Fuel Economy Mythbusters

We all know that if you drive with your windows up and no Air Conditioning you get considerably better fuel mileage than if you drive with the windows down or air conditioning on, but what about the technicalities. I have a few questions myself that are quite puzzling.

For example, if you drive with the air on but no conditioning (just taking the air from the outside and bringing it in) do you hurt the economy and if so, how badly?

How about suspension? Does it lower the economy when its old and needs replacing? What about tires? What about anything else any of you can think of?

If anyone has any questions or answers please post them!

The opening and closing of the door with the windows 1/2 down could damage the window regulators. $400 fix

Also the head liner might drop on you too!

What about the difference of using E85 opposed to 87 octane? In my impala, I see that I get 350 miles on 87 and about 315 on E85. Now, in Chicago I get 87 for 3.89 and 85 is now 3.39. I only purchase E85 when there is a 70 cent gap between. What are your thoughts?