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Old 04-29-2012, 08:09 PM   #1
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Lightbulb Is this the Weigh to skin a CAT? Kinda Long

First for you cat lovers...No cats were harmed in the making of this thread.

Get your calculator and thinking caps on. There will be a quiz at the end of this exam.

OK...I've been having a heck of a time finding a place to get 4 corners weighed. Have had the rig for a couple weeks and Sandee and I have completed a lot of the initial setup including a major project of getting GSD size crates set up and secure. So, today we felt was a good day to get it weighed and see how things were progressing. So, with full fuel, full LP, aprox 65 gal water, 2 people, 2 GSD W/crates and a fair amount of essentials loaded into the rig...off we go.

We picked Sunday to weigh it at a local CAT scale because generally there are less trucks for us to get in the way of. If you aren't familiar, the CAT scale has 3 segments and that makes it easy to get front and back axles and even a toad at one shot but no break down of left vs. right side. An RV with out a toad would your the last 2 pads.

Got to the CAT scale and was #1 in sequence. I get the rig set up on the last 2 pads and call the weigh master. While getting into position I could see there was room that I could drive either the left or right side of wheels onto the pads, there is an arch that won't let you drive up to the place you need to be to get a normal weight. So, I got it weighed and went into the Road Ranger to get the news.

GVWR = 24,000 Actual = 22,300 1,700 available
GAWR Front = 9,000 Actual = 7,380 1,120 - 1,620 available*
GAWR Rear = 15,500 Actual = 14,920 80 - 580 available*

* Front and rear ranges limited to a total of 24,000 so front to rear balance plays a role in weight ranges available to those axles.

I'm Mildly surprised at rear loading but we haven't done anything to move items around to distribute weight. also, given nearly full water tanks I'm not sure where that weight would be felt the most. In real life, I don't expect to carry that much water going down the road.

So, after I talk with the weigh master I ask if I can get weighed with just my right wheels on the FIRST 2 pads which are normally for drive axle and trailer axle for an 18 wheeler. He said sure but didn't think it would work.

I get around again, center my right wheels on the pads which also centers my rig on the left edge of the pad. My left wheels are just a TAD lower than my right wheels on the pads. They weigh me, I back up a bit to get my rig through the arch and I go to the weigh master and get this:

Gross = 10,940
Front = 3,540
Rear = 7,400

So...Theoretically, I should be able to do the math and determine my left side weights:

Front axle total 7,380 - Right front wheel 3,540 = left front wheel 3,840
Rear axle total 14,920 - Right rear wheel 7,400 = left rear wheel 7,520

BTW, the original weighing cost me $9.50 and the second $1.00. Not too bad.

Does anyone see something I have missed? I have 2 slides on left and 1 on right. Does that left right "imbalance" seem reasonable?
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Old 04-29-2012, 09:01 PM   #2
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Quote:
Originally Posted by athuddriver View Post
First for you cat lovers...No cats were harmed in the making of this thread.

Get your calculator and thinking caps on. There will be a quiz at the end of this exam.

OK...I've been having a heck of a time finding a place to get 4 corners weighed. Have had the rig for a couple weeks and Sandee and I have completed a lot of the initial setup including a major project of getting GSD size crates set up and secure. So, today we felt was a good day to get it weighed and see how things were progressing. So, with full fuel, full LP, aprox 65 gal water, 2 people, 2 GSD W/crates and a fair amount of essentials loaded into the rig...off we go.

We picked Sunday to weigh it at a local CAT scale because generally there are less trucks for us to get in the way of. If you aren't familiar, the CAT scale has 3 segments and that makes it easy to get front and back axles and even a toad at one shot but no break down of left vs. right side. An RV with out a toad would your the last 2 pads.

Got to the CAT scale and was #1 in sequence. I get the rig set up on the last 2 pads and call the weigh master. While getting into position I could see there was room that I could drive either the left or right side of wheels onto the pads, there is an arch that won't let you drive up to the place you need to be to get a normal weight. So, I got it weighed and went into the Road Ranger to get the news.

GVWR = 24,000 Actual = 22,300 1,700 available
GAWR Front = 9,000 Actual = 7,380 1,120 - 1,620 available*
GAWR Rear = 15,500 Actual = 14,920 80 - 580 available*

* Front and rear ranges limited to a total of 24,000 so front to rear balance plays a role in weight ranges available to those axles.

I'm Mildly surprised at rear loading but we haven't done anything to move items around to distribute weight. also, given nearly full water tanks I'm not sure where that weight would be felt the most. In real life, I don't expect to carry that much water going down the road.

So, after I talk with the weigh master I ask if I can get weighed with just my right wheels on the FIRST 2 pads which are normally for drive axle and trailer axle for an 18 wheeler. He said sure but didn't think it would work.

I get around again, center my right wheels on the pads which also centers my rig on the left edge of the pad. My left wheels are just a TAD lower than my right wheels on the pads. They weigh me, I back up a bit to get my rig through the arch and I go to the weigh master and get this:

Gross = 10,940
Front = 3,540
Rear = 7,400

So...Theoretically, I should be able to do the math and determine my left side weights:

Front axle total 7,380 - Right front wheel 3,540 = left front wheel 3,840
Rear axle total 14,920 - Right rear wheel 7,400 = left rear wheel 7,520

BTW, the original weighing cost me $9.50 and the second $1.00. Not too bad.

Does anyone see something I have missed? I have 2 slides on left and 1 on right. Does that left right "imbalance" seem reasonable?
NOTICE DO NOT DO AS I DO.
Not to simplify things too much, alas I have never weighed all 4 corners of any of my two Motorhomes. I have however weighed the whole thing. I go by the cold max pressure on the sidewall and in 100,000 miles have never had a problem. There is also a card attched next to the driver seat that tells you what tire pressure to use.
I also use a tread depth gauage on the tires to see if they are wearing evenly across the tread. Works great for me.
REMEMBER, MY METHOD WILL NOT BE APPROVED BY AT LEAST 75% OF THE FOLKS ON IRV2
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Old 04-30-2012, 12:54 AM   #3
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Don, the left/right differences in your weights are insignificant. Most of us would like to be that close. I would set my pressure, using the manufacturer's charts, by the heaviest wheel on the axle and add 5 lbs safety fudge factor.
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Old 04-30-2012, 06:57 AM   #4
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Originally Posted by historyljc View Post
Don, the left/right differences in your weights are insignificant. Most of us would like to be that close. I would set my pressure, using the manufacturer's charts, by the heaviest wheel on the axle and add 5 lbs safety fudge factor.
I was thinking the thing about +5 of heaviest wheel weight. Even at that, I should never need to use the 110 PSI max.

I am also trying to get any second opinions from any of our Mr. Wizards out there. Does the math I used hold up/make sense? So far, getting the folks at the CAT scale to let me run it twice, once full axle per pad then a second with only the right side on the pads, is the only way can even get close to "4 corners".

If I am correct in my assumptions from my "experiment" I would then inflate my Michelin 235/80R22.5 tires to:

1. 85 PSI based on 3840 lbs plus 5 PSI.
2. 95 PSI based on 7520 lbs plus 5 PSI.

Ya, I do work for the government where we measure with a micrometer, mark with a grease pencil and cut with a chain saw. LOL
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Old 04-30-2012, 08:06 AM   #5
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athuddriver, there is nothing wrong with the method you used. In fact, that is the method recommended by Michelin on pages 3-5 of their RV Tire Guide to obtain 4-corner weights if you don't have access to 4 individual portable scales such as those used by RVSEF.

Your side-to-side balance looks good. You say you have 2 slides on the left and one on the right, which seems to explain why your rig is a little heavier on the left.

Most rigs are heavy in the rear. Gassers like ours tend to have relatively long rear overhangs, and DPs obviously have the heavy engine and transmission in the rear.

You can make improvements in the balance by further limiting the amount of fresh water you carry and by being thoughtful about where you store heavier objects.
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Old 04-30-2012, 09:36 AM   #6
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athuddriver, there is nothing wrong with the method you used. In fact, that is the method recommended by Michelin on pages 3-5 of their RV Tire Guide to obtain 4-corner weights if you don't have access to 4 individual portable scales such as those used by RVSEF....
PERFECT! I have seen that guide but obviously hadn't understood what I was looking at!

MANY THANKS!
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Old 04-30-2012, 06:51 PM   #7
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I have had 3 people (dealer, rvsafety.com, and manufacturer) tell me NOT to rely on weights derived if the motorhome is not level when weighed.

I don't have personal experience with what the difference would be, but they all swear it can be significant enough to throw your recommended psi for each tire across an axle off.

I got ours weighed the first time at a moving and storage company which had a level parking lot and level approaches. I am familiar with the CAT scales you mentioned and I recall some pretty significant slopes on either side of the scales.

I would be cautious about the weights until you find a better alternative.

Don
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Old 05-01-2012, 09:43 AM   #8
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Old 05-01-2012, 11:58 AM   #9
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AKADEADEYE - I agree that an out of level scale would or could weigh inaccurately. I would expect CAT scales (especially at truck stops) to be set level and weigh accurately. CAT puts their reputation on the line for OTR drivers. Even if the approaches are incline, as long as the scale bed is level - the weigh should be correct. Just my opinion
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Old 05-01-2012, 12:03 PM   #10
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There was only about a 1-2 inch difference between the platform and the edge where my left wheels were sitting. I would think that is within the "margin of error".
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