Gas mileage with tonneau cover?

[Bobb-o]

Just got a new tonneau cover for my truck and was wondering if i would get better gas mileage on the highway if it was rolled up at the back of the cab or rolled down and secured in place? What has everyone else's experience been? I know from watching Mythbusters that you get better gas mileage with your tailgate up, but what aboot a tonneau cover?

[IFallsRon]

Hard to know without a controlled experiment. I know that when my truck was newer and after I had purchased a fiberglass topper, my mpg increased or was more consistent on the highway.

[BigWadeS]

In my experience, unless you have a full size topper (up to the cab), leave the box open for better mileage. Then again, I got rid of my pick-up due to the regular poor mileage anyway.

[Eckie]

Hey Bobbo..

Can you explain the mythbuster theory of why one would get better mileage with the tailgate up? I've always thought I'd do better with it down, but have no evidence to back up my thoughts (it's just what I've always assumed), so I'm curious to hear another side...

[Fishin4Life]

I saw the same myth busters episode. It was a while ago, but I do remember being suppurised as heck when they gave the results...Anyone have the details on it?

[MuskieJunkie]

I can help, the tail gate down = worse, the tailgate off = better. I think people might be confusing the two. The reason is this, almost half the wind resistance on your truck comes from turbulence caused underneath the vehicle (this is why race cars have air-dams and ground effects), when you put the tail gate down you are extending this turbulent area. With the tailgate up the wind comes down the cab and hits the inside of the tailgate like a billboard. That is why if you have a cover or take the tailgate off you will have less wind resistance than if you leave it up, and much less resistance than with it down. To summarize, covered bed or off is the best, leaving it up is OK, and putting it down is the worst of the three.

[HOF#13]

I put a tonneau cover on my pick-up shortly after I bought it, and I noticed a little bit of improvement in mileage. It varies a bit, but it increased about 1 mile per gallon average.

[rundrave]

heres my interpretation:

a circular pillow of air forms behind the cab of the truck when the tailgate is up. This "separated bubble"/"locked vortex flow" keep the faster moving air from contacting the truck, and thus reduces drag. With the tailgate down, the bubble breaks down and is no longer able to keep the fast moving air out, increasing drag.

Its hard to explain, but its like when you have a pop bottle in the bed of your pickup. Going down the road it doesnt fly out it spins in this so called bubble of air.

In the mythbusters test both identical trucks had equal mileage, same tire pressure, and 30 gallons of gas. one drove with the tailgate up and the other had the tailgate down.

In the episode test they had to maintain the speed limit,

All acceleration must be done by cruise control,

No drafting ,

Windows up, A/C must be exactly the same in both cars

After 300 miles there didn't appear to be much difference in the gas consumed, but after 500 miles (tailgate down truck) ran out of gas. Tail gate up truck made it another 30 miles before he ran out of gas.

[huntingislife]

With the tailgate up, a rotating "bubble" of air forms inside the box. The majority of the oncoming air over the cab "rides" over this bubble and flows behind the vehicle. Driving with the tailgate down disrupts the bubble and results in worse gas mileage.

[huntingislife]

exactly rundrave, you posted while I was typing

[Fishin4Life]

Great explanations, very interesting!

But....what about the milleage with / without a topper or tonneau cover? Maybe we should send myth busters a note to check that out!

[BobT]

If the difference between tailgate down vs tailgate up results in only about a 1mpg change, is it possible that adding a topper may reduce drag but add weight and therefore the result is immeasurable? Would the addition of the topper create more drag as the rear of the vehicle is now more prone to creating a low pressure pocket? What about the added surface area on top of the topper? Does this add resistance to the flow of air? Would the addition of a tonneau cover be a better solution than a topper?

The mystery continues...

Bob

[Fishin4Life]

Bob you make me laugh LOL . The minute we think we have an answer, haha. Good questions

[Guest]

I get about a mile and a half per gallon better with a tonneau cover.

[united jigsticker]

My trailer brakes went out on my boat a few months ago.

I couldn't afford to repair them, so I attached a large parachute to my truck to help me slow down when I tow.

I am kinda lazy, so I just leave it on all the time now, and it makes the gas milage 5% better.

I also reduced to tire pressure to about 22 PSI in the rear and 24 up front (help support the extra engine weight) and that has helped alot too.

[Fishin4Life]

Quote:

---

My trailer brakes went out on my boat a few months ago.

I couldn't afford to repair them, so I attached a large parachute to my truck to help me slow down when I tow.

I am kinda lazy, so I just leave it on all the time now, and it makes the gas milage 5% better.

I also reduced to tire pressure to about 22 PSI in the rear and 24 up front (help support the extra engine weight) and that has helped alot too.

---

I'm sorry, but I have to ask, are you serious? If so explain, LOL. I picture a big ol parachute like on a drag car LMAO

[BigWadeS]

LMAOAW

[united jigsticker]

Yeah....

That was a....uh...what do they call them things....???

Oh...A joke...a spoof....a silly....a fun-fun....a tickler.

In modern world driving, they should have more then "City/Highway" milage ratings to reflect actual driving situations and conditions.

This vehicle earns the estimated milage as listed below:

• City: 14 mpg

• Highway: 19 mpg

• Freeway: (80 mph) 13 mpg

• Rush Hour: 6 mpg

• Friday Night with the Buddies: 5 mpg

• Taking Grandma to the Doctor: 25 mpg

• Ice Fishing on Upper Red Lake: 0 mpg

Yeah, that's what I think right there...

***Oh, and it's not actually a "parachute" per-say, but a couple pairs of under briefs off Aunt Betsie's clothesline will do the magic trick.

[Fishin4Life]

Thats what I thought, but then i read it twice and it sounded so serious. LMAO

Yeah yeah yeah, gullible written on the ceiling, blah de blah blah, hahahaha .

Love the gas milleage thing to, that was great.

[Pat K]

Ford's testing results according to a soon to be unemployed engineer at the ST. Paul Ford plant. He weasn't sure if it was 2500 or 5000 miles same truck was run, with all accessories pre-set.

Best to Worst: 1)Truck with topper level with top of cab.

A tie at 2)Truck with tail gate up.

Truck with toneau cover.

3)Truck with mesh straps for tail gate.

4)Truck with topper or camper extending above cab.

He didn't know about tail gate down but guessed it would fall between 3 and 4. He's an engineer in hydraulics not aerodynamics (sp?) but assume he knows more about it than me.

Pat K

[Valv]

My own experience, I gain 2mpg with a vinyl tonneau cover on my Dodge 3500 long box.

I truly hate the guts out of mine, it's the old fashion style snap on, but on long trips I recorded savings between 1 to 2 mpg.

Since then I snap it closed every time I travel except in the city or short trips.