 pounds, the tongue weight will be close to a 1,000 pounds (I see more than that on our new unit with the ProPride hitch head attached and no mattresses in the back, just full propane and fresh water tank and none of our stuff yet). If the trailer were loaded to the maximum gross vehicle weight, one could think that each tire in theory would be carrying 25% of the 9,000 pounds or 2,250 pounds. But, if we theorize there is a weight distribution hitch in use, then 33% of the tongue weight gets reflected back to the wheels and tires. The tires and wheels are now loaded to 2,333 pounds or 4,666 pounds for an axle.

The GYM ST225/75R15D factory tires are rated 2,540 pounds at 65psi. The Michelin LT225/75R16/E LTX M/S2 tires are rated 2,680 pounds at 80 psi. Neither of these two tire sizes installed by Airstream would have an adequate safety margin based upon these numbers.

At least the axles are rated 5,000 pounds each.....

Looks like one might need to leave a 1,000 pounds of stuff home ....
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Old 04-04-2014, 06:24 PM   #103
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Maxxis Load Inflation Table

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Originally Posted by Tireman9 View Post
Nickmeloy

RE Load & Infl tables.
I left a message with the importer of Gladiator tires. Will let you know what I learn.

I found the following load inflation table for Maxxis tires, but am unsure if it applies to Gladiator tires.


http://ecx.images-amazon.com/images/I/71x0iLT9jAS.pdf
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Old 04-04-2014, 07:00 PM   #104
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So our Michelin LT245/75R16 are each rated to support 3042# at their maximum 80 psi. Using the 31% load figure, and considering a significant portion of the load is supported by the tow vehicle through it's receiver, even the heaviest of Airstreams are not likely to overload a tire. Well, that is if the owner has some common sense.

Note: The heaviest current Airstream model is 10,000# with maximum load.
Correction: We do not have Michelin LT245/75R16 rated 3042#. We have Michelin LT225/75R16 rated 2680# at 80 psi.

Plenty of reserve for all but the heaviest, maximum loaded Airstreams, using the 31% load figure. They'll have to leave some stuff at home.
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Old 04-05-2014, 07:12 AM   #105
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It is a little confusing so let me try to say what I think I'm hearing from you.

If I still had the GYM ST tires - it would be wrong to inflate to less than 65 PSI even if the trailer sees only 5880#. The placard takes precedence.

And I didn't see it as "stumbling", personally. :-) Knowing the trailer was seeing 5880, I sorted through everything I had read here and in the DOT standard that was posted about derating a P tire for trailer application and felt confident in making the switch because of the load capacity and 26% headroom on the derated figure. Different tire entirely, plenty of capacity, but 50 PSI is the max for that tire and that takes precedence over the placard as far as I could tell.

Blowing these up to 65 PSI would be a mistake, in my (admittedly unprofessional but hopefully forum-informed and self-researched) opinion.
OK, sort of - and I have to be very careful here to word this correctly.

Cars, pickup trucks, SUV's, vans, and trailers all have vehicle tire placards. Those placards will list the original tire size and the inflation pressure specified by the vehicle manufacturer for that size. Use a different size (or type) and that specification is no longer valid. (and that was what we used the weights for.)

More detail: Over the years, the methods used by the vehicle manufacturers to specify the tire size and inflation pressure have changed and improved. The last change was completed by 2008 - for cars, pickup trucks, SUV's, and vans. I have great confidence that those placards are just fine and can be used without hesitation.

Prior to 2008, pickup trucks, SUV's, and full sized vans used marginally sized tires. I think those vehicles could be helped with an increase in load carrying capacity.

On the other hand, cars have been pretty good until we get back into the mid-1990's. If you've got a vehicle that old, you probably aren't using it much - OR - it's a toy and has already been given an upgrade in tires.

And here's where the problem lies. I am not entirely sure that trailer manufacturers got the message. It seems Airstream has, but not only do I not have a good handle on that, I don't know when that occurred (if it occurred). **If someone from Airstream is monitoring this thread, it would be great if they contacted me to sort this out.**

For this reason, I advocate weighing trailers by individual wheel position. We've seen considerable variation in side to side and front to rear loading.

I also advocate using no more than 85% of the rated capacity of the tire.

So that's it in a nutshell.
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Old 04-05-2014, 09:46 AM   #106
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CapriRacer's post above sent me to my calculator.

GYM Load D rating is 2,540 85% = 2,159 four tires = 8,636

Mich Load E rating is 2,680 85% = 2,278 four tires = 9,112

If a truly safe margin is the 85% suggestion, then Airstream is selling the 31' Classics with inadequate tires for the job. Especially in the Model 30 where the factory literature tongue weight is 733 pounds leaving the tires supporting 9,267 pounds of the 10,000 pound GVW. Even the 16" Michelins would be undersized.

I am sure that my empty trailer would not have the same load on each tire due to the factory cabinets and appliances locations. After we load our bedding and stuff, it will be interesting to see the real numbers. Thus one or more tires could easily exceed these safety margins because of a heavier "corner" of the trailer.

While it was a tongue in cheek comment in my earlier post about not loading the trailer to capacity, perhaps there is incorrect factory information as to the real load capacity for the two 2014 31' Classics. These are the only two Airstream models where the GVW weight could max out or exceed the suggested safe tire usage. The next heaviest trailer is the Classic 27FB at 9,000 pounds which would have more than the safety margin suggested. All the other 30/31 foot models have a GVW of 8,800 pounds so have an even slightly better margin.

One would like to think that Airstream's $100,000 trailers would at least have adequate tires and suspension for the advertised load capacity.
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Old 04-05-2014, 10:47 AM   #107
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Originally Posted by nickmeloy View Post
I am currently using a tire brand called Gladiator. This is an import from China. The tire sidewall information is DOT J2 TD GTS and 2830 pounds at 80 psig.


The previous tires were GYM ST225/75R15 LRD.


The placard on the side of the trailer is for the GYM classification and lists the tire pressure at 65 psig.


Many thanks for this insight.
Because you are still using ST tires the placard pressure can still be applied to your Gladiator tires. At 65 psi you will still have the same load capacity as the OE LRD tires. That’s as low as you should go with the air pressure. To gain load capacity reserves you can go all the way to 80 psi for maximum load capacity. Your rims will have to be rated for that pressure for safety.

Sometimes ST tire manufacturers require their tires to be aired to the full sidewall pressure all the time and will say so in their warranty package.

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Old 04-05-2014, 11:29 AM   #108
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Tire Load Capacity Not Adequate?

Quote:
Originally Posted by switz View Post
CapriRacer's post above sent me to my calculator.

GYM Load D rating is 2,540 85% = 2,159 four tires = 8,636

Mich Load E rating is 2,680 85% = 2,278 four tires = 9,112

If a truly safe margin is the 85% suggestion, then Airstream is selling the 31' Classics with inadequate tires for the job. Especially in the Model 30 where the factory literature tongue weight is 733 pounds leaving the tires supporting 9,267 pounds of the 10,000 pound GVW. Even the 16" Michelins would be undersized.

I am sure that my empty trailer would not have the same load on each tire due to the factory cabinets and appliances locations. After we load our bedding and stuff, it will be interesting to see the real numbers. Thus one or more tires could easily exceed these safety margins because of a heavier "corner" of the trailer.

While it was a tongue in cheek comment in my earlier post about not loading the trailer to capacity, perhaps there is incorrect factory information as to the real load capacity for the two 2014 31' Classics. These are the only two Airstream models where the GVW weight could max out or exceed the suggested safe tire usage. The next heaviest trailer is the Classic 27FB at 9,000 pounds which would have more than the safety margin suggested. All the other 30/31 foot models have a GVW of 8,800 pounds so have an even slightly better margin.

One would like to think that Airstream's $100,000 trailers would at least have adequate tires and suspension for the advertised load capacity.
After reading several threads over time on this forum concerning tire failures, I begin to suspect that there are several issues in play at the same time that may well be causing the tire failures that we are seeing.


(1) Owner issues - hitting things, under-inflation, over - age tires, driving too fast, etc. No ranting please. These things happen.


(2) Quality issues for certain tire manufactures. I am not yet convinced that this is the major cause of our tire problems. No ranting, please. It is very difficult for us to obtain reliable data to prove or disprove this cause.


(3) The tires specified by the trailer manufacturers are inadequate for the tasks they are being asked to perform. This issue is the one that I am beginning to suspect may play a large role in our tire failure experience.


If the Mich. 16" Load E rating is 2,680 pounds at 80 psig, then I should be slightly better off with the Gladiator 15" LRE tire rated at 2830 pounds at 80 psig without going to the added expense of switching from 15" rims to 16" rims. I am not yet certain that this is true, but I have no data on which to base a decision.


However, the individual wheel loads that I have are static loading values. It is unclear to me what the dynamic loads would actually be on these tires as I tow down the road at 55 mph and how these dynamic loads will affect our tire failure experiences. I suspect that the margin of safety that we need to avoid tire failures in our application may be larger than we are actually currently using.


Perhaps the tire guys will comment on these thoughts?
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Old 04-05-2014, 08:01 PM   #109
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Yes, if the 31' Classic models are loaded to the maximum GVW of 10,000 pounds, the tongue weight will be close to a 1,000 pounds (I see more than that on our new unit with the ProPride hitch head attached and no mattresses in the back, just full propane and fresh water tank and none of our stuff yet). If the trailer were loaded to the maximum gross vehicle weight, one could think that each tire in theory would be carrying 25% of the 9,000 pounds or 2,250 pounds. But, if we theorize there is a weight distribution hitch in use, then 33% of the tongue weight gets reflected back to the wheels and tires. The tires and wheels are now loaded to 2,333 pounds or 4,666 pounds for an axle.

The GYM ST225/75R15D factory tires are rated 2,540 pounds at 65psi. The Michelin LT225/75R16/E LTX M/S2 tires are rated 2,680 pounds at 80 psi. Neither of these two tire sizes installed by Airstream would have an adequate safety margin based upon these numbers.

At least the axles are rated 5,000 pounds each.....

Looks like one might need to leave a 1,000 pounds of stuff home ....
The 25% per tire is only seen when TT are perfectly balanced side to side and axle to axle. The reality is that almost no TT is perfect.
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Old 04-05-2014, 08:22 PM   #110
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Nickmeloy asked
"However, the individual wheel loads that I have are static loading values. It is unclear to me what the dynamic loads would actually be on these tires as I tow down the road at 55 mph and how these dynamic loads will affect our tire failure experiences. I suspect that the margin of safety that we need to avoid tire failures in our application may be larger than we are actually currently using."

I would not invent more things to worry about. I don't know of any tire company that is expecting you to get your RV weighed while traveling down the highway at 50 mph.

Static load on level ground is the standard method of weighing vehicles when we do tire testing. Dynamic loading is taken into consideration by tire companies. While side load due to wind or road crown can have a minor effect on tire load there is a difference between "Measurable and Meaningful". I have written on this topic.
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Old 04-05-2014, 11:16 PM   #111
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What I'm getting from the tire experts in this thread and other information they have written, is the correct tire pressure is the recommended pressure on the Airstream's placard, if using the original specified tire, which is usually the maximum cold pressure printed on the tire.

The reason for this is to minimize lateral force damage to the tires over time. And to offer the best opportunity to ensure the tires have adequate load capacity, as it may be unlikely each tire is carrying an equal share of the load.

For those with Airstream stock Good Year Marathon 15" tires that is 65 psi cold as on the trailer placard and the tire sidewall. For us using the Airstream Eddie Bauer model stock Michelin 16" tires on other Airstream models, we must assume the Eddie Bauer placard recommending 80 psi cold, which is also the maximum pressure on the tire sidewall.

The only reason I can see for not doing this would be too rough a ride causing trailer structural or component damage. But apparently Airstream has considered this in their trailer design, or they wouldn't recommend these tires and pressures.

So do we choose the benefits of tire reliability with safety implications, or a softer ride for the Airstream? Or is there more to it than this (too simple, I'm sure there is)?
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Old 04-06-2014, 05:59 AM   #112
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Originally Posted by nickmeloy View Post
After reading several threads over time on this forum concerning tire failures, I begin to suspect that there are several issues in play at the same time that may well be causing the tire failures that we are seeing.


(1) Owner issues - hitting things, under-inflation, over - age tires, driving too fast, etc. No ranting please. These things happen....
I think this is playing the same role that it plays for other types of vehicles. Maybe travel trailers are subjected to a few more instances of running over objects, but I don't think this is much more sognificant than for other types of vehicles.

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Originally Posted by nickmeloy View Post
.......
(2) Quality issues for certain tire manufactures. I am not yet convinced that this is the major cause of our tire problems. No ranting, please. It is very difficult for us to obtain reliable data to prove or disprove this cause.....
I'm going to subdivide "Quality" into 3 groups:

a) Consistency from individual to individual. Balance and uniformity are good examples here. I don't think this is a major player.

b) "Factory defects" - things that aren't supposed to be there or things that aren't there that should be. Foreign material and missing components, for examples. Another minor player.

c) Robustness of design - How good is the design for the designated task. This is where I think the major issue is and why ST tires and Chinese tire manufacturers are singled out compared to LT tires and the major tire manufacturers.

Quote:
Originally Posted by nickmeloy View Post
......
(3) The tires specified by the trailer manufacturers are inadequate for the tasks they are being asked to perform. This issue is the one that I am beginning to suspect may play a large role in our tire failure experience.....
I'm sure this is not helping and clouding the issue with the tires themselves.

Quote:
Originally Posted by nickmeloy View Post
..........If the Mich. 16" Load E rating is 2,680 pounds at 80 psig, then I should be slightly better off with the Gladiator 15" LRE tire rated at 2830 pounds at 80 psig without going to the added expense of switching from 15" rims to 16" rims. I am not yet certain that this is true, but I have no data on which to base a decision......
The problem here is that you are comparing an ST with an LT and the way those load rating are obtained (and tested) are different. ST's are restricted to 65 mph and that allows for a higher load rating.

Quote:
Originally Posted by nickmeloy View Post
......However, the individual wheel loads that I have are static loading values. It is unclear to me what the dynamic loads would actually be on these tires as I tow down the road at 55 mph and how these dynamic loads will affect our tire failure experiences. I suspect that the margin of safety that we need to avoid tire failures in our application may be larger than we are actually currently using.......
I don't think dynamic loads are much different than static loads. Unlike Formula 1 with the wings and other aerodynamic devices, and the severe load transfer during braking, the only thing I suspect would influence loading of a travel trailer while underway is crosswinds. If there is an area where vehicle manufacturers have been slack, it's in the static loading - and in particular the side to side and front to rear variation.


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.......Perhaps the tire guys will comment on these thoughts?
You are quite welcome.
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