The rain (greater rolling resistance) plus the extra weight of those shelves is easily good for another 1-2 (or more) mpg. Thanks for the report.
The rain + weight certainly was a big factor!
I took at 148 round trip to Kansas City today with avg speed of 67.x MPH. 41.5MPG avg.
Yeah, but one of the major selling points of the Sonic is "great fuel econemy" and for it not to have an instant or average mpg display is kinda silly.
I'm sure people are tired of hearing my reports, but I took the Sonic from Topeka -> Des Moines this weekend. With only the wife and our weekend luggage we got 38.9MPG avg with an avg speed of 72.x.