Posted: May 05 2008 at 1:56pm | IP Logged

Lots of studies done on this by variuos groups almost all show WORSE mileage with the tailgate off than on and closed.  The normal position (closed) seems to create an air buble that allows air to flow right over the bed.  Reoving the tailgate allows air to get down in the bed and increase drag.  One study I saw removed the tail agte and repalced it with one of those lightweight mesh gizmos.  This did increase mileage by lowering weight and keeping air flow out of the bed.

Air up your tires, drive slower, keep a clean air filter and fuel filter, accelerate reasonably and combine trips.