Pickup tailgate up or down
 

Skyl4rk's my name and Engine Off Coasting's my game.

Below is a reasonable facsimile of my Toyota pickup. After watching the vids and checking out the mini hurricanes which form over the bed, it will be obvious that a boattail is desperately needed. However at this time my options are tailgate up or down.

I find it difficult to interpret the vids, however one thing is for sure, the back of the cab is a major problem, causing lots of turbulence. Vids were done at 2,500,000 Reynolds.

What say ye? up or down?

YouTube - Pickup tailgate up, air turbulence

YouTube - Pickup tailgate down, air turbulence

Tailgate up, if the only choice is up or down. If you believe mythbusters, tailgate off or tailgate off with a net would be better.

What about with a low cost tonneau cover on the bed?

They say no on the tonneau. Here's some info:

PickupTrucks.com Forums: Gas Savings With Tonneau Cover?

Another test says yes:

Testing The Tonneau/ Fuel Economy Theory - Ford Truck World Articles

The mesh probably breaks up the wind back there and helps direct it out the bed.

Conclusion? I bed cap that slopes from the top of the cab, down to the tailgate would be ideal. Jury's out for the tonneau - needs some real-life testing. NasTrucks have them. I have an aluminum tailgate with louvers for towing my 5th wheel, but I can't tell the difference in FE.

Tailgate up, at least from the videos.

With the tailgate up you're leaving a shorter wake -- the gate catches some of the turbulence from the cab and puts its momentum back into the vehicle.

ETA: "Shorter" as in vertical height. The trailing length isn't as important, it's the perpendicular area of the dead wake that "pulls back" on the vehicle.

Have to agree with 99metro. He's right!

While the video looks good, the turbulence in the bed causes more drag than helping the air flow it kinda cancels out the advantage.

If the Mythbusters data is correct then it appears to me that the web type tailgate should easily be worth the money to buy or build it. They say they got 5% better efficiency. This means that a $4 gallon of gas would have an equivalent cost of only $3.80. With every 20 gallon fill up you would save 4 dollars.

You could easily make a web tailgate out of any old scraps of rope, canvas, clothing or whatever.

I also think it would be easy enough for anyone to test the actual fuel usage with a cruise control, a scangague or other means of measure fuel injector duty cycle (pulse width) and a level, traffic free road of a couple miles length in which to do some A-B-A testing. I may do it sometime but where I live I would have to drive at least 30 miles to get to such a road and would have to do this at 3 or 4 in the morning to avoid any traffic.

This link was copied from the sticky at the top of the general efficiency forum. In wind tunnel tests the best result was "up".

http://ecow.engr.wisc.edu/cgi-bin/ge...hi1/pickup.pdf

up or down
 

All trucks are different.In the aggregate,gate up is better,but so little different that unless very careful at the pump,you'd never know.GM has a patent for 1/2 tonneau ( back half only ),they say its as good as full cover.Ford research shows otherwise.I know that a 1/2 tonneau works on Toyota,Dodge,Chevrolet,and Ford half-tons.Figure on about 5% mpg improvement.

I've seen tests of up, down, mesh, covers, and partial covers. However I have not seen anybody try louvers. Naively it would seem like better flow might be achieved by placing a series of horizontal louvers (perhaps just thin boards) where the tailgate used to be. If it's too turbulent side to side vertical lovers could also be added. With proper design it might straighten the flow out of the bed of the truck. Might.