Flat bed Fuel economy costs?

[Robbie Antonosn]

I am considering adding a flat bed or box style bed to my truck for my camper. I personally like the Idea of some of the work box style of beds for storage. I am considering Aluminum over steel for weight saving.
Since this spoils the Air flow around the Brick of a body, there has to be some Fuel economy costs.
With my camper on my current short bed truck. I do know the slower I go, the better fuel economy I will get to a point. Yes, Maybe I should not worry about it, and just get what I want. But I like to work out ideas in advance to consider the options. I figure Steel will cost me more in fuel ecomany over Aluminum(weight being the primary concern).
Also, I still travel a lot with out the camper, and want to have an idea of the penalty of the different bed styles. So please share any experience with me.
Thanks in advance for Sharing experiences.

 

[slowmover]

Aero penalty is severe. I would start at 3-4/MPG off the annual average. (You’ll have to know what that is).

Reducing it is keeping headache rack no taller than cab, and bed width no wider than same. Under-bed aero help via “skirting” would be needed. I’ve seen this bed (without skirts, just boxes) several times while on the road.

IMO, the penalty will pay for a nice utility trailer in only a few years.

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[Robbie Antonosn]

Thanks for the Response Slowmover.
I see lots of people looking, but no other commenting.
I did see a 2 gen 3500 with a beat up supper short flat bed behind the cab the other day. Nice couple, the young man behind the wheel stated he only
lost about 1/2 to 1 mile per gallon wiht the bed. He did have a manual transmission behind his 2004.5. Was happy to have added his flat bed, and would no
go back to a regular bed. I did not really ask much on how he uses it, He did tell me it only had like 75,000 mile on a failry nice looking truck wiht the
well used flat bed.

 

[Diesel85]

For my next truck, I wouldn't put out of the cards to do a CC3500 (or higher depending on the deal) with a simple aluminum flatbed.

I'm just fearing I won't like it or it won't suit my needs versus a regular pickup bed.

Never really thought about fuel economy.

 

[mwilson]

There may be a penalty, but I can’t imagine it’s significant…

Just for a benchmark my 3500 C&C gives 15 to 16 mpg when empty…which I’m quite happy with.

And here is something to consider…you can reach stuff on the body without climbing on something.

 

[Diesel85]

There may be a penalty, but I can’t imagine it’s significant…

Just for a benchmark my 3500 C&C gives 15 to 16 mpg when empty…which I’m quite happy with.

And here is something to consider…you can reach stuff on the body without climbing on something.

Another reason I like flatbeds is the fact that they are more durable than regular truck beds these days. Ask me that 15 years ago, eh... kind of a different story.

Along with easier side access (unless you install toolboxes) to the vehicle itself for servicing.

Also some of the perks like the "commercial" menu on the CC models that isn't included in the regular 2500/3500 to change even more settings. Maybe that'll change in 2025 and be across 2500 and up... who knows.

Fellow at work has a '18 CC 5500 Cummins with a Knapheide aluminum flatbed. Has a nice single toolbox behind the headache rack. Looks clean and sharp.

 

[slowmover]

A work truck doesn’t go far, it’s a wash. Bumping around pasture and some runs to Tractor Supply and the feed house. Dairy Queen. Proportion of highway traffic ngine hours (not miles) is low.

High-speed, steady state: it’s like hauling a 11x9 squared box. That drop from cab roof to bed creates a huge vacuum.

Here’s an ideal aero shape superimposed over a Dodge. That’s the shape needed. Don’t get too far from it, is the idea.

Flatbed has to pay for itself in increased work efficiency, ideally. Then add annual MPG penalty to that payout. Will possibly double it’s purchase price. And continue as a penalty since gallons-consumed is an engine life marker, not just odometer miles.

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[Ozymandias]

That's how the trucks are designed since 3rd Gen, to keep the airflow above the tailgate.

 

[mwilson]

I don’t know if it’s really that big of an issue. I liken it to running around with the tailgate down.

My headboard just barely rises above the cab so that’s not an issue. Possibly the air going underneath and fetching up against the rear panel could create some drag.. if so maybe an enclosed CM body would be better drag wise?

Not arguing, just pondering out loud..

 

[mwilson]

So took a few pictures just now..

Headboard height relative to the cab..

 

[mwilson]

Width beyond the cab..

 

[mwilson]

Air could create turbulance in the open area above and behind the tires…

Without any toolboxes it would be worse..I think.

 

[slowmover]

I don’t know if it’s really that big of an issue. I liken it to running around with the tailgate down.

My headboard just barely rises above the cab so that’s not an issue. Possibly the air going underneath and fetching up against the rear panel could create some drag.. if so maybe an enclosed CM body would be better drag wise?

Not arguing, just pondering out loud..

Bed sides matter. Airflow attachment.

A half-inch above cab roof is a penalty.
Think: Lifetime of the truck.

It’s a measurable difference to tape over the cab/bed gap. Then bumper edges. Etc.

Airliners shave rivets flush. Got away from that to use adhesive-bonded panels.

The little stuff adds up. The BIG stuff is like taking a 50-HP hit to the power.

 

[slowmover]

Width beyond the cab..

View attachment 140328


View attachment 140329

Ironically step rails act as skirts.

Boxes help. Cover the gaps. But can’t do much with empty bed or flow exit at tail.

The curvature and attachment makes these skirts a thing of beauty. This pic doesn’t do it justice (Gemini Transport):

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[mwilson]

All good points!

 

[Diesel85]

Looking at the diagram that @slowmover showed above, what does a full tonneau cover do? Does it help or negate the airflow?

I'm making an educated guess that it does.

 

[slowmover]

Let’s say you used a common blue tarp to create a sloped run to near bed rear edge. Nothing underneath.

You ain’t gonna make it to Portsmouth, NH it stays together.

The wind forces behind a semi-trailer are flat unreal.

 

[slowmover]

Looking at the diagram that @slowmover showed above, what does a full tonneau cover do? Does it help or negate the airflow?

I'm making an educated guess that it does.

Helps.

But the real trick is to take some plywood to cover the bed and starting from the tailgate, first attempt should go halfway to cab. Open space behind cab into bed.

Equal pressure both sides of tailgate.

Get out the manometer set. Shorten as needed.

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[slowmover]

Cab height bed topper is almost a wash. Depends on wind direction and severity (increase in side sail area).

However, with the Silver Streak in tow, it “helps” with that 5’ gap from tailgate to trailer bow.

Ideal vehicle gap is 30” or less.

Heres a highway ideal (longer = better) and taper from vertical & horizontal.

About 28-30/MPG with Coyote V8, IIRC. (55-58/MPH).

Cant do much with flatbed. Leverage afforded means a significant fuel penalty. Work truck.

I used one in oilfield hotshot. No one gave a flip about FE. Get there yesterday was SOP. ‘08 Deleted DRW 6.7 & G56 it was funnest road vehicle since high compression 440 in a big Dodge.

Strap down a 60# wood crate 1x2x1 and haul tail.

That said, I nearly ran out of fuel one day after re-filling in Laredo deadheaded to Corpus Christi 150-miles away. Speed limit (70). 45-50/MPH headwinds crossing 3/4 bow. Maybe 4-MPG.

Mine does 22 @ 70 with no headwind or heavy traffic. 20, to plan. That day I’d have stayed in double digits, barely (at 65).

.

 

[Diesel85]

View attachment 140333

Cab height bed topper is almost a wash. Depends on wind direction and severity (increase in side sail area).

However, with the Silver Streak in tow, it “helps” with that 5’ gap from tailgate to trailer bow.

Ideal vehicle gap is 30” or less.

Heres a highway ideal (longer = better) and taper from vertical & horizontal.

About 28-30/MPG with Coyote V8, IIRC. (55-58/MPH).

View attachment 140334

Cant do much with flatbed. Leverage afforded means a significant fuel penalty. Work truck.

I used one in oilfield hotshot. No one gave a flip about FE. Get there yesterday was SOP. ‘08 Deleted DRW 6.7 & G56 it was funnest road vehicle since high compression 440 in a big Dodge.

Strap down a 60# wood crate 1x2x1 and haul tail.

That said, I nearly ran out of fuel one day after re-filling in Laredo deadheaded to Corpus Christi 150-miles away. Speed limit (70). 45-50/MPH headwinds crossing 3/4 bow. Maybe 4-MPG.

Mine does 22 @ 70 with no headwind or heavy traffic. 20, to plan. That day I’d have stayed in double digits, barely (at 65).

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That would be a neat trick to try with my EcoD with that sloped topper. See if I can do better than 33 mpg during the summer time.