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Old 06-22-2019, 03:34 PM   #1
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Tire pressure confusion

A couple of years ago we bought a new 28 FC. It came delivered with Michelin Defender LTX M/S tires on 15 inch rims. I.e., not LT tires. The load rating is 2271 lbs which is more than sufficient to handle the GVWR of the trailer (7600 lbs).


Now, my confusion is this. The maximum pressure stamped on the tires is 50 psi. The trailer's tire info plate specifies ST tires with a max pressure of 80 psi. Should I inflate to 50 or 80? My gut says 50 psi. Any dissenting opinions?
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Old 06-22-2019, 03:59 PM   #2
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I run those tires. Inflate to 50 psi as that is the maximum for that tire and is so stated on the tire. The tag on the trailer is for different tires. Maybe a dealer put those tires on? I greatly doubt if the Airstream factory did. Airstream will install 16 inch Michelin tires and wheels.

In the USA your load rating for those tires on a trailer is decreased by 10% of the rating stamped on the tire for trailer use. You still have plenty of reserve. The tongue carries part of the weight. You need to figure from the axle weight rating for the trailer. The 4 tires with the 10% reduction has to exceed the combined axle rating.

I like the tires. On my 3 rd set of that series in 11years. Some people are appalled at using them on a trailer.
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Old 06-22-2019, 04:16 PM   #3
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Bill, I am glad to hear that you've gone through three sets without a blowout. That gives me greater confidence in the tire pressure (50) I've been using.



Yes, I suspect the dealer installed the tires (though they are the original 15 inch rims). Good point about the GAWR. In my case, though, the GAWR is exactly half of the GVWR. So I guess my tongue weight is zero?
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Old 06-22-2019, 04:23 PM   #4
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IF you bought the trailer new, the Federal Regulations require that the tire information label on the trailer match the tires the trailer was eqipped with at delivery. Contact Airstream and ask for a new label.


Run 50. You should never inflate a tire above the max on the tire.


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Old 06-22-2019, 05:06 PM   #5
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50 psi has taken ours to Alaska twice and Newfoundland once and across the country multiple times. I change them every 4 years use. Have no visible wear at the end of the cycle.
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Old 06-22-2019, 06:24 PM   #6
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Quote:
Originally Posted by IrkdScientst View Post
A couple of years ago we bought a new 28 FC. It came delivered with Michelin Defender LTX M/S tires on 15 inch rims. I.e., not LT tires. The load rating is 2271 lbs which is more than sufficient to handle the GVWR of the trailer (7600 lbs).


Now, my confusion is this. The maximum pressure stamped on the tires is 50 psi. The trailer's tire info plate specifies ST tires with a max pressure of 80 psi. Should I inflate to 50 or 80? My gut says 50 psi. Any dissenting opinions?


Did you buy this new from a dealer? Not even “gently used” but brand new at a dealer? If so - they have some ‘splainin to do.

That said - I ran the 15” Michelins on my 2012 27FB which hitched up shows 6000# on the axles so even de-rating the tire as you need to (for a P run on a trailer) you have good headroom/capacity. The Michelins were great - I just swapped them out after 5 years for the GYE ST tires.

You should be fine with the Michelins but there’s no way those 15” tires should’ve sold on a new trailer with 80 PSI on the placard. Those would HAVE to be the LT 16” version of those tires.

I would ask the dealer what happened and when are they replacing the tires and rims with what AS shipped out of the factory...maybe that’s just me. Your mileage can vary on that - the 15s should be fine....

Good luck!
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Old 06-22-2019, 06:48 PM   #7
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Quote:
Originally Posted by IrkdScientst View Post
A couple of years ago we bought a new 28 FC. It came delivered with Michelin Defender LTX M/S tires on 15 inch rims. I.e., not LT tires. The load rating is 2271 lbs which is more than sufficient to handle the GVWR of the trailer (7600 lbs).


Now, my confusion is this. The maximum pressure stamped on the tires is 50 psi. The trailer's tire info plate specifies ST tires with a max pressure of 80 psi. Should I inflate to 50 or 80? My gut says 50 psi. Any dissenting opinions?
It says 50#... good enough
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Old 06-22-2019, 07:35 PM   #8
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As I recall, CanAm Andy Thomson, who has installed hundreds of those Michelins, suggests 44 psi. 50 psi is the maximum.
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Old 06-23-2019, 01:06 AM   #9
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While I don't exactly run that brand of tire, I run an equivalent P-rated same load rating tire.

I find that 47psi up to 50psi to be a significantly harsher ride for the trailer. 45-46 seems to be the sweet spot for my 27FB. Andy Thomson must know a thing or two and I'll take his suggestion.
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Old 06-23-2019, 07:24 AM   #10
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Thank you all for your replies - most informative. I will check with Andy Thomson re. appropriate pressure.


FWIW, all 2017 Flying Clouds shipped from the factory with 15 inch rims and Goodyear ST tires. I don't suspect any monkey-business from the dealer except for the "oversight" of not changing out the information plate.
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Old 06-24-2019, 02:51 AM   #11
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Quote:
Originally Posted by IrkdScientst View Post
Thank you all for your replies - most informative. I will check with Andy Thomson re. appropriate pressure.


FWIW, all 2017 Flying Clouds shipped from the factory with 15 inch rims and Goodyear ST tires. I don't suspect any monkey-business from the dealer except for the "oversight" of not changing out the information plate.


I’m still confused. Was it a brand new trailer or was it a very gently used pre-owned trailer? Either way, if the placard says Goodyear ST tires at 80 PSI (I might have missed that point earlier) it wouldn’t have been 16” LT Michelins but 15” Goodyear Endurance (GYE) ST tires with an E load rating at 80 PSI and the dealer can’t change the placard - it reflects what the manufacturer shipped.

IF you purchased “brand new” it should have had GYE 15” tires. If you bought “very gently used” the prior owner may have replaced the GYE tires with the 15” Michelin P-metric LTX tires. Which again should be fine but you can’t assume the full load rating of a P-metric tire when used on a trailer - you have to divide the capacity (2217 did you say?) by 1.1 (for 2015# per tire or 8060# for your trailer).

So did you buy brand new or very gently used?
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Old 06-24-2019, 06:19 AM   #12
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I noticed that no where does anyone mention the actual tire sizes involved. That is very important.

I can gather from the OP that the Michelins are 235/75R15 XL, but what size is on the vehicle tire placard? The information provided - ST @ 80 psi - just means they are Load Range E. If they are ST225/75R15 LR E then the load carrying capacity is 2830#, which is much more than the 2065# (2271 divided by 1.1) for the Michelins. That should be a bit concerning.
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Old 06-24-2019, 06:20 AM   #13
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How did AIR get so confusing on the AIR Forums?🤔

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