2017 prius prime roof rack MPG impact?

From Consumer Reports.

 

For any vehicle, only install when needed (if not often) - or for the 'season', if that applies.

We did recently manage 57 mpg per the car's display, on a round-trip to Joshua Tree (~500 miles), including the full battery usage, with a Skybox 16 and loaded down Prime. I did keep it 5 mph lower than our standard highway speeds, though (65-70). Previous trips with a bare roof were 65 mpg, at the higher speed (70-75), for comparison.
The bare OEM racks also produce noticeable wind noise and I'm happy to take them off and on for when we need them.

 

hm.... 11% is a lot... I am not sure if that is the hit I am getting. Maybe I need to take off the roof rack and test it out. Ha!

 

I ran a theoretical calculation using drag coefficient and frontal surface area for just the naked Prius Prime and for the Prius Prime plus Yakima Skybox 16, and found that the mpg difference is around 8mpg. That's for 65mpg on a flat highway. I can try to post a link to the calculation, but I think since I don't have enough posts on this site it may not let me so I'll just post this then I'll start a new post with the link just in case!

 

Yeah, it can eat into your long distance range if going somewhere far on vacation. I'd take it off if not going anywhere.

 

FWIW, I've put on a set of used oem roof racks with no cargo box on my 2017 prime for about 1000 miles.
So far my mpg went down 0.1 to 0.2 mpg.

I don't drive too crazy on local roads, but I do tend to keep the fwy cruising betweem 75~80 mph.