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Old 02-26-2016, 04:59 PM   #1
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Need a math teacher for tire pressure confirmation

I have weighed the coach, done the math and checked the Michelin pressure chart, but it doesn't seem right. Please confirm that I am correct or point out my error. Thanks.

Michelin 275/80R22.5 H XZA3 tires.

150 Gallons of Fuel
Fresh Water Full
Fridge Full
Liquor cabinet Full

Steer axle: 12800#
Drive Axle: 15020#
Tag Axle: 7380#
Total 35200#

When I check the Michelin chart, I get:
110 psi on Steer
75 psi on Drive
75 psi on Tag.

I know it is a big difference on load per tire from the front to the back, but it just seems like a big difference in pressure on front and rear.

PLEASE NO GUESSING. PLEASE NO OPINIONS. JUST PURE KNOWLEDGE.
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Old 02-26-2016, 05:09 PM   #2
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I'm assuming the rears are dually tires on each axle? If so the load is spread over many more tires than the steering ones. That would both make sense and give more sidewall flex and smoother ride in the rear.
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Old 02-26-2016, 06:40 PM   #3
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The sidewall of the tire tells the true story. For optimum tread wear and tire life run your tires at 110 front 90 on the rear. These are TRUCK tires and are to be treated as such. If you run a tire that size at 75psi you are basically 60% deflated. Running to low of pressure will cause overheating leading to early tire failure.


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Old 02-26-2016, 07:06 PM   #4
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Dual's always run less than a single, I would run what is rated by the tire manufacturer for the weight you have on them. I always add a little more for a margin factor. I don't just put in the max pressure just to run max pressure.
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Old 02-26-2016, 08:57 PM   #5
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Quote:
Originally Posted by Blackrock View Post
The sidewall of the tire tells the true story. For optimum tread wear and tire life run your tires at 110 front 90 on the rear. These are TRUCK tires and are to be treated as such. If you run a tire that size at 75psi you are basically 60% deflated. Running to low of pressure will cause overheating leading to early tire failure.


This ain't a Cadillac so don't expect a Cadillac ride.

This absolutely the wrong advice.
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Old 02-26-2016, 09:01 PM   #6
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Twice, I don't have a tag axle but I run less pressure in my dual rears than I do in my steer tires. If you are getting these pressures from the Michelin tire chart then I would say you are correct.
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Old 02-26-2016, 09:31 PM   #7
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I share Campin Cajun's opinion, and would add that you may want to consider left and right weights and base pressure on the heavier side of the axle. Tire pressures should be the same on both sides of the axle, but that pressure should relate to the heaviest side.


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Old 02-27-2016, 08:04 AM   #8
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I share Campin Cajun's opinion, and would add that you may want to consider left and right weights and base pressure on the heavier side of the axle. Tire pressures should be the same on both sides of the axle, but that pressure should relate to the heaviest side.


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Yes, exactly!


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Old 02-27-2016, 08:14 AM   #9
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Welp, looks like I got Flamed pretty good on this one. I only been in the heavy truck fleet repair business for thirty plus years so I guess I need to bow out of any tire related issues on this forum.
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Old 02-27-2016, 09:15 AM   #10
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Welp, looks like I got Flamed pretty good on this one. I only been in the heavy truck fleet repair business for thirty plus years so I guess I need to bow out of any tire related issues on this forum.
Seems many from the heavy truck world recommend max pressure in all tires. Motor homes are different thing and the manufacturers sometimes recommend adjusting the tire pressure based on the way to give the best ride.
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