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Old 06-23-2014, 03:13 PM   #1
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Correct tire pressure

Ok I know this can be a confusing topic at least for me. I would like to know a rough ballpark pressure for my tires? I have an 05 Neptune and the back axle weight is 17,000lbs, so I assume each side is half the total. That is before loaded down. Now for some further info: at the most we will have a full tank of fresh water; full tank of gas, and a full tank of propane. Besides my wife and I we will not have a whole lot more weigh. Purchased last year and had two new tires put on front, they read 116psi? The back are 104psi. Am I running to much psi for my load? Hope I do not stir up a hornets nest here. The reason I ask is the ride is a little rough. Just had the new trailing arms and new shocks installed and did not notice any difference in the ride? Peter
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Old 06-23-2014, 03:19 PM   #2
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Peter - you need to get a weight loaded as you will normally travel. You say it is 17,000 before you add water, fuel, propane, DW, DH, and now I am guessing. Some bedding, clothes, food, beer, wine, dishes, cutlery, towels, etc.

While it does not seem like much that small stuff will add up quickly.

If possible the best weights to get are corner weights. Happy hunting for the recommended tire pressure.
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Old 06-23-2014, 03:19 PM   #3
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This is one of the most discussed topics on the forum. The only real way to know if your tires are properly inflated is to get your coach weighed when it's ready for typical travel. You need to get at least each axle weighed but it would be best if you can find a way to weigh each corner.

Then you go to your tire manufacturer's inflation tables and look up what the PSI should be for your particular weight.

In the absence of getting it weighed, the safest thing to do is inflate to what the sidewall pressure indicates. I believe this is the minimum pressure you should inflate to when carrying the maximum weight the tire is designed for.

Yes, it may well give you a harsh ride but it's much better to put up with that than to have tires under inflated and run the risk of a blowout. Getting actual weights is the only way to do this properly.

Best of luck.

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Old 06-23-2014, 03:37 PM   #4
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I appreciate your response. The label behind the seat in the front says 85psi for the front and 90psi for the back. I seem to be way off that mark at the moment. I assume I would not be more than 2,500lbs more added weight (water 750lbs, fuel 450lbs, propane 150lbs, and my wife and I). I know this still does not narrow it down to the pound, but is there any ballpark figure? Some people say put the tire max in and others are more particular in weighing each side of the MH. Maybe I am asking a question that can not be answered without weighing my vehicle, just know what we will be taking. That weight estimate is probably overkill for me, thanks, peter
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Old 06-23-2014, 04:50 PM   #5
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I would follow the Packard supplied by the manufacture as to tire size and pressure.


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Old 06-23-2014, 05:11 PM   #6
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Quote:
Originally Posted by jaminman View Post
Ok I know this can be a confusing topic at least for me. I would like to know a rough ballpark pressure for my tires? I have an 05 Neptune and the back axle weight is 17,000lbs, so I assume each side is half the total. That is before loaded down. Now for some further info: at the most we will have a full tank of fresh water; full tank of gas, and a full tank of propane. Besides my wife and I we will not have a whole lot more weigh. Purchased last year and had two new tires put on front, they read 116psi? The back are 104psi. Am I running to much psi for my load? Hope I do not stir up a hornets nest here. The reason I ask is the ride is a little rough. Just had the new trailing arms and new shocks installed and did not notice any difference in the ride? Peter

Here is your brochure:

http://www.holidayrambler.com/Static.../05neptune.pdf

According to this brochure, your drive axle is rated at 17,000 pounds and your steer axle at 8500 pounds. These are the GAWR of these axles. This is the total amount of weight your coach is rated to carry. Until you weigh your coach, you should inflate your tires to carry this weight.

Here is a Michelin inflation guide:

https://www.michelinb2b.com/wps/b2bc...s_Brochure.pdf

Your tire size is 255/70R22.5. According to this inflation guide, if you inflate your tires to 90psi on both axles that will carry your weight if you are reasonably well balanced side to side. To allow for the possibility of imbalance, I would add a 5-10 psi fudge factor. 100 psi in all tires will carry your weight if loaded to the max allowed.


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Old 06-23-2014, 05:32 PM   #7
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Originally Posted by jaminman View Post
I know this still does not narrow it down to the pound, but is there any ballpark figure? Some people say put the tire max in and others are more particular in weighing each side of the MH. Maybe I am asking a question that can not be answered without weighing my vehicle, just know what we will be taking. That weight estimate is probably overkill for me, thanks, peter
Yep, your question cannot be specifically answered without weighing the rig but Steve gives great info on your GVWR and advice for you to follow below.

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Here is your brochure:

http://www.holidayrambler.com/Static.../05neptune.pdf

According to this brochure, your drive axle is rated at 17,000 pounds and your steer axle at 8500 pounds. These are the GAWR of these axles. This is the total amount of weight your coach is rated to carry. Until you weigh your coach, you should inflate your tires to carry this weight.

Here is a Michelin inflation guide:

https://www.michelinb2b.com/wps/b2bc...s_Brochure.pdf

Your tire size is 255/70R22.5. According to this inflation guide, if you inflate your tires to 90psi on both axles that will carry your weight if you are reasonably well balanced side to side. To allow for the possibility of imbalance, I would add a 5-10 psi fudge factor. 100 psi in all tires will carry your weight if loaded to the max allowed.


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Old 06-23-2014, 10:44 PM   #8
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Thanks for your reply Steve. I am a little confused. Is 17,000lbs the weight of the rear axle unloaded or total of what is allowed? My vehicle is 25,500lbs. The front axle is 8,500 and the back axle is 17,000 that comes to a total of 25,500. It also says that the gross combined weight is 32,500lbs does that mean I have 7,500 to play around with? Sorry if I sound a little confused. At the moment the back are 104psi and the front are 116psi , for the moment change them all to 100psi until I weight my vehicle? thanks, Peter
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Old 06-23-2014, 11:03 PM   #9
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If your confused, go with the tire pressures on the tag beside the drivers seat.
Thats for a loaded coach.
Once you get a chance to run across an acurate scale, you can adjust your pressures to the tire makers specs, for the weight they are holding.
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Old 06-24-2014, 04:07 AM   #10
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The 25500 you probably yust calculated as being front GAWR and back GAWR togehter. But mostly the GVWR ( Gross Vehicle weigt rating ) is a bit lower, so for instance here 25000 lbs , and is what you are maximum allowed to weigh the total rig with loading.
so they are no empty weights as you think.

The 32500 is the Gross train weight rating and is what Vehicle + trailer is maximum allowed to weigh.
Thats the reason that everyone is advising to weigh, because yudging it by the numbers mostly are inacurate.

Filled in your given data but check the tires on sidewall if they are right.
Now filled in in my MotorhomeRV tirepressure calculator in wich in case of GAWR's filled in I take a reserve for overloading and unequall loading R/L wich is almost always the case, even crossed weight differences.
then calculated with my own formula wich is even saver then the officially used by ETRTO european one. The American list of your Michelin link, uses a formula to determine the pressure loadcapacity lists that leads to to much deflection in the lower pressure/loadcapacity range, wich still leads to tire damage.

Here a picture of it and it shows that the front can be lower so that is probably the cource of the rough ride, because you are driving at front and feel mostly the bumping of the front wheels.

If you ever weigh those values can be filled in and a more specific advice can be given.

To my idea such a heavy RV is seldom overloaded , not GVWR and GAWR's ( Gross axle weight ratings) so most likely even lower pressure is enaug to give no damage to tires and a long lifetime of them. The lower the pressure the more gripp and comfort, but to low gives tire-damage. So the advice given in the picture is most likely already a worst case scenario, Higher is not needed. the front from 104 to 96 psi and the rear from your 116 to 111 and probably then still some bumping because your real wheel( pair) loads are lower. But I realise this is a dangerous conclusion.

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Old 06-24-2014, 06:45 AM   #11
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Correct tire pressure

Quote:
Originally Posted by jaminman View Post
Thanks for your reply Steve. I am a little confused. Is 17,000lbs the weight of the rear axle unloaded or total of what is allowed? My vehicle is 25,500lbs. The front axle is 8,500 and the back axle is 17,000 that comes to a total of 25,500. It also says that the gross combined weight is 32,500lbs does that mean I have 7,500 to play around with? Sorry if I sound a little confused. At the moment the back are 104psi and the front are 116psi , for the moment change them all to 100psi until I weight my vehicle? thanks, Peter

Peter,

The axle ratings (17,000 and 8,500), which total to 25,500 is the max allowed weight of your coach, payload and all. The GCWR of 32,500 is the 25,500 plus a max of 7,000 of towed vehicle weight. If you tow 4 wheels down then all of the towed vehicles weight would be included in the 7,000. If you use a dolly or trailer then the tongue weight would be included in the 25,500 and the weight on the trailering tires would be in the 7,000. Your total allowable, down the road weight, towed vehicle and all is 32,500.

If the tires are 255/70R22.5 then the 100 psi all the way around will support the weight of your coach if at the max of 25,500. Yes, in my opinion, you should run these pressures until you get weighed. At that time you can drop to what ever is recommended in the inflation table but I always add a 5-10 psi buffer. The pressure in the table is the MINIMUM recommended pressure to carry that particular weight. Running a little over pressure is harmless, running under pressure can have serious consequences. You should check the date codes on your tires so you know for sure how old they are.

I'm glad to see that you are concerned about this issue. Many folks, new and not so new, don't give it much thought.

I also recommend you read up on "tire pressure monitoring systems" and decide if you need one. In my 11 years of using a TPMS, I needed it badly only once. That one time paid for what ever I spend on the system for my lifetime.


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Old 06-24-2014, 09:23 AM   #12
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Thanks once again Steve and all others that posted. I will put 100psi all around until I get them weighed. This brings me to another question where do you go to get it weighted and do you have to pay? I live in Canada but travel back and forth to the US so either/or works for me. Do you go to truck stops? Peter
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Old 06-24-2014, 09:41 AM   #13
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Thanks once again Steve and all others that posted. I will put 100psi all around until I get them weighed. This brings me to another question where do you go to get it weighted and do you have to pay? I live in Canada but travel back and forth to the US so either/or works for me. Do you go to truck stops? Peter

Peter,

You can go to a truck stop that has a big "Cat Scale" sign. Farm supply stores often have scales or landscaping places that sell stuff by the truck load. They will charge about $10 but you will get a weight for each axle and not each wheel position. The axle weight is ok but doesn't tell you which wheel is heavier. Getting a 4 position weight is harder to find. There is a group that does weighting at the big FMCA rallies and they weigh each position.

If you get an axle weight just add 5-10 psi to allow for a side to side imbalance & you'll be good to go.

Safe travels.

Steve


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Old 06-24-2014, 10:21 AM   #14
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Thanks once again Steve and all others that posted. I will put 100psi all around until I get them weighed. This brings me to another question where do you go to get it weighted and do you have to pay? I live in Canada but travel back and forth to the US so either/or works for me. Do you go to truck stops? Peter
In Alberta you can go to any DOT weigh scale. If they are open it may be courteous if you ask them to weigh you. They will likely give you a printed weigh ticket. If they are closed the scale will be on and you can see the weights as you drive across the scale on an outside display.

The scales I have been able to see in the US do not appear to have an outside display but I will suggest they will accomodate you if you ask them if you can weigh.
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