I like this site as a estimate, but would not “swear” by it…i mean, like the above poster said, this site runs on some assumptions that cannot be played out in reality.
A few other things that a person needs to expect to change fuel economy:
-are you running with proper tire pressure?
-are you driving with a full load of passenger or just yourself?
-is the trunk full or luggage or empty?
-are you driving with a/c (summer) or defrost (winter)?
-are you driving against the wind?
-are you driving at a constant speed or not?
-are you using in car items like dvd player, plugged in item in the car port (phone charging, laptop, etc)
All these when you think about it, add up on long drives.
Personally I have taken my car on an 8hr drive on a single tank (alone) and been unable to get that result when there are a few people and suitcases in the car.
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