Okay, this is coming from a co-worker so i'm not sure how accurate her information is, but it begs the question....would you save gas and how much if you removed the roof rack accessory when not in use?

 

yes, it does help. I'm sure someone can do the actual math as it depends on the users driving habits. I noticed 1-2 mpg drop with my previous cars, and the worst being the storage top boxes. I had a soft bag for road trips, that was -6/8 and made for awful steering. The hard plastic cargo boxes would be better.

 

Anything you add to the exterior of the car adds more wind resistance, which means more fuel consumption. I take my roof rack off in the summer since I don't use it very often, whereas in the winter, I go skiing frequently so I leave it on.

With it on, I see a 1-2mpg drop in fuel economy.

 

Crap, so it sounds like she was right. Well definitely good to know.

 

Yep, roof racks are gas hogs. On the R53 it was closer to 3 - 4 MPG hit on highway trips up the mountain with the bike mounted. I can't confirm what it would be on the CM because so far I have transported the bike inside the car. My rack is still in its original unopened box!

 

Also, because wind resistance increases with the square of velocity, your mileage loss (as a percent of overall mileage) will be greater the faster you go. So an all-highway trip with speeds of 80 MPH will have much greater losses than a backroad trip with speeds of 50 MPH.