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Old 07-25-2013, 06:10 PM   #1
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Balancing a 4320 DS down the road...


My family and I are curious as to how "passengers" riding behind the two front bucket seats (living room couch and dinette) affect the ride/balance of the coach from a structural and safety prospective.

This 2007 4320 DS has a 3 person couch and 4 person dinette all on the driver side. It seems as though most of the passenger weight (based on the layout) is close enough if not on top of the chassis to a degree that it should not be an issue?

Your feedback is appreciated.

Thank you

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Old 07-25-2013, 06:27 PM   #2
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Your coach weighs nearly 40,000 pounds. Four 200-pound passengers weigh 800 pounds. That passenger weight is only 2% of the total weight of the coach. It's not going to matter where they sit, you will never feel the difference.

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Old 07-25-2013, 06:35 PM   #3
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Originally Posted by Rich-n-Linda View Post
Your coach weighs nearly 40,000 pounds. Four 200-pound passengers weigh 800 pounds. That passenger weight is only 2% of the total weight of the coach. It's not going to matter where they sit, you will never feel the difference.
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Old 07-25-2013, 06:37 PM   #4
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Plus you figure the entertainment center, kitchen, refrigerator and downstairs freezer are all on the passenger side. I tried explaining this to my dad earlier lol
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Old 07-26-2013, 02:31 AM   #5
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Plus...... on most large coaches, the air bag leveling system will even things right out.
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Old 07-26-2013, 05:00 AM   #6
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Im not sure if our 2007 DS has that "air bag leveling system?" I know it has a front and rear air gauge but not sure about the leveling...
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Old 07-26-2013, 06:25 AM   #7
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We have a 4320 and I am pretty sure yours will have the air bags also. The air gauges are for the air supply system tanks. I do not pay much attention to loading balance but it is heavier on the passenger side. I put a lot of weight in the basement, wood working tools etc and have not been able to feel the extra weight.
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Old 07-26-2013, 08:05 AM   #8
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Originally Posted by RHURRICANE View Post
Im not sure if our 2007 DS has that "air bag leveling system?" I know it has a front and rear air gauge but not sure about the leveling...
You have automatic height adjustment that keeps the air bags inflated to the correct height when driving. There are some coaches that have some kind of active air leveling systems so they don't need to put jacks down to make the floor level but that is different from ride height.

Do yourself a favor and try to attend the Spartan Owner's training course. It is a week long and well worth the time. We went there this spring and it was awesome.

Spartan Chassis

Our 2006 DSDP 4320 is pretty well balanced L/R wise. I think the 4 slides vs 3 helps in that area. When we last weighed ours we had full fuel & water, basement loaded, Sandee in the co-pilot seat and our GSDs in their crates. The one difference from yours is that we removed the desk/dinette to put 2 large crates but crates and 2 90# GSDs is pretty close to a wash. Also, from a few previous test weights we kinda knew how we wanted to arrange things in the basement for proper L/R balance too. In the end we were only about 300# difference on the front wheels.

NOW...(we all have our soap boxes)...your biggest concern is probably NOT L/R balance but front axle weight. This would normally only be true if you have the grouted tile floor which is WAY heavy.

Spartan rates the front axle at 14,600# but Newmar derated it to 14,200# because of tire selection. Assuming the 2007 models are basically the same as 2006 you have 305/70R tires all the way around. I can not begin to imagine any situation where you will have any problem with the drive & tag wheel weights. Now...as to the front wheels...

Because Newmar used the same chassis through out the DSDP line they had multiple configurations of slide combinations which would lead to varying levels of corner weight balances. Because of that they had to consider the highest potential front corner weight and thus, after engineering and building in safety margins they derated the axle. Had they chosen to use 315/80s this wouldn't have been necessary and, in there defense, it would have added costs. They could have even opted to run 315s up front and 305s in the back. Again, it is a marketing choice.

So...seeing as you have potentially a MH that is reasonably easy to balance L/R based on Michelin tire pressure charts you could find that you actually load the front axle to 14,600# and still not have to put in more than 115 PSI. Currently I have had pretty good luck in staying below 14,200# up front and being balanced so I haven't had to "go there" but if needed, I wouldn't think twice FOR ME to go all the way to 14,600# if needed. You have to keep in mind that almost all the fuel weight is on the front axle so it will get lighter as you travel. Again...this is something I am fully comfortable doing. Others may not and that is not bad.

Now...finally, that leads to my over arching point. You may not have enough available weight left on the front axle to sit 4 people (3 seat belts behind driver and 1 behind co-pilot) in the cabin because you might exceed your front axle weight limit if you are already close to it for travel without those guests. Remember, your couches are very close to the front axle so almost all the weight would be added to the front axle.

ASSUMING that you normally only travel with you and a co-pilot the bottom line is that you really need to know what your corner weights are under normal loads. Pay particular attention to front corner weights. After that you will have a ball park idea of how many folks you can carry on the couches because you should assume that 100% of that weight will be on the front axle. As long as you start out with a reasonable L/R balance under normal conditions and you know the combined weight of passengers will keep you below your max axle weight (and you balance them L/R as best you can) you shouldn't have any issues with L/R balance.

I know, it sounds complicated and if you haven't really delved into the whole weight and balance vs tire pressure thing it is at first. HOWEVER...it IS important that you do so.

Finally, a bit of a side bar but it may help...

You should find that once you have the drive and tag axle weights that you only need to run 75 PSI or maybe, at most, 80 PSI on the drive wheels. (Another reason not to have 315/80s back there because it would be like riding on balloons I think. LOL) Specifically, in my case, I need 75 PSI (because that is the minimum you can run) in the tags and 77 PSI in the drives wheels. HOWEVER...I run 85 PSI in the drives for a specific purpose. I roughly calculated how many pounds of weight were being carried per PSI for the tag and drive wheels and found the tag was carrying more. My theory (I am NOT an engineer) is that would allow more weight to sit on the tag and steerers allowing the drives to sag a bit. Instead I chose to run 85 PSI in the drive wheels to keep them inflated to be "rounder" and act as a fulcrum. This should allow the weight in the back to unload some weight from the front wheels. I tested this out one day and found that I unloaded about 125# off the front axle when I did this. I was very careful in this because when I first weighed it I actually put chalk marks on the CAT scale so that when I came back around my wheels were in the exact same place.

Being anal retentive it is a curse!

Don, Sandee & GSD Zeus. Gardian Wings earned are GSDs Gunny (7/11/15) & Thor (5/5/15)
2006 DSDP 4320, Spartan MM IFS, 2013 CR-V, Blue Ox Avail, SMI AF1, Samsung 197R Refer.
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