I drive a hybrid - a Toyota Prius. For the last year or so, I've had a bike rack attached to the (custom installed) trailer hitch which I didn't bother to remove when driving around. I finally got around to removing it during my last tank of gas. I went and made sure my tires were inflated, removed unneeded heavy crap from my car, and didn't use much A/C (the weather has been good). Today the experiment ended as I had to fill up again.
My goal: maximize my MPG for this tank.
Result: 475 miles even on one tank of 8.814 gallons = 53.9 MPG
I was hoping to get to 500 miles on the tank. I probably could have, I think the tank is 10 or 11 gallons, but the gauge was showing me the blinky bar wednesday (2 days ago) which means that the Prius won't tell you how much you have left any more. Interestingly, I didn't have the rack off for the entire tank, maybe about half of it, so I'm interested in seeing how well I can do on my next tank.