Little story from today to illistrate my point.
I got home early today and loaded up my bike on my hitch rack. When I got up to speed I noticed my
ScanGauge reading about 10 MPG lower than I would have expected it to. For 20 miles I'm driving just thinking about what strange aerodynamic phenomenon I've caused to loose 20% of my fuel economy. On arrival I notice that my right rear tire is nearly flat DOH!
Moral; just because you make a change, does not mean that it is the only change made.