on my '05 4.4i with a well maintained engine/tranny (as I'm sure most of you have as well), I get 531miles to a tank when cruising at 65mph. I've done that a bunch of times and its funny cause I NEVER thought I'd be able to get that. And thats not math from the RANGE either, its legit begin to end of trip mileage.
This is also in winter when gas gets sucked back more, BUT I run 255/55R18's too, so it kinda evens out I guess.

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S