All three pickups (a Toyota SR5 and two Ford Rangers) I've owned got better fuel economy with a standard topper on than with just an open bed, typically about 10 % better.
I've never tried a tonneau.
With my present truck, I did try it with an open bed and the tailgate on and off (not down, completely off). I didn't notice any difference in FE, though I probably wouldn't have noticed anything less than a couple of percent difference.
Last edited by sid; 03-08-2011 at 09:13 PM..
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