[COcyclist]

I have a couple more tips, some obvious and one debatable one.

1. Never put roof racks on your car (unless you have to). The roof of the car is in some of the fastest air flow and adding a roof rack adds to frontal area and disrupts what should be an area of attached flow. Putting bikes up there just makes it worse. Some people leave cargo boxes on the roof racks or even deflectors to get rid of the wind noise. The wind noise is turbulence and drag making its presence known. Take them all off!

If you have to pick up some lumber or carry a ladder across town, roof racks make a lot of sense, just remove them when you are done.

2. Carrying a bike on a rear bike racks add drag. I will add a rear rack if I am meeting a friend to go biking but I drive to his house with my bike inside.

Now the debatable one...

3. Get a trailer hitch? I have a small receiver hitch that I mostly use for a 2 bike rack. The rack folds compactly when not in use but can carry a bike for myself and a passenger. Back to the double the per passenger mpg argument. Effective per person 100 mpg.