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Old 03-19-2015, 10:26 AM   #15
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If your at 85psi and your front axle is at 10000 lbs, then you have exceed the rating of the tire.

Either reduce the load or increase the pressure.

The rule of thumb is to look up your weight in the table, make sure the pressure your filling your tires to will support the weight your placing on the tire(s).

I copied the data from the Firestone chart that matches your tire.

The same tire can be mounted as a single (front or tag axle) or as a dual, your rear dully axle. The pressure / load ratings differ between these two installations..

I don't think it would be responsible of me to just say "Fill to X pressure and your OK" without looking at the tables, looking at the vehicle weights and tire sizes to ensure that, what I'm telling you is within the safe operating specification of the manufacture
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Old 03-19-2015, 10:37 AM   #16
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The maximum weight your tire will handle in a single mode is 7000 lbs, But it must be filled to at least 120 psi to do this.

HOWEVER - that's a cold pressure - what happens when the tire gets warm and the pressure goes up, You've just exceed the maximum pressure for that tire.
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Old 03-19-2015, 11:13 AM   #17
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Quote:
Originally Posted by Waiter21 View Post
...
You must also consider "What is the pressure when the tire is hot?. That pressure should not exceed 120psi (the max for your tire)
Everything else in your post looks OK, but I'm quite sure that this statement is incorrect. Can you provide a source for your statement?
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Old 03-19-2015, 11:14 AM   #18
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Quote:
Originally Posted by Waiter21 View Post
Front tires = 3520lbs (div 2)
Rear tires = 4350lbs (div 4)

From the Inflation tables,

http://www.firestonetrucktires.com/p...Load_Table.pdf

The minimum cold pressure to support these weights is

Front = 85psi (4920lbs)
Rear = 85psi (4590lbs)

The pressure is the minimum in the table, it doesn't go lower, The weight is what is listed for that pressure)
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See what your placard says, It should give a tire size, pressure, and max weight.

Since the actual weights are well below published pressure weights, I'd probably go with 85psi cold.

Front actual weight = 3520lbs.. Max weight for 85psi is 4920lbs
Rear actual weight = 4350lbs.. Max weight for 85psi is 4590lbs

The tire charts post a minimum and maximum pressures and corresponding weights that can be supported for the tire if its mounted as a single or a dully.

For that tire its minimum 85 psi, maximum 120 psi.

I would not exceed 120 psi with that tire. Max weights at that pressure are 7000 lbs (single) and 6395 lbs (dully)
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Originally Posted by Waiter21 View Post
NO, that is not correct - The weights are for each tire, not each axle.

Please refer to the table, find your tire, then you can look at the pressure vs load.

According to the table, at 85psi cold, the maximum weight your tire will support is:

Front tire - 4920lbs .. Front axle = (4920 * 2 = 9,840lbs)

Dully tire - 4590lbs .. Rear axle = (4590 * 4 = 18,360lbs)

The pressures from the table are Minimum pressure for that load. You can put in higher pressure if you wish, I would not exceed 120psi for that particular tire.

You must also consider "What is the pressure when the tire is hot?. That pressure should not exceed 120psi (the max for your tire)
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NO -

The load rating is 9840 max if you inflate to 85psi. That number comes from the table that you need to refer to.

That table will give you the load rating at different pressures.

If you wish to carry 10,000, you will need to increase the pressure to at least 90psi, That will provide a maximum load of 5160 lbs per tire for a single tire load, or 10,320lbs maximum for your front axle.

What do you mean by "Dual Purpose" tires?
Quote:
Originally Posted by Waiter21 View Post
If your at 85psi and your front axle is at 10000 lbs, then you have exceed the rating of the tire.

Either reduce the load or increase the pressure.

The rule of thumb is to look up your weight in the table, make sure the pressure your filling your tires to will support the weight your placing on the tire(s).

I copied the data from the Firestone chart that matches your tire.

The same tire can be mounted as a single (front or tag axle) or as a dual, your rear dully axle. The pressure / load ratings differ between these two installations..

I don't think it would be responsible of me to just say "Fill to X pressure and your OK" without looking at the tables, looking at the vehicle weights and tire sizes to ensure that, what I'm telling you is within the safe operating specification of the manufacture
Quote:
Originally Posted by Waiter21 View Post
The maximum weight your tire will handle in a single mode is 7000 lbs, But it must be filled to at least 120 psi to do this.

HOWEVER - that's a cold pressure - what happens when the tire gets warm and the pressure goes up, You've just exceed the maximum pressure for that tire.
thanks for the info
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Old 03-19-2015, 11:25 AM   #19
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my coach came with 255-70-22.5's

the wall says pump to 120psi front...10,500gvw

and 105 psi rear... 17,500 gvw

on the charts 120psi is 11,020

and the rear 105 is 18,440

that's 500 over in the front and 940 in the rear...

on that same tire if you weigh the coach

front 7000 rear 17500 the chart says front 80psi (lowest on chart)
and the rear...95 psi...


that's a lot of difference....that's 40psi in the front less

do you think that taking into consideration motorhome body roll, hard braking, road hazard .. wind .... that the builder figures in some engineered
factor and inflates the pressure to compensate
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Old 03-19-2015, 11:26 AM   #20
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Are your tires Firestone (matching the inflation tables above)? If not, you should check the inflation tables for your specific tires, since the values may differ from the Firestone ones. For instance, here is the Goodyear RV Inflation Table and you'll note that the values do differ.
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Old 03-19-2015, 11:35 AM   #21
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I have read everywhere where people are setting tires to actual scale weight... not gvw...and lowering the pressure to obtain a better softer ride


has any one tested this theory??? has anyone actually recorded tire heat with the lower psi vs the posted?


I for one think there is a formula for choosing tires and psi of tires
and a sliding scale if you will that gives a happy percentage of cushion
over for safe psi


so say you have a 10500 gvw... why would the builder demand 120 psi to be in compliance when Michelin states only 110 psi????
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Old 03-19-2015, 12:38 PM   #22
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Quote:
Everything else in your post looks OK, but I'm quite sure that this statement is incorrect. Can you provide a source for your statement?
Chris,

Please refer to the table, The max pressure for the tire listed is 120 psi.
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Old 03-19-2015, 01:14 PM   #23
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Quote:
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Chris,

Please refer to the table, The max pressure for the tire listed is 120 psi.
That is the max COLD inflation pressure. Tire pressures will rise significantly as the tire heats up in use--that is all allowed for in the cold inflation pressures specified in the table(s).
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Old 03-19-2015, 01:49 PM   #24
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That is the max COLD inflation pressure. Tire pressures will rise significantly as the tire heats up in use--that is all allowed for in the cold inflation pressures specified in the table(s).
you are correct from what I have learned...that's why they always give you cold pressures and tell you to check them when they are cold
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Old 03-19-2015, 01:55 PM   #25
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Yes, I also interpret that as the max pressure allowed in the tire.
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Old 03-19-2015, 02:34 PM   #26
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this is what goodyear has to say...

Proper Tire Inflation

Correct tire inflation is a key component in tire care. The recommended maximum inflation pressures for your tires are indicated on the certification label or in your owner's manual. Since RVs can be loaded with many different configurations, the load on each tire will vary. For this reason, actual air pressure required should be determined based on the load on each individual tire. Inflation pressure should be adjusted to handle the tire carrying the heaviest load, and all tires on the axle should be adjusted to this standard.
Each manufacturer provides load and inflation tables specific to their products to help you determine the correct tire inflation pressure for your vehicle's loading.
Underinflation brings a higher risk of susceptibility to damage due to road hazards, reduces casing durability, and causes a loss in fuel economy, plus uneven or irregular tire wear. Severe or prolonged underinflation brings about an increased risk of tread separation.
IMPORTANT: It's a common practice for RV owners to lower tire pressure in their search for a smoother ride. This is not only dangerous, it's relatively ineffective, as the difference in ride quality is not significant. When minimum inflation pressure requirements are not met, tire durability and optimum operating conditions are compromised. Tire inflation pressure should always meet at least the minimum guidelines for vehicle weight.
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Old 03-19-2015, 02:36 PM   #27
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Tire Inflation Guidelines

Check your tires' air pressures at least once a month, before each trip and each morning you drive during a trip. Tire pressure should be checked cold, or before you have driven that day, as tire pressure ratings have been designed with typical running heat/pressure build-up in mind. Remember to check the air pressures of the inside tires in dual fitments and make sure the valves and caps are free of dirt and moisture.
  • It may be necessary to inflate your tires at a truck stop or truck service center in order to achieve adequate air pressure for your coach's needs
  • Only permanent air seal metal valve caps should be used
  • Be safe - if a tire has been run 20% underinflated, it must be dismounted and inspected by a trained professional. It should not be aired up without a fullinspection or without using a safety cage. Use a calibrated gauge. If your tire is rated for higher inflation pressures, a special gauge will be required designed for larger tires.
  • Maintain mated duals at equal inflation pressures
  • Don't bleed air from warm tires to reduce pressure buildup
  • Don't inflate tires to cold PSI rating beyond rim specifications
  • Don't run one dual at low inflation pressure or flat
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Old 03-19-2015, 02:38 PM   #28
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Tire Loading

Tire pressure is what enables your RV tire to support loads. Overloading your tires can have serious consequences for passengers and your RV. Too much weight can cause stress on your RV's suspension system, brake failure, shock absorber damage, handling and steering problems, irregular tire wear and possible tire failure. Excessive loads or underinflation can lead to an excessive amount of heat and tire failure. If you discover that your tires cannot handle the load, lighten the weight of the load or install tires with a higher carrying capacity. Remember to consult your owner's manual, a Goodyear retailer, or the RV manufacturer for information concerning selection and installation of new tires.
Tire pressure should never be reduced below the vehicle manufacturer's recommended levels to support load conditions in order to improve the ride quality of a vehicle. The difference in ride quality is not significant. When minimum inflation pressure requirements are not met, tire durability and optimum operation can be affected.






Inflation Pressure for Uneven Vehicle Weight Distribution:



  • Select a tire with load carrying capacity designed to handle the maximum load point
  • For each axle determine the correct inflation pressure needed for that size tire to handle the maximum load
  • Inflate all tires on that axle to this same inflation pressure



Inflation Pressure for Uneven Vehicle Weight Distribution:

  • Select a tire with load carrying capacity designed to handle the maximum load point
  • For each axle determine the correct inflation pressure needed for that size tire to handle the maximum load
  • Inflate all tires on that axle to this same inflation pressure
RV Inflation Guide>
Download Load Inflation Table>
Download RV Tire & Care Guide>
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