Something on the roof really hurts mileage. Here's our trips to the Outer Banks for vacation:
With my 2003 Audi A4 Avant 3.0q:
2004: 1,572 miles; 25.80 mpg.
2005: 1,576 miles, 26.63 mpg.
2006: 1,408 miles; 23.31 mpg (bike rack and 1 bike on roof).
2007: 1,345 miles; 20.76 mpg (bike rack and 2 bikes on roof).
2008: 1,307 miles; 21.53 mpg (bike rack and 2 bikes on roof).
2009: 1,350 miles: 21.99 mpg (bike rack and 2 bilkes on roof).
With 2011 JSW TDI:
2010: 1,451; 47.76 mpg (both bikes fit in JSW due to significantlly larger interior storage).