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Old 12-12-2013, 12:53 PM   #71
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I am really confused now. I just called Airstream to find out what the difference between the LTX MS/2 P235/75R15XL and the LTX (P) would be for my AS and was told that under no circumstances should i use either of these tires. What's up? They told me that i should only use a tire that is ST. Help!

>>ron<<
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Old 12-12-2013, 12:55 PM   #72
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I do not use cruise control when the pavement is wet or slick.

True dat! NEVER use cruise on wet pavement! Ask me how I know! When hydroplaning on cruise you have already lost it before you have time to correct- if not on cruise you just pick your foot up off the accelerator! On cruise it just keeps spinning out of control...
I have bad joints- ankles, knees, hips- I have to use cruise control-
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Old 12-12-2013, 02:47 PM   #73
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Originally Posted by carver 1 View Post
I am really confused now. I just called Airstream to find out what the difference between the LTX MS/2 P235/75R15XL and the LTX (P) would be for my AS and was told that under no circumstances should i use either of these tires. What's up? They told me that i should only use a tire that is ST. Help!

>>ron<<
Maybe because the load rating of these 15" tires (derated for trailer use) is too low. Airstream offers the 16" Michelin LTX MS/2 as an option, and uses them as standard on Eddie Bauer models.
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Old 12-12-2013, 04:06 PM   #74
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Maybe because the load rating of these 15" tires (derated for trailer use) is too low. Airstream offers the 16" Michelin LTX MS/2 as an option, and uses them as standard on Eddie Bauer models.
What does "derated" mean?
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Old 12-12-2013, 04:58 PM   #75
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Standard answer to a common question

Quote:
Originally Posted by carver 1 View Post
I am really confused now. I just called Airstream to find out what the difference between the LTX MS/2 P235/75R15XL and the LTX (P) would be for my AS and was told that under no circumstances should i use either of these tires. What's up? They told me that i should only use a tire that is ST. Help!

>>ron<<
Hi Ron,
There are lots of threads about Airstreamers using the Michelin LTX M/S2 P235/75/15XL on their trailers.
Here are some of the more informative threads.
http://www.airforums.com/forums/f438...ire-71294.html
http://www.airforums.com/forums/f438...5-a-67720.html
http://www.airforums.com/forums/f438...-xl-96185.html
http://www.airforums.com/forums/f438...ade-99125.html

Pay particular attention to posts from Capri Racer, Tireman9 (Tire Engineers) AndyT (Airstream Dealer) and Rich Luhr. Rich is the editor of Airstream Life and has been using the Michelin LTX M/S LT235/75/15 LRC tires on his 30' bunkhouse.
I'm sure Airstream has the "standard answer" for these types of questions, and I believe that is what you got. The standard answer of "you should use ONLY ST tires on a trailer" or "You should ONLY use the type, size and rating that is listed on the MFR's tire load card" are what you typically hear from tire sellers, some trailer dealers and others in the business. This mindset is hard to overcome. It can be debunked by reading the Tire and Rim Manufacturers Association publications. switz has them handy for you to read.
Just like most tire choices, someone will tell you are making a mistake. Whatever choice you make, make it a good one that is based on safety, experience, research and your own best judgement.
Good luck and Happy streamin!
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Old 12-12-2013, 09:19 PM   #76
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What does "derated" mean?
In the case of P rated tires it means that the Tire and Rim Manufacturers Association state that the weight rating for P rated tires is lowered by 10% when used on light trucks or trailers.
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Old 12-13-2013, 09:14 AM   #77
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The reason a tire is derated for load capacity is spelled out in the federal regulation:

49 CFR 571.110

Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less.


S4.2.2.1
Except as provided in S4.2.2.2, the sum of the maximum load ratings of the tires fitted to an axle shall not be less than the GAWR of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. If the certification label shows more than one GAWR for the axle system, the sum shall be not less than the GAWR corresponding to the size designation of the tires fitted to the axle.

S4.2.2.2
When passenger car tires are installed on an MPV, truck, bus, or trailer, each tire's load rating is reduced by dividing it by 1.10 before determining, under S4.2.2.1, the sum of the maximum load ratings of the tires fitted to an axle.

S4.2.2.3
(a) For vehicles, except trailers with no designated seating positions, equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent of the derated load rating at the vehicle manufacturer's recommended cold inflation pressure for that tire.

(b) For vehicles, except trailers with no designated seating positions, equipped with LT tires, the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the vehicle manufacturer's recommended cold inflation pressure for that tire.

So my Michelin LTX (P) 235/75R15 XL tires that were mounted on our 25FB International Serenity in January 2013 had 2,183 pounds as the load limit on their sidewall. Thus, per the regulation above, the tire was derated to 1,985 pounds load capacity for sizing purposes. They were fitted to the Airstream axles that are rated 3,600 pounds, so two tires were rated 3,970 pounds and exceeded the axle rating per the regulation.

Despite the letters "LTX" in the tire "name" it is NOT a truck tire. The "P" tells the user it is a passenger tire and the "XL" says it has an extra load rating capacity.

For my camping ready 25FB, there was about a 22% safety margin between the actual axles load and the derated capacity of the tires.

For my heavier Classic model 30 trailer (by 2,700 pounds GVW and empty weight exceeding the GVW of the 25FB), I needed a greater load rating tire. So I selected the same tire used by Airstream on their Eddie Bauer models (Michelin LT225/75R16/E LTX M/S2 Michelin part number 05681) and in the hallway for sale at the factory store along with the SenDel T03-66655T wheels. These tires are rated 2,680 pounds and are attached to 5,000 pound rated axles in the three Classic models.

Note that the first two letters are "LT" which stands for light truck and there is no letter "P" in the description. Thus this tire does NOT need to be derated for either truck or trailer use.

Neither Michelin tire has a speed restriction of 65 mph and can be run at all legal speeds posted in the US.

If I installed two of the 15" Michelin tires mentioned above with a combined capacity of 3,970 pounds on 5,000 pound rated axles, I would be in violation of the regulation quoted above and in case of an incident might have some issues for knowingly installing underrated tires on the trailer.

The Chinese made GYM tires are rated 2,540 pounds and are speed limited to 65 mph. I was not pleased reading about their service history and damages caused by frequent failures on this and other RV related forums.

I tend to err on the side of extra capacity and the best tires available for all my vehicles. All of my four wheeled vehicles currently have Michelin tires as have all the others over the last 48 years with no blowouts or other tire failures.

The 2014 Classic model 30 Airstream trailer, when new, is an expensive item to purchase. Spending 1.5% of that cost on high quality tires and wheels to prevent a tire related issue makes sense to me. If I have to ask what it costs to operate a luxury item, I should not be buying that luxury item.

YMMV
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Old 12-13-2013, 11:02 AM   #78
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I don't understand "derating".
Does a 4,000# car weigh more than a 4,000# truck or trailer?
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Old 12-13-2013, 11:14 AM   #79
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I don't understand "derating".
Does a 4,000# car weigh more than a 4,000# truck or trailer?
From what the tire engineers write, it has to do with different physics and dynamics of cars, trucks and trailers.
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Old 12-13-2013, 11:32 AM   #80
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Obviously, the core issue is the tire construction with car sidewalls offering a soft ride and truck walls overing a stiffer ride to carry heavier loads in weight and side loads imposed for example by a large slide in camper with a lot of sail area to catch cross winds and transfer that stress to the tires.
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Old 12-13-2013, 12:18 PM   #81
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"I don't understand "derating".
Does a 4,000# car weigh more than a 4,000# truck or trailer?

No. They weigh the same. But the trailer puts more force on tires than the car. On a car the wheels are spaced near the corners. So only about 25% of the car weight can be on each wheel. A car has a long, soft spring travel compared to a trailer.

Dual and triple railer axles are close to each other. How the trailer sits determines if there is more force on one axle or the other. When a dual or triple axle trailer turns it puts a large sideways loading on the tires. When the trailer suspension runs out of travel it hits a stop and puts sudden loading on the tire. All in all trailer use is hard on tires.
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Old 12-13-2013, 01:04 PM   #82
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I don't understand "derating". Does a 4,000# car weigh more than a 4,000# truck or trailer?
Took me awhile to get the difference. They weigh the same, but exert different force loads. Therefore, "P" tire load ratings are not equal to LT load ratings. The increased height of the center of gravity on trucks decrease the load capacities of P tires by about 10% (from tirerack.com). The p tires sidewalks aren't as rigid as the lt's. I have noticed a great change in the way my sequoia handles. Without the tt, my sequoia, with lt tires, rides much more like a truck even with a low 50 psi, but at hwy speeds, unhitched and say 70-75ish mph the crosswinds don't push it around as it did with the P tires. Btw same truck and same make, model, tread, and size of tire just comparing P to LT tires. I'm using general tire grabber hts LT 245/75R16 on the sequoia and kumho lt 225/75R16 on the streamline. I love the general tire and the kumho have about 4000 miles on them and seem just fine.
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Old 12-13-2013, 03:09 PM   #83
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Another interesting twist to add:

A P235 75 15XL tire has a derated rated capacity of about 1985 lbs.

An LT235 75 15 load range C tire has a normal capacity of 1985 lbs.

There is really no load carry capacity difference between these two tires when used on a trailer.
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Old 12-13-2013, 03:37 PM   #84
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So- could willapus put LT tires on the Deuce and tow his trailer?
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