The tire OD is only 1" larger running an 18" in the rear, not sure that will make a big differance.
As for the "feel", keeping with the countach design is the way to go IMO. This is a way to update the the look without a permenant alt. and the originals could be reinstalled at anytime.
The idea behind this is the same reason most of us own these cars, for the fun of it.



Greg