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 > air pressure

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Danford50

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Posted: 02/03/19 12:48pm Link  |  Quote  |  Print  |  Notify Moderator

some what confused here I weigh my camper and the steer axle weigh was 4320 lbs do I take the 4320 and divide it by 2 and then look up that weigh on the tire chart to see how much air I need in my steer axle tires?

Desert Captain

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Posted: 02/03/19 01:03pm Link  |  Quote  |  Print  |  Notify Moderator

Yes, be sure to use the numbers from the tire manufacturers load/inflation tables. The same process for the rears, divide the rear axle weight by 4. These weights should be based upon the rig being loaded for a normal trip. Many folks add a fudge factor of about ten percent additional psi over the tables without problems. More than that can be problematic as overinflated front tires have their contact patch reduced and steering becomes loosey goosey.

Ignore the pressures listed on the stickers on your door jambs or the max psi on the sidewalls... while these numbers "could" {as in might maybe} be correct chances are they are not.

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wolfe10

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Posted: 02/03/19 01:48pm Link  |  Quote  |  Print  |  Notify Moderator

Desert Captain wrote:

The same process for the rears, divide the rear axle weight by 4.
[emoticon]


That is NOT universally correct. Michelin, for example in their RV tire guide lists:

Single
Dual

For dual, it is the weight carried by BOTH tires on that side of the axle.

SO, best advice is to follow the process recommended by your tire manufacturer.

Neither way is better/worse, just different. The good news is that most tire guides are pretty well written.

And, if in doubt as to whether their recommended PSI a given load is for a single tire in the back (with duals) or weight on both tires, pretty easy to determine:

Carrying capacity of an individual tire in a dual set up is LESS than that same PSI would carry in a single location-- ALWAYS.

So, per the example in the Michelin RV tire guide, for a 275/80R22.5,100PSI will support 5780 pounds. In back (duals) both tires on a side at the same PSI will carry 10,520 (yes, less than 2X 5780).


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Desert Captain

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Posted: 02/03/19 04:34pm Link  |  Quote  |  Print  |  Notify Moderator

wolfe10 wrote:

Desert Captain wrote:

The same process for the rears, divide the rear axle weight by 4.
[emoticon]


That is NOT universally correct. Michelin, for example in their RV tire guide lists:

Single
Dual

For dual, it is the weight carried by BOTH tires on that side of the axle.

SO, best advice is to follow the process recommended by your tire manufacturer.

Neither way is better/worse, just different. The good news is that most tire guides are pretty well written.

And, if in doubt as to whether their recommended PSI a given load is for a single tire in the back (with duals) or weight on both tires, pretty easy to determine:

Carrying capacity of an individual tire in a dual set up is LESS than that same PSI would carry in a single location-- ALWAYS.

So, per the example in the Michelin RV tire guide, for a 275/80R22.5,100PSI will support 5780 pounds. In back (duals) both tires on a side at the same PSI will carry 10,520 (yes, less than 2X 5780).




You need to reread both posts...

The first line of my post reads:

"Yes, be sure to use the numbers from the tire manufacturers load/ inflation tables"

Michelin provides different load/inflation ratings for singles vs dual {as do all tire manufacturers} but If you use those tables as I suggested it IS universally correct

The OP has axle weights, NOT 4 corner weights, therefore you divide the front axle weight by 2 and rear axle weight by 4 {we are talking a dually here which does not have 22.5"tires} and then go to the Michelin guide.

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JumboJet

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Posted: 02/06/19 04:43pm Link  |  Quote  |  Print  |  Notify Moderator

Formula: ((Axle Weight / # Tires)/ Tire Weight Rating) x Tire Max Pressure Rating = Suggested PSI

Suggested PSI x 110% is what I have run for years.

My Class A Front Axle 7040 / 2 = 3520 3520 / 5510 = .64 120 x .64 = 77

77 x 110% = 84 PSI

rjstractor

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Posted: 02/06/19 07:50pm Link  |  Quote  |  Print  |  Notify Moderator

I'm assuming your motorhome is on an E450 chassis, judging by the size listed in your profile. If so, don't overthink it and follow the manufacturer's tire inflation sticker on the door post. 65 psi front, 80 in the rear should be very close to optimal pressure. The tire inflation tables are great for when you're running a lower weight than max GVWR, but a larger class C motorhome is going to be fairly close to max weights.

OFDPOS

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Posted: 02/10/19 09:37pm Link  |  Quote  |  Print  |  Notify Moderator

Even clicking on Michelin load and inflation tables for RV tires , it still comes up with the XPS Rib tires .
These are NOT the Michelin tires we are running , most are running the Michelin Defender or LTX tires.
Wonder if the tire pressure rating is the same ?

DrewE

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Posted: 02/11/19 08:51am Link  |  Quote  |  Print  |  Notify Moderator

OFDPOS wrote:

Even clicking on Michelin load and inflation tables for RV tires , it still comes up with the XPS Rib tires .
These are NOT the Michelin tires we are running , most are running the Michelin Defender or LTX tires.
Wonder if the tire pressure rating is the same ?


If it's the same basic tire classification and size and load range (classification as in "light truck" or LT tires), then the chart will be the same, or close enough for all practical purposes. That's also true across brands, incidentally. The only exception I've seen is a few tires that allow higher pressures than standard and so have the chart extended a bit more...but usually the Ford (and I suspect Chevy) stock wheels are not rated for more than 80 psi anyhow, so it's rather a moot point for most class C motorhomes.





IAMICHABOD

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Posted: 02/11/19 12:40pm Link  |  Quote  |  Print  |  Notify Moderator

OFDPOS wrote:

Even clicking on Michelin load and inflation tables for RV tires , it still comes up with the XPS Rib tires .
These are NOT the Michelin tires we are running , most are running the Michelin Defender or LTX tires.
Wonder if the tire pressure rating is the same ?


Yes they use the same chart for all of them.
Here is the chart.
I have the the LTX MS/2 and use the same chart as the XPS


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OFDPOS

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Posted: 02/11/19 10:29pm Link  |  Quote  |  Print  |  Notify Moderator

Kinda figured that, thanks for the replies...

Last 2 MH's went with the LTX MS/2 as well.
Last MH actually just had the recalled tires replaced and once I bought the MH , the same tire shop allowed me to exchange the BFG tires that replaced the recalled Michelin's back to Michelin's. ( hope that makes since ? )
Not sure why ? But the tire shop put on the Defenders instead of the LTX's ?

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