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Old 02-21-2015, 12:18 AM   #1
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Tire pressure question?

Hi all,

My Moho has a w24 chassis with a gvwr. of 30,000lbs, the tires are Michelin XRV 235x80x22.5 rated for max load inflation of 105lbs. if divided by 6 tires each could carry 5000lbs. I had my front end weighed at just under 8500lbs or 4250 lbs per front tire. PO had set the tire pressure at 105lbs per tire. Coach rides like a truck and we can feel every bump on the road. There are just 2 of us travelling and we travel fairly light. My Question is, what can I safely reduce tire pressure too, so as to improve ride with out under inflating tires? Is there a chart available?
TIA
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Old 02-21-2015, 02:31 AM   #2
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Quote:
Originally Posted by Milom View Post
Hi all,

Is there a chart available?

Milo
A quick google search revealed this Load and Inflation Tables | Michelin RV Tires chart.
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Old 02-21-2015, 06:25 AM   #3
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Also found this site with google and more specific this page.
Load and Inflation Tables | Michelin RV Tires
See if this link gives it directly.

But checked the calculation and found out it is calculated the american way, wich leads to to high loadcapacity's for the pressure.
Also your sise given as 110 psi G-load.
Best is to use my made lists wich take care of the same deflection of tire over the whole range, by wich you can go verry low in the pressure.

You can find in next map and can read lists in pdf for per tire/single axle.The Michelin list gives it per singe and dual axle.

https://onedrive.live.com/?cid=A526E...E092E6DC%21904

But my first impression is that you cant go much lower , so bumping must have an other cource.
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Old 02-21-2015, 11:01 AM   #4
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Your GVWR IS 24,000.

Your GCWR is 30,000.

My W24's actual FULLY LOADED weight is 23,200. I inflate all tires to 95#s.

My ride is excellent. My suspension is all stock.

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Old 02-21-2015, 09:00 PM   #5
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Take the time to read this pdf from the Rubber Manufacturers Association, of which Michelin, Goodyear, and many other mfgrs are members. Chapter 4 is for RV tires, pay close attention to page 55. It says in no case should tires be ran at less than the tire placard requirement.
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Old 02-21-2015, 09:47 PM   #6
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MILOM: "TOM N" is correct, and you shouldn't simply divide either of those ratings by 6 to determine tire pressure. And, FWIW, your tires allow a MAX cold inflation of 110PSI, but you surely will not need them set at that pressure. I don't agree with using the "placard pressure" because THAT is likely nothing more than a calculation based on the axle ratings, and the author of that placard (either WBGO or WCC) could not possibly take into account YOUR actual loaded weights.


The ONLY way to determine what pressure you should be running is to get individual axle weights at a truck scale and then consult the Michelin pressure charts. It is entirely possible that the fronts can be different from the rears, but you should have all tires on each axle set at the same pressure. Also, the charts will show a different pressure for the same weight for the rear "duals", so make sure you take that into account when determining the pressure for the rear tires.
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Old 02-22-2015, 10:30 AM   #7
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edgray has given you good advice. I had my axels weighed under full load ready to travel and found that by using the Michelin chart I should set the rears at 87# and the fronts at 97# cold. I have been doing this for the past several years and my tire wear is even and we have not had any tire problems. Bear in mind the tire pressures will raise 5# to 10# do to temperature increases. I learned that when I installed my TPMS.

Don
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Old 02-22-2015, 12:45 PM   #8
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You write your GVWR is 30000 lbs wich rest on 6 tires wich are allowed to carry each 4675 lbs if singel load configuration, together 28050 lbs.
So or your GVWR is lower or your tires are not allowed under your motorhome( or I am mistaken and its a 5th wheeler).

How did you came by those figures ? Best is to read it from the MH and tires.
Can be your tires are H load so with higher maximum load of tire. Or you assumed the GVWR to be 30000 and it is not.

In case of motorhome 30% is minimum adviced on front, wich you apperantly weighed to be 8500 lbs. Little calculation gives then total vehicle weight of 28300 lbs.
added my made list to use
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Old 02-22-2015, 04:35 PM   #9
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Weighing done at the iRV2 Ohio national rally.

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Old 02-23-2015, 08:50 AM   #10
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Then with the data Tom N gave I made picture of my filled in spreadsheet.
Then only part 1 and 3 used and assumed rear dual load , so 4 tires on one axle. Also assumed the same tires as TS so G-load .
If the data are different then I assumed , correct me and I will make a new one.
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Old 02-23-2015, 09:51 AM   #11
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Lots of excellent info in the Michelin RV Tire Brochure.

https://www.michelinb2b.com/wps/b2bc...s_Brochure.pdf
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Old 02-24-2015, 03:40 AM   #12
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Wanted to chanche the picture, because it was hardly readable, but this is not possible in this forum.
So again here larger and with some extra remark.
What Tom did is the best way, that weighing per wheelpair.
So if TS Milom has the same specifications, do some weighing, you will be surprised. I asumed Tom weighed fully loaded so as he uses it on the trips.
Otherwise you should add the persons and payload that where not in the motorhome .

Also here a crossed weightdifference between the axles, in spreadsheet I express it in weightdifference R/L difference between axles.
of 520 lbs . This gives torsion in the frame wich compensates the real weight difference a bit. If you could level the MH by some means ( Pneumatic) per wheel(pair) more weightdifference would be measured.

And Dual load , so 4 tires on one axle needs lower maximum load of tires, so gives higher presssure advice but lower because devided over 4 tires.
In the spreadsheet this is all done automatically , only give the right data in part 1.

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Old 02-25-2015, 11:40 AM   #13
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Originally Posted by Ray,IN View Post
Take the time to read this pdf from the Rubber Manufacturers Association, of which Michelin, Goodyear, and many other mfgrs are members. Chapter 4 is for RV tires, pay close attention to page 55. It says in no case should tires be ran at less than the tire placard requirement.
That placard ASSUMES your are running your RV at max gross weight. Tire manufacturers publish tables of weight/pressure for a reason. If you have not yet weighed your motorhome, then, indeed, use the tire pressure on the placard.

To the OP, I strongly recommend you obtain a 4 corner weigh and adjust your Michelins to the manufacturers recommendation! This is based solely on my opinion and just at 95,000 miles and 10 years of motorhoming full time. Curious as to why you had only the front axle weighed and not the back. Also, keep in mind, that axle weighing is second best to 4 corner weighing, as dividing an axle weighing by two is not necessarily giving you the weight of each axle end.

As a side note, just because a manufacturer is a member of an association, does not necessarily mean they endorse every thing the association says or prints. In the case of Michelin, they have some pretty specific recommendations with respect to RV tires, pressures, and maintenance that does not entirely coincide with the above "quoted" .pdf . . . just sayin'
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