Depending on your reason for doing so, be aware that the change may move the engine out of its most efficient range resulting in a loss of mileage as well as placing and additional load on the engine and transmission.
Where you do the majority of your driving as well the terrain may also be a factor to consider
this ^^^^^
if this were me, [you really DON'T want to be me
] i would try to borrow a much larger [taller] set of rear tires to see how this would affect your mileage. you can mathematically get close to figuring out what gear ratio the taller tires would simulate, then go from there.
this would be easier, quicker, and cheaper than buying a gear set and having it installed [if you can't do it yourself].
if you find something you don't like, drive-ability wise, you could try a different height tire and test again.
as above, i have seen a loss of mpg going to a shorter gear set many times, even though a well figured out equation suggests otherwise.
just my opinion and experience. your "mileage" will vary.
