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Old 05-26-2011, 06:25 PM   #1
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Can These Tire Pressures Be Right?

My coach is four years old. 35,000 miles with original Michelin 275/80R22.5 XZE tires. When new, I had some after market items added at Henderson's Line Up in Oregon and they inflated the front tires to 90lbs and the rears to 95 after performing a four corner weigh.

At the time I couldn't find the inflation tables for the XZE looking at Michelin RV tires so I stuck with the pressures Henderson's had established.

I'm getting ready to hit the road for the summer and after reading several threads discussing the XZE tires I thought I'd take another look at the proper pressures. I was able to locate the XZE chart now via Michelin's RV tire site and Michelin North America RV Load & Inflation Tables ... if I'm reading the tables correctly (a really big if)... it calls for 80psi front and rear.

Can this be correct? Do others driving a 30,000lb rig run such low pressures???

My weights are 10180 and 19100. The coach came from the dealer with all tires inflated to 110 and the first 500 miles nearly knocked the fillings out of my teeth! I'm all for dropping the pressures and have a good lazer temp gauge so I can check the tire temps for a while to make sure I don't get into trouble but this just feels scary to me.

Insights please.....

Rick
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Old 05-26-2011, 06:32 PM   #2
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I would say that 80# should cover it. To feel more at ease, maybe add 5# front and rear.
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Old 05-26-2011, 06:43 PM   #3
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Sound right to me, I'll add 5psi to each to.
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Old 05-26-2011, 07:20 PM   #4
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Tables say LR H XZE for your size are around 80-85 psi for your tire size. I agree with the other posts. Add +5psi. Make sure to check cold.

I also agree that over-inflated tires are probable the #1 reason for a rough ride and poor handling in a motorhome.

I had the same problem when I picked up my new coach. Tires were inflated to max 110 psi, and it road and drove like a garbage truck. I quickly figured this out and now run 90 psi all around. Handling is MUCH improved.
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Old 05-26-2011, 07:29 PM   #5
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Thanks guys. I just wanted some validation before I did something silly.

Now I get to reprogram my TPMS. I was going to have to do some of that anyway because I have three new sensors on the way to replace three (more) that have failed. That's five failed sensors in two years.

Thanks again...

Rick
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Old 05-26-2011, 07:42 PM   #6
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A GVW of 20850 loaded 235/80 22.5 chart says 80 lbs. Thats what I keep in them and they ride good for a gasser.
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Old 05-26-2011, 08:11 PM   #7
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Rick,
I have you at tire size 275 by your original post.

Does this help:

Front Axle:
PSI-------Per tire----2 tires-----Total Tire Cap----Gross Difference
80 -------4915-------x2--------9830 (Underinflated)
85 -------5175-------X2--------10350 ------------170 lbs
90 -------5435-------X2--------10870 ------------690 lbs
95--------5690-------X2--------11380------------1200 lbs

Rear axle

PSI-------Per tire----2 tires-----Total Tire Cap----Gross Difference
80 -------9560-------X2--------19120-------------20 lbs (Not much of a margin)
85 -------10030------X2--------20060-------------960 lbs
90 -------10500------X2--------21000-------------1900 lbs
95--------10970------X2--------21940------------2840 lbs

For every 1000 feet of altitude, tires will see a .48 psi change for every 1000 feet of altitude.

For temperature changes there will be a 2 percent increase or decrease, as appropriate. Considering these factors, consider what pressure you want to run at that will leave you a margin where you don't have to adjust tire pressure for hot/cold/hot or cold/hot/cold weather, and altitude.

Example: at 85 psi, changing temperature -30 degrees would be 6 percent loss of air
or about 5.1 pounds. This will cause your front tires to be under-inflated. At 90 psi, a 30 degree drop in temperature will be 5.4 pounds and will still leave you at 85 psi, still within range of tire loads.

Now consider DW gains some weight (I didn't say that). At 85 psi you can add an addition 170 pounds of weight (lay off the donuts). Whereas, at 90 pounds you can add 690 pounds of weigh eating as many donuts as you want.

You have to be the judge of where your comfort weight is and put in the PSI right for you and within tire manufacturers specifications.

Personally, I'd run your tires at your weights at 90 psi.

Good luck.

p.s., I'm not a tireman - I just looked at the chart. I hope my figures are correct. The above is/are my humble opinion.
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Old 05-26-2011, 08:17 PM   #8
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Thanks much Wayne. It does help and makes sense.

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Old 05-27-2011, 12:57 AM   #9
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One thing to take into account is that Michelin (as do others I'm sure) revise their weight/pressure charts from time to time. I know in some of my Michelin literature they state that it's been revised.
So the pressure the Hendersons put in was probably correct at the time. Knowing Hendersons and their reputation plus having them evaluate our DSDP I'm betting they were right at the time.
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Old 05-27-2011, 04:54 AM   #10
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Tire pressure

What does the placard say on your coach? I have a 2008 tour and run 110 in front and 90 in the rears. This is what my placard says and is the same as one of the Winnie regional reps who had the same coach. Handling and ride have been very good and I get 9.2 with the 400 isl towing a grand Cherokee.
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Old 05-27-2011, 05:56 AM   #11
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Quote:
Originally Posted by RickO View Post

Now I get to reprogram my TPMS. I was going to have to do some of that anyway because I have three new sensors on the way to replace three (more) that have failed. That's five failed sensors in two years.

Thanks again...

Rick
Rick,

What brand of TPMS do you have?

If I had 5 sensors fail in 2 years, that's one brand I would stay away from.

I purchased the Doran Pressure Pro and only had one sensor crap out on our initial trip to Alaska last year. They shipped a replacement to Alaska and after 15,000 miles all sensors are still performing flawlessly.

I always take them off after reaching my destination to save battery life.

Dr4Film ----- Richard.
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Old 05-27-2011, 07:08 AM   #12
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So you actually did pay attention during the tire part of Camp Freightliner.



Quote:
Originally Posted by Wayne M View Post
Rick,
I have you at tire size 275 by your original post.

Does this help:

Front Axle:
PSI-------Per tire----2 tires-----Total Tire Cap----Gross Difference
80 -------4915-------x2--------9830 (Underinflated)
85 -------5175-------X2--------10350 ------------170 lbs
90 -------5435-------X2--------10870 ------------690 lbs
95--------5690-------X2--------11380------------1200 lbs

Rear axle

PSI-------Per tire----2 tires-----Total Tire Cap----Gross Difference
80 -------9560-------X2--------19120-------------20 lbs (Not much of a margin)
85 -------10030------X2--------20060-------------960 lbs
90 -------10500------X2--------21000-------------1900 lbs
95--------10970------X2--------21940------------2840 lbs

For every 1000 feet of altitude, tires will see a .48 psi change for every 1000 feet of altitude.

For temperature changes there will be a 2 percent increase or decrease, as appropriate. Considering these factors, consider what pressure you want to run at that will leave you a margin where you don't have to adjust tire pressure for hot/cold/hot or cold/hot/cold weather, and altitude.

Example: at 85 psi, changing temperature -30 degrees would be 6 percent loss of air
or about 5.1 pounds. This will cause your front tires to be under-inflated. At 90 psi, a 30 degree drop in temperature will be 5.4 pounds and will still leave you at 85 psi, still within range of tire loads.

Now consider DW gains some weight (I didn't say that). At 85 psi you can add an addition 170 pounds of weight (lay off the donuts). Whereas, at 90 pounds you can add 690 pounds of weigh eating as many donuts as you want.

You have to be the judge of where your comfort weight is and put in the PSI right for you and within tire manufacturers specifications.

Personally, I'd run your tires at your weights at 90 psi.

Good luck.

p.s., I'm not a tireman - I just looked at the chart. I hope my figures are correct. The above is/are my humble opinion.
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Old 05-27-2011, 08:29 AM   #13
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I know my tire pressure charts. They taught me how to read. Well, almost.
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Old 05-27-2011, 08:42 AM   #14
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Quote:
Originally Posted by gmanatl View Post
What does the placard say on your coach? I have a 2008 tour and run 110 in front and 90 in the rears. This is what my placard says and is the same as one of the Winnie regional reps who had the same coach. Handling and ride have been very good and I get 9.2 with the 400 isl towing a grand Cherokee.
I often type this: Two pressures all but guaranteed to be wrong are the one on teh placard and the one on the tire.

In the case of the placard.. It is the proper pressure for the coach (or it should be) EMPTY, no water, no waste, no food, no cloths, no grill no tools no (or nor more than 1/2 tank) propne. and just the driver.

That is the proper pressure as it was driven out of the assembly plant.

The pressure on the tire (110 for XRV's) is the maximum pressure if and only if you are loaded to the maximum load.

Weight is the determining factor and it MAY BE DIFFERENT side to side.

RV Safety, Merritt Island, Florida

The link to weigh your rig is on the left side of the page.
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