After doing yet another analysis of whether I want to keep my current roof setup (which includes a roof box) or change it up, I checked my MPG notes to see what, if any, impact the roof box has had on my MPG. Here's what I found:
This data is from a 9 month road trip with no other significant variable changes between the two (except for the varying terrain being driven).
Without roof box: 14.9mpg average over 4,124 miles
With roof box: 13.2mpg average over 11,500 miles
On the one hand, 1.7mpg difference is notable. Over 25k miles, that equates to +217g more of gas (~$660, depending on price). On the other hand, I'm somewhat skeptical that the roof box actually had that much of an impact... We installed the roof box while in CO and proceeded to spend the next 11,000 miles driving throughout CO, WY, MO, CA, OR, WA, which all have a lot more mountains compared to the 4,000 miles without the roof box that was mainly driven on the east coast/middle america. Curious if other users have any thoughts/input/data from their experience with/without roof boxes.