everything shakes loose - Page 5 - Fiberglass RV


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Old 09-10-2018, 10:25 AM   #81
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Name: Carl
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Originally Posted by Jon in AZ View Post
My 2008 13' Scamp has a sticker that recommends 50 psi. That just happens to be the maximum sidewall pressure for the tire they supply as OEM.

According to the tire manufacturer, it will carry a maximum load of 1360# per tire or 2720# per axle. The heaviest Scamp 13's don't even come close to that. So, at least one manufacturer does not base their recommendation on weight.

Early Scamps and Bolers recommended 26 psi and I assumed that was because they used different tires back then. I could be wrong about why they changed their recommendation. One thing that has changed over the years is the trailers have gained some weight, and there is greater variation as the number of models and options list grew.

I have found in practice that running 40-42 psi gives a noticeably less bouncy ride on my basic, lightly optioned Scamp 13, while still retaining a comfortable margin of safety on weight, according to load-inflation charts. I will admit there is nothing particularly scientific about my choice, except that for higher speed (62-65 mph) highway use in triple digit temperatures, I'd rather err on the side of overinflation. Obviously I drive in much different conditions than the OP.
Ok, that makes sense. I will have to check the tire manufacturer recommended pressure by weight. Thanks.
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Old 09-10-2018, 11:55 AM   #82
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pressure vs weight is pretty much the same for any brand tire in the same size. different size tires have different pressure/weight profiles, and of course, the higher load range tires allow higher pressures, which allow greater weights.
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Old 09-10-2018, 12:36 PM   #83
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Originally Posted by Yellow Boler View Post
Ok, that makes sense. I will have to check the tire manufacturer recommended pressure by weight. Thanks.
Just realize that those figures are minimums, not recommendations. Many ST tire manufacturers- including Carlisle whose tires I am currently running- make a blanket recommendation to run at full sidewall pressure on a trailer.

I am of the personal opinion that their recommendation is partly motivated by liability, since (1) far more failures are cause by underinflation than overinflation, (2) users commonly underestimate the weights of their fully loaded trailers, and (3) many tow at higher speeds than they probably should. But out of the same caution, I generally advocate staying well above the minimum pressure indicated in load-inflation charts. For one thing it gives you more time to catch a slow leak before pressure becomes catastrophically low.

At low speeds in off-highway use, I can see a reason to air down more.

There will always be controversy on this topic.
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Old 09-10-2018, 01:13 PM   #84
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Originally Posted by Jon in AZ View Post
Stephen, the OP is not talking about rock crawling, but unpaved back roads, and particularly the Al-Can highway.
They completed the paving of the entire route of the Alcan in 1992. But as with any highway now and again you will find them making road repairs on sections that might temporarily become a mile or two of gravel.
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Old 09-10-2018, 01:20 PM   #85
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They completed the paving of the entire route of the Alcan in 1992. But as with any highway now and again you will find them making road repairs on sections that might temporarily become a mile or two of gravel.
I was wondering about that. I still read accounts of lots of gravel damage, so I thought portions were still unpaved. Thanks for the information.

My point stands: the Al-Can is not at all the same as backcountry exploration. With care, and expecting some minor damage, a garden-variety RV can reasonably make the journey.
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Old 09-10-2018, 01:37 PM   #86
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Having just gotten back from the Alcan there was only 30 miles of construction. The rest was paved. I did the Alcan in 2014 and conditions were dramatically worse. This time the road was better than what I see in North Carolina. Came back on the Cassiar Highway, there I saw less than two miles of construction.

Road did have the typical dips, some potholes, all with adequate warning (slow down).

I would not take my Miata up that road but it would be fine with a Honda Civic, a minivan, or in my case a 2WD F150.
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Old 09-11-2018, 02:46 PM   #87
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Originally Posted by Jon in AZ View Post
Just realize that those figures are minimums, not recommendations. Many ST tire manufacturers- including Carlisle whose tires I am currently running- make a blanket recommendation to run at full sidewall pressure on a trailer.
This is an interesting article on the subject - https://www.boatingmag.com/properly-...-trailer-tires

According to the article if you run the ST175/80R13 tires at 35PSI you still have over 1100 pounds max per tire which is still more than enough for the boler. Which makes me wonder what pressure one should use or what is the minimum tire pressure. Or the optimum tire pressure. Max tire pressure would be 65psi.This would give max load which I don't need and make the ride stiffer.

Under inflation means not enough pressure in the tire for the load. But for the boler this would be considerably less than the max air pressure of the tire. That is I guess where the trailer manufacturer's recommendation can be useful.
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Old 09-11-2018, 03:51 PM   #88
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Florida
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As to air pressure the air supports the tire and the tire holds the air.
Lower air pressure will flex more, rife softer and heat up more.
If your axle is "dead" then the tire is the whole suspension and the ride will be rough.
You will be like the new stock cars that ride on bound springs and tire pressure actually sets the spring rate and very small differences make big difference in handling.
Over rated axles contribute to harsh ride as well.
If you install a 3500 lb rated axle on a 2400 lb trailer you can expect a harsh ride.
When I replaced my 16' Scamp axle I knew the trailer would be heavier than stock, but the 3500 would be too stiff so I had it made with the rubber suspension set for 3000 lbs.
So we have the hubs and steel parts, bearings etc rated for 3500, but the spring rate for 3000 lbs.
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Old 09-11-2018, 09:33 PM   #89
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Ok, that makes sense. I will have to check the tire manufacturer recommended pressure by weight. Thanks.
No it doesn't... be aware that the those are MINIMUM PRESSURES by weight NOT recommended pressures by weight.
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Old 09-12-2018, 07:25 AM   #90
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Originally Posted by Yellow Boler View Post
This is an interesting article on the subject - https://www.boatingmag.com/properly-...-trailer-tires

According to the article if you run the ST175/80R13 tires at 35PSI you still have over 1100 pounds max per tire which is still more than enough for the boler. Which makes me wonder what pressure one should use or what is the minimum tire pressure. Or the optimum tire pressure. Max tire pressure would be 65psi.This would give max load which I don't need and make the ride stiffer.

Under inflation means not enough pressure in the tire for the load. But for the boler this would be considerably less than the max air pressure of the tire. That is I guess where the trailer manufacturer's recommendation can be useful.
Load range C ST tires typically have a maximum operating pressure of 50 psi. That's what Scamp installs and recommends. Load range D has a maximum operating pressure of 65 psi, but it is not commonly available in the 13" size used by Scamp and others.

Regarding trailer manufacturer recommendations, rather that go by what was best practice 40 years ago, you might investigate what manufacturers of similar trailers today recommend. I've already shared what Scamp recommends. You could ask Happier Camper, Relic, Armadillo, and Weiscraft what tires they run on their small trailers and what operating pressures they recommend.
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Old 09-12-2018, 07:32 AM   #91
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Originally Posted by floyd View Post
No it doesn't... be aware that the those are MINIMUM PRESSURES by weight NOT recommended pressures by weight.

Or are they the maximum weights by pressure?

I think we are all actually agreeing here.
Whatever pressure is required for the load is the min pressure you should use.
As we know tires slowly lose pressure - and we are all lazy humans, so add a few pounds over minimum to compensate, then go camping.

I use 50 where the specs says I need 45.

Jim
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Old 09-12-2018, 08:41 AM   #92
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Originally Posted by widgetwizard View Post
Or are they the maximum weights by pressure?

I think we are all actually agreeing here...
I guess it depends on which you consider the independent and which the dependent variables...

In my mind, weight is the independent variable, since the fundamental purpose of a trailer suspension is to move some predetermined weight down the highway. The pressure you set in the tires in some fashion- about which there is far from complete agreement in the towing community - depends on the weight you need to move.

I will admit that all the load-inflation charts I've seen are written as if it's the other way round!

A pressure anywhere between the load-inflation minimum and the sidewall maximum is defensible. Optimal?...
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Old 09-12-2018, 08:48 AM   #93
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Originally Posted by widgetwizard View Post
Or are they the maximum weights by pressure?

I think we are all actually agreeing here.
Whatever pressure is required for the load is the min pressure you should use.
As we know tires slowly lose pressure - and we are all lazy humans, so add a few pounds over minimum to compensate, then go camping.

I use 50 where the specs says I need 45.

Jim
Actually they are the pressures below which the tire must be removed from the rim and inspected for damage when subjected to the chart weights. Generally, This forum has not been in agreement on this issue for years.
It seems that some folks who panic at a few pounds over a tow rating,are complacent or even encourage underinflated tires. Many of the same folks believe that tires deteriorate over a short time and must be replaced in as little as three years. The charts apply to new tires in good condition.


An appropriate tire , run at a few pounds under maximum sidewall pressure, is not the issue. Substantially underinflated tires (as described on the charts) are dangerous,especially as they "age out".
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Old 09-12-2018, 09:48 AM   #94
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When I first picked up my trailer, at the first fuel stop I felt the bearings, which felt cool. Then I happened to touch the tire - it was hot! I checked the pressure (while kicking myself for not checking before I set out) and they were around 20-25 psi. I aired up to 35 and at the next stop the difference was dramatic, they were a little warm (as is normal) but MUCH cooler than before! Seeing as I still had three states to go, I was glad I caught it, albeit a bit tardier than I should have.
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Old 09-12-2018, 10:05 AM   #95
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Actually they are the pressures below which the tire must be removed from the rim and inspected for damage when subjected to the chart weights..
That is NOT true and you know it.
If you run at 20% UNDER those pressures you need to dismount and inspect.

I can see we are not going to agree on using the published figures so I will shut up now.

Jim
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