17" rims and fuel economy

[songa]

hey guys...anyone here running their yaris on 17" rims? although i love my FE on my stock (15" steelies), i am starting to consider putting 17" rims on there because of the looks. however, how drastic will this change affect the FE? lets assume that the 17" rims are about 20-21lbs each, which should be about 3 or 4lbs heavier than the stock 15" steels (which are around 17lbs each if im not mistaken). with that total of 12-16lbs heavier wheels, how much will that hurt the FE? and does it also depend on the diameter of the tires as well? i plan on using 205/40/17 tires. im not sure how much they should weigh tho. maybe this quetsion is a little too hard to answer =P if anyone has their own experience with 17" id like to hear them tho at least ! thanks