half tonneau length
 

Has anyone tested various half tonneau lengths? Maybe also on various bed lengths? Or does half of any bed length seem to be perfect?

Find out where the template would touch the bed rails- that'd be a good starting place for the leading edge of a half tonneau. If you need it farther back to give more bed access, try experimenting, but I'd start with the template coming down from the cab roof.

I think I saw a template on my truck and it may have not come down inside the bed. I've got a ranger with a 6' bed

I don't think the Template will do it.

What your looking for is a rolling cylinder of air in the bed. It may have more to do with the distance from the bed floor to the top of the cab.

I figured the tonneau would make the bed floor moot.

For a full tonneau, sure. The question is a half-tonneau.

Maybe a curved mid-wall?

various lengths
 

In the original 1986 US Patent,GM offers a drag table showing the change in drag coefficient,from zero,to full length.
*Any coverage,of any length provides a drag reduction.
*The drag minimum occurs at 50% (half) coverage (back half).
*They tested on a C-10 1/2-ton.
*The half tonneau gave a 8% drag reduction.
*The full-tonneau gave a 5.6% reduction.
*The 1/2-tonneau with forward bulkhead had 12.8% higher drag.
*And the 1/2-tonneau cut rear lift by 30%.
--------------------------------------------------------------------------
In 1988,Texas Tech investigated the tonneau and also advocated the 1/2-tonneau.
If you need numbers for various bed lengths you're on your own.

http://www.google.com/patents/US4573730
http://patentimages.storage.googleap...S4573730-1.png

Thanks for the info. Google kept giving me links to half tonneau covers to cover the rear seats of old convertibles.

That's why we're here. We keep chanting the Old Wisdom in the hope of keeping it alive.

It seems like it could be workable — butterfly opening hatches on the half tonneau and the 'mud room' area ahead of that could be waterproof so you could use it for a bath tub.

It might be interesting to hinge the top of the bulkhead to the tonneau in such a way that the tonneau could be flipped all the way to the front, thus enclosing the front instead of the back. (Assuming the bulkhead remains stationary.) Worse aero, but might be useful depending on the cargo you are carrying (it's hard to get to the front open area to load and unload stuff with the half tonneau in the usual position).

My half tonneau is smaller because I have a Rambox, and can be slid out of the Rambox rails, flipped over and laid on the floor in case I need the whole box. I did find however that it expanded enough when it got wet this winter, that I was no longer able to slide it into the rails. There's always something...

I'm going to use a piece of plywood with some small holes cut for 4 c clamps. Then I can just undo the clamps and lay it on the bed floor. It will sit on top of the bed rails and have beveled edges. I'll probably seal it up pretty good with some marine epoxy I have then paint it.