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Flat Beds--COG Can Be A Problem!?

CG Center of Gravity Flat Beds Tundra FWC COG FWC Accident Stabiity Flatbed

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#11 ALLAN BRILL

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Posted 25 November 2019 - 03:06 PM

Many thanks for the thoughts and experiences...& well wishes!  I'm pouring over these issues, continuing to look for a workable low-CG solution for a non-DIY person that's affordable.  Any further ideas appreciated and will report any good finds!

 

BTW, the 2004 Tundra to my novice understanding has only a stock/light duty front anti-sway bar, and installing a rear one with all that's there including my Billsteine 1500s & air bags is an expensive custom job.  I've also been advised that the rear sway bar may be overkill with the airbags.

 

And thanks for the point about the problem with moving the camper back some inches for gas cans/bikes front storage, also  increasing instability.

 

Below are discussions of aluminum flat beds and CG from expedition portal.

 

Happy and safe travels!

 

Allan\

 

 

https://expeditionpo...d-trays.203882/

 

https://expeditionpo...options.169565/


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#12 Kolockum

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Posted 25 November 2019 - 03:09 PM

I also have spent a lot of time thinking about high ground clearance service bodies. You would probably have to have the bottom of the camper modified since the service body is narrower than the tires for the whole length of the bed but it would give you lots of storage.

 

Here is a link to a thread on Expedition Portal

https://expeditionpo...ce-body.191931/

 


Edited by Kolockum, 25 November 2019 - 03:51 PM.

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#13 ntsqd

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Posted 26 November 2019 - 02:41 AM

What I've been thinking is to move the batteries and waste tank(s) to the truck. The fresh water I'd keep in the camper to help keep it from freezing and I'd be looking to insulate the battery box.. The spare I'd move out from under the truck. I've pondered hanging it on the rear, but I've always liked the method that Rob Gray used on "Wothellizat". So upright in a support cradle on the pass side next to the frame between the rear tire & the back of the cab. Since stuff expands to fill the void placing the spare there reduces some of that void. In my mind's eye it would have an access door much like the cabinet that would be there were it a service bed, but be fully open on the bottom.

 

Allan, If the air springs have a common pressure line then they will not do much to control sway. They'd need to be plumbed independently.

 

From what I've seen while looking at them you have to be careful with service beds. Most are quite deep, or maybe said better, the top of their side boxes is usually though not always taller than a normal bed.

 


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Thom

Where does that road go?

#14 klahanie

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Posted 26 November 2019 - 02:48 AM

Allan, thanks for the follow up.

 

On reflection, it makes sense about the lack of a oem rear stabiliser bar. The mfr prob doesn't want one on there unless it would be a strong benefit for most owners (because of the application), or they demand it.

 

Because they are designed to reduce body roll, I like the idea of them and think it helps on our truck but could be hard to tell because ours also has extra stiff springs. I don't know much about air bags so can't comment on them.

 

I flipped through those links. Don't think I saw a flatbed with wheel housings/arches. Nor, from a quick scan, one constructed in a way that might be easily be altered to lower height. The base of our deck for eg is two large channel beams that sit ontop of the truck frame. They are 6" but could have been spec'd at 4" or 8" or something else any of which would have altered the deck height. I guess contacting some mfrs about your requirements could be a next step.

 

You mentioned the under camper platform on the previous camper. On the replacement camper is the bottom to overcab  dimension the same as on the old one ? If it is now smaller it would seem that the difference would  help toward the the flatbed height increase. You mentioned up to 6" - we can agree, that's a lot, especially after your experience (bad luck indeed).

 

I'm curious about your storage idea for extra fuel and bike. Just for fuel, how much front to back space will you need ? And the bikes, I can't get my head around that. Or are they foldable type ? Have you ruled out carrying them at the front or rear of the vehicle ?

 

Thom's (ntsqd) idea is an interesting one. [ON EDIT referring to post #4]. I'm thinking a small footprint, low riser frame (or flatbed) could allow for large, flexible storage space at the sides. I don't know the CA of the Tundra but wonder if it would be enough for fuel cans and/or bikes - if they were folders. Trick would be the finishing, and finding a fabricator ...


Edited by klahanie, 26 November 2019 - 02:51 AM.

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#15 ntsqd

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Posted 26 November 2019 - 02:04 PM

The Rule of Thumb in road racing is "The axle with the stiffest roll spring rate will have the least cornering traction." What this means is that to maintain the designed-in Understeer you have to increase the front sway-bar diameter when you add a rear sway-bar or increase the size of a rear sway-bar.

 

If you don't do this you will likely create a vehicle that has a stiffer rear roll spring rate than in the front. This means that the rear axle will try really hard to pass you on the outside of a turn! Obviously this is highly undesirable and could easily result in re-creating the picture in the first post of this thread.


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Thom

Where does that road go?

#16 Mighty Dodge Ram

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Posted 26 November 2019 - 04:17 PM

ntsqd: I assume that’s a “universal” axiom. If separately plumbed airbags are used in the rear this could stiffen roll rate and increase the tendency to “drift”?


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Richard
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#17 Vic Harder

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Posted 26 November 2019 - 05:53 PM

ntsqd: I assume that’s a “universal” axiom. If separately plumbed airbags are used in the rear this could stiffen roll rate and increase the tendency to “drift”?

yes.... any stiffer rear makes the tail happier to wag, as it were.   That said, I would not want my airbags linked, as that would hugely increase the amount of sway.  

 

The other factor to consider is how the weight of the camper increases traction at the rear.  Worst case, you have a 2 ton load in a 1/2 tone pickup and the front wheels are barely on the ground... no traction up front.  Then the back end is not going to come around first... instead, the truck would "plow" or understeer, around the corners.

 

I can see why truck manufacturers do not put in rear sway bars... most folks would be driving them empty, and they would be hugely tail-happy with rear sways.   If you do have a camper on there full time, a sway bar and/or separately plumbed air bags would provide useful rebalancing back towards the original unloaded handling characteristics.


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#18 Mighty Dodge Ram

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Posted 27 November 2019 - 04:05 PM

Interesting points Vic. I have the ‘02 2500 HD and it did not come with a rear sway bar, yet Dodges from the same era come with one installed. Different engineers with different design profiles I assume. 
 

Apologies for the hijack but good info nonetheless. 


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Richard
1996 Dodge Ram 1500 4x4, lightly lifted, ARB bumper/Warn winch, BFG AT/KO2, Snugtop shell. SOLD! But not forgotten!
2002 Chevy 2500HD XC LB 6.0L 4X4, Leer Hi-Rise shell, completely stock...for now!

#19 ALLAN BRILL

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Posted 02 December 2019 - 03:19 AM

What I've been thinking is to move the batteries and waste tank(s) to the truck. The fresh water I'd keep in the camper to help keep it from freezing and I'd be looking to insulate the battery box.. The spare I'd move out from under the truck. I've pondered hanging it on the rear, but I've always liked the method that Rob Gray used on "Wothellizat". So upright in a support cradle on the pass side next to the frame between the rear tire & the back of the cab. Since stuff expands to fill the void placing the spare there reduces some of that void. In my mind's eye it would have an access door much like the cabinet that would be there were it a service bed, but be fully open on the bottom.

 

Allan, If the air springs have a common pressure line then they will not do much to control sway. They'd need to be plumbed independently.

 

From what I've seen while looking at them you have to be careful with service beds. Most are quite deep, or maybe said better, the top of their side boxes is usually though not always taller than a normal bed.

Many thanks for the creative thinking!

I'm at a disadvantage as have neither the skill, knowledge or tools to do work myself...and not the bucks to pay others to do much either.  If I could find a reasonably priced (ie. not custom likely) FB that could set down to the current frame, not go over the tires, and therefore not raise the CG, it would be ideal.  But after many hours of research haven't come up with it...yet.  Boxes for the FWC would be about 22" high and fit under the overhang of the camper, providing increased stability.  The air springs are independently pressured, but not sure how that affects the ability to mitigate sway...any hints appreciated! 


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#20 ALLAN BRILL

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Posted 02 December 2019 - 03:33 AM

yes.... any stiffer rear makes the tail happier to wag, as it were.   That said, I would not want my airbags linked, as that would hugely increase the amount of sway.  

 

The other factor to consider is how the weight of the camper increases traction at the rear.  Worst case, you have a 2 ton load in a 1/2 tone pickup and the front wheels are barely on the ground... no traction up front.  Then the back end is not going to come around first... instead, the truck would "plow" or understeer, around the corners.

 

I can see why truck manufacturers do not put in rear sway bars... most folks would be driving them empty, and they would be hugely tail-happy with rear sways.   If you do have a camper on there full time, a sway bar and/or separately plumbed air bags would provide useful rebalancing back towards the original unloaded handling characteristics.

My FWC popup weighs only about 1000 pounds.   Likely to have camper on full time.  Can someone explain if "separately plumbed air bags" means the capacity to have different pressure in each bag?  Trying to understand the dynamics you guys are discussing.

And how does this make a difference in handling?  Sorry to be such a novice...

Allan

PS A guy I know has placed his FW camper on his truck with a 6" lift...he seems to have no qualms about CG!


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Also tagged with one or more of these keywords: CG, Center of Gravity, Flat Beds, Tundra, FWC, COG, FWC Accident, Stabiity, Flatbed

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