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Old 07-24-2018, 03:19 PM   #1
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Weighed RV - Tire Pressure??

I have a 2017 Winnebago Adventurer 37F (Ford F53 Gas 24K chassis). I took it to a Cat Scale today and they had room on the sides of the scale for me to load it right/left for two different weights front/rear on each side.

I had a full tank of gas (80 gal), a full freshwater tank (78 gal), full propane tank (27 gal) and everything onboard except food in the fridge and my wife in the passenger seat. I've added in her weight and an estimate of food weight for a normal packing job in the numbers below.

I ended up with:
Left Front: 3760
Right Front: 3650
Left Rear: 7740
Right Rear: 7980
Total weights are:
Front: 7,410 - Rated axle: 9,000
Rear: 15,720 - Rated axle: 15,500
Total: 23,130 - Rated chassis is 24,000
I learned that I'm 220lbs over weight on the rear axle. Which isn't good. But then I never travel with 640 lbs of fresh water in my tank (located on right rear). I usually keep it 1/3rd full when traveling - which is 214 lbs. With my normal water on board I'm (only) 300 lbs underweight for the axle. Just squeaking by there.

I'll try to move some heavy items forward just to be safer, too.

My tires are Michelin XRV 255/80R/22.5

According to Michelin's website for this tire I should air my front tires to just 70 PSI and the rears to 85 PSI. But I normally keep my tires at 95 PSI front and 100 PSI Rear.

I'd love to lower my Tire Pressure and end up with a softer smoother ride - one of the main reasons I weighed the coach. I was thinking of setting my tires at 75PSI front and 90PSI Rear.

What do the knowledgeable folks at IRV2 think??
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Old 07-24-2018, 03:48 PM   #2
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I'm surprised that a 2017 has a harsh ride at all, even with the higher pressures you're running the tires. BTW, that's the pressures I run mine. But my ride isn't harsh at all.

Are you saying that for your weights you can run the air pressures across the front axle at 70PSI and the rear axle at 85PSI? Or is that just a recommended pressure for a 'soft' ride, not counting the weight the tires are carrying?

Doesn't your chassis have an air bag system? If it does, isn't there some kind of adjustments you can make to them that will accommodate your higher tire pressures?


Just thinking out loud here. Good luck!
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Old 07-24-2018, 03:54 PM   #3
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Hey Jim, no my coach is a F53 Gas RV. No airbags. Basically it's a heavy duty dump truck chassis. Rides just like a truck. As do just about all Gas RVs based on this Ford Truck Chassis.

The Michelin tire guide recommends those PSI settings for the actual weight I have on the axles. At those settings (70/85) my tires are supposed to carry more weight that I actually have on each axle.
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Old 07-24-2018, 04:05 PM   #4
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No need to second guess the inflation tables. They are there to give you the best contact patch, best ride, best traction and best longevity. If your weights are correct, set the pressures and run it.
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Old 07-24-2018, 04:08 PM   #5
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Here's the chart for my tires:
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Old 07-24-2018, 11:32 PM   #6
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Here's the chart for my tires:
In my opinion, 70 psi for the fronts would be too low. That's cutting it too close for what your corners weigh. Running 75 psi heads you into the right direction but I think jumping up to 80 psi might be better yet. That would give each tire a load capacity of 4300 lbs, about 500 lbs more than your heaviest corner. Myself, I think I would try it first to see how the coach rode.

On the rear, running 95 psi gives the duals an 8820 lb capacity, a little over 800 lbs more than your heaviest rear corner weight. That would be close to the 10% safety margin that is routinely suggested.
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Old 07-24-2018, 11:45 PM   #7
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For a second there I thought you were going to list your wife's weight, instantly thinking to myself...he's a dead man.

I'd suggest setting the tires to the recommended pressure and driving it several miles and see if it makes a difference.

I also run Michelins and have set mine higher than the recommended 80lb. I run 90 all the way around.

I was running the fronts lower but started to see wear on the outside edges so I upped them to 90.
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Old 07-25-2018, 07:42 AM   #8
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FWIW, I posted the results of running tires for 50,000 miles @ a pressure 10% higher than the inflation table recommended. When I measured the tread depth across the face, I found that the middle was worn more than the outer edges. That is an example of over inflation for the load. I was and still am concerned about being under inflated so I, like a lot of people, run a slightly higher pressure that the tables to avoid it on the colder mornings. However, I wonder if it is necessary. Isn't it best if the tires have even wear? Doesn't that give the best ride, traction and longevity?
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Old 07-25-2018, 09:13 AM   #9
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Do you tow? If so you should consider the GCWR which is a way Mfg's have of reducing the load on your MH even more.

Yes the better the contact patch is the better the tires will preform.

220 lbs on a 22000lb coach is 1 percent or an amount that is negligible. Throw the golf clubs in and don't worry. If you fill your tires in the morning you will have different pressure than if you fill in the evening. That small a pressure difference is not an issue. Don't worry, be happy. Keep us posted
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Old 07-25-2018, 02:52 PM   #10
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Calculated with my made spreadsheet, based on axleweight gives front 85 psi and rear 98 psi.
Based on your given axleend weights it gives front 86 psi and rear 100 psi.
This is with maximum reserve with still acceptable comfort and gripp.

Also notice the crossed weight-difference front and rear. 9 out of 10 you have this.
Not important for the pressure advice, because R/L needs to be the same pressure to the view of the tire- and car- makers.

This advice is cold measured ( inside tire- temp = outside- tire-temp, that simple, and calculated back to 65/68 degr F. So on hott days you need to fill higher cold pressure, but on cold days you can do with lower.
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Old 07-25-2018, 03:49 PM   #11
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jadatis, Can you provide details of your spreadsheet? Why are the pressures shown in your spreadsheet so much higher than the Michelin Tire fitment charts? Is your spreadsheet for Michelin XRV 255X80R tires? Or some other tire/brand/size?

Not disputing your advice, just curious about what you're using to come up with those numbers.

Also, I'm unclear what you mean by "crossed weight-difference front and rear."
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Old 07-25-2018, 04:00 PM   #12
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Quote:
Originally Posted by creativepart View Post
I have a 2017 Winnebago Adventurer 37F (Ford F53 Gas 24K chassis). I took it to a Cat Scale today and they had room on the sides of the scale for me to load it right/left for two different weights front/rear on each side.

I had a full tank of gas (80 gal), a full freshwater tank (78 gal), full propane tank (27 gal) and everything onboard except food in the fridge and my wife in the passenger seat. I've added in her weight and an estimate of food weight for a normal packing job in the numbers below.

I ended up with:
Left Front: 3760
Right Front: 3650
Left Rear: 7740
Right Rear: 7980
Total weights are:
Front: 7,410 - Rated axle: 9,000
Rear: 15,720 - Rated axle: 15,500
Total: 23,130 - Rated chassis is 24,000
I learned that I'm 220lbs over weight on the rear axle. Which isn't good. But then I never travel with 640 lbs of fresh water in my tank (located on right rear). I usually keep it 1/3rd full when traveling - which is 214 lbs. With my normal water on board I'm (only) 300 lbs underweight for the axle. Just squeaking by there.

I'll try to move some heavy items forward just to be safer, too.

My tires are Michelin XRV 255/80R/22.5

According to Michelin's website for this tire I should air my front tires to just 70 PSI and the rears to 85 PSI. But I normally keep my tires at 95 PSI front and 100 PSI Rear.

I'd love to lower my Tire Pressure and end up with a softer smoother ride - one of the main reasons I weighed the coach. I was thinking of setting my tires at 75PSI front and 90PSI Rear.

What do the knowledgeable folks at IRV2 think??
You coach seems to be fairly well balanced with a difference of 130 lbs side to side.

Did you by chance compare the axle weight to the sum of the corner weights on each axle? Generally the sum will be higher than the axle weight.
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Old 07-25-2018, 04:14 PM   #13
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These forums on tire pressure will drive you nuts.

I have talked with tire store experts and with Michelin customer service. They all told me to run the pressure shown on the chart using the heaviest corner as the weight standard on the chart.

Those numbers seemed low based upon what my coach sticker suggested (significantly lower) so I run them 5LBS over on the rear duals and on the steer tires 10 LBS over, to allow for any unexpected leakage.

I have had two experiences with valve extensions leaking slightly when sitting.

I now check tires every day when I am going to be driving. Usually they hold fine, but one day last month, I was checking at a campground before a 7 hour drive and was shocked to find an inside dual was down almost 10 LBS.

God forbid if I hadn't checked and it kept losing air!

The moral is to check tires before you start your day (with cold tires) and carry a compressor, just in case.
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Old 07-25-2018, 05:02 PM   #14
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Why do people including myself, consult the inflation tables written by tire experts who have tested and calculated a safe pressure and then if we feel they are too low, we add 5-10 psi to make us feel safer. Why bother checking with the experts if we are not going to follow their advice? I suspect that when they wrote the tables, they knew some mornings would be colder and allowed for that. It's like an axle rating. The sky won't fall if a 17,000# axle carries a 17,500# load for 10 years. So I doubt a tire will fail if it starts 2-3 psi lower than the posted pressure a few times. On most days, if one started at noon instead of 7am, the pressure would be above the chart number.
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