On average, from what I have had an Engineer Tell, the wheels that come with the Hybrid as opposed to say a normal Civic Wheel averages the Hybrid an extra 4-7MPG....just because of the Design and reduced airflow allowed into the wheel well....

So if you change them...try to find a replacement that is of the same weight or lighter...and are blocking as much airflow into the wheel well as possible.

 

I think it has to do more with weight than wheel design... I have the stock 16 LX steel rims w/hubcaps ... they are 10lbs heavier then the stock 15" (hybrid) wheels ...