Tonneaus

I've had the high top cap, a regular cap flush with the roof, and a soft trifold tonneau. I didn't notice any change in MPG.
Not saying there isn't any, but it would have to be really slight.
I would decide on whether or not to buy one based on the way I use the truck.
I doubt you'll see any noticeable difference.
Not like the savings are going to pay it off in it's lifetime.

There was a magazine article about 10 years ago on improving the milage on a diesel PU. They did all the PC stuff and also added a tuner got it up to about 19-20. Added a cover and I think they got it up to around 22 or so. But who really wants to drive at 55, windows up, no ac etc.

So overall yes I think a cover will help but how much will depend on how you drive. I got one off CL for a short bed truck and then cut it to sit behind my crossover tool box so I have the best of both. A box I can get into easily and a cover for the rest of the stuff. Havent really paid any attention to whether or not the MPG changed, wanted a cover for the in bed security.

On my old truck I tried with and without a shell, saw no real difference, just gave me a higher cover to work with thus a little more verticle room.

Mythbusters did a piece on this and it had virtually no impact on mileage. I had one on my truck for awhile and liked it. It allowed me to keep things in the bed without worrying about them being stolen. Mine wasn't completely weather tight, so I couldn't put groceries back there if it was raining.

mabynack is right about the myth busters show. I think they also proved that having the tailgate down does not help. Aerodynamics built into new vehicles take all this into account. I have one and love it. Not for fuel savings but the fact that I can put stuff back there and it's not seen. Mine locks but that is just security in your mind not reality.

I have an undercover flex on my truck and really like it. Good dry secure storage. The tailgate on the Ram locks with the doors by remote.

I had a topper on my last truck (cab height) and hated it. It was a real impairment to rearward visibility.

We have soft rollup cover (Truxedo LoPro) on our truck which leaves stake pockets open so we can use rack to carry kayaks. I bought one for my daughter's truck, same cover except it covers the stake pocket holes. My daughter had a cab high hard shell and did not like it, she likes the bed cover.

bob213 wrote:
mabynack is right about the myth busters show. I think they also proved that having the tailgate down does not help. Aerodynamics built into new vehicles take all this into account. I have one and love it. Not for fuel savings but the fact that I can put stuff back there and it's not seen. Mine locks but that is just security in your mind not reality.

Good point about the security. There's an old saying that "Locks only keep honest people honest" A determined thief with a pocket knife could get to the contents of your truck bet if they knew it was there and wanted it.

ib516 wrote:
I have an undercover flex on my truck and really like it. Good dry secure storage. The tailgate on the Ram locks with the doors by remote.

I had a topper on my last truck (cab height) and hated it. It was a real impairment to rearward visibility.

What is an "undercover flex"? It sounds like one of the soft ones, as opposed to a plastic one. But undercover?

I know the soft ones don't present a deterrent to bad guys. I'm just thinking about hauling stuff home from Costco without my TP flying out all over the interstate.

Does anyone have a hard cover? The flat kind that fits right on top of the bed?

I have a soft tri-fold one that I use just for dry storage and keeping things out of sight. I have not noticed any difference in fuel consumption. I would have gotten a roll-type, but I live in a very snowy area and the roll types don't work so great in the cold snowy weather.