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Coach weight distribution after weighing


donh

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Hello,

Not sure if this is the right forum.

We had our Class A Newmar Bay Star 3401 weighed this week.  We are 400 lbs over on the rear axle and 700 lbs under on the front axles.  Unfortunately, most of our useable storage is behind the rear wheels.  My question is, would payload behind the rear wheels cause the front to be lighter, with the rear axle acting as a fulcrum?  I was told no, because, removing or adding a few hundred pounds behind the axle on a 24,000 lb coach would not have any effect.  I remember my college statics course, and I do have a formula for calculating the change on the front axle.  

We ordered our coach and had the chassis upgraded from a 22,000 to the 24,000 chassis, but actually the 24,000 chassis added 1000 lbs to GAWR (9000 lb) on the front, but only 500 lbs to the rear GAWR (15,500).  

thank you

 

Don

2017 Newmar Bay Star 3401, fulltimer.

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Yes, putting weight behind the rear axle will affect the load on the front axle (lighten it).  How much the front axle is affected is directly related to how much weight is behind the rear axle.  If you move weight from behind the rear axle to in front of the rear axle, that will obviously shift some weight from the rear axle to the front axle.  How that weight is distributed between the two axles will depend on how much weight it is and were it is placed between the two axles.  It is all a numbers game until you come up with the correct combination.

If you plan to tow a trailer behind your motorhome, the tongue weight will also affect front and rear axle weights to a certain extent.  If you tow a towed vehicle four down, then there is no tongue weight added to the motorhome.

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The farther behind the rear axle stuff is stored the bigger the impact (more front axle offloading).  Keep the heavy stuff close to or in front of the rear axle.

I sometimes carry a 900# Harley  on the rear of my rig and it adds over 1300# to the rear axle and offloads the front over 480#.  Keep in mind, it extends a fair bit behind the rear axle so there is significant leverage.

Lenp

 

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2012 F150 4x4

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2019 HD Ultra Limited

 

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thank you.  lenp, that is a great illustration.  It only makes sense, if you think about, isn't that how a skate board works? 

I believe putting weight in between the two axels would distribute the weight in the same proportion as the distance from the rear wheel to the wheelbase.  the formula I have for the weight behind the wheels is:

Fn = Fo - W*(L/Wb) and Rn = Ro + W + (Fo - Fn)

where Fn = Front new, Fo = Front old, W = weight added or removed, L=length behind the rear axle, Wb = wheelbase, Rn=Rear new, Ro = Rear old.

I think we will get it weighed by some one else next time.  It would be nice to be able to just sit on the scales and be able to move a few items around and see what happens.  We are heading north through California this spring up to Canada this summer, maybe we can find someone to do it for us on the way.

 

Don

 

2017 Newmar Bay Star 3401, fulltimer.

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Welcome to the Escapee forums!

13 hours ago, donh said:

We are 400 lbs over on the rear axle and 700 lbs under on the front axles.  Unfortunately, most of our useable storage is behind the rear wheels.  My question is, would payload behind the rear wheels cause the front to be lighter, with the rear axle acting as a fulcrum? 

Absolutely it will. It sounds as though your question was answered by an RV salesperson. It isn't easy to pin down the amount of effect because you have to figure out exactly where that weight is located, but the impact is there and it is important. It is a very common practice by the RV builders to add extensions to the rear of the frame rails of a gas chassis in order to build a longer coach on the shorter chassis which costs less than one with a longer wheelbase. That extension of the frame then gives the builder not only a larger coach but also an area with no chassis components to build in basement storage. It is very common to have most of the largest basement storage behind the rear axle of a gas chassis and most of the extra weight capacity on the front axle. In my opinion, that is the biggest weakness in gas coach design. I had a similar problem on the F53 chassis coach that we were fulltime in, along with the fact that the front axle rode quite stiff because of the lack of weight there. I improved on that some by building some watertight storage space mounted behind the grill, attached to the front frame rails in which I put some heavy things like my jack and some tools. You do need to keep that storage small and avoid blocking air flow to the radiator, but in doing this I moved about 200# forward in total effect. I also kept all of my tools in bays as close to the front as possible and the same for other heavy items.

The actual weight of what I moved up was about half of that. It was some time ago so I don't recall exact figures but remember the problem well. It got to where we kept nothing that was heavy in our rear basement storage spaces. I had a blue portable waste tank there and similar bulky items of low weight. As you deal with this, it would also be a good idea to get side to side weights as that too can be off as ours was. We were left side heavy also because too much kitchen was on that side. Loading of heavy items can impact the handling of the RV. 

Good travelin !...............Kirk

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10 hours ago, donh said:

We are heading north through California this spring up to Canada this summer, maybe we can find someone to do it for us on the way.

I don't know where you are now, but if you're in Arizona, the SKP park in Congress has scales that weigh each tire position.  It costs $45 for a motorhome, but, as I recall, you can get another weigh for free.  So you could do the first weigh, move stuff around and get re-weighed.

Here is the Escapee's SmartWeigh page with information including contact information:

https://www.escapees.com/knowledge/smartweigh

LindaH
2014 Winnebago Aspect 27K
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When I had no passenger I kept a box of canned goods strapped to the passenger seat and my tool kit on the floor in front of it. With no passenger it is doubly hard to get that right front corner weight balanced. It does indeed make a difference in handling.

Linda Sand

Blog: http://sandcastle.sandsys.org/

Former Rigs: Liesure Travel van, Winnebago View 24H, Winnebago Journey 34Y, Sportsmobile Sprinter conversion van

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I won't say where I got the opinion, but it was not a salesman.

We are in La Quinta, CA now.  I have been searching for somewhere to get the 4 point RV weigh in Oregon or Washington.  We will not be near any of the rallies at the right time.  I think for now, I will go to a CAT scale and at least see if the front/back is better after moving things around.  If anyone knows somewhere in the Northwest to get a 4 point, let me know.

 

thank you

 

Don

2017 Newmar Bay Star 3401, fulltimer.

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When you come through Oregon the highway (DOT) scales are always left activated even when the scales are "closed".  If you travel one of the lesser traveled routes and find a scale, stop and experiment.  Just be prepared to move on if they decide to "open" the scales or someone else want to use it.

Lenp

USN Retired
2002 Winnebago Ultimate Freedom

2012 F150 4x4

2018 Lincoln MKX

2019 HD Ultra Limited

 

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On March 14, 2018 at 3:11 PM, donh said:

Hello,

Not sure if this is the right forum.

We had our Class A Newmar Bay Star 3401 weighed this week.  We are 400 lbs over on the rear axle and 700 lbs under on the front axles.  Unfortunately, most of our useable storage is behind the rear wheels.  My question is, would payload behind the rear wheels cause the front to be lighter, with the rear axle acting as a fulcrum?  I was told no, because, removing or adding a few hundred pounds behind the axle on a 24,000 lb coach would not have any effect.  I remember my college statics course, and I do have a formula for calculating the change on the front axle.  

We ordered our coach and had the chassis upgraded from a 22,000 to the 24,000 chassis, but actually the 24,000 chassis added 1000 lbs to GAWR (9000 lb) on the front, but only 500 lbs to the rear GAWR (15,500).  

thank you

 

Don

Don, good evening,

i mostly troll around the HDT section however we also have a class A Diesel Pusher as well as a class Frightliner tandem truck that we tow various RV trailers so.........we have a LOT of variable loadings that we deal with.......

Having flying gigs for most of my life I had to deal with aircraft weight and balance calculations often several time a day so RV weight and balance is a walk in the park once you define the baseline weights and then measure your variable loads and their various locations.........

So to make life easy I have composed a live-data weight & balance spreadsheet that you just fill in the weight and locations and the spreadsheet calculates the axle loads LIVE as you make various changes to your load profile of your coach so........instead of spending a bunch of time shifting weights while your coach is at the scales you are much better off by making simple changes on the spreadsheet until you arrive at your desired axle loads and then just switch your actual loads in your coach and then drive to the scales to confirm your load profile.

if you would like use my spreadsheet just try my cell at (520) 891-3695 and if you get my voice mail just leave your return phone number because we are boondocking way way out in the middle of nowhere for a few weeks with spotty cell and almost no net service .........

Once every few days we get a bit of Internet so if you include your email on your voicemail I could likely attach the spreadsheet and the instructions to a email to you.

Cheers,

Drive.........(Keep your rigs weight in .........balance)

 

 

 

 

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