Archives

I think Ken has more data on this than most anyone I've contacted, but I'm interested in P/U bed aero-mods. I've heard they break down like this (from worse to best)... I'll correct the list based on feedback (1=worst)

Empty uncovered bed, tailgate up.
Empty uncovered bed, tailgate down
Covered full bed, tailgate up
Back half (near tailgate) covered, front half uncovered.


Anything I missed? Is the order correct?

11011011

swap #1 and #2 for short bed trucks... for 8' beds its actually pretty close to same results but tailgate down was still worse than tailgate up. The full tonneau is best in head or tailwinds to I think it was about 15-20% off, the shorty was better in crosswinds. I'll try to find that link in just a bit.

here's the link: http://ecow.engr.wisc.edu/cgi-bin/getbig/me/363/ghandhi1/pickup.pdf

if you google Phil Knox, there's some pics of his truck with an angled bed cap, full belly pan, disc hubcaps, fender skirts...

The open bed with a closed tailgate is Bad…

I had a Chevy Luv (made by Isuzu) it barely had enough power to get up to 65. I made a bed cover using 2 medal doors, 2x4’s and 2x6’s. I am guessing it weight between 150-200 pounds. My mileage went up (I forget how much). It made such an aerodynamic improvement over the open bed that even with the extra weight I could hit 75mph!

My thoughts, cheapest to more costly.
I believe there would be a lot of improvement if your removed the tail gate. (it is illegal in many places to drive with it down.)
If you can spring for one of those flow thru tailgates, I would think that would be great.
A flat bed cover would cost a bit more, but I think it would do a bit better.

And the best I have seen.
I saw a truck with a topper that was a wedge. Full height at the cab sloping to the tailgate.

A pickup truck in general is horrible as far as aerodynamics go. However, the SAE has proven that tailgate up is best just as SlowHands said. A flat cover is going to be better than that, and an wedge shapped aerodynamic truck topper (not a normal boxy one) would be best.

This is Phil Knox's truck:
http://www.evworld.com/images/pknox_toyota.jpg

I once read a research paper on this subject. They looked at various combinations of bed cover, open, tailgate up and down on a pickup with wind tunnel testing. The surprise result was that a partially covered bed showed the lowest drag. The front half of the bed was open, and the rear half closed. Apparently this induces a large vortex that smooths airflow over the vehicle. Of course, a fastback type cover would probably be better.

I had one of these http://www.rollnlock.com/ but I wasn't hypermiling at the time. Its a very nice cover that is very strong and secure. If i had a truck now i would have one of these on it. Has to help out with FE.

claytori look in my post on this page... it has the research you mention.

So after reading the pdf. linked above I'm left wondering a couple of things.

Would a 20% cover in the tailgate be even better if you sloped the top to match the air flow pattern? or would it screw up the vortex that forms in the empty truck bed.

and would a spoiler on the back of the cab help (perhaps one that also comes down the sides to the bed kinda like a roll/light bar)? Or again would it screw up the vortex in the bed?

I'm a Aero-novice and often have my truck loaded down but I'm thinking I could easily make a tool box for the back 20%. (My load is typically a Miller welder and Torch bottles). Thus I really can't go for the full bed cover. But I can sacrifice a little space.


Just another truck related question. I'm assuming that since I often pull fairly heavy loads for my truck that grill covers either aren't an option or they should be easily removable?

Hi Ken:

___The short-bed 03 Ranger's FE is better with the tail gate down as well.

___Good Luck

___Wayne

Mythbusters did a show on this a while back. Initially they just did tailgate up/down. They then revisited the myth and tried up and down again. They added on a cover, removing the tailgate all together, and one of those net type things. They found that the net was the best, I think tailgate up was next, then I don't remember.