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Old 05-23-2014, 07:57 PM   #1
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Michelin Tire Pressure questions

Hi All, I got my RV weighed today and it is 20,020 lbs total with full water and 3/4 fuel and a normal load of gear with 1 person onboard.

Front axle weight was 5,840 and Rear was 14,180.

My RV has the Michelin XRV 235/80-22.5 tires.

The tire tag inside the RV says to set tires to 90PSI front and rear.

The Michelin online guide for tire/axle weight and pressures for my tire says I should be at 70 psi fronts and 85 psi rears.

At 5,840 for the complete front axle half of that is 2,920. The minimum weight that the chart shows is 3,255 at 70 psi. I am 300+ lbs lighter than that per tire.

So should I be running less than 70 psi? Or should I just set them at 70?

Is my RV too light in the front?

I could move a few things to the front compartments like the BBq but it really only weighs 40 lbs or so. I only have one real compartment behind the rear axel.

I have added a trac bar and it has helped with the tail wagging dog syndrome.

Looking for guidance as it still is hunting while driving down the road.

I did lower the pressure in the middle of a test drive from 100 to 80psi but the tires were already up to temp so I did not want to reduce to 70.

I did not notice any major difference reducing pressures in front.

2013 Winnebago 35G, CHF, UltraTrac 2, 5 Star Tune.
2005 Jeep Rubicon Unlimited Toad
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Old 05-23-2014, 08:36 PM   #2
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Using this chart, I think you should do as you said, 70 psi front, 85 psi rear. The 90 psi on the sticker by the driver's station is usually the maximum inflation. I wouldn't go lower than 70 psi.



Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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Old 05-24-2014, 10:59 AM   #3
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Hi Rvbuzz,
Go by the Michelin tire chart, based on the weight the tires are carrying with one caveat. Do not go below the minimum PSI recommended by Michelin.
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Old 05-24-2014, 12:05 PM   #4
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Asuming the tire data right with 110 psi pressure needed for maximum load.
Here a picture of my filled in calculator.
In that I use even saver formula then Michelin uses in Europe, and add a reserve to weighed axle loads of 10% , wich will still give no bumping and leaves as much possible resserve.
The front is 29.2% of the total weight , once read that minimum of 30% is adviced, so yust on the border.
Because of the reserve , you dont have to be worried if you mesure on the road cold a lower pressure , with zero % reserve calculated gives F67/R88psi , but that would be dangerous because there is always a R/L difference per axle.
So yust to show where the borders are.

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Old 05-24-2014, 12:22 PM   #5
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We just did this drill with my BIL's rig, and it's worth noting that Michelin is very specific that pressures should be set according to the heaviest axle end, here quoting from this Michelin page
For RV use only, Michelin displays tire loads per axle end in the load and inflation tables, as we recommend weighing each axle end separately and using the heaviest end weight to determine the axle's cold inflation tire pressure.
If you haven't weighed all four corners, you can't know what that number might be. Just halving the total weight might leave you with a pressure too low.

You'd be surprised how much variation in weight there can be from side to side- I forget what the numbers were for BIL, but they were different enough to affect the final pressure number.
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Old 05-24-2014, 10:20 PM   #6
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Thank you for the replys.

Unfortunately the only scale in my town does not have room on the side of the scale area to allow weighing a single corner.

I will add 10% to the half weight of each axle and work from there.

I will still be way less pressure in the front than what was stated by Winnebago and only 5 psi less in the rear.
2013 Winnebago 35G, CHF, UltraTrac 2, 5 Star Tune.
2005 Jeep Rubicon Unlimited Toad
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Old 05-25-2014, 01:52 PM   #7
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You only need one side of the scale free for weighing per wheel(pair).
then you first wheigh per axle , and then if only right side of scale is free , drive over the schale with the left wheels on scale and the right wheels besides the scale. Write it all down and later get your calculator and substract the left wheel weighing per axle from the axle weighing to get the right wheel weight.

But thats also a reason why I add 10% when axle weighing .
If you ever weigh per wheel( pair) use part 3 of my spreadsheet .
Then dont be surprised if for instance front Right is more heavy then left and rear the otther way around so left is more heavy then right . Crossed weight differences per axle are often seen at motorhomes

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