Tonneaus and mpg

[RangerGress]

I've been poking around the idea of getting a tonneau or maybe a cap. I looked around for some articles on mpg. Didn't find anything on mpg and caps, but there's a fair amount of info ot there re. mpg and tonneaus.

Bottom line up front. Tonneaus good, putting the tailgate bed down bad.

The 1.8% better mpg # is kind of bogus because it's at 48mpg. Aero drag goes up by the cube of velocity so the mpg difference should be a lot more at freeway speeds. It would have been better to give us a number for 70mph (maybe 10% better?) and then just tell us that around town it won't matter.


GMC Pickups 101: Busting Myths of Truck Aerodynamics

Century Fiberglass, Inc. | Fuel Savings

 

[salibas007]

I did notice an increase in mpg's after putting on the tonneau cover. I can't say exactly how much, but it did get better.

If fuel economy is of concern, I don't think the wisest choice is to get a full size pickup with a hemi. But that's just my opinion. I guess if one needs it for work, they don't really have a choice.


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[jbr]

I put on a bakflip Fibermax.. I didn't see any improvement. But I really bought it for a dry, locked bed not for mpg.

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[NYCruiser]

The MPG increase from a tonneau cover is BS. I think it was even tested and debunked by Mythbusters on one episode. Anytime I see MPG savings advertised for a tonneau cover I find it insulting. Makes me wonder what else the manufacturer is BS'ing about.

 

[Arctic-Rodz]

i didnt see any increase with mine, then again that wasnt the purpose for me getting one.

i got it because when the wife and i go out of town with our family, theres no way our luggage is going in the back seats. having the tonneu is awesome to use the bed as a weather sealed trunk.

purpose served.

 

[RangerGress]

The MPG increase from a tonneau cover is BS. I think it was even tested and debunked by Mythbusters on one episode. Anytime I see MPG savings advertised for a tonneau cover I find it insulting. Makes me wonder what else the manufacturer is BS'ing about.

You are saying the mpg increase is BS based on what? Simply an episode of Mythbusters? It seemed to me like the studies were reasonably carefully done. Surely a windtunnel is a more rigorous test then a couple guys driving trucks down a road for a while.

 

[bouf0010]

I call bs on the tonneau cover increasing mpg as well - if it were true guys would be running them at the track

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[Cruizer]

I'll tell you from experience in a place with lots of flat fields, a tonneau does decrease wind drag. I can tell a difference in MPG based on a windy day and a non-windy day. I also know that if my tonneau is off, I get pushed around by wind more than when it's on. I haven't tried an actual comparison on MPG, but based on the difference in wind pushing on my truck with it on or off, I can see it making a difference at state route and highway speeds.

 

[Cruizer]

Nah, it doesn't make a difference. That's why these trucks beds are flat on top.

 

[WhiteExpress]

There are a lot of variables that would decide if you'd see an MPG improvement from a bed cover.

A blanket statement does not do this justice.

As a generalized statement, the longer the bed, the more net positive effect a bed cover will have. (IE 8' bed would see more improvement over a 6.5 or 5.5' bed)

The trick with a bed cover is if it really helps reduce the trailing wake.
Most short beds are barely long enough to catch and smooth the disturbed air from the top of the cab. Hence the extended tailgates "lips". Still not ideal.

 

[jsl6v8]

Nah, it doesn't make a difference. That's why these trucks beds are flat on top.

My understanding on why the tonneau covers doesn't give you better MPG is because the air comes over the cab and slams down into the tonneau cover, which would give those rear tires a better grip, essentially a far less effective sand bag in the back of the truck. My understanding is that the best MPG is with no tonneau cover and tail gate up as it creates a pocket of air in the bed for the wind to run over making your truck more aerodynamic. Granted I run a tonneau cover, came with my truck as the HFE model. Now if you look at the brochures from 2013 they actually claimed that you received .1% increase in fuel efficiency, thats what RAM advertised as the increase with their cover. So you are looking at what on yalls V8s .1 MAYBE going down a mountain .2 mpg increase.

 

[Cruizer]

All I know for sure, a Vararam is not good for MPG, lol. It might be if you weren't so tempted to stomp all over the skinny pedal.

 

[NYCruiser]

I think that even if they reduce drag at sub 150mph speeds, it will be so slight that one good open throttle highway merge will negate the entire benefit from an entire tank of fuel.
Get a tonneau cause its useful to you and like it. Not for alleged fuel savings.
It would take 50 years to recoup the cost of it in fuel savings.

 

[Cruizer]

^^ That's true. I have mine because I put stuff in the bed that I don't want to get wet. That and I like how it looks when it's all shiny, lol.

 

[Sparkyy]

My truck came with a tonneau cover and it's great to have a 6 1/2 foot locking tailgate for those rare times I have to haul crap around, plus comes off easily.

Mythbusters did debunk this myth and I think real world tests prove more effective then a wind tunnel that has it coming head on.

Someone posted earlier the best is open bed but closed tailgate to have the air swirl in the bed.

Tonneaus just make life easy to not have to keep anything in the cab that isn't needed, not for .00001 MPG increase.

 

[Exhausted]

yep, buy it for the fuction of a bedcover not the mpg, never happens

 

[charonblk07]

To add more discussion to this thread

Tailgate Up, Tailgate Down Revisited | Medium Duty Work Truck Info

Nah, it doesn't make a difference. That's why these trucks beds are flat on top.

Those trucks are also a one piece composite body, to simplify the design they don't design a bed into them. You'll notice the air deflectors on the 'tailgate', they're positioned perfectly to catch the stream of air that comes off the cab and push the back end down, which is more important for the truck's handling at the speeds they drive at.


The length of the 'bed' and the location of the 'tailgate' is a more important design factor than if the bed is higher or not. In trucks with beds, you WANT your tailgate up because it generates a rolling vortex in the box and pushes the main air flow over the bed and reduces drag behind the cab, this happens to a much smaller degree with a hard tonneau cover but is less affected by a soft cover that will deflect and allow a larger rolling vortex.

If you want to increase MPGs in a truck, every thing you need to do should be geared towards that end, lower rolling resistant tires, smaller mirrors, front air splitters, remove the bug deflector, decrease overall weight, things like that, you might even pick up 0.5mpg with it all.

 

[Ocelot]

There really isn't any bolt on item out there that will save more gas then it cost to buy. Chrysler, Ford, Chevy, would love to have some cheap gizmo that they could add and claim an additional couple miles per gallon.

The number one way to save gas in any truck or car is to ease up on the skinny pedal.

Ray

 

[NYCruiser]

The wind tunnel tests that I've read were done a while ago on 2006 or so model trucks.
I'm not sure how the newer aerodynamic trucks like the 4th gens would compare.
The wind tunnel tests did show some slight decrease in wind drag with a tonneau (fiberglass ones better than vinyl and aluminum/vinyl for some reason), and then they used math to calculate that into an MPG savings.
The problem is that the math doesn't take into account the real life factors such as adding the weight of the cover to the truck.
Even still, the calculated savings were nowhere near the "10%" I've seen manufacturers advertise.
Here's a link to one:
Sema.Org

Although Ram brags that adding their wheel-to-wheel steps on the '14's bought them something like .7 MPG…LOL

 

[The Crow 1994]

I have a BakFlip VP on my '13 Big Horn. I bought it to keep stuff I put in the bed of the truck dry and I love the way it looks. I don't think it does anything to add to the MPG's of my truck.

Here's an example of why I don't think it matters on way or the other.

Ram 1500 picture # 86 of 99, Technical image, MY 2013, 800x600