Homestead

Hohn is right.

When I used to carry my 12ft aluminum fishing boat on the top of my truck, I got better mileage carrying it backwards than when I carried it nose first. The teardrop shap is correct for better mileage.

bentwings

hohn, you're right on. I did some fluid dynamics studies along this line a few years ago while learning to use the software. There's more to it but you said it pretty clearly. It would be difficult to practically improve the truck aerodynamics without extensive computational fluid dynamics to give some direction. TLAR (that looks about right) just won't work. The wedge idea with a camper back has some merit but beauty, usefullness and practical?? well I don't know if you can buy it yet but the market seems a bit slow LOL

I do know that you can mess things up pretty easily. As high off the ground as our trucks are any lowering would help. Fat tires sticking out of the wheel wells ...obvious. Those "hips" on our dualies ...I was talking on the phone and mentioned "hips wider than my dualie" my wife thought I was talking about her LOL
How about the big ole mud flaps front and rear...they are like air brakes on an F-18!!!

My initial truck model I used for CFD studies was so dirty (aerodynamically) that I thought the model was messed up.
The styling studio at DC must be a lot higher up the food chain than the analysis guys. Maybe someday they will make a Viper Quad cab with a CTD, 6spd, 4wd and dual rear wheels

bentwings

Barrett_Fodder

Im a 3rd gen'r but figured i would throw a little something in the mix here. When i was in college a few years back we took a scale model of a 1999 Dodge ram and did some wind tunnel testing on it our results were as follows. (wind speeds at 70 knts)

Aerodynamic drag changes were:
.43 base

.51 with windows down and tailgate open
.49 windows down tailgate up
.43 windows up tailgate up
.37 windows up tailgate up tonneau on.
.32 windows up tailgate up tonneau on, and underbody sheeting in place.
The "underbody sheeting" was basicly like advertised on the new lexus. Only we didnt dimple it like a golf ball strictly out of lack of desire. But we found it interesting that if you were to do a large "skid plate system" under the vehicle how much drag you cut down. to go from .51 worst to .32 is a 37% increase in aerodynamic efficiency which should account for a 18.5% increase in fuel economy.

Another thing is that based on drag to run the AC compressor you would get better mileage with the windows up tailgate up and AC on than with the windows down in the same configuration.

I am currently working on a lightweight aluminum underbody sheeting unit for my truck to see if i notice any increase on a couple of 1200 mile trips i have coming up. Should be interesting.

RowJ

Thanks...You answered a question I have been wondering about for 2 yrs!
Bgt my daughter a VW Jetta diesel 2 yrs ago and was curious why they cover the bottom of the engine compartment with a fairly flimsey (dimpled) sheet of plastic. Dealer didn't know...I assumed maybe thermal stability for under the hood. Real pain to remove, with 17 +/- screws, for oil changes.
Now I know how they get 50 MPG!

Oh, one other thing B_F; Rereading your next to the last paragraph; guess I knew this fact intuitively..cause I never run my truck with windows down, tailgate up and the A/C on!!!

Maybe someone with more patience than I have could come up with the same idea (pan cover) as an after market add-on? Also, how about a tear drop shaped rear end piece attached to my 5th wheel ball with grooves to slide down over a closed tailgate for support?? Probably not.......think I need less keybord time and more of a life!
RJ