Calculations/ weights for bed Build needed

[Brian C]

Hello all. 

BLUF (Bottom Line Up Front) I need the mathematical formula to be sure the bed build and the toys on the bed/hitch/fifth wheel pin weight do not unload the front axle too much.  (Thus requiring me to move the tandem axles, which I am ok with, but don’t want to  unnecessarily.)

I recently purchased a Volvo truck and I need to stretch the frame about eight to nine feet to put a vehicle and some motorcycles lengthwise on the truck, and still pull our 5er  

Truck is a 2013 volvo VNL64T730 D13 ishift  with a 230” wheelbase. We plan to put a 14’ two door Jeep, under ~4000lbs, ~1000lbs of motorcycles, 3k pin weight and a 400lbs hitch, not including the extra frame and the bed itself. 

I have no idea at all how to figure this out, and I really do not want to make the truck unsafe. The nearest Volvo dealer will stretch the frame and mount the hitch, and a local trailer and flatbed company is going to build the bed and install it  

I am planning to dovetail the end of that matters at all  

 

Thank you much!

Brian

Edited July 17, 2019 by Brian C

[SuiteSuccess]

Singled or tandem?  Google formula for fulcrum and it will give you an idea.  Do you have Power Point?  If so I have multiple slides that have the formulas and how to calculate.  Just personal message me an email address and I will try to send to you.

[Star Dreamer]

You will need dimensions of your truck wheel base and pin location plus individual axle weights and the locations on the bed for each of the items.  You will have to calculate the weight of the bed behind the centerline of the rear axle and in front of the rear axle. Anything located behind the trucks rear axle centerline will add weight to rear axle and off load front axle. Weights in front of the rear axle centerline will add weights to both front and rear axle proportionately to both depending on location. If you plan on storage boxes under the bed, you will have to include these and any items in them in your calculations.

When I built our bed 7years ago, there was a spread sheet on the HDT Escappees forum forum that I used but there was some errors that I had to adjust for.

Dave

[Exile]

The biggest thing is to get the weights and centers of gravity of all the loads going onto the bed, including hitch load.  If you locate the axles under the centers of the summed loads, it will keep your front axle the same.

[noteven]

Hi Brian C - 

I once posted how to calculate the loads you are wanting to do not using software but tape measure, pen, paper, and calculator including the formula. I was scolded and ridiculed for suggesting such a thing could even be done to figure out a Big Truck towing a Big RV.  “A disaster waiting to happen...” one poster said...

So no expertise is being implied whatsoever. The math used in the following description is math than can be found in a book or on line. It was used for commercial vehicles not Big RV HDT’s. I cannot verify it would work for BRVHDT’s.

I used to lay out truck mounted oilfield service units of different types, 4 axle daylighter  trucks, twin steer crane trucks etc “on paper” prior to the customer ordering a truck with wheelbase and factory equipment located to meet the weight and dimensions law and equipment build requirements. Or calculate whether an existing truck on the ground is suitable to use for a proposed application   - which is what you are doing.

I am not implying RV expertise whatsoever because the following methods were for commercial trucks:

Step 1. For building on an existing truck (not factory order) I would start by obtaining the base weight and dimensions of the truck. I might look up specs on a computer but to be accurate I would  use a tape measure on the truck itself and actually weigh each axle or group (tandem) on a scale. I would not fill fuel tanks but look and measure tape fuel on board then calculate fuel not on board as a load to be added. I would note (as in write on paper) the location and dimension of anything already frame mounted - tanks, suspension mounts, cross member bolts, etc I would take images with the tape measure in the image  for dimension reference if necessary.

I would then obtain the weight and dimensions regulations that apply to the application to reference all calculations to throughout the process.

The weight and dimensions of everything to be mounted or hauled we called point loads - the weight and centre of gravity of each piece of equipment or cargo was calculated and noted.

All equipment was prioritized to must have and optional nice to have if it fits.

Then if it looked like the vertical centre of gravity of all the mounted equipment and cargo as a whole was staying below 65” above the frame rail we would not involve an engineer just yet. Every truck has a design cg to meet braking standards and stability. 

Again I’m not sure what physics apply to BRVHDT’s - but don’t worry a class 8 truck’s vertical c of g is below the frame when it leaves the factory. You should be good with a flatbed with a Jeep on it. Depends though how top heavy the semi trailer you tow on a fifth wheel is, and where the trailer begins to apply roll force to the truck - almost right away with a solid fifth wheel, after so many degrees with an oscillating fifth wheel, or never with a single pintle (not a stacked double). 

At this point the truck truck between the axles is a “beam” supported by its axle centrelines with two cantilevers ahead of the front axle and behind the rear axles.  I would sketch out each load to see where it fits and calculate the weight distribution to each axle or axle group based on point loads along the beam.

Loads behind the rear axle group centre line or in front of the steer axle are calculated using lever math. 

Loads in between the axles I.e. within the wheelbase are calculated using beam math.

 In the truck world the formula we used always solved weight distribution to the steer axle 1st because the distance from the steer axle to back of cab (or sleeper) does not change but the wheelbase can change.  Wheelbase, point load, and distance from point load to the steer axle are in the formula. Weight rear is the difference between total point load and what distributed to the steer axle. 

Wheelbase is the distance frame the centre of the steer axle to the centre of the rear axle or group. 

If you are laying out a simple build like a deck, headache rack,  4 boxes, a generator, a Jeep on the deck, bikes behind, rear bumper or skirt, and a hitch I suggest learn to do the math by sketch pad, tape measure, and calculator standing beside your truck vs going to software and a screen just yet. You will be able to visualize body swing, ground clearance, departure angles, trailer swing and dip clearance, receiver hitch angles through dips, etc etc.

In cases where a “trailer hitch offset” (distance from rear axle or group centreline to the hitch point) was near regulations limit, and the truck may or may not be loaded - like an empty dump truck hauling a loader on a pintle hitched flat deck - an engineer was involved to do a braking and stability review before the torches and welders came out. These calculations were done for both loaded and unloaded truck configurations. 

Substantially unloading a steer axle through excessive rear hitch offset was considered bad design and would be failed by the engineer at some point. Some was allowed depending on wheelbase of trailer and truck (look at a class 8 tow truck they are long) but this involves moment of inertia calculations to make sure vehicle stability  is maintained. 

Takes way longer to type than walk around your truck with you and lay it out on a pad of paper

Again I have no expertise in Big RV HDT’s so I can’t post actual formulas I used or recommend any of the above methods are applicable to your project.

 

 

 

 

 

 

[Alie&Jim's Carrilite]

Look at DollyTrolley Posts.  He has a computer sheet already made that you enter your dimensions and known weights.  You can also measure it out and use NotEvens method.  

[noteven]

19 minutes ago, Alie&Jim's Carrilite said:

Look at DollyTrolley Posts.  He has a computer sheet already made that you enter your dimensions and known weights.  You can also measure it out and use NotEvens method.  

Yes correct I used spreadsheets for builds with “many pieces”. Or juggling wheelbase possibilities on a factory order truck.

and then the second stage body manufacturers engineers for sure use design software 

But we would not “draw out a truck” to see if 4 things would fit

but always started with knowing the front and rear available payload, then pad, pen, and tape measure and weight and dimensions regs in hand beside the victim truck and trailer whenever possible.  I found it to be the best 3D view.

Did I mention always start with knowing the available payload? It is the sum of the max allowable axle loading where you plan to travel or door sticker axle GAWR whichever is less, minus the tare weight of the truck before you start bolting stuff on.

Hint: weight distribution math between the axles is ratio ciphering. A point load 150” from front axle on a 200” wheelbase is distributed 25% front 75% rear.

past the axles is levers: a point load 100” behind the rear axle on 200” wheelbase distributes 100% to the rear axle (fulcrum) and removes 50% of the point load weight off the steer axle due to leverage. 

[Big5er]

15 hours ago, Brian C said:

I recently purchased a Volvo truck and I need to stretch the frame about eight to nine feet to put a vehicle and some motorcycles lengthwise on the truck, and still pull our 5er  

The ex cop in me just has to ask...How long do you expect this thing to be?? 

[rickeieio]

4 hours ago, noteven said:

past the axles is levers: a point load 100” behind the rear axle on 200” wheelbase distributes 100% to the rear axle (fulcrum) and removes 50% of the point load weight off the steer axle due to leverage.

Magic?  Lawrence, you might wanty to cipher that one again .   Down here, south of the border, if you remove 50% from the front, you'd put 150% on the rear axle.

That said, I wholley agree with the idea of using a tape and paper to lay it out.  Sort of like using a pencil to solve a problem rather than a calculator, and just having blind faith the electronic thingy is correct.

And Phil, he's gonna pull a very short trailer.😜

[noteven]

Oops Rick you are correct I forgot to add the weight of the lever (truck) in my headlong rush to show how smart (not) I am🤣.

My therapist has caught me posting Big Stories on line again and has prescribed a min two week motorcycle trip to forget about Big Clumsy RV’s 😁. 

... and we’re off!

[rickeieio]

I guess I'm only half as crazy, cuz I only get one week of wandering around the Smokies.........

[adept99]

Yeah, that length thing will be self explanatory if you try to drag it thru the Smoky's at what must be a million inches long. 

I used a bastardized "Weight & Balance" spreadsheet when I relocated one of the axles on our 44' toy hauler. I combined elements of the Dolly Trolly and the Noteven spreadsheets. Worked quite well, and increased the pin weight by the predicted amount and eliminated the wild sway I had had been experiencing up to that time.

I like the idea of pencil and paper first. You already have a few limiting dimensions. Legal length limit, usually 65', but can stretch that a bit. Center to center on axles, front to rear. Dimensions of the expected load. Etc, etc

Go ahead and start your design. There's plenty of folks here who will be thrilled to help you spend your money to get your rig just perfect...

[Brian C]

Thank you everyone. 

I cant believe I failed to say that it is in fact a tandem truck. Apologies. 

On the length, I have yet to see nor had anyone show me where there is a length limit on an HDT towing. The only thing even remotely applicable is that the truck can be any length you like and the trailer can not exceed 53’ in most states. So I am none too worried about that. Thanks for your concern though folks. 

I don’t disagree with the pen and paper idea, but my brain simply does not work that way. I think I grasp the explanations, and I understood the lever & fulcrum concepts. But I fail to grasp how I might determine the center of the weight on the Jeep to know how that works in, and I seem to be at a total loss for how I’d know the weight of the bed. I guess I would have to speak with the bed builder and get his thoughts.  

A big thing right now that is eating at me is “will I need to relocate the axles or not, and if so how far, and what will that do to my turning radius?”  

If I felt comfortable at least with that i fo I could take it to the frame folks and get them going on the stretch, hitch removals and new hitch mount, and possible axle relocation. 

I wish I could just find a one stop shop similar to RVH but for about a third the price. I recon the folks I have worked out can do it for significantly less than even that, but for such I have to do the math and tell them what to do, and it is on me if I screw up. Sadly all of the folks around here who could do it won’t because it is not for a commercial application. How weird is that, right? Sigh. 

Below are the measurements I believe you are asking for, at least what I have now. If I am missing something let me know. 

 

Wheel base to center of tandems 230”

BOC to second axle 5’6” (66”)

BOC to third axle 9’9” (117”)

Average, or BOC to midpoint between tandems  7’7.5” (91.5”)

BOC to end of frame rails (including slope) 12’3” (147”) Hope that makes sense.

 

Please let me know if I appear to have made any blatantly obvious errors. LOL  

 

Thanks again,

Brian

 

 

Edited July 16, 2019 by Brian C

[Steve from SoCal]

Well,

 

I really didn't want to comment on this because you seem to be LAZY, you have done no home work.

 

Let's start with the length, are you going to be a commercial vehicle?     If yes, then your right 53' trailer and no limit on the tractor, on the national network and STAA routes.     Other roads you may be subject to length and width restrictions and or by permits.      If you plan on the truck and trailer being a private personal RV then the state you register in WILL have an overall length limit may states are 65"

 

If you want to carry a 14' long car on YOUR truck flat then you will need at minimum 20' of deck or a stinger type of hitch at least the swing distance of the trailer behind the car.     As a wild guess the keep the front axle about the same you would need to have a 260ish? wheel base.      Depends on the loading and axle weight of the car.     For example, you could go shorter WB but would have to carry the car and be hitched to the trailer.      Car only too heavy steer axle, trailer only too much steer axle unloading.      A truck with 260-270" wb is long but there are plenty of trucks with that wb, you won't turn great, plan your routes carefully and, it's another thing to remember to consider when you are off the big roads.

 

You really want to do this inverse to your question, establish what the state regs are and work forward with trailer, truck and payload on truck.     A rough guess of the truck is 16' bumper to back of the cab.    Add 20' of deck and yo could tow a trailer with 29' behind the fifth wheel.    Could you tow a 39' or 45' trailer, yea but you would be subject to an over length ticket in your front yard.      Do folks do it and get away with yes until they don't.     

 

One other thing about RV length limits, they vary state to state.     Most states won't bother you if you are 65' or less, 75 or 80' stands out easily.      There are a few folk here that have really long rigs, they can offer their own perspective.      

On edit,

 

Rick is correct, only truck tractors with droms built on or before 12/01/82 are allowed the same unrestricted length limit.     That is again only on the STAA routes.    Each state has their own rules about trucks with payload on the chassis.     As mentioned often, 65' is the magic number for both commercial and private vehicles in most states.

 

Edited July 16, 2019 by Steve from SoCal

[rickeieio]

Hopefully big5er will step in and correct me if I'm wrong here, but as Steve said, there's no length limit on a road tractor.  But, when you carry a lod on a bed, it's no longer a tractor, it's a truck, no matter what type hitch.  Most states have a length limit of an rv at 45', and 65' for combination.  This is NOT reciprocal, so local law applies when you leave your home state, same as any other length/width/weight laws.

You have a lot of homework to do.  Good luck.

[HERO Maker]

Steve and Rick have said it pretty bluntly, and I agree, you have some homework to do!  Like you are finding out with the builders that you are working with, until you figure out the weights of what will be on the points of your measurements, not many will be involved with giving you a plan (and if they do, well there is no liability).

Sounds like you haven't been to a Rally yet (next one is in Oct), or read enough of the postings about bed builds, or looked in the Resource Guide.

It's homework time.   So how short is your trailer?????

[DesertMiner]

No need to Judge people by where you "think" they are from!  That type of attitude is not appreciated on this forum!  I bet you will get your wish and get no more answers that you don't want to hear 'cuz you already "know it all"...you need to "move along"!

Oh and by the way FB might suit your questions in a more "positive" light!  You should fit right in with the other folks that have accomplished your "quest" with varying degrees of success!

 

 

Edited July 16, 2019 by DesertMiner

[Steve from SoCal]

22 hours ago, Brian C said:

 

 

I happen to be in Hutchinson Kansas and, I am a proud FIFTH generation Californian.     

 

You feign mea culpa and then attack the truth.      Go ahead and do it your way, it'll work until it don't.     Your way over your head and it is glaringly obvious you don't know what you don't know.      Perhaps a reading comprehension course.

 

 

Edited July 17, 2019 by Phil D
Removed quote of prohibited post

[rickeieio]

Brian, settle down please.  All you'll need to know pertaining to length laws is available in the Heavy Haulers Resource Guide, compiled by Mark Bruss.  It's all well documented, and has many links to state and federal laws.  Please do some reading before accusing those who've offered advice of just "thinking" they know the laws.  This not the 1st, or even the 100th, time this subject has been beaten to death.  And you are not the first person to come barging in thinking they know all about HDTs.

Do some homework, then come back and we'll try to help.

 

 

[phoenix2013]

I was going to offer some thought, maybe on weight and balance, asking where the motorcycle was going to be placed, point out the handling issues with long overhangs, etc., etc. I think I'll wait until this gets settled.

   

[Jack Mayer]

Let's all use good judgement here. We don't want the thread closed, or members suspended.  Personal attacks work on Facebook, but are not tolerated here. 

Edited July 17, 2019 by Jack Mayer

[Brian C]

20 hours ago, rickeieio said:

Brian, settle down please.  All you'll need to know pertaining to length laws is available in the Heavy Haulers Resource Guide, compiled by Mark Bruss.  It's all well documented, and has many links to state and federal laws.  Please do some reading before accusing those who've offered advice of just "thinking" they know the laws.  This not the 1st, or even the 100th, time this subject has been beaten to death.  And you are not the first person to come barging in thinking they know all about HDTs.

Do some homework, then come back and we'll try to help.

Thank you Rick, I am aware of it and I have read through it multiple times.  

I am simply trying to gain information on how to calculate the weight and balances. I know I will need to get the weights I just don’t know how to plug them in to insure my truck is safe. 

I appreciate any any advice offered in kindness. 

 

Regards,

 

[Brian C]

4 hours ago, phoenix2013 said:

I was going to offer some thought, maybe on weight and balance, asking where the motorcycle was going to be placed, point out the handling issues with long overhangs, etc., etc.

Thank you for your intent. I would appreciate your thoughts. 

One of my concerns is, in fact, having an over hang that is too long or too short. Too long, obviously, as I am sure you will point out, will unload the front axle and provide very scary and unsafe conditions. By too short I mean that it would limit my turning angle significantly, and while I want it as far back as needed to be safe, I’d rather not go al the way back when it is not needed. I hope that makes sense. 

The motorcycle, I plan to park the Jeep either to one side allowing access for bikes up the other side, or preferably the Jeep in the canter with the bikes on either side. Lastly I have considered putting a shelf above the hood of the Jeep, to hold the bikes. Not unlike the rack RVHLifestyles recently built to hold a pair of spider trikes. I should mention one bike is an adult dirt bike, and three children’s bikes. 

 

Anyhow, thank you for your time. 

 

Brian

[Jack Mayer]

It is going to be challenging to get a motorcycle on next to a Jeep. How are you going to get it into place? What mechanism will hold it safely? Where will you find the "room"?

On the "rack" above the Jeep hood, what are you going to use to elevate it? It is not at all simple to do safely. It has to be braced very securely and the Jeep below it will cause challenges in that regard. Our stacker system was very carefully designed to take these forces into account. It was VERY challenging to get that design correct and implemented. 

You say you want to build a bed to carry a Jeep and motorcycles for 1/3 less than our beds. Our modular bed that carries a smart is about 18K in its most expensive optioned state (rear light panel, boxes, etc)....more or less. Without a hitch. You want to add a lift mechanism and motorcycle racks to that, lengthen it significantly, and get it delivered to you for around 6K by your statement. That is simply not realistic. You could not build a simple deck of any quality for that. If you paid someone to do the work I'd be surprised if you got anyone to build anything useful for 6K. If you do the work yourself you will have more than that into it by the time you are done.  I think it is time to step back and look at what you really need, and reassess how you are going to get there.....

You can "crowdsource" a design for a Jeep deck. That will get you an outline you can build. But even if you do much of the work yourself you will be spending  over 10K to complete the project. At least in my opinion, and we do this every day....

[noteven]

OY! Quitcher arguing and look at some design limits. 

Max overall length for any class of single motor vehicle over pretty much all the USA and Canada without special permits - limo, RV, bus, straight truck is 40ft - 41ft, some places are a bit more maybe.

Combinations including an RV are 65ft in many places, longer in some others.

There are also regs around the maximum length of body that can extend beyond the rear wheel base to limit “body swing” making turns. 

Weight and dimension laws apply locally where yer at.

So my design criteria for a CanAm capable rig would be a max 65ft overall combination length, including up to 40ft tow vehicle (480”).

So Brian you are starting with what bumper to BOC “? Write that number down.

On the frame you want say a 200” 4x4, a 90” moto or 48” if you cross load it. Let’s say 200” + 48” = 248”.

Add 60” to couple and swing a 5th wheel trailer. (Add 0” if bumper tow trailer.)

So 308” needed back of cab for 248” of Jeep and bike plus 60” 5th wheel trailer swing.

Add your truck’s bumper to back of cab inches to 308”. If this is less than 480” you meet length law everywhere. . 

As the truck gets shorter than 480”, those inches can be added to trailer length.

Once the rig sketches out dimensions wise then you go to calculating weight distribution

rickeieio - please check my math I’m partially incapacitated due to ridingitis.

dont tell my therapist