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Old 04-06-2014, 12:30 PM   #113
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RE Gladiator
They sent answer to my question about Load/Inflation tables and simply provided the max load at the max inflation. It appears their support people have little or no functional knowledge about tires. To me this indicates they are just selling round black things. Not a good sign in my opinion.
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Old 04-06-2014, 06:52 PM   #114
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I am Confused

Quote:
Originally Posted by CapriRacer View Post
...
Quote:
Originally Posted by nickmeloy
..........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...

I am confused about this point. I tow at 55 mph, so let's say that whatever tire I use, it is being run at 55 mph.


Under these conditions, why may I not directly compare the load specification at 80 psig for the two tires mentioned above?


Are you saying that the LT tire is a more robust tire, as compared to the ST tire, even at 55 mph, and that its load capacity is actually greater than the sidewall molding states?


Thank you for these replies. They are proving to be of considerable value to all of us on the Forum.
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Old 04-07-2014, 12:40 AM   #115
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Update from original poster

This has all been very interesting and informative to me, as a new Airstream owner last summer.

One point suggested by others recently is that running tires at the maximum cold sidewall pressure might make for a hard ride. I may now have an example to offer.

Twice this winter, the streetside corner front window on our '71 Safari has shattered. The first time was while towing it on rough dirt and gravel roads in Baja California, Mexico, without a rockguard to protect the front windows.

G&C Trailers in Bellflower, CA fixed the window for us over the winter, and added the previously-missing rockguard. However, while returning 40 miles to our storage spot in Irvine, CA afterwards via a smooth Interstate highway (I-5), the same window shattered again, even though protected by a rockguard.

I now wonder if perhaps high tire pressure may have been a factor in the rebreak, even though we drove 2,000 miles without incident earlier last fall, from Illinois to California via Interstate. The tire pressure was 60 PSI, with a cold sidewall maximum tire pressure of 65 PSI.

I'm convinced now that running at 65 PSI would be better for the tires, but wonder if it would be worse for the window? If so, a tire I can find in stock easily may be more expendable than a window that took over 2 months to order and receive.
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Old 04-07-2014, 05:31 AM   #116
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Originally Posted by MrJim View Post
This may be covered elsewhere, but I'm not finding it, so I'll ask: How do I calculate the correct tire pressure to use on my "new to me" 1971 Land Yacht Safari 23' Airstream trailer with dual axles? Airstream of Chicago put new Marathon Trailer Service tires (size ST225/75R15, load range D) and new aluminum rims on it. When I asked our dealer, he recommended inflating the tires to 65 PSI when cold. That's the maximum cold pressure.

However, the tires were actually inflated to 42 PSI on delivery, and have been fine for the couple of hours I've had them on the highway thus far, so I'm wondering if there is a way to calculate the correct tire pressure to use more precisely? Since I've also seen bike tires explode on hot days when inflated to their maximum rated pressure, I'm not eager to push any limits unless there is a good reason for me to do so.

The trailer weighs 3530# empty, and has 4 tires to bear that load. I'll try never to let the total weight exceed 4,500#, as that is the maximum rating for my tow vehicle.

Goodyear's RV tire care guide (http://www.goodyearrvtires.com/pdfs/tire-care-guide.pdf) doesn't suggest a specific pressure, but does show what weight each tire can hold at various pressures, and suggests dividing the total load evenly among the 4 tires to achieve that. To me that suggests the idea for filling to 65 PSI is overkill, as each tire can hold 2540# at that pressure, and I'll never need it to hold more than 1125#, which Goodyear's chart suggests can be borne even at 20 PSI.

I'm inclined to stick with the actual delivered 42 PSI, rather than the suggested 65 PSI, but would love to hear from anyone who actually knows the ideal pressure to use.

Thanks much,
-MrJim
I registered to this forum to give an answer.
Been busy with tire-pressure calculation since 2008 , but am not a tire-specialist.
Already "met" Tireman9 and Capriracer on other fora.
Hovered over the 9 pages but now quoted your first post, in wich you already gave all the information about Airstream and tires and filled them in my calculator, in wich I lowered the maximum load by 6 LI steps to give the ST tire the same deflection as an LT tire with speedcode Q ( 160km/99m/h) would have and so longer livetime and almost zero chance on tire-failure.
then and advice of even as low as 32 psi !!!!!
And that is because as exeption to the rule for travel-trailers the Airstream tires are pretty oversised.
2 tires can carry the GVWR and your TT has 4 .

So if you want to be a on the save side, I assumed to be your tires off-road kind with large profile blocks that cover a part of sidewall so less sidewall to flex and angain 8 LI steps back so 20% lesser maximum load to laws of nature then given on sidewall so LI99 with maxload of 1709 lbs a tire.
Then even an advice of 42 psi .
So 65 psi is in this case not needed and will tremble things loose.
So my advice would be 42 psi with all the reserves that are needed.

Here the picture of the 32 psi advice with lower maxload of tires for speed of ST.
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Old 04-07-2014, 08:16 AM   #117
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Quote:
Originally Posted by nickmeloy View Post
I am confused about this point. I tow at 55 mph, so let's say that whatever tire I use, it is being run at 55 mph.

Under these conditions, why may I not directly compare the load specification at 80 psig for the two tires mentioned above?........


I think you are confusing things.

First is that ST tires are specifically designated for trailer service and limited to 65 mph.

LT tires are designated for a more broad usage, and they are NOT limited to 65 mph. Because of that, the max loads are different.

To give you an example, in the Tire and Rim Association Yearbook, there is chart for LT tires showing the allowable increase in load for various speeds. Here are 2 of interest:

56 thru 65 mph - No increase in load
46 thru 55 mph - +9% increase in load

See how that works?

Quote:
Originally Posted by nickmeloy View Post
...Are you saying that the LT tire is a more robust tire, as compared to the ST tire, even at 55 mph, and that its load capacity is actually greater than the sidewall molding states?.....


No, I am NOT saying an LT is a more robust tire - but I am saying the load carrying capacity printed on the sidewall has to be understood in context - the context being what service the tire is in.

Quote:
Originally Posted by nickmeloy View Post
....
Quote:
Originally Posted by nickmeloy View Post
Thank you for these replies. They are proving to be of considerable value to all of us on the Forum.
Quite welcome.
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Old 04-07-2014, 11:38 AM   #118
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Quote:
Originally Posted by MrJim View Post
This has all been very interesting and informative to me, as a new Airstream owner last summer.

One point suggested by others recently is that running tires at the maximum cold sidewall pressure might make for a hard ride. I may now have an example to offer.

Twice this winter, the streetside corner front window on our '71 Safari has shattered. The first time was while towing it on rough dirt and gravel roads in Baja California, Mexico, without a rockguard to protect the front windows.

G&C Trailers in Bellflower, CA fixed the window for us over the winter, and added the previously-missing rockguard. However, while returning 40 miles to our storage spot in Irvine, CA afterwards via a smooth Interstate highway (I-5), the same window shattered again, even though protected by a rockguard.

I now wonder if perhaps high tire pressure may have been a factor in the rebreak, even though we drove 2,000 miles without incident earlier last fall, from Illinois to California via Interstate. The tire pressure was 60 PSI, with a cold sidewall maximum tire pressure of 65 PSI.

I'm convinced now that running at 65 PSI would be better for the tires, but wonder if it would be worse for the window? If so, a tire I can find in stock easily may be more expendable than a window that took over 2 months to order and receive.
Another MAJOR concern for how the trailer rides is the condition of your axles. It has been stated that torsion axles (especially from the '70s) only last 20-25 years on average and you have a 71 so your trailer is over 43 years old which could mean it's time for the axles to be replaced the second time and they might still be original. Search for check axles and you will find an article on how to check them.

WARNING; many trailer places (even a couple Airstream dealers from whats been posted) have no clue how to check torsion axles, so don't believe the "pros" when they say your axles are fine, unless you know how they tested them.
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Old 04-07-2014, 11:47 AM   #119
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I run my new Towmasters at 55# road side and 60# curb side. They ran at around 110* temp measured with infrared thermometer, on a 500 mile trip to the Florida Keys this past week. Also FYI the Towmasters are rated at 75 MPH max speed vs Marathons at 65 MPH.
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Old 04-08-2014, 09:06 AM   #120
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Quote:
Originally Posted by Pick View Post
I run my new Towmasters at 55# road side and 60# curb side. They ran at around 110* temp measured with infrared thermometer, on a 500 mile trip to the Florida Keys this past week. Also FYI the Towmasters are rated at 75 MPH max speed vs Marathons at 65 MPH.
What kind of Towmaster tires do you have?

Tire Information | Towmaster

BA
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Old 04-09-2014, 04:01 PM   #121
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Quote:
Originally Posted by Pick View Post
I run my new Towmasters at 55# road side and 60# curb side. They ran at around 110* temp measured with infrared thermometer, on a 500 mile trip to the Florida Keys this past week. Also FYI the Towmasters are rated at 75 MPH max speed vs Marathons at 65 MPH.
All tires on an axle should be inflated to the same cold (ambient) inflation.

I see only one Towmaster rated above 65 and many at only 62 (100 KPH)
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Old 10-20-2014, 05:01 PM   #122
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Old 10-20-2014, 05:43 PM   #123
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I've noticed that 50 psi cold at sea level at ambient 65F is 54-55F at 6,000 to 7,000 feet.

Should while touring should I deflate to 50 psi cold at 7,000 feet if I'm hanging around there for a day or two?
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