In my experience the 17's are not as efficient as the earlier models.
My 17 "GT" has 25,000km on it now and I'm hard pressed to match the fuel economy of my previous 14 Mirage.
While the 14 routinely logged 4.4L/100km with the occaisional 3.3L/100km on my work commute.
The 17 has never been able to accomplish these numbers. My best commute so far has been 4.6L/100km and it won't do this every day.
note: Both cars were/are top trim level CVT equipped.
While the 17 has 15" tires the winter tires/rims are 14" and this offers no improvement in mpg.
I run/ran them the same over same commute, tires @ 35psi with climate control on auto except in winter where I have to choose settings that keep windshield clear. I never turn off the air cond. The little snowflake is on whenever it wants to be. (both cars)
While I believe the 17's are less efficient I'm still getting a good return for my gas dollars so I'll run it until it turns to red dust.
Will weld for beer.
View my fuel log 2014 Mirage SE 1.2 automatic: 45.3 mpg (US) ... 19.3 km/L ... 5.2 L/100 km ... 54.5 mpg (Imp)