Tonneau Covers VS MPG Performance

[Biggiehorn]

So I'm not currently in the market for a bed cover, but it is something that I have been looking into as I do plan on adding one down the road. In my research, I see the frequent MPG discussion brought up more often than not. I have read that some manufacturers claim increased MPG performance as high as 15% due to the reduced drag, while some first hand users state that the increased weight, styling, and material of the cover itself can actually rob you upwards of 10% or more. Expecting a 10% gain and finding a 10% loss could cause some serious pain and suffering to those die hard owners that stress over their mpg numbers lol.

I've read about the Mythbusters testing and also some general product reviews, but has anyone in our group specifically done any in-depth testing with bed covers and our Ram trucks? Obviously dozens of potential variables come into play here such as location, driving habits, engine platform, tire pressure, other modifications, weight/material, etc. that may make it tough to measure results in real world testing, but I was just curious what covers you all are using and what impact have you seen on your mpg from them, if any. I'm sure this has been discussed in here before, but figured I'd ask as it seems to be a pretty common topic across the board with all variations of bed covers. Since it is advertised so heavily, let's discuss it.

Let me be the first to say, I won't lose any sleep over this lol. This is more of a general curiosity question than anything.

 

[834k3r]

There are actually two Mythbusters tests for this one. The first (which I remember better than the second) seemed to point out no tonneau cover is better than the other options, but they revisited the testing (second episode) which (if I remember the episode correctly) pointed to tonneau covers being better for MPG than no cover or a canopy.

I'm interested in this as well, so I'll follow this thread.

 

[vincentw56]

I noticed no difference with and without. Of course your mileage may vary. See what I did there.

 

[Biggiehorn]

There are actually two Mythbusters tests for this one. The first (which I remember better than the second) seemed to point out no tonneau cover is better than the other options, but they revisited the testing (second episode) which (if I remember the episode correctly) pointed to tonneau covers being better for MPG than no cover or a canopy.

I'm interested in this as well, so I'll follow this thread.

I didn't know they did more than one test. I'd like to go back and look into these. In my reading, I came across several that claimed the original test was basically invalidated for several factors (those which I cannot remember).

I noticed no difference with and without. Of course your mileage may vary. See what I did there.

Thanks for playing! That is always a good go to answer! lol

 

[834k3r]

I didn't know they did more than one test. I'd like to go back and look into these. In my reading, I came across several that claimed the original test was basically invalidated for several factors (those which I cannot remember).

That jives with my recollection. The second episode they mention having to revisit it, but my senile brain can't remember the specifics.

I'd really be interested to see if anyone's done a wind tunnel test on the three configurations. I'll have to webcrawl for that one; if I find anything I'll share here.

 

[Trooper4]

Mythbusters study MPG savings of various bed modifications

www.dakota-durango.com

Do tonneau covers save gas? - Peragon®

It’s all about drag. Generally, anything that reduces the drag on a vehicle while it’s going down the road will improve its fuel efficiency. Does a bed cover improve gas mileage? It does if it reduces drag.

www.peragon.com

From the Mythbusters:

Tailgate Up or Down Revisited: Mesh tailgate, hardcover, tailgate removal​

See: Tailgate Up or Down

For the original myth they did a driving test and a water vortex test, both of which showed that you save more gas with the tailgate up. Their viewers suggested that they test three new conditions:

• Hardroof cover over pickup bed
• Mesh tailgate
• Remove the entire tailgate

They had a much simpler test setup this time. They had an electronic flowmeter hooked into fuel line of Jamie's pickup. Adam: "For anyone out there that wants to e-mail telling me that we screwed up this test, we have already calibrated this thing, to this car. So it's going to be perfect!" They drove the pickup truck up and down the stretch of 101 around Candlestick and the Cow Palace.

• Tailgate down: 5.2 gallons/hr @ 55mph. 1.2 gallons/hr @ 25.
• Tailgate up: 5.0 gallons/hr @ 55mph. No reading for 25mph given, but tailgate up was once again confirmed as more efficient.
• Hardcover over pickup bed: 5.0 gallons/hr @ 55mph. 1.2 gallons/hr @25mph
• Tailgate mesh: 5% more efficient
• Tailgate removed: about the same as tailgate up and hardcover

Mesh was most efficient by 5%

 

[Biggiehorn]

I'd really be interested to see if anyone's done a wind tunnel test on the three configurations. I'll have to webcrawl for that one; if I find anything I'll share here.

I'll do some digging as well. From the general web searches I've done, results seem to be all over the place, but that wasn't limited to any specific vehicle. I'm really interested in what results people are seeing with our trucks. Not positive how much variation there is from brand to brand, but obviously the aerodynamics of the actual vehicle will come into play as well.

 

[Biggiehorn]

Mythbusters study MPG savings of various bed modifications

www.dakota-durango.com

Do tonneau covers save gas? - Peragon®

It’s all about drag. Generally, anything that reduces the drag on a vehicle while it’s going down the road will improve its fuel efficiency. Does a bed cover improve gas mileage? It does if it reduces drag.

www.peragon.com

From the Mythbusters:

Tailgate Up or Down Revisited: Mesh tailgate, hardcover, tailgate removal​

See: Tailgate Up or Down

For the original myth they did a driving test and a water vortex test, both of which showed that you save more gas with the tailgate up. Their viewers suggested that they test three new conditions:

• Hardroof cover over pickup bed
• Mesh tailgate
• Remove the entire tailgate

They had a much simpler test setup this time. They had an electronic flowmeter hooked into fuel line of Jamie's pickup. Adam: "For anyone out there that wants to e-mail telling me that we screwed up this test, we have already calibrated this thing, to this car. So it's going to be perfect!" They drove the pickup truck up and down the stretch of 101 around Candlestick and the Cow Palace.

• Tailgate down: 5.2 gallons/hr @ 55mph. 1.2 gallons/hr @ 25.
• Tailgate up: 5.0 gallons/hr @ 55mph. No reading for 25mph given, but tailgate up was once again confirmed as more efficient.
• Hardcover over pickup bed: 5.0 gallons/hr @ 55mph. 1.2 gallons/hr @25mph
• Tailgate mesh: 5% more efficient
• Tailgate removed: about the same as tailgate up and hardcover

Mesh was most efficient by 5%

Good info here! I was actually on the Peragon page not long ago, but I didn't see the specific page that you linked. I see they referenced a test that SEMA did and linked their wind tunnel paper. I'm sure that will be an interesting read as well.

 

[834k3r]

Mythbusters study MPG savings of various bed modifications

www.dakota-durango.com

Do tonneau covers save gas? - Peragon®

It’s all about drag. Generally, anything that reduces the drag on a vehicle while it’s going down the road will improve its fuel efficiency. Does a bed cover improve gas mileage? It does if it reduces drag.

www.peragon.com

From the Mythbusters:

Tailgate Up or Down Revisited: Mesh tailgate, hardcover, tailgate removal​

See: Tailgate Up or Down

For the original myth they did a driving test and a water vortex test, both of which showed that you save more gas with the tailgate up. Their viewers suggested that they test three new conditions:

• Hardroof cover over pickup bed
• Mesh tailgate
• Remove the entire tailgate

They had a much simpler test setup this time. They had an electronic flowmeter hooked into fuel line of Jamie's pickup. Adam: "For anyone out there that wants to e-mail telling me that we screwed up this test, we have already calibrated this thing, to this car. So it's going to be perfect!" They drove the pickup truck up and down the stretch of 101 around Candlestick and the Cow Palace.

• Tailgate down: 5.2 gallons/hr @ 55mph. 1.2 gallons/hr @ 25.
• Tailgate up: 5.0 gallons/hr @ 55mph. No reading for 25mph given, but tailgate up was once again confirmed as more efficient.
• Hardcover over pickup bed: 5.0 gallons/hr @ 55mph. 1.2 gallons/hr @25mph
• Tailgate mesh: 5% more efficient
• Tailgate removed: about the same as tailgate up and hardcover

Mesh was most efficient by 5%

Now I remember more: I couldn't understand then (and I'm still baffled by it now) why a mesh tailgate would be better than tailgate removed or down. Laminar flow? Inadvertent vortex generator?

 

[Biggiehorn]

Now I remember more: I couldn't understand then (and I'm still baffled by it now) why a mesh tailgate would be better than tailgate removed or down. Laminar flow? Inadvertent vortex generator?

That one is beyond me as well . I thought I read the post wrong initially and just went back and reread it. That is really interesting lol.

 

[vincentw56]

Now I remember more: I couldn't understand then (and I'm still baffled by it now) why a mesh tailgate would be better than tailgate removed or down. Laminar flow? Inadvertent vortex generator?

I believe they explained that because of the way the air swirls in the bed, it creates a cushion that moves more air over the top of the tailgate. The mesh lets air through, but still creates that cushion in the bed.

 

[834k3r]

I believe they explained that because of the way the air swirls in the bed, it creates a cushion that moves more air over the top of the tailgate. The mesh lets air through, but still creates that cushion in the bed.

Guess I'll have to re-watch the video myself. It would've been really sweet had they had access to a wind tunnel to see the air behavior in and exiting the bed.

 

[MurphBigHorn]

I have no change in MPG with before and after the cover.

Now after installing my fx muffler I noticed a little decrease. It’s ether because I’m harder on the throttle or Because I started todo the mds lockout.

 

[Whoa_Ram]

I didn't notice a MPG change either. Like MurphBigHorn said, I did notice a decrease when I installed my Borla muffler though.

 

[Biggiehorn]

Now after installing my fx muffler I noticed a little decrease. It’s ether because I’m harder on the throttle or Because I started todo the mds lockout.

I did notice a decrease when I installed my Borla muffler though.

Think I’m starting to see a trend here. Noted! I haven’t done an exhaust on my truck yet, but at least I have some good concrete data now to help me predict what will happen when I do!

 

[Shots]

I've done "testing" with covers and without. By testing I mean I've calculated/logged mileage on my Ram before buying covers and continued after installing them. This "testing" has been on multiple Rams with various cab and bed configurations with various engines (4.7L and 5.7L). It may also be worth noting that I am an engineer (Mechanical, not Automotive so take it for what it's worth).
I've had pretty much every iteration of tonneau cover over the years, including vinyl, aluminum roll top, solid hinge, tri-fold (aluminum and composite) and different design/manufacturer of most of them. I've had very little difference in fuel efficiency which was closer to 5% on the best, rather than the 15% they may claim.

Even if you could reach 15% though, how much do you have to drive to recoup the cost of a cover?

Calculating the lofty, and personally unmet, estimate of 15%.
Lets figure the average mpg of 18 for the 5.7L (15 city / 21 hwy per the window sticker).
If you drive 500 miles, you'll burn 27.77 gallons of gas.
A 15% increase from a tonneau results in 20.70 mpg. Over 500 miles you'll burn 24.15 gallons of gas.
You've saved 3.62 gallons over 500 miles.
At the current average mid-grade fuel cost of $3.14 per gallon, you'll save $11.36 for every 500 miles you drive.
With tonneau covers ranging from $200 for an affordable vinyl cover to $1100 for a solid fold like the Bakflip MX4 you've got a wide range of cost to recover.
The mileage required will be from 8,802 miles to 48,415 depending on the cost of the cover assuming you get the unverified 15% savings.

If you take my real world results of roughly 5% that distance to recoup the cost goes up because the savings goes down.
To do it all again for 5%:
If you drive 500 miles, you'll burn 27.77 gallons of gas.
A 5% increase from a tonneau results in 18.9 mpg. Over 500 miles you'll burn 26.45 gallons of gas.
You've saved 1.32 gallons over 500 miles.
At the current average mid-grade fuel cost of $3.14 per gallon, you'll save $4.14 for every 500 miles you drive.
The mileage required will be from 24,154 miles to 132,850 mile, using real world savings.

In short, buy the cover because you want a cover not to save money. It's no economically beneficial to buy it for the fuel savings. Even at the lofty estimate of 15% you would have to drive 2-4 years before you start seeing a savings (using 12K miles per year average).

[to calculate the distance required for a specific cover, divide the cost of the cover by the savings ($11.36 for 15% or $4.14 for 5%), then multiply that result by the 500 miles required to save that much fuel]

 

[RebelWraith]

Wind tunnel testing of the fifth gen Ram. This shows why adding a tonneau cover will not help with fuel mileage and the added weight will actually hurt gas mileage fractionally.

 

[Shots]

Wind tunnel testing of the fifth gen Ram. This shows why adding a tonneau cover will not help with fuel mileage and the added weight will actually hurt gas mileage fractionally.
View attachment 104173

Good visual reference, and on a very small scale I suppose the weight of a cover could matter. Although I doubt there'd be an appreciable difference, since they're pretty light comparatively speaking. If the truck's efficiency were that sensitive you'd notice the difference of adding a single passenger which probably weighs more than a typical cover.

 

[Shots]

If I'm reading that ticker correctly in the background the test is being done at 20.2 mph (32.5 kph). I wonder how much, if at all, the flow changes at highway speed.

 

[RebelWraith]

Good visual reference, and I on a very small scale I suppose the weight of a cover could matter. Although I doubt there'd be an appreciable difference, since they're pretty light comparatively speaking. If the truck's efficiency were that sensitive you'd notice the difference of adding a single passenger which probably weighs more than a typical cover.

Precisely why I said fractionally. It would be about the same as having a child sit in your truck.