Phil, I don't know which sentence you were referring to. Are you saying that Mythbusters "proved" that having the gate up on an 8-foot bed decreases aerodynamic drag?

Or, are you saying that the "sloped" bed box increases drag?

In either case, I doubt very much that Mythbusters put these things into a wind tunnel where they could get a precise drag measurement.

- Jack

 

A screw it... Tailgate up, windows down, A/C on at 90 MPH while rolling on 38"s. Who needs fuel economy anyway???

 

having your tailgate down does not increase fuel economy,in some states it's illegal for it to be down as well as missing

 

Cool - I thought maybe that was the part you were talking about. What made me say it might be better down was the bed length. An eight foot bed, and possibly a low cab height could combine to add drag with the gate up. However, I suspect the effect either way is minimal.

I didn't know it was illegal to have the gate down in some states. Does this mean you can't use a bed extender in those places? Sounds like a "well-meaning" law that's possibly gone too far.

Bill's probably got the right idea though, except he forgot to lockout the overdrive.

- Jack

 

I agree a wind tunnel is the best way to do these tests, there's just too many variables for you or me to say something does or doesn't work. However I can say that on 3 separate occasions, driving to Atlanta and back, I averaged 43-47 extra miles to the tank with the tailgate DOWN on my SCAB with a 6' bed. I'll drop it on long highway trips, but could be "luck" that I got those extra miles.

 

Good thread.

 

I saw the "Mythbusters" thing where they said it didn't make any difference. I don't know what to believe there, but I think the bed cover theory is probably right. Nascar trucks have a flat surface on top of their mythical beds, and I doubt they do that for nothing. Money is on the line, they have wind tunnels, and I believe the hard bed covers probably reduce drag a good deal. Problem is, you don't have a real bed anymore, just a big trunk. But a lot of people these days don't use the bed anyway, and it would probably boost their mileage a good bit.

 

although they do not look as nice on the truck, you can buy the Aluminum roll up tonneau covers so that you can still have full use of you bed when you need it. personally if i were to buy one, that is what i could get. everything else is just so unconventional

 

If you drive behind (do any of you in this forum drive behind anything?) a pickup with an open bed and the tailgate up, have you noticed that if there's a piece of paper in the bed, that it just seems to "float" up and then go back down - never blowing out? What you're seeing there is a "stagnation point". The air in the bed is essentially just "locked" in there and is moving right along with the truck. The 75+ mph (if you're going that fast) airflow is deflected up over the cab and can't really make it down to the tailgate in time to hit it (to cause drag, or blow anything out). So, having the gate up or down makes little difference.

There's a bit of turbulence in the bed, that's why you see the paper blowing up and down, and that is an indicator of drag.

A smooth tonneau cover will reduce the "stagnation area" behind the cab and should decrease drag. It effectively "streamlines" the airflow behind the cab somewhat.

A cap on the bed that is no higher than the cab eliminates the stagnation point in the bed but moves it all to the rear of the truck. Essentially, a cap creates a BIG vacuum (and turbulent area) behind the truck that is formed when all the airflow that moves past the truck has to "suck" in and "rejoin". This probably puts you back to the same situation as having an open bed.

So, a "racing truck" will have a bed cover - no higher than the cab. But, I'd be willing to bet money that a "streamlined cover" that started at the top of the cab (sort of like the helmets bicycle racers wear) would give even better results. Ideally, it should come to a "point" at the rear. This would look goofy as hell, and who would want to drive something like that?

- Jack

 

I'm still wondering about that MythBuster with the mustache.

 

I like those. I've had the vinyl covers several times and I always noticed that on the highway the front part of the cover is pushed down and the back part is lifted up by the airflow. Don't know what to think of that, but there it is.
I would like one of the hard covers, but I am always afraid I will be off somewhere away from home and run in to a killer deal on a refrigerator or something. And a bigger problem is those covers cost almost as much as my truck.

 

Aren't there already a bunch of threads on tonneau covers?

 

I have an 8' bed with a soft snap on toneau cover and it's just the opposite. In fact I had to add a bow 18" in front of the tailgate to keep the air from pushing it down so far! The front lifts up. And it fits tight, too. You can't tell me that all that air slamming into the closed tailgate doesn't make a lot of drag. The air may well go over the tailgate on a 6' bed, the location my cover gets pushed down would indicate that.

 

You're right. My memory failed me again. Up in front and down in back. I don't remember any significant MPG increase, certainly not like I get with synthetic oil over dino oil. And I've heard the benefit of a hard cover is offset by the added weight.
All things considered, I think the posters best chance for increased mileage is driving habits. Nothing else can deliver as much. Second is synthetic oil, but I think he is already using a synthetic blend.

 

It's not worth it to waste your money on a product that ONLY provides economy, without any performance gains.

The factory PCMs are very powerful pieces of equipment, the OEMs spend millions of dollars engineering them.

It's possible to have performance when you put your foot to the floor, and economy while you are just cruising.

My performance tunes don't hurt mileage one bit while cruising without a trailer, there is no sacrifice or trade off when it comes to performance vs mileage.

And the mileage tunes I make can improve MPG while cruising normal or while towing, and the power will still be there when you floor it.