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Old 07-21-2015, 06:44 PM   #1
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Tire pressure?

The data sheet inside the pantry of my '73 Argosy 24 states that tire pressure should be 45 PSI. I am running GYMs and not exceeding the speed for them. I thought I saw most folks here posting about going with 65 PSI for those tires. That would surely give a harsher ride would it not? I have also seen a lot of folks trash talking those tires.
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Old 07-21-2015, 06:57 PM   #2
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What's the load rating on your GYM's? The ones that came on my Bambi were C rated, and so the max inflation was 51#, as I recall. The replacement GYM's I purchased a few years ago are D rated, with a max inflation of 65#. I could run them at 50#, and they'd have the same weight capacity as the original tires. I don't need the full capacity to have a safety factor that I'm comfortable with, so I run my D rated GYM tires at 60#.
You only get the full weight capacity at full inflation, so you can run lower safely in many cases. You are right in that raising the inflation will make the ride harsher.
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Old 07-21-2015, 07:15 PM   #3
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The more plies the tire has for a given size, the firmer the tire will be without any air. It will also be rated to be able to handle more tire pressure. If you run the full rated pressure you are doubling up on the stiffness. You can run lower pressure, provided you know how much load you are actually putting on that tire. Published Airstream weight does not reflect how much junk you put in it. A trip to the scales is in order, if you want to scientifically ( or engineering) want to establish a logical tire pressure. Another way would be count how many pop rivets you are losing per mile and check the heat gain on the tires. Under inflated tires get hot.
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Old 07-21-2015, 07:35 PM   #4
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If memory serves from my engineering days - fading fast into the past - the suspension component attributable to the tires - hard or soft - was in fact minimal in comparison to that of the primary suspension of the vehicle. In the case of newer Airstreams, rubber torsional springs.

Maybe somewhat can correct me if this is not so - certainly wouldn't be the first time I was all wet!


I do know that we run 75psi in our 16" Michelins (with centramatics), and I have yet to find a popped rivet after a few cross-USA trips.


Brian.
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Old 07-21-2015, 08:02 PM   #5
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My trailer specs call for 50 pounds with 14 inch wheels. That is what I run my GYMs at. I confirmed this with Goodyear and Jackson Center.
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Old 07-21-2015, 08:10 PM   #6
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Tires are the primary shock absorber and hydraulic shocks are the secondary shock absorber. Tires have little spring action and don't contribute to the suspension in a spring fashion much at all.
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Old 07-22-2015, 06:11 AM   #7
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Quote:
Originally Posted by Gearheart View Post
The data sheet inside the pantry of my '73 Argosy 24 states that tire pressure should be 45 PSI. I am running GYMs and not exceeding the speed for them. I thought I saw most folks here posting about going with 65 PSI for those tires. That would surely give a harsher ride would it not? I have also seen a lot of folks trash talking those tires.
First, there should have been a tire size associated with that pressure on what you called a data sheet - and BTW, people in the tire industry call that the vehicle tire placard.

I'm going to bet that a vehicle from 1973 used a completely different sizing system than we use today - and because the size is different, the pressure would be different, too!

So to really address your question, we need to know what size the placard says, and what size you are using now? Anyone who answers your question without knowing those things just doesn't understand what is going on - and their answer would be appropriately wrong as well.
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Old 07-28-2015, 10:42 PM   #8
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Quote:
Originally Posted by CapriRacer View Post
First, there should have been a tire size associated with that pressure on what you called a data sheet - and BTW, people in the tire industry call that the vehicle tire placard.

I'm going to bet that a vehicle from 1973 used a completely different sizing system than we use today - and because the size is different, the pressure would be different, too!

So to really address your question, we need to know what size the placard says, and what size you are using now? Anyone who answers your question without knowing those things just doesn't understand what is going on - and their answer would be appropriately wrong as well.
The tires that were on the trailer in 73 were bias ply. You can still buy them but the newer trailer tires are radial. The maximum cold inflated pressure is posted on the tire. According to the tire supplier I use, you should inflate the tires to "close" to the maximum listed on the tire. In my case, the max is 65lbs cold. I run them at 60lbs, and so far have had no issues.
Wait - you are talking about the trailer tires, right? Not the TV tires? If it's the TV tires, disregard this. I'm going to have another glass of wine.
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Old 07-28-2015, 11:35 PM   #9
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I have a 2008 25' and run 15" GYMs. (on my second set). Trailer calls for 65lbs pressure and the tires max is 65lbs.... so that's what I run them at. I regularly run 75 mph speed limits without issue.
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Old 07-29-2015, 06:23 AM   #10
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Just so everyone understands:

Even trailers are supposed to have a vehicle tire placard - a sticker that lists the original tire size and the specified pressure for that size. The regulation has been in effect since the 1970's, and I am pretty sure trailers have been covered from the beginning.

While it is so very common for placards on trailers to specify the maximum pressure for the size, it isn't a given. That is, it is only by circumstance that trailer manufacturers specify tires in such a way that the maximum pressure is also the specified pressure. Trailer manufacturers could have done what motor vehicle manufacturers did (and do!) and that is specify an oversize tire, but specify a reduced pressure.

In fact, the vast majority of us tire engineers think that trailer manufacturers usually specify tires with not enough load carrying capacity - which is why we recommend people weigh their trailers.
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