Truck owners have long debated how to improve the aerodynamics of the cargo bed and if doing so was worth the effort. Conventional wisdom dictates that an empty bed with the tailgate up would capture air flow and the added drag would reduce fuel economy. To get to the bottom of this myth, we ran a series of tests with our 2013 Dodge Ram V8.
The truck was fitted with an inline fuel meter, just as we do for our routine fuel economy tests. We tested the Ram on the highway at 65 mph with the tailgate up, tailgate down, and with a factory soft tonneau cover. The tests were performed following our usual procedure for testing highway fuel economy, including making runs in both directions. (Learn how we test cars.)
We found that adding a tonneau cover or lowering the tailgate hurt fuel economy, rather than helped it.
With the tailgate up and no tonneau, we got 22.3 mpg. Dropping the tailgate decreased efficiency to 21.5 mpg. That 4-percent difference means that driving the Ram all year exclusively on the highway could cost the owner an extra 20 gallons of gasoline. (In reality, this big workhorse is likely to see a mix of driving and a variety of chores, limiting the potential penalty.)
We found that covering the bed with a soft tonneau cover was even more detrimental, dropping fuel economy to 21.4 mpg.
Given that even the latest pickup trucks have an insatiable appetite for gasoline, it is natural that owners will want to maximize their fuel economy. Unfortunately, these tricks proved to be ineffective.