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Author Topic: help me understand  (Read 1259 times)

danford50

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help me understand
« on: August 26, 2017, 11:42:57 AM »
I had my motorhome weight and here are the weigh steer axle 4320 and drive axle 7920,  the steer axle is which tires front or rear, and the drive axle is which tires front or rear, I am trying to figure out the weigh for each axles. according to the placard on the door jam the front axle is 5000 and the rear 9600, my weigh that I have are they within tolerance, if so should I put in the amount of air base on the placard.
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Larry N.

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Re: help me understand
« Reply #1 on: August 26, 2017, 02:59:26 PM »
The "steer" axle is the front axle, the one you steer with. So you're allowed 5,000 and have 4,320 -- sounds fine to me. The drive axle (wheels that provide propulsion) generally have the heavier load, and you're allowed 9,600 but have 7,920. Sounds fine.

But the other question that must be asked is, "Was this loaded for camping or was it with an empty rig?" It makes a difference.
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John From Detroit

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Re: help me understand
« Reply #2 on: August 26, 2017, 03:08:50 PM »
An easy way to think of Drive and Steer axles is this

The Steering wheel operates the Steer axle

THe Engine the Drive Axle

DO NOT READ THE REST OF THIS LINE: And yes. on cars with Front wheel drive. Same axle

There are exceptions but not in the RV world
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LarsMac

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Re: help me understand
« Reply #3 on: August 26, 2017, 03:32:15 PM »
An easy way to think of Drive and Steer axles is this

The Steering wheel operates the Steer axle

THe Engine the Drive Axle

DO NOT READ THE REST OF THIS LINE: And yes. on cars with Front wheel drive. Same axle

There are exceptions but not in the RV world

Even in the RV world, are exceptions:
http://www.gmcers.org/

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TonyDtorch

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Re: help me understand
« Reply #4 on: August 26, 2017, 06:01:39 PM »


There are exceptions but not in the RV world

In the RV world there was the GMC and Revcon Class A motorhomes that used front wheel drive...so there is exceptions in RV's.


... as to the amount of air in the tires,  he should just go by the door tag for the recommended amount of air pressure regardless of the actual weights .
« Last Edit: August 26, 2017, 06:08:49 PM by TonyDtorch »

SeilerBird

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Re: help me understand
« Reply #5 on: August 26, 2017, 06:08:45 PM »
I think you should use the air pressure listed on the manufacturers tire inflation chart.
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GaryA

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Re: help me understand
« Reply #6 on: August 26, 2017, 06:30:29 PM »
I think you should use the air pressure listed on the manufacturers tire inflation chart.

Ditto
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2kGeorgieBoy

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Re: help me understand
« Reply #7 on: August 26, 2017, 09:18:05 PM »
Be sure that the tires on your vehicle at least match the tire size and load rating listed on the placard. I know it's an RV but I've seen people at our shop running different sized tires than listed as OEM on the placard, usually in a positive direction, but a few have gone the other way with smaller, less load rated tires. Like 4 ply tires on a diesel truck.
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mel s

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Re: help me understand
« Reply #8 on: August 27, 2017, 09:20:46 AM »
I think you should use the air pressure listed on the manufacturers tire inflation chart.

I agree

danford50

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Re: help me understand
« Reply #9 on: August 27, 2017, 12:15:17 PM »
looking at the Michelin tire chart for my size of tires which is LT 225-75-16 load range E, base on that chart for the front I should have 60 psi and for the rear I should have 60 psi also.
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SeilerBird

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Re: help me understand
« Reply #10 on: August 27, 2017, 12:37:03 PM »
looking at the Michelin tire chart for my size of tires which is LT 225-75-16 load range E, base on that chart for the front I should have 60 psi and for the rear I should have 60 psi also.
And I bet you will be amazed at how much better your RV handles once you get the tire pressure set correctly.
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GaryA

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Re: help me understand
« Reply #11 on: August 27, 2017, 01:47:53 PM »
And I bet you will be amazed at how much better your RV handles once you get the tire pressure set correctly.

I bet the door jam information says 75 in front and 80 in the rear.  Why in the world would you run 60#???????
Gary Alexander
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GaryA

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Re: help me understand
« Reply #12 on: August 27, 2017, 01:50:29 PM »
If the mfg recommendation is 60 it must be for something other than a heavy motorhome.
Gary Alexander
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Waxhaw, NC

SeilerBird

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Re: help me understand
« Reply #13 on: August 27, 2017, 02:15:02 PM »
If the mfg recommendation is 60 it must be for something other than a heavy motorhome.
The manufacturers recommendation is because that is the proper air pressure for the weight of the motorhome. Read this article and it will answer all your questions.

https://www.thefitrv.com/rv-tips/how-to-set-the-tire-pressure-in-your-rv/
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Larry N.

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Re: help me understand
« Reply #14 on: August 27, 2017, 02:24:52 PM »
If the mfg recommendation is 60 it must be for something other than a heavy motorhome.

Which means it would be lighter weight. The tire manufacturer's tables are calculated for a specific amount of weight on the axle, not caring if it's a truck, RV or railroad car. It's not a one-size-fits-all figure, but rather a table with a specific range of weight vs pressure. Note on this Michelin page that it is laid out by tire size (19.5" 22.5", etc.), by model of tire (XZE, XRV, etc.), and by single tire or dual tires, each table having pressure vs. weight. The tire obviously doesn't ""know" what's causing that weight (nor "care"), but physics cause it to react according to the various forces applied to it, which are strongly affected by weight and psi of pressure.

These tables are the tire manufacturer's way of saying, "This is how we've designed the tire to operate."

Note that these tables also show you the "Maximum load & pressure on sidewall" figure that is imprinted on that sidewall, the same as the highest weight rating for a SINGLE in the table, and so it shows that tires are NOT designed to have only a single pressure under all circumstances.
« Last Edit: August 27, 2017, 02:30:56 PM by Larry N. »
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GaryA

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Re: help me understand
« Reply #15 on: August 27, 2017, 02:37:18 PM »
danford50, was your motorhome empty when you went on the scales and got those numbers?
Gary Alexander
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danford50

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Re: help me understand
« Reply #16 on: August 27, 2017, 06:38:08 PM »
the 12420 was empty
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danford50

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Re: help me understand
« Reply #17 on: August 27, 2017, 06:39:39 PM »
however I do not carry water and my fuel was about 3/4 full and we always pack light, the max weight for my motorhome is 14500
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GaryA

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Re: help me understand
« Reply #18 on: August 27, 2017, 07:00:59 PM »
According to Michelin, the difference between 60# (which I understand to be your "nothing loaded" weight) and 75# in your ties is 2,020 pounds.  2 adults,  groceries, stuff in the storage areas, propane, gas, fresh water??????????????????  Anyone's guess until you weigh it loaded as you would when you hit the road.
Gary Alexander
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Waxhaw, NC

danford50

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Re: help me understand
« Reply #19 on: August 27, 2017, 09:09:57 PM »
so now I am more confuse , what should I air my tire too. 60 or what the placard say.
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SeilerBird

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Re: help me understand
« Reply #20 on: August 28, 2017, 04:11:39 AM »
so now I am more confuse , what should I air my tire too. 60 or what the placard say.
Weigh the motor home and then consult the manufacturers charts.
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GaryA

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Re: help me understand
« Reply #21 on: August 28, 2017, 06:48:11 AM »
Weigh the motor home and then consult the manufacturers charts.

I agree with what SellerBird says.  Until you get it weighed would it make sense for you to estimate your added weight and then go to the chart.  Or go with 75# as you know you're adding some weight and then adjust when you get weighed with your load.
Gary Alexander
2014 Thor 28z
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Gary RV_Wizard

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Re: help me understand
« Reply #22 on: August 28, 2017, 07:05:11 AM »
There is no need for all this anxiety,   60 psi is the minimum pressure for your unloaded weight, whereas 75 is optimal for a fully loaded coach. Since you won't travel empty, your actual weight will be somewhere in between and thus the optimal pressure will be somewhere in the middle as well. If you go with 75 psi, you know you have sufficient pressure and at worst you will be 5 or so psi above optimal. 

The only downside to a bit of extra tire pressure is a [maybe] slightly harsher ride, and even that may be offset by slightly improved fuel economy. The only thing you really need to worry about is insufficient inflation, so much better to be high than risk being too low.   Stop worrying about it and use the 75 psi shown on the weight & tire placard.
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GaryA

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Re: help me understand
« Reply #23 on: August 28, 2017, 07:29:15 AM »
There is no need for all this anxiety,   60 psi is the minimum pressure for your unloaded weight, whereas 75 is optimal for a fully loaded coach. Since you won't travel empty, your actual weight will be somewhere in between and thus the optimal pressure will be somewhere in the middle as well. If you go with 75 psi, you know you have sufficient pressure and at worst you will be 5 or so psi above optimal. 

The only downside to a bit of extra tire pressure is a [maybe] slightly harsher ride, and even that may be offset by slightly improved fuel economy. The only thing you really need to worry about is insufficient inflation, so much better to be high than risk being too low.   Stop worrying about it and use the 75 psi shown on the weight & tire placard.

BOOM!
Gary Alexander
2014 Thor 28z
Waxhaw, NC

mel s

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Re: help me understand
« Reply #24 on: August 28, 2017, 07:45:52 AM »
so now I am more confuse , what should I air my tire too. 60 or what the placard say.
danford50
You should air your tires to the pressures shown on the tire manufactures inflation chart based on the weight your tires actually carry when your RV is loaded for travel with driver and passenger(s) on board.

See: http://www.minderresearch.com/what-should-i-set-the-cold-pressure-of-my-tires-to/

Or as SeilerBird said in a earlier message: https://www.thefitrv.com/rv-tips/how-to-set-the-tire-pressure-in-your-rv/

TonyDtorch

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Re: help me understand
« Reply #25 on: August 28, 2017, 10:29:16 AM »
put 75 psi in the tires (or what ever the max loaded pressure is).   No one ever deflates their tires when they unload a truck.

Mile High

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Re: help me understand
« Reply #26 on: August 28, 2017, 10:55:12 AM »
put 75 psi in the tires (or what ever the max loaded pressure is).   No one ever deflates their tires when they unload a truck.
wanna bet? :)
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kdbgoat

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Re: help me understand
« Reply #27 on: August 28, 2017, 11:57:59 AM »
Looking at the GVWR minus the unloaded weights you provided, you have about 2200# of carrying capacity. Even "packing light" you can eat up a lot of that 2200#. I would be willing to bet those weights were with no people sitting in it either. Two people can easily add 300# plus directly on the front axle. That leaves you with 380# left on the front axle. By the time you load up your coach, you will be very close to the max on that axle. There is so little leeway in the weight carrying capacity of the tires, just run the fronts at 75, and the rears at 80 according to the placard. You will hit your max weight and most likely will go over it at some point.
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GaryA

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Re: help me understand
« Reply #28 on: August 29, 2017, 07:12:19 AM »
danford50, what did you decide for your tire pressure???
Gary Alexander
2014 Thor 28z
Waxhaw, NC

gravesdiesel

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Re: help me understand
« Reply #29 on: August 29, 2017, 09:15:49 AM »
put 75 psi in the tires (or what ever the max loaded pressure is).   No one ever deflates their tires when they unload a truck.
EXACTLY!  I run all Load Range E tires on my trucks and they are max 80 PSI cold (per tire manufacturer).  I keep em all right at 80 PSI because I often carry heavy loads of feed, equipment and my camper plus two golf carts.  Tires run cooler when fully inflated, which also reduces the risk of a blow out and helps handling.
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