Good Sam Club Open Roads Forum: Class A Motorhomes: I promise...last psi question
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 > I promise...last psi question

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goufgators

Crawfordville, Florida

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Posted: 07/04/18 05:11am Link  |  Quote  |  Print  |  Notify Moderator

RE: 2017 Winnebago class A: With my tires aired to required minimum (by factory recommendation... not by weight) steering is very good. But, (we're in Fl and roads get hot this time of year) as miles increase, pressures increase up to and sometimes over 15 psi above starting pressure. This increase in pressure reduces steering stability. I intend to weigh the coach before next trip and will have more reliable info with which to work. However, here's my question: If, for example, the min. psi required by weight is 80, would it be ill advised to start the trip at 75 psi (5 below the 80) knowing that within a very few miles psi will have increased to 80 and above. Starting at 75 would ultimately keep the top-end pressure at at least 5 psi lower than it would have been had I started at the recommended rate thereby making steering somewhat less stressful.
I have mixed feeling about this and would appreciate your comments. By the way, I have had a steering stabilizer and rear trac bar installed. These have helped but...


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rgatijnet1

Florida

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Posted: 07/04/18 05:24am Link  |  Quote  |  Print  |  Notify Moderator

ALL tire manufacturers recommend checking your air pressure with the tires COLD, before you get on the highway. The tires are designed for any increase in air pressure from temperature increases by friction or by increasing ambient temperatures. The ALL recommend AGAINST removing any air from a HOT tire to bring it down to your desired tire pressure for the sake of a better ride.
The number one thing that reduces tire life and increases the possibility of a blowout is underinflation. This is what you would like to do and they all recommend against it.
Follow the manufacturer's guidelines and inflate your tires at the specified air pressure when COLD, before you drive on them, and then just leave them alone until the next day, when they are cold again.

CapriRacer

Somewhere in the US

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Posted: 07/04/18 06:46am Link  |  Quote  |  Print  |  Notify Moderator

There's a part of this post that I find disturbing:

goufgators wrote:

….. But, (we're in Fl and roads get hot this time of year) as miles increase, pressures increase up to and sometimes over 15 psi above starting pressure. …….


Rule of thumb: Operating tire pressures should not increase more than 10% - and anything over 15% requires immediate action.

If I am reading this right, the tires are 80 psi max - so 15 psi is about a 20% increase. Something is wrong and it needs to be addressed.

The obvious thing is the starting pressure. Are you measuring in the cold of the morning? Tire pressures increase about 3% for every 10°F increase in ambient temperature. So if you start when it is 60°F, and get another reading when it is 90°F, you should see a 9% increase just due to the increase in ambient temperature. You shouldn't count that - and I suspect this is a major source of the pressure increase.

So take some careful measurements, taking into account the ambient temperature vs increases due to operating temperature. If you are still seeing high pressure increases - SLOW DOWN!! That's the easiest way to reduce the increase. Then figure out what to do next.


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Sam Spade

North Central Florida

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Posted: 07/04/18 07:01am Link  |  Quote  |  Print  |  Notify Moderator

CapriRacer wrote:



Rule of thumb: Operating tire pressures should not increase more than 10% - and anything over 15% requires immediate action.



I don't think that is true AT ALL, at least not for motorhomes.

IF....all of your tires increase about that much, then it is the tire design and the environment that is causing it.....or your starting pressure is too low.

If the fronts increase a LOT more than the rears, then it might be an alignment problem.

The fix for a large increase in pressure NEVER is to lower the starting point. Quite the opposite, in fact.


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frankdamp

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Posted: 07/04/18 07:58am Link  |  Quote  |  Print  |  Notify Moderator

Inflate based on measured weight - pounds per axle is fine for the weight. Just divide by 2 for the front tires and 4 if you have duallies on the back. The "manufacturer's recommendation" molded into the tire's face is its maximum allowed pressure based on the maximum load it's allowed to carry and is usually way over what you need for the loaded weight of the rig.


Frank Damp, DW - Eileen, pet - female Labrador (9 yrs old), location Anacortes, WA, retired RVers (since Dec 2014)

Tom/Barb

Oak Harbor, Wa

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Posted: 07/04/18 08:30am Link  |  Quote  |  Print  |  Notify Moderator

When My tires heat too much I add 10 pounds (when cold). and repeat as necessary to stop the over heating. your tires should never get too hot to place your hands on.


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Ivylog

Blairsville, GA and WPB, FL.

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Posted: 07/04/18 11:29am Link  |  Quote  |  Print  |  Notify Moderator

"5 psi
lower than it would have been had I started at the recommended rate" NO!


This post is my opinion (free advice). It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.

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Monkeyman_and_Lady

Severn, Maryland

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Posted: 07/04/18 11:36am Link  |  Quote  |  Print  |  Notify Moderator

Tire manufacturers account for the psi increase. Are you running a tpms system? I have one and am getting used to the pressure and temperature increases that occur while driving.

Get weighed and pressurize accordingly.

80 psi is your max? What size tires are these? My tires are Max 110psi cold. I'm running at 80 given my weight.


Monkeyman, Lady and little chimp
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edm3rd

Tennessee

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Posted: 07/04/18 12:11pm Link  |  Quote  |  Print  |  Notify Moderator

Also consider the impact of the sun when checking "cold" tires. I have seen a 10# difference from the sunny side tires to the shady side tires in the am before driving.

CALandLIN

SC

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Posted: 07/04/18 12:54pm Link  |  Quote  |  Print  |  Notify Moderator

Thermal expansion/thermal equilibrium has always been accounted for in the tire engineering processes. Therefore, the vehicle manufacturer’s recommended cold inflation pressures are the correct inflation pressures for your vehicle, unless the vehicle manufacturer has seen a need for exceptions. Any exceptions will be described in the vehicle owner’s manual.

Are all of your tires increasing more than 15-20% above recommended cold inflation pressures? There are two thoughts that come to my way of thinking. The tires may be entering into a form of fatigue/tread separation. Or, they are overloaded. Some troubleshooting into what loads they are carrying may answer the overheating condition. Side note, make sure your inflation gauge is accurate.

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