Your mileage WILL vary!

Super-hypermiler +Wayne Gerdes is taking another 48 state road trip this week as he and his driving partner try to reset the world record for fuel efficiency through the 48 contiguous states in a non-hybrid car. The current record was set by Australian couple Helen and John Taylor with +Volkswagen USA Jetta TDI in 2009 when they averaged 67.90 mpg.

As Wayne passed from Florida into Mississippi in a new Passat TDI they hit a torrential downpour and afterwards he did some calculations. It turns out that the extra resistance of driving in the rain dropped fuel mileage by 25%. 

Remember that fuel economy is affected by three main factors, temperature, terrain and technique.  You can't do anything about the first two, but Wayne and his followers can teach you all kinds of tips and tricks in the forums at cleanmpg.com.