Watching the speedometer. Usually drive the car 70 mph/plus highway and get around 29 mpg.
Dropping to a hair less than 60 mph gives me 31 and 55 mph gives 33.
Alot of people have slowed their speed and you don't risk getting your mirrors blown off at 60, at least on weekends.
Hard to stay in the right lane though.
Don't wanna know what the truck gets.
