Better mileage with shell?

16 miles on 405 freeway: Long Beach to HB. Doing 70-75. Just got shell last week and was expecting slight reduction due to weight. I do this drive often. I never got better than 22-23 mpg with oem tonneau on truck.

For those of you unfamiliar with the area, this is flat freeway near coast. No downhill and no wind today.

 

I haven't noticed a significant change in MPG with or without a shell on any truck I've owned.

 

shell, tonneau, tailgate up, tailgate down, it really honestly doesnt matter, despite what mythbusters say. A quick google search shows that every pickup owner with a blog tried this experiment, and they all reached different conclusions. Weed out the ones that didnt perform the test under controlled conditions (almost all of them), and you still have conflicting results. In statistical lingo, that means the actual difference does not exceed the variance seen under normal driving conditions. Or in other words, negligible.

The 405 is a strange animal to do the test on; there are way too many variables besides wind. Theres a major draft effect when you get a mass amount of vehicles going in the same direction. (did you ever notice a morning where the fog has settled on the surface streets, but the freeways are oddly clear?) That draft effect changes by the minute, depending on traffic density, speed, ratio of trucks to cars, etc. Theres also subtle changes going on in your foot. Chances are fewer cars jumped out in front of you today, which means fewer corrections on the pedal.

Id say the difference is all in your foot. And if youre achieving numbers north of 21 consistently, be proud of yourself, youre doing it right.