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Old 06-10-2015, 11:59 AM   #1
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Tire pressure question

Hi,

I'm the new owner of a 2004 Gulf Stream Sun Voyager (first motorhome) and it came with 2 year old Sumitomo ST727 275/70R 22.5" tires.

I got the coach weighed after we moved all our stuff in and my per-wheel weight is ~3700lb all around, which is off the bottom of the chart for those tires.

The lowest weight rating on the Sumitomo chart (http://www.sumitomotire.com/assets/p...ck_Catalog.pdf) is 4920 (single) and 4590 (dual) at 85psi.

Does that mean I can safely run the 85psi with plenty of safety margin?

Thanks in advance for any advice.

-Matt
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Old 06-10-2015, 06:39 PM   #2
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Yes, seems like you have a lot of safety factor.
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Old 06-10-2015, 08:25 PM   #3
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I run mine @ 100 to 105 psi and never weighed the coach in 13 yrs of ownership. On my 3rd set of tires now and never have had a tire problem.
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Old 06-10-2015, 09:32 PM   #4
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Run what the tire placard inside the MH states and you can't go wrong.
The RMA=Rubber Manufacturers Association,pg 51, states to never run less air pressure than what the tire placard states.
quote: "
Inflation pressure recommendations may also be
determined based on the tire manufacturer's
specifications, which define the amount of inflation
pressure necessary to carry a given load. These
inflation pressures may differ from those found on
the vehicle tire placard or certification label.
However, never use inflation pressure lower than
specified by the vehicle tire placard, certification
label or owner’s manual. Nor should inflation
pressure exceed the maximum pressure molded on
the tire sidewall."
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Old 06-10-2015, 10:27 PM   #5
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The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire.

From the Michelin RV Tire Guide:
Quote:
"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."
From page 6 of the GoodYear RV Tire and Care Guide:
Quote:
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."
From TOYO:
Quote:
Q: What are the consequences of inflating the tires to accommodate the actual loads?
A: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.
But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:
Quote:
The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.
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Old 06-10-2015, 10:42 PM   #6
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I have the same tires on my coach, and they are very good tires.

With your weights, I would run 85 psi in the tires, and you'll have a good safety factor.

Enjoy your coach.

Fred
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