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Old 07-30-2013, 08:16 PM   #85
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eheffa:

Four Michelin LTX (P) 235/75R15 XL tires have a total derated capacity of 7,940 pounds. Using your 6,600 pound axle weight number, there is a 20% load safety factor in the Michelin tires with no 65 mph speed restriction, no constant air leaks, a wider tire for more ground contact which means better braking capacity and with a lower maximum air pressure (50 psi vs 65 psi) there can be a softer ride for your rig.

My 2013 25FB International Serenity has a tongue weight closer to 1,175 pounds camping ready with a full fresh water tank. We saw 5,880 pounds on a recent trip for the axles payload weight. There is plenty of margin at that weight.

As I said in post #72 above, there are many threads on this and other towed vehicle forums discussing the tire failures of of the ST tires. I think I can safely assume that the majority of folks on the Airstream forum that bought a used unit may have had GYM ST tires, but everyone that bought new has had GYM ST tires. That is a large number of folks. There have been many tire issue posts over the years. Somehow, Michelin is not brought up in a negative manner in terms of reliability

Not everyone is aware of forums so they deal with their issues privately. Somehow, I found out about this forum when I got the burr under my saddle to purchase an Airstream. I was reading this Forum for over six weeks before the paperwork was signed.

Before I went to pickup the trailer, the Michelin tires were paid for, the Hensley hitch was in the back of the Mercedes (which had already been to CanAm in London Ontario to get the hitch reinforced). All the good ideas for improvements I learned here.

I have experienced ST tire failures on my tandem axle motorcycle/cargo tailer and had the spare that was never on the ground delaminate on a small single axle motorcycle trailer. I did not want to experience a ST tire failure on the Airstream because of the expensive reported damage.

I have looked at some of the other brand forums and see issues with ST tires. I have not come across threads with users complaining about reliability issues with Michelin tires. I have used nothing but Michelins on all my vehicles for over 45 years and never had a tire failure due to a side wall failure or tread separation. I have had flats from road debris such as screws and nails, but that is not the tires's fault.

I just ordered five SenDel T03-66655T wheels and have a commitment price for five Michelin LT 225/75R16E LTX M/S2 tires. When the tire swap is done, I will sell the OEM wheels and tires from the new 27FB Classic with no mileage (unless the new trailer is towed instead of trucked to the dealership). I expect my net cost will be around $1,200 dollars for piece of mind.

That is a small price compared to the nearly $100,000 list price of the 2014 27FB Classic.

Playing in the Airstream playground is not a cheap endeavor.
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Old 07-30-2013, 09:08 PM   #86
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Quote:
Originally Posted by switz View Post
eheffa:

Four Michelin LTX (P) 235/75R15 XL tires have a total derated capacity of 7,940 pounds. Using your 6,600 pound axle weight number, there is a 20% load safety factor in the Michelin tires with no 65 mph speed restriction, no constant air leaks, a wider tire for more ground contact which means better braking capacity and with a lower maximum air pressure (50 psi vs 65 psi) there can be a softer ride for your rig.

My 2013 25FB International Serenity has a tongue weight closer to 1,175 pounds camping ready with a full fresh water tank. We saw 5,880 pounds on a recent trip for the axles payload weight. There is plenty of margin at that weight.
.
Interesting. My 2012 27FB Flying Cloud has a Mac GVWR of 7600#. My last scale trip with WD applied, full propane and at least 50% freshwater came in at 5880# (same number you used above).

5880/7940=74% of derated capacity. That sounds like plenty of headroom. 7940x.8=6352 which suggests I could add another 472# of weight in the trailer and remain within a 20% margin - correct?

The problem would be going above that weight - anywhere from 6353 to the full 7600# which would erode that margin.

The GYMs have 10160# capacity which means even at max allowable weight, I'd never be over 75% capacity of these tires. I don't want to travel above 65 mph in a 50' TV/TT combo and usually set the cruise for 62. So still not sure why those specs wouldn't serve me well.

However, if I'm understanding your explanation correctly, I'm thinking the 15" Michelins (at 50 lbs not 65) could work for me (provided I limit the trailer weight to 6350). Changing the axle and wheels for 16s just seems like I'm asking to introduce new problems while solving for one I may not have to begin with.

Last - aren't both the Michelins and GYMs belted radials? A blowout/tread separation on either would cause the same damage to the trailer (potentially) though I guess the argument is the Michelins are less prone to tread separation?

Thanks for your thoughtful help with this mystery (despite thousands of posts on multiple threads on this issue!!). I admit I'm incredibly dense on this one. Thx!
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Old 07-30-2013, 10:41 PM   #87
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I've talked about this on some other threads and here too, but I've wracked my brain as to why I've had bad luck with my ST tires. I've tried to upgrade from D to E rated ST's only to have similar failures. There are some constants in all of this. First are the constants. I always inflate for max pressure. 65 on the D rated tires and 80 on the E's. The trailer is garaged when not in use so we don't have UV killing them. I know the load weight based on weighing my previous Airstream and knowing what my typical load is (minus liquids). My practice has always been to replace tires after the 5th season of use. I tow at 60 mph.

I also know that my Classic slide out is the heaviest Airstream built on a tandem axle. My trailer is rated for 9100 lbs and other than one trip a year where I am at that weight (carrying 60 gallons of water), I'm probably weighing in at about 8,500 lbs. So I'm pushing about 15% reserve capacity with the tires.

Luckily all of my failures have been driveway detected. One, which was the Marathon, threw some tread on the highway but held together until I backed the trailer into the drive when arriving home. The stress of the pivot when backing snapped the belt and the tire went flat. On my E rated Maxxis the belts separated from the tread causing the 2 tires to bulge out in the center tread area. Again I caught this when I backed into the drive after arriving home.

Other factors. The Marathon failed on the last trip in its 3rd season of use. The two Maxxis tires failed after the 1st trip of their fourth season.

Now this is a link and a quote that caught my eye. It's from the Discounttire.com website.



Time and the elements weaken a trailer tire.
In approximately 3 years, roughly one third of the tire's strength is gone.
Three to five years is the projected life of a normal trailer tire.


Trailer Tire Facts - Discount Tire Direct

This then led me to the question, if this has credence, could my failures really be caused by the fact that I have such a high load factor, combined with a loss of tire strength? The timing on both the D and E failures would lend some evidence that my tires lost strength and ultimately may have been overloaded based on their age?

Bottom line the LT's I put on last year will tell me in a few years as to whether this conjecture is holding water. So after the last failure I did see the Discount Tire web site and one solution was to move to tire replacement every 3 years rather than the 5 year cycle which worked so well in the past. With the rising cost of tires the justification in my eyes was going to LT's since a 3 year ST cycle will cost me more money in 10 years than the premium paid for LT's. Last year with discounts I paid $180 each for my 16" Michelin LTX MS2 tires. Going back to Maxxis for the 15" E rated tires would have cost between $150-$160. Buying new Sendel T03 wheels and selling the Alcoa wheels set me back $200.

So take it for what its worth but if Discount is correct in their statement that the ST tires lose 1/3 of their strength after 3 years of use, you can see maybe why those of us with some of the heavy Airstreams are pulling the plug on ST's.

Jack
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Old 07-30-2013, 10:58 PM   #88
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Marathon tires work well for us!

Quote:
Originally Posted by SteveSueMac View Post
I agree. 4@2540=10,160 lbs capacity for a max trailer weight of 7700 lbs. currently fully loaded it's 6800 lbs. I set the cruise at 62, sometimes lower, never above. Knock wood, good so far...
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Yep, mine too Chinese Marathons working just fine. Previous owner had blowouts with truck tires on the trailer, so I am happy staying with tires built for travel trailers. I run with proper pressure and do not go over 60 mph. I bet many of the people with blow outs cannot say that.
Last year our 14" Marathon tires became 6 years old... and we replaced them with...
14" Marathon tires!

Marathon tires have worked well for us, especially the way we use them:

1. They are protected from the sun by covers when they are not moving.
2. Before a trip they are at the specified pressure of 50 psi, cold (14" Marathon tires).
3. We travel at or near the posted speed limit for trailers in California, 55 mph, most of the time, and rarely exceed 62 mph. (and that's the key!)
4. Our monthly trips, October through June, never exceed 200 miles, round-trip.
5. During trips, we continuously monitor all trailer and truck tire pressures with PressurePro tire sensors.
6. When home, the trailer tires rest on plywood panels on the driveway.

More information and photos on this are seen in my Air Forums' post, "The updates continue..."
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Old 07-30-2013, 11:40 PM   #89
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The point often overlooked is that a trailer with a GVW of 7,600 pounds GVW to be safely towed should really have a tongue weight between 10% and 15% of the GVW. That thought would imply a tongue weight range between 760 pounds to 1,140 pounds.

For some technical background, my 2013 25FB has a GVW of 7,300 pounds and a factory literature tongue weight of 833 pounds. The sticker beside the door claims there are two axles rated for 3,600 pounds. The factory parts manual for this trailer states the installed axles are really 3,800 pounds rated. The same axles are used on the 28', 27', 25', and 25' & 27' Eddie Bauer trailers where the GVW ratings range from 7,300 to 7,800 pounds.

When I picked the unit up at the dealership, I weighed the jack stand weight with the Hensley hitch head installed and what ever it came with from the factory plus a solar panel and street side and rear awnings. The weight was 1,150 pounds. However, the actual weight camping ready was 1,175 pounds at the same weighing location. For simple math, I raise that number to 1,200 pounds and see that detached from the truck, my rear axles could be supporting 6,100 pounds. If the projected 1/3 tongue weight weight transfer to the rear axles happens when connected, the rear axles could be supporting a maximum load of 6,500 pounds. There is a 22% load margin.

I have a 27FB Classic on order that has a GVW of 9,000 pounds. The literature claims a tongue weight of 792 pounds. The axle sticker by the door should read 5,000 pounds per axle as Airstream per the parts book uses a 5,000 pound rated axle on all three Classic models ranging from 9,000 to 10,000 pound GVW weights.

Since this literature Classic tongue weight includes all the awnings where the street and rear awnings were added to the 25FB, I project that with the Hensley hitch head attached, I will see at least a 1,000 pound tongue weight. The exercise continues that the axles are then supporting 8,000 pounds when not hitched to the truck. Throwing 1/3 back to the trailer axles when connected to the truck, the axles might be supporting 8,400 pounds at full load.

That full load number unfortunately exceeds the 7,940 pound derated load of the 15" Michelins and is too close to the 15" Michelin's sidewall rating load of 8,732 pounds. Thus we jump to the 16" tire and wheel dog and pony show.

I plan to have four Michelin LT 225/75R16E tires installed rated at 10,720 pounds. I will have about a 22% load margin.

Interesting the way the numbers turned out.
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Old 07-31-2013, 01:02 AM   #90
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Evan.

Safety, is the issue.

Some owners abide by it, others kick it to the curb.

In terms of tire safety, it's a rule of thumb to replace them, regardless of how much tread is left, when they are 5 years old.

It's your call.

Andy

Thank you Andy,

I am convinced now that the tires should be replaced.

The big question now is whether I go with P235/75 15 Michelin LTX MS2 or whether to bite the bullet & pay the premium to upgrade to 16 inch LT225/75 16 E's. I think the latter option would be the best long-term choice but wish I didn't have to replace the rims...


-evan
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Old 07-31-2013, 06:26 AM   #91
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GVWR = 7300lbs - ~700lb TW = 6600 lbs

- evan
I like to have individual tires loads, because a) I don't have enough experience to be totally confident about the side to side and front to rear variation and b) I think trailer manufacturers don't always do a good job of estimating how heavily loaded their trailers get. Without those weights, I add a bunch of factors to compensate - and they are really conservative as I want to err on the safe side.

So if the GAWR's add up to 6600#, I would add 10% to compensate for the potential that the trailer manufacturer under-estimated the payload - that's 7260#. There are 4 tires, so divided by 4 = 1815#.

I think there is as much as a 15% load variation in trailers, so the worst case is 2087#. And I think tires should never be loaded to more than 85% of their rating load - 2400#.

So any tire rated to carry 2400# should be good.

But if you chose an ST tire, those are speed limited to 65 mph. If you want to go as high as 75 mph, then add 10 psi. If you want to go to 85 mph, you need a tire rated for 2640# (and use 10 psi more.)

Feel uncomfortable using 10 psi over what is written on the sidewall? Use a tire rated for 10% more = 2905#.

All of a sudden, we are looking at 16" tires if you want to use ST tires and don't want to worry about all those exemptions and exceptions. (which what I think trailer manufacturers ought to be doing).

But if you chose to use an LT or C type tire, then use one rated for 2400#.
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Old 07-31-2013, 08:45 AM   #92
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CapriRacer: I have read numerous places that when using a "P" tire for a trailer application, we do in fact have to use the "de-rated load formula". However, I have read that when using a LT tire for trailer, we do not have to de-rate from the stated sidewall load. Any comment on that would be appreciated.
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Old 07-31-2013, 08:47 AM   #93
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Always weigh your loaded trailer to see where you need to be as far as load rating . Pull your loaded trailer on a scale, don't go by the tag, go by what you know for sure
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Old 07-31-2013, 11:10 AM   #94
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Originally Posted by CapriRacer View Post

I like to have individual tires loads, because a) I don't have enough experience to be totally confident about the side to side and front to rear variation and b) I think trailer manufacturers don't always do a good job of estimating how heavily loaded their trailers get. Without those weights, I add a bunch of factors to compensate - and they are really conservative as I want to err on the safe side.

So if the GAWR's add up to 6600#, I would add 10% to compensate for the potential that the trailer manufacturer under-estimated the payload - that's 7260#. There are 4 tires, so divided by 4 = 1815#.

I think there is as much as a 15% load variation in trailers, so the worst case is 2087#. And I think tires should never be loaded to more than 85% of their rating load - 2400#.

So any tire rated to carry 2400# should be good.

But if you chose an ST tire, those are speed limited to 65 mph. If you want to go as high as 75 mph, then add 10 psi. If you want to go to 85 mph, you need a tire rated for 2640# (and use 10 psi more.)

Feel uncomfortable using 10 psi over what is written on the sidewall? Use a tire rated for 10% more = 2905#.

All of a sudden, we are looking at 16" tires if you want to use ST tires and don't want to worry about all those exemptions and exceptions. (which what I think trailer manufacturers ought to be doing).

But if you chose to use an LT or C type tire, then use one rated for 2400#.
Thank you CapriRacer

I have been ploughing through that 90+ page thread on Woodall's. I appreciate your tenacity & patience.

I do not think that I feel comfortable with reducing my tire load capacity. P - rated (even XL ) tires are not adequate.

I am not happy to replace my GYM ST's with the same again.

On long leg travel days with a tail wind on the open road, my setup happily cruises along around 110-120 Km/hr. I do not want to be at the limit of my tires' tolerance in that situation.

I am beginning to see 16 inch LT's in the near future ...


You mentioned that you do see LT tires failing in Trailering applications. Is this common enough to be a concern? I am thinking to go with the Michelin LTX M/S2's as I have always been totally happy with these LTX tires on my vehicles....

What would you do if you were me with a 7300 lb GVWR trailer?

- evan
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Old 07-31-2013, 11:19 AM   #95
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Weigh your loaded trailer first. The reason I say that is my brother bought a trailer and it was suppose to weigh 2800 # on the decal but when he scaled it ot was 4400 # .
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Old 07-31-2013, 11:27 AM   #96
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Weigh your loaded trailer first. The reason I say that is my brother bought a trailer and it was suppose to weigh 2800 # on the decal but when he scaled it ot was 4400 # .
Thanks wvabeer,

I have only weighed my 'loaded for a trip' trailer once & if memory serves properly, I was reasonably well under the max GVWR (& we don't tend to pack light). The values were in kg & I can't remember the figures because I was also converting to lbs.

I will see if we have time to weigh again before we catch the ferry on the next trip.

-evan
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Old 07-31-2013, 02:18 PM   #97
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Michelin load & PSI table for XPS Rib

Interestingly, Michelin does seem to support the use of the XPS rib for RV applications & provides a table for recommended inflation pressures for given loads:

See:
https://www.tiretraker.com/michelin.pdf

-evan
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Old 07-31-2013, 03:02 PM   #98
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I appreciate the info provided here and in other threads on the Forums. It seems 16" is the smart thing to do so I ordered Sendel T03's and E rated Michelin's. I may go ahead and order Centramatics too. I hope to have several years of worry free towing!
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