Truck Tops?

[cathleeninnh]

Do those words rhyme? tonneau and dunno?

Cathleen

[eques]

I think they do, Cathleen. 

[MaineShark]

Another side-benefit is that either a tonneau or a cap will reduce your drag.  Dunno which is better, though.  A cap looks like it'd create more turbulence behind your vehicle, but a tonneau would have two turbulence zones.

Dunno.  Maybe this wasn't even a question in your mind. 

A tonneau will reduce drag.  A cap will increase it, unless you are pulling a trailer, in which case the cap is better than the tonneau, and much better than an open bed.

Of course, the lowest drag is to run with the bed open and the tailgate down or removed.

Interesting side-note: if you run with the bed open and the tailgate up, you'll get increased downforce on the rear wheels when you are going fast; useless for most people, but if you wanted to drag race and traction was an issue, it does come into play.

Joe

[KBCraig]

Of course, the lowest drag is to run with the bed open and the tailgate down or removed.

Nope. Mythbusters tackled this one twice, in episodes 43 and 69. Myth: busted. Mileage is better with the tailgate up.

Kevin

[eques]

Another side-benefit is that either a tonneau or a cap will reduce your drag.  Dunno which is better, though.  A cap looks like it'd create more turbulence behind your vehicle, but a tonneau would have two turbulence zones.

Dunno.  Maybe this wasn't even a question in your mind. 

A tonneau will reduce drag.  A cap will increase it, unless you are pulling a trailer, in which case the cap is better than the tonneau, and much better than an open bed.

Of course, the lowest drag is to run with the bed open and the tailgate down or removed.

Interesting side-note: if you run with the bed open and the tailgate up, you'll get increased downforce on the rear wheels when you are going fast; useless for most people, but if you wanted to drag race and traction was an issue, it does come into play.

Joe

Oops!

Thanks for the correction. 

[MaineShark]

Of course, the lowest drag is to run with the bed open and the tailgate down or removed.

Nope. Mythbusters tackled this one twice, in episodes 43 and 69. Myth: busted. Mileage is better with the tailgate up.

Do you remember the methodology?  Because the wind tunnel results that I've seen show different...

Joe

[Barterer]

Some mechanical engineers where I went to school did a technical paper (SAE 881874) that supports the "tailgate up is better" theory:



They used a 1/10 scale Ford F-150 truck in a wind tunnel blowing 80 ft/sec (~55mph). 

[KBCraig]

Barterer, that matches the other figures I saw online: that tailgate down reduced mileage 3-5%, and a full tonneau increased it 8-10%.

Joe, as best I recall, they took two identical trucks to a test track, ran them dry, then fueled them with a measured volume of gas. Then they ran them on cruise control at the same speed, half a lap apart to avoid any drafting effect.

If that wasn't Mythbusters, then someone else reached the same conclusion they did, because I watched it being done on TV, and they also got better mileage with the tailgate up.

Kevin