Interesting read on pickup truck aerodynamics.
 

It seems the geometry of a truck bed has a great effect on the Cd of the pickup truck. This research paper presents some interesting wind tunnel data and explains why later model pickup trucks have such high side walls and tailgates.

It seems the manufacturers have sacrificed the utilitarian aspects of earlier model pickups (with low side walls and tailgates) for the taller bed height we see on the late model pickup trucks, especially those trucks with the shorter beds. It's all about reducing the Cd of the pickup truck to improve the fuel efficiency of the truck.

http://www.wseas.us/e-library/confer.../FMA/FMA17.pdf

Happy New Year and may 2011 be a good one for us all.


Bondo

Interesting.
Makes sense though. Same principle of why wagons and stretch limos get better FE.
Apparently flow reattachment over length is more important than I thought it was.

That would explain why all of those late model pickup trucks have such high beds. They're almost like open-topped versions of the traditional van body.

bondo -

Great find! Do you think that this stuff like this could be a missing detail in the "tailgate up/down" theory? That is, it depends on the length of your bed (the geometry!) :

http://ecomodder.com/forum/member-cf...eamline-03.jpg

What do you think?

CarloSW2

yea i guess that makes sense after i think about it

Thx Bondo and cfg83.

I thought the high bed walls were for a more massive/macho look.

That does not explain why the body is jacked up and why the frontal area of a truck is so big! even the little Toyota trucks are a half ton truck, just like F-150's and Toyota made a 1 ton truck that wasn't much bigger then their half ton truck.
That paper seems to agree with the van shape but the big problem with trucks is that you need a step ladder to get in to the truck bed.

It may very well be. You have now attached a theory to a theory but it does make sense. Your graphic does a very nice job of explaining your thought.

That is definitely thinking oustside of the box!


Bondo

This would militate toward the sloped sidewalls of the GM Avalanche.

I suspect they did not get high for aero; they are high because of the ginormous wheel/tire packages driving the entire chassis up. The cabs are higher too.

Huh? :confused:

Right, the bed is not deeper if you are standing in the bed of the truck and I don't think that the sides are all that much higher if you look at the ratio of cab hight to bed side hight, it's not like trucks are getting cattle panel sides.

It's possible for that reason, too. Certainly, larger tire/wheel packages do not help with aerodynamics. I suspect, too, that these new trucks also have lousy undercarriage visibility that contributes to a higher than necessary C(d).

However, the new truck profiles appear to fit more neatly into that teardrop stencil as a result of their higher bed heights. While the cabs themselves are higher, the truck fronts also look like the trucks gorged out on sheet metal and plastic over a holiday season.

Let's see the overlays...

Solving the trig problem on my 24" deep bed with the cab top sitting another 24" above the bed rail, I came up with a 11 degree slope that stayed 8" above the tail gate.

My old bed cover was too steep (17 degrees) hitting right at the top of the tailgate, but it sure beat a flat tonneau.

If the bed were 8" deeper, a straight angled cover would have been just right.

Ahhh, here is why they keep getting taller:

I put some of that gobbledegook into real units:

If model was real it would be a truck 196" long (short box), 208" long (baseline), 219" long (long box) x 72" wide x 66" high.

Baseline bed height (I think it should be called bed rail height because the bed floor height does not change) = 18"; low rails are 10"; high rails are 26" above the floor.

Bed floor is 28" off the ground thus making bed rails 38", 46", and 54" off the ground.

Baseline bed length is 81" (6.75'); short bed is 69" (5.75'); long bed is 92" (7.7').

I have to admit, I don't completely comprehend the figures that purport to show flow vectors. The units and proportions don't make sense to me- is the tailgate a foot thick or what? The flow patterns don't all follow the "rotating box vortice" that in the past I was led to believe all pickups had. The oil tracers all look the same to me as well. :confused: