Just curious how much drag I will have going from a wheel that 8.5 to 9.5? Both will weigh the same or really close but one will be wider. I know the heavy wheel will hurt performance but what if they weigh the same?

 

Would like to know this as well... From what I understand wheels are that are the same diameter 18" to 18" and weigh the same should have no effect on the wheels being wider.

 

You will have increased rolling resistance from wider diameter tire,my last car saw a noticeable decrease in gas mileage. I went from 9x19s up front to 10x20
Rears from 9.5x19 to 10.5x20
Lost about 2-5 mpg's due to added "unsprung weight" & "rolling resistance" from running bigger wheels. Unless your either staying the same or dropping serious weight. You will actually slow the car down. Good luck with your wheel/tire combo.