For Vios, yes around 13km/l to 15km/l for normal driving
depending on your driving style and traffic conditions. As for
20km/l, I would not say it is impossbile, but will probably be
extreme driving...The person most prob drive with aircon off,
nothing in the boot, no passenger, rpm dont exceed 2000rpm at all
times, control the speed till he never really have to brakes,
expressway driving most of the time....
And if one can achieve 20km/l on an auto, what bout manual? Even
better mileage...