Originally Posted by mike-y
could also be a difference in overall tire diameter between the 19s and the 17s.
that. you've got more rotating mass per corner with 19's + tires VS your 17s + tires. and you can't just look at one corner. you have to add up the weights in all four corners. also, your car is lower with 17s VS 19s so it could reduce drag.
and although the mpg calculator in our cars are nice, just keep track of how many miles you run on a full tank (or whenever you fill up). that'll give you a more accurate calculation.