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Old 04-09-2015, 09:05 AM   #1
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Tire Pressure in Phaeton 42QBH

Can anyone with a 42FT Phaeton tell me how many lbs of air they are running in their tires. I weighed the truck last week at 34,658 lbs. Couldn't mess with weighing wheels as there were several not too happy 18 wheelers behind me. Probably add another 1000 lbs of stuff before we get going.

The tires are at 110 psi right now. Drives good. Do I need to go to 120 as Tiffin has on the GVW label ? psi

Thanks
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Old 04-09-2015, 09:16 AM   #2
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Inflation would vary with tire brand and load rating.
Without axle or corner weights any inflation info would be a guess.
If 120 is the max inflation on the side wall of the tire , then 110 should be safe till you get the weights. But personally I'd avoid long trips until your sure.
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Old 04-09-2015, 10:07 AM   #3
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What are the axles weights, front, rear and tag?
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Old 04-09-2015, 02:02 PM   #4
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You can also search for the GAWR's front and right/GVWR ( gross axle/vehicle weight ratings ( mostly on same plate as pressure advices) .
Then also give configuration like number of axles and total number of wheels rear on the road ( tandem axle or dual load axle).

then from tires , 1. maximum load or loadindex, 2. AT-pressure ( probalby yours 120 psi) and 3. maximum speed of tire or speedcode-letter ( N= up to 140km/87m/h).

Then together with the weighed total weigh I can make a estimation of F/R division,and calculate an advice pressure with as much possible reserve, but still no bumping.
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Old 04-10-2015, 09:01 AM   #5
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When you get your stuff loaded, then head back to the truck stop and get your axle weights. You need to pull up to the point that you have an axle on each platform (there are three on the typical CAT scale). Since that takes the same amount of time to do as a truck would, no truck driver is going to be carrying on.

With axle weights iin hand and your tire inflation charts, you should be able to get your inflation pressures, Add 5% to the axle weight (except the tag) to compensate for side to side differences. Tag axles can cause the front axle to be loaded too heavily so you need to watch for that. You inflate the tag axle tires to the same as the drive axle.

Unless you want to drive a cement truck, there is no need to inflate anything past 110 psi until you get reweighed.

Individual wheel weights are the best but they are fine tuning the axle weights. They are also used to find problems, such as ride height misadjustments, that can overload an axle. Wheel weighing places are hard to find so start with the axle weights.
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Old 04-10-2015, 10:01 AM   #6
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I've weighed my LH twice now, and both times the rear axle and tag axle come out very light and actually will not show up on the Michelin tire pressure scale (only goes down to 75 psi. The front axle came out to needing 105 psi and I put 110 psi in them. To be on the safe side, I lower my tag and rear axle to 100 psi, and the coach rides very nice.

I would like to get a individual corner weigh, but most scales are not equipped to do this.

I doubt if the weights will be much different on your QBH.

Hope this helps

Ron
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Old 04-10-2015, 12:00 PM   #7
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Quote:
Originally Posted by lanerd View Post
I've weighed my LH twice now, and both times the rear axle and tag axle come out very light and actually will not show up on the Michelin tire pressure scale (only goes down to 75 psi. The front axle came out to needing 105 psi and I put 110 psi in them. To be on the safe side, I lower my tag and rear axle to 100 psi, and the coach rides very nice.

I would like to get a individual corner weigh, but most scales are not equipped to do this.

I doubt if the weights will be much different on your QBH.

Hope this helps

Ron
Some of the Michelin tables have a misprint.

They state individual tire when they mean axle or the other way around. I can't remember which it is. Anyway, you should use some common sense and apply the chart in a logical way. You will never be off scale on the low side.

For example, I have 2.75 80R 22.5 LRH tires on my MH. The front axle weighs just over 11,000# and I run the fronts at 105#. My rear axle weighs just below 21,000# and I run 95# in the rear duals. These numbers are "logical". Numbers that were twice or 1/2 what I have wouldn't make sense.
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Old 04-10-2015, 08:08 PM   #8
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Forgive me I am not trying to hijack this but this thread is time relevant to me as I just had my axles weighed on my new motorhome. Using the Goodyear load info chart my load does not even meet the min air pressure on it. Front axle per tire was 2900 chart is at 70 psi for 3640, the min. Rear is similar, weight was 2505 with min at 3415, again at 70 psi. Manufacturer recommends 82 psi across the board. I am at total 15930 for a 18,000 lb GVW with a full tank of gas, 3/4 water and the crap we carry.
Now.... back in a former life I owned a tire store and delt with OTR trucks, logging trucks and many cars.. the max air was what we normally put in given the logging trucks were always overloaded, and we based air on tire wear for more normal customers, so if the inside was wearing a bit thinner then the outside we would lower psi.. I know old school by the pant but that is what we did.. now, back in my case my load is far less then min standards, the max psi is 100 yet manufacturer calls for 82psi and the min is 70 by the chart, which could suit me just fine..but... from experience I know mans tend to base psi on ride, nor wear , fuel millage or to a degree, handling..and I know tires inflated higher bring higher mpg by nature as they roll easier,, So.. has anyone really experimented with wide psi ranges for ride or fuel economy vs the manufacturers recommendations?

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Old 04-10-2015, 08:20 PM   #9
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Quote:
Originally Posted by Skip426 View Post
Inflation would vary with tire brand and load rating.
Without axle or corner weights any inflation info would be a guess.
If 120 is the max inflation on the side wall of the tire , then 110 should be safe till you get the weights. But personally I'd avoid long trips until your sure.
The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire.

From the Michelin RV Tire Guide:
Quote:
"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."
From page 6 of the GoodYear RV Tire and Care Guide:
Quote:
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."

From TOYO:
Quote:
Q: What are the consequences of inflating the tires to accommodate the actual loads?
A: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.
But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:
Quote:
The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.
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Old 04-10-2015, 09:44 PM   #10
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Originally Posted by ernieh View Post
Some of the Michelin tables have a misprint.

They state individual tire when they mean axle or the other way around. I can't remember which it is. Anyway, you should use some common sense and apply the chart in a logical way. You will never be off scale on the low side.

For example, I have 2.75 80R 22.5 LRH tires on my MH. The front axle weighs just over 11,000# and I run the fronts at 105#. My rear axle weighs just below 21,000# and I run 95# in the rear duals. These numbers are "logical". Numbers that were twice or 1/2 what I have wouldn't make sense.
So to make sense, "single" and "dual" would refer to how many tires are on each end of a single axle. Correct? If this is true, then my weights still don't make sense. I have the same size tires as you, but are XZA3's and my front axle weighs 12,800 lbs and rear "dual" axle weighs 15,700 and my tag weighs 7400. The chart looks good for the front axle, but the lowest reading for a "dual" is 18,160 and I'm at 15,700. Now if I add my tag (7400 lbs) to the dual, then the entire rear of the coach weighs in at 23,250.....which then the chart "does" call out for a pressure of 105 lbs if it is just for the dual.

Sorry, no way I can make sense of this.

Ron
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Old 04-11-2015, 07:52 AM   #11
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Ron,

You do not add your rear axle weight and tag weight together. You would inflate your rear axle to the indicated pressure and then use the same air pressure in the tag. In your case, I think the air bags in your tag are overinflated and are taking too much weight off your rear axle (and adding too much to the front axle). I'd give Freightliner a call and see if some adjustment of your tag is called for.

You might want to spend some time on tiffinrvnetwork.com and ask other Tiffin owners with tag axles to comment. Most Tiffin tags are on the Powerglide chassis (Tiffin built) and there are lots of discussions on proper tag pressures. The Phaeton is on the Freightliner chassis and not so many discussions.
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Old 04-11-2015, 11:13 AM   #12
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Ron,

You do not add your rear axle weight and tag weight together. You would inflate your rear axle to the indicated pressure and then use the same air pressure in the tag. In your case, I think the air bags in your tag are overinflated and are taking too much weight off your rear axle (and adding too much to the front axle). I'd give Freightliner a call and see if some adjustment of your tag is called for.

You might want to spend some time on tiffinrvnetwork.com and ask other Tiffin owners with tag axles to comment. Most Tiffin tags are on the Powerglide chassis (Tiffin built) and there are lots of discussions on proper tag pressures. The Phaeton is on the Freightliner chassis and not so many discussions.
I agree, his tag is too heavy, but the whole back end is still pretty light for a tag. After adjusting the tag loading, he should air the rears based on the dual axle, but in no case should that pressure be anything lower than what is on the chart.
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Old 04-11-2015, 11:37 AM   #13
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Old 04-11-2015, 01:12 PM   #14
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Quote:
Originally Posted by ernieh View Post
Some of the Michelin tables have a misprint.

They state individual tire when they mean axle or the other way around. I can't remember which it is. Anyway, you should use some common sense and apply the chart in a logical way. You will never be off scale on the low side.

For example, I have 2.75 80R 22.5 LRH tires on my MH. The front axle weighs just over 11,000# and I run the fronts at 105#. My rear axle weighs just below 21,000# and I run 95# in the rear duals. These numbers are "logical". Numbers that were twice or 1/2 what I have wouldn't make sense.
This mistake is probably courced by the fact that in Europe , where Michelin comes from, Pressure/loadcapacity lists are given per axle, so single 2 tires single maxload addes up and Dual 4 tires dual maxload added up.
Then conversing this to the American market , where everything is given per tire, the mistake is easyly made.
Then the only way is to use your common sense, as you write, and see if the loadcapacity given for AT -pressure ( wich is not the maximum pressure ) is 1 or 2 times given maximum load per tire , wich is given mostly too in the list.
Ofcource for Dual axle , 4 times the given maxload for dual .
'
But you can also download my made extra save Pressure/loadcapacity lists from this map
https://onedrive.live.com/?cid=A526E...e092e6dc%21904
Gave the link to the head map, so first open the USA map, where you can open the map for Per tire, single axle and Dual axle, yust what you think is best to use for you.

but can also use my calculator if you go back in the maptree to MotorhomeRV tire pressure calculator.
Or give the needed data here and I will do it for you .
My lists go lower in pressure because then still the same deflection as when maximum load and AT-pressure on tire . In my spreadsheet even lower can be given as answer.
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