Yep, I went from 17 to 18 and although the change is less noticeable there is definitely a difference and it is most telling in the mpg stakes. With hindsight, given the choice now I think I'd probably stick with the 17's and see if my insurance company would agree to me running 205/50/17's which I think could possibly be the tyre the Giulietta should run on. People reckon that the grip with 16's is just the same but just a bit squidgy - 17's sort that. Narrower, lighter tyre would improve mpg, braking & acceleration.
Thing is did Alfa fit 225/45/17's because of the cost or because it really needed the extra 20mm of width??