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Old 03-15-2015, 06:56 PM   #1
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Air pressure

Hello Fellow Travelers,

We have a 2011 Monaco Knight 41+ feet long, not a tandem, what do you suggest for air pressure. It has Goodyear G670 RV-275/80R 22.5 tires. The max stated on tire is 125psi cold. We're getting ready for a trip and wanting to get good mileage but not a rough ride.

Thanks,

Steve
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Old 03-15-2015, 07:01 PM   #2
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Somewhere in your coach is a placard stuck to a wall that has the recommended tire pressure for unit based on the axle weights. Use that. If you want to lower the pressure from the recommended, you will need to weigh your unit based on what you typically have in it then use the Goodyear tire chart to set the proper weight.
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Old 03-15-2015, 07:17 PM   #3
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Quote:
Originally Posted by wildtoad View Post
Somewhere in your coach is a placard stuck to a wall that has the recommended tire pressure for unit based on the axle weights. Use that. If you want to lower the pressure from the recommended, you will need to weigh your unit based on what you typically have in it then use the Goodyear tire chart to set the proper weight.
Good Advice!!
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Old 03-15-2015, 07:22 PM   #4
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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 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 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.
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!!
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Old 03-15-2015, 07:23 PM   #5
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The placard or sticker mentioned in post #2 could be inside a cabinet
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Old 03-15-2015, 07:45 PM   #6
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Instead of guessing you should take your unit loaded for travel and go to a CAT scale and weigh the coach. Then you will have actual axle weights to use for setting your tire pressures based on the Goodyear tire pressure charts. Add 10 lbs per tire for a safety margin.
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Old 03-15-2015, 08:30 PM   #7
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On my Monaco the tire pressure placard is on the wall next to and slightly behind the front drivers seat.

I run my pressure 10 psi over the recommended placard pressures. Front tires are at ~105 psi and the rear is at 95 psi.

Also, if you don't have one invest in a Wireless Tire Pressure Monitoring System which provides you with accurate pressures. I check mine every time prior to hitting the road and then occasionally check while in route. The system will alert you of a tire going flat and or instantaneous loss of pressure. One of the best investments I've put on the Coach.
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Old 03-15-2015, 08:35 PM   #8
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The best thing is to actually weigh your coach & go from there. Too much or too little air pressure can be dangerous & expensive if it cause your tires to wear.
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Old 03-15-2015, 09:33 PM   #9
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Quote:
Originally Posted by Mr_D View Post
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 the Michelin RV Tire Guide:

From the Firestone/Bridgestone RV tire guide:


From the GoodYear RV Tire Guide:


From TOYO
That sums up the topic quite well.
The RMA - Rubber Manufacturers Association, of which all major tire manufacturers are members, states in this pdf, page 55
"However, never use inflation pressure lower thanspecified by the vehicle tire placard, certification
label or owner’s manual.
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Old 03-15-2015, 10:15 PM   #10
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Quote:
Originally Posted by Mr_D View Post
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 the Michelin RV Tire Guide:

From the Firestone/Bridgestone RV tire guide:


From the GoodYear RV Tire Guide:


From TOYO

Good info.
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Old 03-16-2015, 05:36 AM   #11
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Run your loaded rig over a truck scale and get the weights for the axles. Ideally you would want the weight for each wheel assembly, but axle weight is close enough.

Compute the weight each tire is supporting: Divide the front weight by two, the rear dully by four, and tag axle by two.

Go to the Manufacture air pressure tire table and find your tire type (truck) and tire size. These tables are similar between manufactures, so if you can't find your specific manufactures table , use this one:

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

find the tire weight you computed, make sure you differentiate between a dully and a single. (dual isn't two tires, its the weight one tire will support when its mounted as a dully. A dully tire will support a little less than a single tire)

After you find the weight, look up and it will give you the tire pressure.

On mine (225/70R19.5) , the tire weights are to low (2500 lbs) and don't show on the chart, it would probably be about 55 psi if I extrapolated the chart, so I decided to use the lowest value that was shown on the chart (70 psi)

As others have said, This is the minimum cold pressure for that weight. More pressure may be OK, as long as you do not exceed the maximum pressure indicated on the tire.

Ideally, check pressure when its cold. If hot, add 10- 15 lbs.
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Old 03-16-2015, 05:47 AM   #12
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This has been the most confusing thread I have seen about setting proper tire pressure.
Get the rig weighed at a cat scale. Then use the tire manufacturer chart to set the pressure.
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Old 03-16-2015, 06:04 AM   #13
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According to the tire manufactures chart, minimum pressure for that tire is between 80 and 120 psi, depending on the weight (4540 - 6610 lbs) that the tire is supporting and if that tire is a single or one of the dullys.
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Old 07-11-2015, 07:58 PM   #14
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Air pressure

I'm still confused. The manufacturer placard calls for 120lbs for steer axle tires, 120lbs for drive axle tires and 120 lbs for tag axle tires. I have Goodyear 295/80R 22.5 on all three axles......same RV rated tires....8 of them.

My front axle actually weighs 13,633 lbs. divide by 2 = 6,816 lbs and the Goodyear chart says to use between 105 and 110 lbs of pressure......that one is easy.

The scale I went to did not allow for weighing each end of the axle and it didn't allow for weighing the drive axle separate from the tag axle. So my total weight came up to 16,182 lbs. this may be just the drive axle, considering the GVW ratings of my coach shows 20,000 lbs for the drive axle. I don't know what to do with that number with regard to the 6 rear tires.... Do I divide by 2 (to get left side and right side weights). and then divide that result by two (tires) which doesn't make sense when looking at the Goodyear chart.... That equals a little over 4000 lbs which means I would inflate to a lot less than 80 lbs. According to the Goodyear chart. And if I just go with the MGVW of 10,000 lbs. for the tag axle, I am also below 80 lbs. according to Goodyear and why would the the manufacturer placard say 120 lbs...... I am confused.

Any help is appreciated.......
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