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Open Roads Forum  >  Fifth-Wheels

 > Towing a fiver with a 9' flatbed

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okiehutch

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Posted: 08/01/22 10:35pm Link  |  Quote  |  Print  |  Notify Moderator

Hello all. Hopefully a question is OK for a first post. It is what led me to the forums here.

I have a 2008 F350 Dually with a 9' long 100" wide flatbed on it. I am wanting to use this as a tow rig for a fifth wheel but I am not sure the corners of the bed will clear the front of the trailer. I have looked online but can not find what the standard distance is on a fifth wheel from the king pin to the front of the trailer.

Currently it has a fold down gooseneck ball (not recessed) that is actually already a couple inches behind the rear axle. I know it should be over or slightly in front of the rear axle but this was a used flatbed I bought to replace the rusty factory bed. So the gooseneck ball is behind the rear axle a couple inches. With it being a 9' long bed I am not concerned about the hitch to cab clearance or any cab hits. And since it is a flatbed I do not have to worry about it hitting the top of the bed.

But I am concerned the rear corners could hit the front of the fifth wheel in turns. I have NOT purchased a fiver yet or I would just go measure it. Another thought is this bed is 3" taller than most beds. Is there a standard height of the pin box?

I have not decided if I am going to use a goose neck adapter or fabricate a mount for a fifth wheel hitch. I have a Reese 22K fifth wheel hitch and the height on it is adjustable.....I am just concerned that the taller than normal bed height will make the top of the hitch set to high if I go this route. I know you want the fiver to set level when setting on the fiver hitch to make the axle load equal.

So basically, is there a standard measurement that manufactures use from the king pin to the front of the trailer? And is there a standard hitch height that the manufactures use to design the trailers?

Thanks a bunch for reading this long winded post and any help you might give. Below are some pics to clarify what I have to work with.

Hutch in Oklahoma

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Moderator edit to resize pictures to forum recommended limit of 640px maximum width.

* This post was edited 08/02/22 04:44pm by an administrator/moderator *


Hutch
Slaughterville OK
2008 F350, 9' Flatbed

okiehutch

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Posted: 08/01/22 10:41pm Link  |  Quote  |  Print  |  Notify Moderator

I know to get max capacity the hitch does need to set in front of the rear axle....but I am planning on buying a smaller fiver 25' to 28' so if I do have to place the hitch behind the axle for clearance I doubt the weight transfer will be that great. Looking at 7500 to 10000 GVWR trailers. I know that bumper pull TT is WAY behind the rear axles but I want the fiver to pull as good as possible.

Hutch in Oklahoma

JRscooby

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Posted: 08/02/22 04:28am Link  |  Quote  |  Print  |  Notify Moderator

I can't tell you what the "standard" is, or even for sure there is 1. But I think most mount the pin out past the nose of trailer. I don't think it would be rocket science to build the box longer if you needed the extra clearance. Of course, that would lighten pin weight.

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Posted: 08/02/22 04:33am Link  |  Quote  |  Print  |  Notify Moderator

This will be interesting to see the different numbers.

My pin to ground is 40" measured to the bottom of the pin.
From pin center to front of the trailer is 74".

This is my 30' FW
[image]


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Roger10378

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Posted: 08/02/22 05:23am Link  |  Quote  |  Print  |  Notify Moderator

There isn't a standard for height or distance from the pin to front of the trailer. There are many different pin boxes made and they are all different. They are also adjustable for height. I know my trailer sets farther from the truck than many of the others I see. It is 91 inches from the front to the pin. My height is 47 inches.


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Posted: 08/02/22 07:31am Link  |  Quote  |  Print  |  Notify Moderator

There is no standard pin height for trailers. Your 9 foot bed will probably hit most trailers in a turn unless you move the 5er hitch point back behind the axle of replace the pin box with an extended pinbox which is a bad idea as it puts additional stresses on the trailer frame.

Ken


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okiehutch

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Posted: 08/02/22 07:35am Link  |  Quote  |  Print  |  Notify Moderator

Well this is interesting. I look forward to finding out more heights & distances, but at least I know there is at least one trailer (Roger10378) that would work fine the way it is without having to modify the bed (cut corners) or mount the hitch WAY behind the rear axle.

I did not realize the pin boxes came in such a variety of sizes and lengths and as well as being adjustable.

I have a couple RV dealerships about 40-50 miles away. Might just have to go do a walk around and get an ideal of what is typically on them.

JRscooby

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Posted: 08/02/22 10:07am Link  |  Quote  |  Print  |  Notify Moderator

Carry a rag, stiff wire bent in loop, and tape measure on your walk. Can hook tape to wire, in grove of pin, to measure, if tape won't hold itself in the wind.

The rag is incase somebody greased their latch.

valhalla360

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Posted: 08/02/22 10:49am Link  |  Quote  |  Print  |  Notify Moderator

While a couple inches in front of the axle is the preferred, if you run the math, 2" behind the axle will have almost no impact on the forces involved. It's still going to be 99% of the pin weight on the rear axle.

Let's say, a 2000lb pin weight 2in ahead or behind the axle and 176in wheel base. Run the math and it adds or subtracts all of 23lb on the front axle. If it's behind, the 23lb goes onto the rear axle...Not enough to worry about.

This assumes the bed and ball are properly supported and tied into the frame.

The 78" diagonal is likely the stumbling point but it will depend. There is no standard distance and different pin boxes extend different distances forward.

As suggested, to take a measuring tape and see what some measurements are.

You will need to check the hitch height but with no bed sides to worry about, you can drop the 5er hitch to it's lowest set of bolt holes.


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rosewood1

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Posted: 08/02/22 10:59am Link  |  Quote  |  Print  |  Notify Moderator

i am on my second fifth wheel and my third flatbed. my first used the existing ball and i installed a gooseneck adapter. it worked great but my next is a mobile suite and i was leary of using the adapter with it due to the weight so i purchased a conventional hitch. it is a little nose high but i cannot lower the hitch or raise the pinbox any further. it was level until i added the more ryde pinbox. i really like the flatbed. easy acess to everything,durable,easy to touch up the appearance.downside is you have to be careful to strap everything down. never had clearance problems with bed but i could not open front compartment while hooked up for you weight, i would probably go with gooseneck adapter. just my opinion

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