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Old 03-10-2008, 07:26 PM   #6 (permalink)
Big Dave
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Join Date: Jan 2008
Location: Steppes of Central Indiana
Posts: 1,314

The Red Baron - '00 Ford F-350 XLT
90 day: 27.99 mpg (US)

Impala Phase Zero - '96 Chevrolet Impala SS
90 day: 21.03 mpg (US)
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This has been a topic of discussion amongst Ford Super Duty owners. The general rule of thumb is to run with windows down up to about 35 MPH. Above that, the aero drag penalty exceeds the A/C load and it is better to run the A/C.

I have WeatherTech visors which are similar to your and they give me a third option in some weather conditions. I can run with the windows down to about a half inch above flush with the bottom of the Weather Techs and get decent cooling without the drag penalty. When the window gets lower than a slight overlap, you can feel the drag increase.
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2000 Ford F-350 SC 4x2 6 Speed Manual
4" Slam
3.08:1 gears and Gear Vendor Overdrive
Rubber Conveyor Belt Air Dam
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