Richard L,
The foundation of the results for the mythbusters test was the simple scientific principle of air in an enclosed space. The closed bed creates an enclosed space holding a volume of air what with the bed enclosed on all sides but the top. The aerodynamics of the pickup truck, and I dare say save to assume most pickup trucks, have the fast moving air coming over and around the cab on all sides (top, left and right sides) and then coming across the back of the truck, along the top of the bed. That's the only assumption I made.
The air in the enclosed bed is trapped, it cannot escape, and no amount of additional air can easily be compressed into that pocket of air.
The effect is that the wind going across the uncovered box with the tailgate up rides on a cushion, better said, a bubble of trapped air. The drag of that "air on air" is less than the drag of air on cover, or air on bed (as is the case if the tailgate is down).
So, unless you can say you really believe that the ST is so radicially different in its aerodynamics that there is no air rush over the bed (in any direction) as the vehicle travels down the road at high speeds, then I'm not sure what assumptions I made that were so reckless.
Richard also said:
You cannot look at the short pickup bed on the Sport Trac and assume it will have the same aerodynamic effects as the much longer bed of the F150 Heck the short bed might even make the Sport Trac aerodynamicly inferior to the F150.
I never said you would get the exact same results or have the same aerodynamic effects as an F-150. I simply said:
An uncovered box with closed tailgate provides the least drag and therefore the highest MPG.
If the aerodynamics of the ST allow for any amount of air to rush across the bed then the principles that I describe above would still hold true. It would be an unreasonable assumption, IMHO, to assume that NO amount of air travels across the top of the bed...which would be the only way that said principle and effect doesn't have some influence.
Richard L also said:
My opinion is based on about 7 years of Sport Trac owners stating that they are not getting any significant mileage differences with or without the tonneau cover, and my opinion is that the short bed may be the reason why.
Again, I never made any claims to how significant the mileage improvements would be. I think even the mythbusters episode showed the differences as very minor...a few gallons to the tank at best.
Lastly, Richard unreasonable stated:
Unless you can show that the Sport Trac behaves aerodynamicly the same as the F150 then it's just an opinion based on nothing.
I never said aerodynamically the same. You did. I explained why I said what I orginally said. Can you show any reason to believe that the ST would have "no amount" of air rushing across the top of the bed at highway speeds? I assume there is some. That's a valid assumption. Can I prove it...of course not, I don't have a wind chamber at my disposal. But it is still a very reasonable assumption, and the unreasonable assumption would be that NO AIR flows across the bed at driving speeds.
Show me how assuming that some amount of air traveling across the bed of an ST at driving speeds is a faulty or reckless assumption and we can talk. But please don't give me lame "you should never assume" quotes, because frankly, life is a set of assumptions. If we only acted on what we really know, we would hardly ever act.
TJR
