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Old 08-11-2012, 09:59 AM   #1
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Lowering tire pressures

I drive on some really rough roads at times. I keep my tires fully inflated, to the weight/psi chart recommendations. I understand the coach will ride smoother if I let some air pressure out. I always thought that a tire run at 80% of maintenance inflation pressure was considered to have been run flat, with associated internal damage, and eventual failure. But a tire expert has posted here that it takes a lot more air pressure loss to result in that: "run low flex failure occurs when the tire has run, usually at highway speed with ultra low ( less than about 30% of the correct inflation) down to zero inflation pressure". Is there a new, much lower 'considered run flat' threshold with modern RV tires?
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Old 08-11-2012, 10:50 AM   #2
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I would not recommend lowering pressure.

That said: I know many people who inflate to the sidewall Maximum pressure, Which is almost always the wrong thing to do.

Some believe the sticker inside the RV which usually gives a lower pressure which likewise is almost always wrong.

Some have the RV wehied, each wheel, and inflate to the pressure recommended by the tire manufacturer, which is the right way.. In your case I will not suggest adding a few PSI but rather more frequent checking.

In fact .. Try a TIRE PRESSURE MONITORING SYSTEM such as Smart Tire or Pressure Pro... Nothing like checking your tire pressure every few minutes, even while toolidn down the freeway at 55-60 MPH. .. Wait a minute, it is exactly like that!.
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Old 08-11-2012, 02:04 PM   #3
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Quote:
That said: I know many people who inflate to the sidewall Maximum pressure, Which is almost always the wrong thing to do.

Some believe the sticker inside the RV which usually gives a lower pressure which likewise is almost always wrong.
The psi on the sidewall or the placard inside isn't "wrong", but it's probably more than needed. Perhaps much more, though that varies by coach and tire. Maybe it would be better to say those psi's are "sub-optimal" for most RVs?
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Old 08-11-2012, 02:06 PM   #4
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Is there a new, much lower 'considered run flat' threshold with modern RV tires?
Not that I've heard of. Most experts say anything less than 70-80% of the recommended amount for the load is likely to cause internal damage. Maybe not an immediate blow-out, but will weaken the tire and shorten its life.
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Old 08-12-2012, 01:36 AM   #5
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ON TRUCK size tires the cold pressure on the sidewall is the MINIMUM required to support the maximum weight rating of the tires. Same with the tire charts, it's the MINIMUM cold pressure to support the weight.
From page 2 of the 06/07 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 the Firestone/Bridgestone RV tire guide:
Quote:
Bear in mind that these are maximum ratings. The sidewall of the tire shows maximum load and minimum inflation pressure for that load
From the GoodYear RV Tire 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.
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Old 08-12-2012, 08:24 AM   #6
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Agreed

I fully agree Mr. D. I have used that method for what seems like forever. But things sometimes change. I had always read that tire damage can start at 20% loss of air pressure. But now I have read here a much higher air loss is need to damage a tire. That's why I asked, to see if that had changed. If damage does not start until 70% loss of maintenance air pressure, could the tire be run at a lower pressure over rough roads to improve the ride?
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Old 08-12-2012, 09:37 AM   #7
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Old 08-12-2012, 09:52 AM   #8
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A month ago I had a blowout on one of my rear duals and did not hear or know about it until I went to install a tire monitoring kit. After that I decided to replace all six tires. When the technician was here installing the new ones I asked him what tire pressure he was using and he told me 100 psi. I told him that the sticker inside my driver door specified a recommended pressure of 70 psi. He said "If I left here knowing that you only had 70 psi in the tires on that rig, I would not sleep well tonight. It would just be a diaster waiting to happen and that if you were running 70 psi before then that is why you just had a blowout." So I am running 100 psi all around. The rig certainly rides and handles nice with those pressures.
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Old 08-12-2012, 11:08 AM   #9
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Since I have not yet had a chance to weigh our rig, I run my tires at the tire manufacturer's recomendation for the maximum axle weight rating. The ride can be a bit harsh on bumpy roads, but I feel we are safer this way. When I finally get around to getting it weighed we will adjust the pressures accordingly.

I would hesitate to lower the tire pressures and risk a tire being over loaded. I'd rather endure a harsher ride then suffer tire damage for beign under inflated.
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Old 08-12-2012, 11:50 AM   #10
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Low tire pressure means more heat to the tires and greater chance of blowout. Also of concern is the mileage goes down with the tire pressure
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Old 08-12-2012, 01:24 PM   #11
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First, never ASSUME. Many RV manufacturers put the minimum tire possible on the RV and you need to air it up to the max on the side wall for max carrying capacity.

Get the rig weighed and run your air pressure according to the tire manufacturers pressure/weight charts to keep the tires running cool and as long as possible.

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Old 08-12-2012, 03:44 PM   #12
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[QUOTE="wa8yxm"

In fact .. Try a TIRE PRESSURE MONITORING SYSTEM such as Smart Tire or Pressure Pro... Nothing like checking your tire pressure every few minutes, even while toolidn down the freeway at 55-60 MPH. .. Wait a minute, it is exactly like that!.[/QUOTE]

From the SmarTire website: "SmarTire products are no longer available in the recreational vehicle market and the company has ceased support for this product category." bummer!
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Old 08-12-2012, 04:59 PM   #13
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Quote:
Originally Posted by corvettec3 View Post
A month ago I had a blowout on one of my rear duals and did not hear or know about it until I went to install a tire monitoring kit. After that I decided to replace all six tires. When the technician was here installing the new ones I asked him what tire pressure he was using and he told me 100 psi. I told him that the sticker inside my driver door specified a recommended pressure of 70 psi. He said "If I left here knowing that you only had 70 psi in the tires on that rig, I would not sleep well tonight. It would just be a diaster waiting to happen and that if you were running 70 psi before then that is why you just had a blowout." So I am running 100 psi all around. The rig certainly rides and handles nice with those pressures.
What is the maximum cold pressure stamped on the tire?
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Old 08-12-2012, 09:21 PM   #14
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The pressure stamped on the tire sidewall is the MINIMUM pressure to handle the MAXIMUM load stamped on the tire. The maximum pressure for the tire would be the pressure rating for the wheel.
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