Roof box impact on MPG?

[Quetico]

Have any of you 5th gen guys have tracked your MPG both with and without a roof cargo box? From your first hand experience, what was the MPG difference?

I am planning for a ~2500 mile road trip. I have a Thule cargo box. I don't really need it, but it would be really nice to have. So I'm trying to figure out what the MPG difference would be, and how much it would cost in fuel to have it along. I get 19.5mpg average right now, and usually 21+ on highway trips.

 

[Prolex7]

I have a yakima loadwarrior. When I have it fully loaded up top it's not as aerodynamic as the Thule box would be but I only lost about 2 mpg. That was with the inside loaded down, too. I've driven from North Dakota to Louisiana with it like that. Also depends on how much stuff you're going to cram into your vehicle as well.

 

[brockeverly]

I have traveled many miles with gas cans and storm cases on my roof and never noticed a huge MPG drop. Then again, I am normally pulling my trailer when I do so my results may be skewed. I would say max 2mpg, but probably closer to 1mpg.

 

[Qjake]

Rent a Prius for your trip :shrug:

 

[GregGimbert]

At highway speeds my RTT costs between 3-6 mpg depending if I am going 65 or 80 in my 4th gen FWIW