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Old 04-16-2013, 12:43 PM   #1
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Tire pressure - for last time

Ever since joining this forum I have been interested in the tire pressure issue and how I can adjust mine to improve ride but remain in safe range. Not sure what you can do about this within the parameters of the manufacturers information.

Let me explain, when I got my coach tires were at 110 psi, felt like I was driving on old wagon wheels, felt every line and joint in the road, miserable. Then I started reading up on tire pressure issues, but after fussing with this and going to get my coach weighed today, I can't help but wonder why all the fuss. My coach is a 2004 National Seabreeze 1341 (Ford F-53), loaded, ready to run, full gas, full LP, "stuff" on board, and me. Only thing missing is DW and I don't dare ask what she weighs!! But seriously she is about 110, insignificant here. Front axle 6,200 lbs. , rear 12,460 lbs. So now go to Goodyear chart, for tires after 2006 manufacturer date, 80 psi is lowest pressure on chart, which I assume means I should consider that minimum pressure allowed, or better said, recommended. Well using that chart, 80 psi single load is 3,640 per tire, so 7,280 front....way over my 6,200 weight. Per chart again at 80 psi dual load is 3,415, so for four 13,660, way over my 12,460 again. SO......I Can not adjust pressure to my load, right?? Can only use minimum pressure on chart. Matter of fact at the minimum pressure the total is capacity is 20,940, only 1,060 from max gross chassis weight of 22,000.

Sooooo, unless you have a 22,000 lbs chassis loaded to the gills, bordering on overloaded, you would not need more than minimum recommended tire pressure of 80 psi.

I am missing something?!
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Old 04-16-2013, 01:02 PM   #2
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Mine was at 105 to 110 per tire also when I got it, and recommended pressure according to the guidlines for my actual weight is between 80 and 85. I personally don't like it that close to the minimum, so I run it at 90 all the way around. Seems to work well, the ride is better and gives me a comfortable cushion above the minimum.
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Old 04-16-2013, 01:57 PM   #3
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I'm within 500 lbs of you coach weight. I run 82 on all 4 rear tires and 90 on the front two.
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Old 04-17-2013, 02:51 AM   #4
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Edit: reading back I see that the loads you gave where the weighed loads , and what I assumed to be the maximum load of your tires , can be the loads you read from the chart at 80 psi, wich makes the right calculation different. So give the GAWR's or the real maximum load of the tires and I will correct that. You can also do it yourselfes in the spreadsheet.

Filled in my spreadsheet and uploaded it to my examples-map on my skydrive that belongs to my hotmail adress.
In that spreadsheet you can chanche to your needs, the percentages reserve.
I did that in the example, normal is to add 18% to the back GAWR to get as much reserve as dont give bumping ( using 85% of the loadcapacity that belongs to the pressure). made it like that for Dutch campers that almost always go over the GAWR at the back, but for your heavyer RV you probably stay under GAWR so chanched it to only 5% adding.
So if your real weights ( when you ever weigh) are much lower , you can fill in those , and a new pressure advice is given.
Mind the division F/B of 33%/66% , once read that it is adviced to keep the front at minimum of 30% of total weight.
So you see , even with help of my spreadsheet, there is still space for your own input, and that is why there are so many different advices.
Here the link to the map with the examples beginning with your nickname here.
Download goes like this, rightclick and choose download.
After download and eventual virus-check , open in Excell or Open Office Calc , to use it. If youleftclick it is tried to open in the browser, but this cant handle some things I used in it, so gives error-message, then go back and try again right-click.
https://skydrive.live.com/?id=A526E0EEE092E6DC!935&cid=a526e0eee092e6dc&

Also made loadcapacity-lists to look back in , if you prefer that, but the load-determination is your own responcibility , and mostly yudged to low.
They are made with my own formula wich gives lower loadcapacity for the pressure then the American way and even the European way , so is save, and takes care that the deflection stays the same over the whole range , and allows to go lower in the pressure save.
https://skydrive.live.com/?id=A526E0...E092E6DC%21904
Also included the right listst for you in this post , given per axle single and Dual, so you dont have to do that part of the calculation. Dual calculates a little different so if you take 2 times single , you are a few LBS off , wich can do also so not a real problem.
also attached a gif-picture of the filled in spreadsheet to this post.

Questions ?? yust ask futher here.
Greatings from Holland
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Old 04-17-2013, 06:18 AM   #5
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OK

spread sheet will not work on my computer. My actual weights as posted were 6200 front and 12460 rear, GAWR front 7000 and rear 12460. I have rears at 85 front at 82. What do you think?
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Old 04-17-2013, 06:43 AM   #6
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I am still missing the maximum load of your 110psi G-load/14ply tires.
In the list you read it from, at 80 psi probably was fatt printed or/and E printed after it, so I cant yust use that . For every maximum load/maxloadpressure- combination a seperate list has to be made to get it phisically right.
That is one thing that is done wrong in the list you get on the american internet.

Did you read the 82 and 85 from my list or was this the actuall used pressure.
If you read it from my list , you automatically read the right pressure for the load ,and interpolated between 80 and 85 for front, wich is ok.
But best is to add a reserve, for presssureloss in time, misreadings of pressure- and load-scales, uneven loading R/L, incidental extra loading, and what I might have forgotten.
If you add more then 18 % , wich is the same as making the weighed load 85% of the load you look back the pressure for, things go bumping, I concluded from reactions,so is discussable.

In the spreadsheet I use 91% =adding 10% to the load, in case of given assumed actual load.
6200front +10%=6820 to look back for in the list.
12460+10%=13766lbs to look back in the list for the dualload maximum load.
Can be you asume to have the pressure for that 91% used of loadcapacity, but in real , because of misreadings of scale and uneven loading R/L one tire comes even close to 100% , wich is still save for the tire. Above Load% of 100% tire-damage begins , but even yust at higher speed. For lower speed more load may be carried.
All Truck-tires and some LT- tires in Europe, and probably also in America, give an additional loadindex for a lower speed. Search for it on the sidewall, and be amazed.
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Old 04-17-2013, 07:18 AM   #7
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Inflation Must Be According to Manufacturer

Quote:
Originally Posted by trode View Post
Ever since joining this forum I have been interested in the tire pressure issue and how I can adjust mine to improve ride but remain in safe range...

Sooooo, unless you have a 22,000 lbs chassis loaded to the gills, bordering on overloaded, you would not need more than minimum recommended tire pressure of 80 psi.

I am missing something?!
Here is Goodyear's description of their tables, and how they expect them to be applied.

A good read, and something to be periodically reviewed.

I like the technique of going 5psi over, to cover for the possibility of pressure bleed between inflations.

You're where I was, with my first RV, nestled at the bottom of the chart. The 80 psi should be good, verified by tire temps circa 120F after sustained driving. A reminder: cruising with direct sun on the tire will elevate temps slightly, about 20F.
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Old 04-17-2013, 09:46 AM   #8
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trode,
It will never be "for the last time." So much has been written regarding all aspects of tires.

One of the better sites to look at is Tireman9's (Roger Marble) tire safety blog. You will find extensive (good) information there.

Personally I would never set tire pressure to the minimum as it leaves no room for changes. You state that your minimum is 80 psi. If you set it at that and there is a 10 degree drop in temperature, you will loose about 2% for each 10 degrees at the higher pressures. Also, for every 1000 feet of elevation change there will be a .48 psi difference. I would set the pressure for an 80 psi minimum tire to at least 85 pounds. That should give you enough leeway should there be temperature or altitude changes. I would also do the same for any tire on the high end. Set it for 5 psi below and the only exception would be if the weight by the charts actually required the high end site, or you can tell DW to loose weight. (I didn't say that!)
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