Oh n=1 but when we first bought wife's e53, it reported a ludicrous mpg: 25 or so for 4-5 hour freeway drive.

I stopped about 40 miles from home and decided to check the tire pressure: it was FIFTY!

That car would regularly report 23-24 on highway after setting the pressure down but also spent a lot of its life on 235s which had to be more fuel efficient.

I use soft winter tires year 'round and that certainly costs me in the mpg.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)