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Old 10-20-2015, 10:18 AM   #1
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Newbie That Needs Help With Tire Pressures

I am the owner of a 2006 National Dolphin 36 ft. gas model with a Ford V-10. I just bought this as my first ever RV in June and my wife and I are leaving on 10-31-15 for a 6 month trip South. I just put 6 new Michelin XRV 235/80R/22.5 tires on this week and plan to weigh the unit on our trip, as soon as I get to the nearest weight scales in N.H. My vehicle specification chart shows the following: GVWR: 22,000 lbs
Front Gross Axle Wt Rating: 7,500 lbs
Rear Gross Axle Wt Rating: 14,500 lbs
The Michelin Tire Chart shows for my size:
Single : 3,805 lbs ( times 2 = 7,610 lbs) = 85 PSI
Dual : 7,180 lbs ( times 2 = 14,360 lbs) = 85 PSI
GVWR: 21,970 lbs
When I put the new tires on this week, the tech put 100 PSI in all 6 new tires, with the RV having a full tank of gas and a few items on board, but not fully loaded (none of the wife's clothes yet!!). My first question is: Have I calculated the numbers correctly above, based on my present condition of not being fully loaded yet, and should I lower my pressures to 85 PSI for all 6 tires before I leave and until I can get officially weighed?? Also, Michelin's Tire Chart says that at 100 PSI (which is what the tires are at now) the following numbers apply: GVW: 25,00 lbs
Single: 4,330 lbs ( times 2= 8,660 lbs) =100 PSI
Dual: 8,170 lbs ( times 2 =16,340 lbs)=100PSI
But I assume that I cannot exceed my vehicle's GVWR of 22,00 LBS, even though the tires are rated higher ??
I am sorry for posting so much information, but I am new to this and I want to make sure I follow the proper procedures, as this is a safety issue to me. I would appreciate any input and guidance people can provide.
Thank you,
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Old 10-20-2015, 10:41 AM   #2
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You are correct in that you should never exceed the Max GVWR of the chassis, no matter what tires you use.

Looks like 85psi would be about right for the weight of your coach. You might want to increase it about 10% for safety. Check the manufacturer's data plate in the motorhome, and make sure it doesn't call for higher pressure. If it does, default to the data plate suggestion.

Finally, never pay any attention to what the Tire Techs do! Most of them don't know anything about inflation charts, weight, or anything else. Unless you tell them what pressure you want, they just inflate to whatever pressure they find on the sidewall of the tire.
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Old 10-20-2015, 11:42 AM   #3
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DL,

The tire guy put 100psi in the tires because it is easier to let air out than it is to drag the hose out to put more air in.

Why are you going to NH? (I know there is a scale in Kittery, but that might as well be NH.
There are truck scales all over. The highway weigh station will probably not give you a weigh slip, but you can and will get one at a truck scale. If you don't want to pay for a scale, find a scrap year or grain and seed place. You can usually work with them if you do it so you don't interfere with the operation.

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Old 10-20-2015, 07:25 PM   #4
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Don't trust what the tire jockeys told you. When I got new tires last December, they told me that all my tires were inflated to 100 psi. When I checked them the next morning, they were all different, between 90 and 115 psi.
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Old 10-21-2015, 05:26 AM   #5
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If you are serious a bout your tires and you sound like you are. Get a 4 corner weigh when you can. I know these are done at Escapee parks in Bushnell, FL and Congress, AZ(look on their site). Also, get a TPMS system. Besides giving some peace of mind it is the easiest way to check your tire pressures, just by pushing a button. We check ours each day before we leave.

Also, make lots of check lists and review them each time you travel.
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Old 10-21-2015, 06:27 AM   #6
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I believe 100 psi is standard.
I have gone through sets of tires and new rv purchases and for some reason they all go to a 'default' of 100 psi.
No biggie. A lot easier to let 10 psi out than to add.
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Old 10-21-2015, 12:12 PM   #7
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I believe 100 psi is standard.
If laziness and a one-size-fits-all attitude is a "standard', then you are probably right. That doesn't make it right, let alone optimum.

dlduck: there will be a placard on the interior sidewall by the driver seat and it will give the recommended pressure for the OEM tires. Your new ones are the same size, so the placard data is still valid. I would suggest you use that psi. It's probably a bit higher than optimal, but should be sufficient for your axle GAWRs (max loading).
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Old 10-21-2015, 12:32 PM   #8
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Weigh the front axle, divide by two (single wheels) = load on each tire
weigh rear axle, divide by four (dual wheels)= load on each tire.
Consult your manual or tire spec chart and inflate the tires accordingly,
I personally add 5-to 10 psi ( better a little high than too low) but don't exceed the tires max inflation specs! If you haven't weighed it yet you should be safe with the 100psi until you can!
Happy Trails!
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Old 10-23-2015, 02:35 PM   #9
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Newbie Needs Help With Tire Pressures

Quote:
Originally Posted by dlduck View Post
I am the owner of a 2006 National Dolphin 36 ft. gas model with a Ford V-10. I just bought this as my first ever RV in June and my wife and I are leaving on 10-31-15 for a 6 month trip South. I just put 6 new Michelin XRV 235/80R/22.5 tires on this week and plan to weigh the unit on our trip, as soon as I get to the nearest weight scales in N.H. My vehicle specification chart shows the following: GVWR: 22,000 lbs
Front Gross Axle Wt Rating: 7,500 lbs
Rear Gross Axle Wt Rating: 14,500 lbs
The Michelin Tire Chart shows for my size:
Single : 3,805 lbs ( times 2 = 7,610 lbs) = 85 PSI
Dual : 7,180 lbs ( times 2 = 14,360 lbs) = 85 PSI
GVWR: 21,970 lbs
When I put the new tires on this week, the tech put 100 PSI in all 6 new tires, with the RV having a full tank of gas and a few items on board, but not fully loaded (none of the wife's clothes yet!!). My first question is: Have I calculated the numbers correctly above, based on my present condition of not being fully loaded yet, and should I lower my pressures to 85 PSI for all 6 tires before I leave and until I can get officially weighed?? Also, Michelin's Tire Chart says that at 100 PSI (which is what the tires are at now) the following numbers apply: GVW: 25,00 lbs
Single: 4,330 lbs ( times 2= 8,660 lbs) =100 PSI
Dual: 8,170 lbs ( times 2 =16,340 lbs)=100PSI
But I assume that I cannot exceed my vehicle's GVWR of 22,00 LBS, even though the tires are rated higher ??
I am sorry for posting so much information, but I am new to this and I want to make sure I follow the proper procedures, as this is a safety issue to me. I would appreciate any input and guidance people can provide.
Thank you,
** Update:
I just had my RV weighed as a total vehicle weight only and I came in at:

20,680 lbs (my GVWR is 22,000 lbs)

Should I continue to run all 6 of my tires at 100 PSI or lower them to
85 - 90 PSI? Driving back from the weigh station the vehicle seemed to handle fine. I am just wondering if running them at 100 PSI will do any damage to the tires even though I am currently at 1,320 lbs below my GVWR.
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Old 10-23-2015, 03:52 PM   #10
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Get your rig weighed on all 4 corners. Then go to your tire manufacture for a table that will tell you what you should air at. You may need to move stuff around to make your weights evenly balanced. We started out running 100 all the way around. Rough ride, etc. Henderson lineup in Oregon got us straight after weighing and getting the chart from Toyo. Now for us its 95 in front and 110 in rear. After 2 years our tires lokje great, steer and riudes perfect
Bottom line there's no standard answer every rig is built with weight in different places and loiaded with personal stuff differently too.
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Old 10-23-2015, 09:49 PM   #11
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I have a 2005 national dolphin lx with same size tires. I run 95 in front and 90 in the rear.
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Old 10-24-2015, 07:57 AM   #12
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Originally Posted by Lewis D View Post
I have a 2005 national dolphin lx with same size tires. I run 95 in front and 90 in the rear.
My 05 5355 Dolphin with the factory tires i ran these presures and also with my new Toyo's.
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Old 10-24-2015, 09:35 AM   #13
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I have a 36' Itasca with the same tire you have. It has 8000# front axle and 15000# rear axle. Any responsible tire tech will put 100 or 110# of air in the tires because of the liability of the load you might put on the tires. If they underinflate the tires and you have a failure due to overloading for the pressure they put in them, they can be held liable. If they inflate the tire up to the max. on the sidewall, then they can't be held liable if you overload the tire beyond it's load limit. The tire teck. can't be expected to know how you are going to load the coach.
I weighed my coach front & rear when returning home from a camping trip so it was mostly loaded, and according to Michelin pressure charts for this tire, I can run 75# in the front and 80# in the rear. To make it easy, I just run 80# all the way around.
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Old 10-24-2015, 09:58 AM   #14
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100lbs. is too much. Your front and rear gross ratings shouldn't be exceeded and both axles need 85lbs. according to Michelin, maybe even a bit less for the front. I'd leave them at 85lbs. until you get weighed.
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