Bigger and heavier wheels kill my MPG

Well at least thats what I am suspecting....never noticed the difference in mpg when I had these 20's on my E60. Now transferred to my X35d, I avg at about 19mpg per tank and sometimes even down to 17mpg when I tried to have a little fun in city drivings. I had them put on the first day I took deliver and never had my stock wheels driving experience expect the 10 miles I drove to the tire shop from the dealer.

Anyone here has the same experience but perhaps did a comparison back to back with stock and aftermarket wheels? I am just curious to know, and too lazy to swap the wheels

this board is so dead.......