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Old 09-13-2016, 08:42 PM   #1
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Tire Pressure Sanity Check

Just because there aren't enough threads about Tire Pressure...and I think I've read them all, however, the numbers I have come up just seem low.

2004 CC Intrigue 40' Tag. I just put on new 8 XZA2 Energy 315 80R 22.5.

The badge on the coach called for 120-110-120 (steer,drive,tag), but that was on the H Rated Toyo 12r's.

These new tires are "L" rated with MAX of 130.

The coach weights are the following:

Front - 14,500/2 = 7250
Drive - 22000/2 = 11,000
Tag - 12000/2 = 6000

Total = 48.5K

Using the chart for this tire on Michelins site, they say the following:

Front - 105
Drive - 85
Tag - 85

Seems low to me...thoughts, comments, suggestions?



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Old 09-13-2016, 08:45 PM   #2
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Well, first off the pressure on the sidewall of a truck size tire is not the maximum it should ever have. It is the minimum to support the maximum rating of the tire.
If you've read the charts right with the correct weights then I would take the chart pressure and add 5 psi to it since you don't have four "corner" weights.

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Old 09-13-2016, 09:18 PM   #3
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Originally Posted by Mr_D View Post
If you've read the charts right with the correct weights then I would take the chart pressure and add 5 psi to it since you don't have four "corner" weights.
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Old 09-13-2016, 09:43 PM   #4
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Seems about right, and X3 with Mr D.

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Old 09-14-2016, 05:00 AM   #5
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Going from a load range H to L I would expect to see a drop in recommended pressures for the same weight. Since the new tires are not the same class as originally installed (load range change) on the coach the builder's placard is no longer applicable. Sticking with Michelin's recommended pressures with an addition 5 PSI to account for variations in day to day loading and temperature changes.
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Old 09-14-2016, 12:16 PM   #6
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If you look at a load chart for the H rated tire for a given weight and compare it to the recommended pressure for the same weight on an L rated tire, the numbers will be the same. The L of course can carry more weight, but at a higher pressure. When I asked a Michelin rep about the different minimum pressure ratings he said they were correct and that I could run more as long as I did not exceed the amount listed on the side of the tire. He said that all of the different psi ratings were the minimum, however, the 120 psi on the side of my tire was the minimum cold pressure for the load, but was also the maximum cold psi for the tire.

EDIT: I need to correct part of my statement: I just put on some G rated trailer tires replacing E rated ones. It uses the same load range chart, however, continues past the maximum load for the "E" rating to the max for the "G". To carry 3000# for either tire the min psi is the same. This may no apply to the 22.5 RV tires.
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Old 09-14-2016, 05:16 PM   #7
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Go by the chart...
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Old 09-14-2016, 06:50 PM   #8
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Go by the Michelin chart fopr that model and size. The Toyo's were a smaller tire (12R is smaller than 315/80), so naturally the required pressure was higher.

As others have explained, the L vs H rating has little to do with pressure requirements - it's mostly a higher max load & psi. And you can only compare load range & psi for identical size tires anyway. With different sizes, all bets are off.
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Old 09-15-2016, 02:57 PM   #9
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I got a new set of Michelin 295/80R22.5 XZA2. I had my coach weighted at the FMCA Rally in Albany,Or (4 corner wt) With a combined wt of 33,620lbs FR 6,405lbs-FL 6,065lbs RR 10,195lbs-LR 10,955lbs I need to run 105 PSI in the front and 100 PSI in the rear. They give you a print out of your coach wt's and the air pressure to run. This is the only way to get a true wt reading and know what PSI to run, money well spent.
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Old 09-15-2016, 03:07 PM   #10
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Pressure numbers look about right for 315/80's.

BTW...... Thats one heavy 40' coach!

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2008 43' Holiday Rambler Scepter PDQ
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