Flat Beds--COG Can Be A Problem!?

[ALLAN BRILL]

Greetings Wandering Brothers & Sisters.

From my sad experience (see attached photo of my FWC after accident), I can say that even without the approximate 5" lift flat beds generally require above my 2004 Tundra 4WD Double Cab stock bed, COG can be a problem. My platform for the FWC raised the camper 3" above the sides of the bed unnecessarily, which I believe increased the COG height enough to make the swerve less controllable. I avoided a car swerving into my rig but couldn't control the resultant sway/instability. The oncoming, thundering 18-wheelers scared but avoided me despite the 3 blocked lanes!

I am considering a flat bed to replace the damaged stock one on my Tundra, so I can add boxes for storage & carry bikes/gas cans in front of my my current 2013 Hawk slide-in. The mass produced flat beds I've seen sit above the tires, and raise the COG between 3-6 inches above the stock beds depending on model & different estimates. As you can imagine, since I escaped the recent tip-over with little damage (though the camper was totaled and truck took substantial repair), I'm grateful and not feeling like risking anything like that in the future. BTW I've added a sway bar, heavier duty Bilsteine 1500 shocks, and airbags to assist with stability.

SOOOO...anyone have any experiences, leads, expertise or understanding about these issues? Have others you know of endured turn-overs as pictured below? I've been unable to find a mass produced or affordable custom flat bed that can actually anchor directly to the Tundra base & around the wheels, and thus keep the COG lower. I'm a newbie to these issues, so any tips or opinions much appreciated!

Allan

 

[klahanie]

Hello. Glad to read you were ok after that !

Question: Are you saying you didn't have a rear stabilizer bar on the truck before and if not is that a Tundra thing ?

If you are thinking to put bikes and fuel cans in front of the camper on the flat deck and then re positioning the camper rearward along with carrying more weight (stuff) in under deck storage boxes I don't see how that is compatible with, not wanting to risk anything like that in the future. That's not a criticism, just that I think all of those changes are going to reduce emergency handling.

On the flat deck, I'd expect it would be tough to find a stock one with wheel housings, esp for your vehicle size so a modification to a stock unit may be the answer. One thing with the "true", over the wheels flat deck is the underdeck boxes can be taller and therefore possibly carry more weight which does bring the cog down a bit (but adds to total weight). Anything you can relocate lower helps.

I haven't found a noticeable difference handling or tippy wise with our current flatdeck vs the previous F250 PU with the same camper but this newer vehicle is a much heavier and longer wb model. The higher camper position is offset somewhat by a 3-400 lb aux fuel tank between the frame rails, all the junk we carry in the under deck boxes and the relocating of some of the camper items like LPG and water storage.

That said, accidents can happen to anyone. Hopefully you've had your last.

One other thing, with a factory PU box repairs might be easier, in terms of insurance and repair shop. Repairs on custom ... maybe not.

 

[Wango]

When i began doing the leg-work for our present setup, i had some initial concerns regarding cog.
My friends have may flatbeds on their work trucks and i had been around them to see how loads were managed.
Our camper was built with the vast majority of the load in front of the rear tires. The outside boxes contain our house batteries, chains, fluids and recovery gear, again most of which riding in front of the tires.
The suspension work was all geared towards controlling sway as well as loads.
After many thousands of miles/trails i can say that for the most part, sway has been somewhat mitigated, but have still felt it at times, mostly off-camber, heavily rutted surfaces. Even as light as these campers are, comparing to other rigs. They can add sway.
We are looking into our next build(it's an addiction) and one thing we are seriously considering is a cab and chasis truck to start with, just to lower the bed height.
All of this being said, if i had to choose between a flatbed on a truck or a regular truck bed, i would take the flatbed 10 out of 10.
Good luck going forward, and very sorry about your accident. Thankfully your ok.
w

 

[ntsqd]

Every time I've pondered the design of a flat bed specifically for a camper I end up lowering the deck as low as it can go. Which creates wheel-wells in the deck, making it no longer flat. I'm OK with that because of what it gains me in reducing the COG. With good jacks the camper does not have to slide between the fender-wells, It can go over the top of them before being lowered into place.

Lately my thinking has been no bed at all. Just a platform that the camper sits on bolted directly to the frame. Included in the platform structure will be the anchor points. As I'll likely be working with a pick-up chassis that platform will bolt to where the bed bolted to. Only. Then I'll in-fill under the camper and around the rear tires with storage boxes.
At least, that's my current train of thought....

 

[ski3pin]

The few times I let myself dream of and design a new truck and camper for us, it is right in line with your thinking.

Every time I've pondered the design of a flat bed specifically for a camper I end up lowering the deck as low as it can go. Which creates wheel-wells in the deck, making it no longer flat. I'm OK with that because of what it gains me in reducing the COG. With good jacks the camper does not have to slide between the fender-wells, It can go over the top of them before being lowered into place.

Lately my thinking has been no bed at all. Just a platform that the camper sits on bolted directly to the frame. Included in the platform structure will be the anchor points. As I'll likely be working with a pick-up chassis that platform will bolt to where the bed bolted to. Only. Then I'll in-fill under the camper and around the rear tires with storage boxes.
At least, that's my current train of thought....

 

[Vic Harder]

The few times I let myself dream of and design a new truck and camper for us, it is right in line with your thinking.

+1

 

[JaSAn]

The few times I let myself dream of and design a new truck and camper for us, it is right in line with your thinking.

+2
Great minds think alike.

I'm thinking that when the wheel wells rust out on the Ram pickup box (a problem in Minnesota), I'll pull it and do ntsqd's design.
Should lower the CG as the batteries, propane tank, tools, recovery gear, et.al. will be lower (and outside the camper).

jim

 

[Durango1]

We are looking into our next build(it's an addiction) and one thing we are seriously considering is a cab and chasis truck to start with, just to lower the bed height.

Totally agree on looking into a cab and chassis, Wango. The design possibilities are greatly increased as long as you can live with lower trim options. For example, our 2018 Ram Chassis Cab (in the regular cab model) didn't come with the Laramie trim! BOO-HOO!

 

[Kolockum]

This has opened an interesting conversation. I have long dreamed about flatbeds but never liked the significant bed raise required to to achieve them due to the cost of COG. I keep coming back to a modified flatbed with wheel arches.

I have always thought that if I go for broke and make a flatbed then I would incorporate components such as water/grey water and propane tanks into the flat bed to lower COG and then have quick connects to attach them to the camper.

x2 glad you're ok.

 

[ALLAN BRILL]

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\

[SIZE=10.5pt] [/SIZE]
[SIZE=10.5pt]https://expeditionportal.com/forum/threads/looking-for-feedback-on-flatbed-trays.203882/[/SIZE]


[SIZE=10.5pt] [/SIZE]
[SIZE=10.5pt]https://expeditionportal.com/forum/threads/aluminum-flat-bed-options.169565/[/SIZE]

 

[ALLAN BRILL]

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\

[SIZE=10.5pt] [/SIZE]
[SIZE=10.5pt]https://expeditionportal.com/forum/threads/looking-for-feedback-on-flatbed-trays.203882/[/SIZE]


[SIZE=10.5pt] [/SIZE]
[SIZE=10.5pt]https://expeditionportal.com/forum/threads/aluminum-flat-bed-options.169565/[/SIZE]

 

[Kolockum]

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://expeditionportal.com/forum/threads/fwc-with-service-body.191931/

 

[ntsqd]

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.

 

[klahanie]

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 ...

 

[ntsqd]

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.

 

[Mighty Dodge Ram]

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”?

 

[Vic Harder]

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.

 

[Mighty Dodge Ram]

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.

 

[ALLAN BRILL]

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!

 

[ALLAN BRILL]

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!