[lord of the racks]

Good question. This is something the car rack companies don't do a great job of addressing. Adding a wind fairing to a roof rack system that has a roof box will actually decrease fuel efficiency. I roof fairing directs the air up and if there's a roof box it will be blocked by the box. Instead you want to encourage the air to flow under the box.

A roof rack fairing does reduce the wind noise however. A lot of people have success with wrapping a small bungee cord around the front load bar from end to end in a corkscrew fashion. This will eliminate any wind noise and still allow the cargo box to mount properly. A thin black bungee cord is ideal and no one will even see it. I still don't know why car rack compaines don't make an acessory like this for when a fairing can't be used or when people just don't like the look of the fairing.