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Old 02-14-2015, 01:14 PM   #1
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Opinion on tires

We have a 2005 safari 25' ab gross vehicle weight is 6300 lbs.. I'm looking at Michelin Ltx 235-75-15 . They handle a weight of 2183 lbs each X 4 = 8732. Minus 20% = 6986. So am I correct in assuming these tires would be able to safely carry the safari down the highway?


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Old 02-14-2015, 03:35 PM   #2
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Absolutely safe to use those tires, and don't forget that between 800 and 1,000 lbs. of your trailer's gross weight will be on the tongue (and thus your tow vehicle) and not on the four trailer tires providing you with an even greater margin of safety.
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Old 02-14-2015, 04:43 PM   #3
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Perfect tire, good choice.

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Old 02-14-2015, 05:56 PM   #4
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I am running these tires on my 2004 25 Safari with the same weight as yours.
I am very pleased. I have run the tires for 4 years and an estimated 20,000 miles with no problems whatever.
I have taken several multi day freeway drives during very hot weather with no blowout. When running ST tires, I had multiple failures.
Additionally, inflated to 50 lbs, the tires deliver a very smooth ride.
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Old 02-14-2015, 09:35 PM   #5
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Originally Posted by handn View Post
I am running these tires on my 2004 25 Safari with the same weight as yours.
I am very pleased. I have run the tires for 4 years and an estimated 20,000 miles with no problems whatever.
I have taken several multi day freeway drives during very hot weather with no blowout. When running ST tires, I had multiple failures.
Additionally, inflated to 50 lbs, the tires deliver a very smooth ride.




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Old 02-14-2015, 09:40 PM   #6
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Did you replace the spare too? A smoother ride would be nice. Or bathroom vanity sliding doors keep falling off. Thanks for everyone's help! It's cheaper than buying new rims, although all the pics of the 16's look really nice!


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Old 02-14-2015, 09:58 PM   #7
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The Michelin LTX (P) 235/75R15 XL tires are rated 2,183 pounds when inflated to 50 pounds. Since they must be derated 10% per 49 CFR 571.110 (see below for trailer use, their net payload is 1,985 pounds each or 7,940 pounds for four tires. Andy at CanAm suggests 44 psi for these tires on Airstreams.

I really liked the ride our 25FB got after this tire conversion plus the larger foot print made for better braking. Click on the "images" link below my avatar to see the factory GoodYear ST tire beside the 15" Michelin as well as beside the 16" Michelin in another picture. The 16" Michelins are on my 31' Classic.

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.
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Old 02-15-2015, 06:39 AM   #8
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"Opinion on tires".....the trailer won't move without them. I have 5. YMMV




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Old 02-15-2015, 07:10 AM   #9
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More math:

Like switz said, those tires have to be derated by a factor of 1.1.

Also, the load isn't evenly distributed front to rear and side to side. I've been using a very conservative 15% difference to account for this.

And as AnnArborBob pointed out, the GVW of the trailer includes the tongue weight.

and lastly, I don't think any tires ought to be loaded to more than 85% of their rated load.

So doing all that math, I get that the trailer needs tires that are rated to 1770# and the tires are actually rated to 1985#. Sounds good!

The only open question is: How good did Airstream do in estimating the actual GVW? To answer that question, you need to weigh the trailer fully loaded.

Side note: It might be good if someone started a chart showing the Year, and Model of Airstream and the GVW listed for each - and then compare that to actual loaded weights. That would give folks a way to determine how well the engineers did, and if there was a model year where they changed their methodology.
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Old 02-15-2015, 07:40 AM   #10
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I made the change on a previous AS and went to 16" while we were making the change. Improved overall performance, could be our imagination, but that is ok too.
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Old 02-15-2015, 07:45 AM   #11
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Will the Michelin LTX 235/75/15 fit in the wheel well on a 34? I would need 3 per side.

John
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Old 02-15-2015, 08:09 AM   #12
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Very good choice of tires. I am on my second set for our 25' trailer. Would not want to leave home with anything else.
You have more margin on those tires than you have calculated. Our trailer also has a gross wt of 6800 lbs. But fully loaded we have 800 lbs added to the TV and 5600 actually on the trailer wheels.
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Old 02-15-2015, 08:36 AM   #13
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Quote:
Originally Posted by sandlapper View Post
Will the Michelin LTX 235/75/15 fit in the wheel well on a 34? I would need 3 per side.

John
Yes. They are only about 1/2" wider and taller than 225/75 15.
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Old 02-15-2015, 08:46 AM   #14
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Quote:
Originally Posted by ROBERT CROSS View Post
"Opinion on tires".....the trailer won't move without them.

Response of the year so far :-)

I too have the 15" Michelins. Scales show 5800# on the trailer axles which leaves PLENTY of headroom even on the derated load capacity of 1984#/tire. I keep them at the 50PSI max - they already ride soft and I would worry about having them at a lower pressure both on the highway (where I would expect a higher rise in temp with lower pressure) and also in tight turns backing in where any multi-axle trailer is going to want to scrub the tires right off :-)

I replaced a pair on the curb side just a few months in because I scuffed them pretty badly on 95N which was under construction - the sidewalls scraped against the cut tar. I probably could have kept them but I didn't want to risk anything.
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