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Bed Build - Tandem Axle 6' Stinger


VegasFlyer

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After much deliberation, we finally got started on building a bed for our truck. Some of the highlights or key points we incorporated into the design, were:

 

Adding a 6' extension, without a dedicated frame extension;

Facilitate the possibility of changing between the bed and a commercial fifth wheel hitch;

Provide access to drivetrain components for maintenance;

Provide accessibility to fuel fillers;

Provide secure mounting provisions for an rv air fifth wheel hitch.

 

To provide the needed strength required for a hitch mounted on the end of a six foot cantilever, we came up with a plan to use 4"x4" steel tube with .25 wall thickness. These tubes run the length of the frame on top of hardwood spacers above both frame rails and are secured to the truck with a piece of 1/4" steel plate that was broke 90 degrees, with one side being welded to the bed frame and the other side laser cut with holes that mirror the fifth wheel mounting plate.

 

The two tubes are supported by two additional 4"x4"x0.25" tubes which are attached to the inside bottom of the truck frame rails and run parallel out the back of the truck.

 

The two sets of tubes will be connected with bracing by means of lateral and vertical tubes, as well as shear bracing of a 0.50" plate for mounting the air hitch and 0.25" diamond plate lining the cutout in the rear of the bed for the air hitch.

 

Here are a couple crude solid works screenshots showing the basic design, minus any of the bling.

 

 

 

 

 

image_zps2ycnkos2.jpeg

 

 

image_zpsmui5yqqb.jpeg

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Looks good.

Are you going to cut that last rear tube and maybe the next one so the RV hitch will sit below the bed or are you planning on putting the hitch on top of the bed?

Dave

Thanks Dave,

 

The hitch will sit in a pocket at the back. The frame is just tacked in those photos and the rear piece is helping to keep everything square during construction.

 

If you look at the passenger side picture, you can see a couple of the vertical braces tacked in place.

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This will be removable and allow the commercial hitch to be bolted on?

 

Yes, the upper rails bolt to the same angle mount that the commercial hitch utilizes, the lower rails bolt through the existing truck frame.

 

To remove the bed, it slides back and then is raised off the truck.

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While looking at your design it does look really good. There will be plenty of space underneath for storage, if utilized.

 

When I built our bed with an adjustable sliding hitch off the back of the bed, I installed a 2x5x1/4" wall support at a 45degree downward angle to the rear. Then at 45 degrees up to support the sliding hitch. It is inside the storage boxes on the back of the bed so you cannot see them unless you open the doors.

Then when the hitch is extended so the centerline of the pin is 17" behind the bed I install cat 3 top links to supper it at a small angle.

 

On the measurement of 17" it might be more. I have not measured it for awhile. Later today ,if my mind remembers to measure it ,I will get back to you.

 

I think the hitch pin is about 57" behind the rear axle centerline. Better get a tape measure out today before providing any more statements .

 

Also with the hitch extended and 6000 lbs of weight on it, it picks about 1000 pounds of the front axle.

 

Safe Travels, Vern

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If you remember last March you could have seen it in person

 

The centerline of the hitch is 70" behind the centerline of the rear axle.

 

My DW updated our IPad and my iPad mini. They will not let me load any photos on the forum .

 

 

 

The Dear Wife still knows that I am irritated for her computer wisdom .

 

If you go to the test post section you can find some before the update.

 

Or some else on the forum may post some.

 

Safe travels, Vern

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  • 2 weeks later...

Wow! Looking awesome! Any updated pics???

I gotta ask, Why so long? What are you pulling again?

 

Thanks Walter,

 

I will try and get some more photos up in the next few days, we basically got a good portion of the deck on and framed most of the tool boxes.

 

It is extended six feet past the frame to allow us to put a 4 seat RZR or jeep on the deck while hauling the Toyhauler. We have a Weekend Warrior right now, though may be going after a new Fusion in a few months.

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Hi VegasFlyer,

I am following your thread because I will need to extend the wheelbase to do the Smartcare deal and use a Semi Framed RV.

 

I was wondering why you didn't extend the frame and move the Tandems back?

 

How much are you estimating your Pin weight to be?

Les,

 

I am not answering your questions for Vegas but I am wondering if you have computed your weight and Balance to arrive at your trucks desired configuration.

 

A couple of weeks ago we of the ....."too-long-bed-club" (Ronbo , Vegas and me....there are others) had dinner together and we chatted about how versatile our trucks are with tandem long beds and aft hitches.

 

At first glance one might think that our combos are a handful but after you run the weight & balance calculations things make sense.

 

The far aft hitch locations making backing up almost fun but you do have to be mindful of your tail swing.

 

Remaining tandem may or may not be a good choice for some but if you are configured for a far-aft hitch remaining tandem brings a level of stability that a singled rig can't touch and your loading options are vastly better.

 

As ones bed loading get longer it's pretty important to be mindful of the Actual numbers before you go to far into the design and building phase.

 

Class 8 trucks have a fair fudge margin however if you keep things in moderate balance the payback is a much better ride and improved handling that is hard to beat in a RV.

 

Drive on.....(stay in....balance)

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Les,

 

I am not answering your questions for Vegas but I am wondering if you have computed your weight and Balance to arrive at your trucks desired configuration.

 

A couple of weeks ago we of the ....."too-long-bed-club" (Ronbo , Vegas and me....there are others) had dinner together and we chatted about how versatile our trucks are with tandem long beds and aft hitches.

 

At first glance one might think that our combos are a handful but after you run the weight & balance calculations things make sense.

 

The far aft hitch locations making backing up almost fun but you do have to be mindful of your tail swing.

 

Remaining tandem may or may not be a good choice for some but if you are configured for a far-aft hitch remaining tandem brings a level of stability that a singled rig can't touch and your loading options are vastly better.

 

As ones bed loading get longer it's pretty important to be mindful of the Actual numbers before you go to far into the design and building phase.

 

Class 8 trucks have a fair fudge margin however if you keep things in moderate balance the payback is a much better ride and improved handling that is hard to beat in a RV.

 

Drive on.....(stay in....balance)

 

Don't want to hijack the thread, but...

 

Reading as much as I can on these topics. I'm going to remain Tandem'd. I am thinking of a Semi based Frame(Spacecraft) with 3' front overhang, and a SmartCar bed. The trailer may run around 35,000 or "so" loaded and have a Pin of 9-10K. These are estimates.

 

It is always interesting to see everybody's solutions to these things. But I keep thinking if you are running this much weight, you should try to keep the pin close to one of the drive axles. Ideally the middle of the Tandem. Also if you hit the brakes and start to yaw, if you have the trailer on a lever, it has that much more leverage to jacknife you. Just trying to spool this around in my head and understand why folks do these things the way they do.

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Don't want to hijack the thread, but...

 

Reading as much as I can on these topics. I'm going to remain Tandem'd. I am thinking of a Semi based Frame(Spacecraft) with 3' front overhang, and a SmartCar bed. The trailer may run around 35,000 or "so" loaded and have a Pin of 9-10K. These are estimates.

 

It is always interesting to see everybody's solutions to these things. But I keep thinking if you are running this much weight, you should try to keep the pin close to one of the drive axles. Ideally the middle of the Tandem. Also if you hit the brakes and start to yaw, if you have the trailer on a lever, it has that much more leverage to jacknife you. Just trying to spool this around in my head and understand why folks do these things the way they do.

Les, indeed you bring up some very good points....

 

As you point out as your loads become larger it is virtually impossible to guesstimate your rig configuration with any degree of accuracy to arrive at a moderate weigh and balance solution as I tend to preach at times ...

 

Once in a while I get on my soapbox regarding lateral handling qualities of a HDT & trailer combo and the subject can get pretty complex considering all of the cross-coupling that occurs with towing.

 

For the most part most of the HDT group are concentrating on vertical axis quality as a effort to protect the trailer and it's contents.

 

For the most part class 8 tractors / trucks are designed to have a substantial loading range and balance envelope due to the highly variable tasks that commercial operations demand. The thing to keep in mind is that truck operations become more demanding as operations push the limits of the envelope.

 

While towing dynamics can be complex the calculations of towing weight and balance is not very difficult IF you obtain accurate data BEFORE you start your calculations...

 

Unfortunately some RV units are lacking reasonable design for weight & balance and some needless damages occur when tires and axles fail or cross-coupling results in lack of control situations.

 

As you seek to configure a towed RV combo it can be a challenge to obtain valid data to arrive at a reasonable operating unit as your RV becomes LARGE......size does matter.

 

 

Drive on.....(strive for reasonable....numbers)

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