How much will my miles per gallon change? I am thinking about going from 17" to 20" on my F150. Anyone have any experiences similar?

About 1 MPG. When I went from driving F150's with the 18" to the 20" that's what I realized in fuel drop.

Its not so much your wheel choice that will affect you mpg, it's your tire choice. An F-150 with 20s would look bada**, but dont tell me your getting rockstars.<img src="http://www.wakeworld.com/MB/Discus/clipart/sad.gif" border=0>

Depends on what the actual overall diameter change is and the width. Take in consideration of weight change and it all adds up. I run aftermarket 18 inch rims with wrangler tires in the winter and 22 inch rims in the summer. Each are about the same width and overall diameter but I get better mileage with the 22's due to they are acutally lighter by weight.

I have the 4X4 SuperCrew and I trying to decide what to put on it. I am leaning towards some MotoMetal 20" 951's.