Roof box recommendations for m3?

[pnwadventures]

Yakima RocketBox 11, third year with it.

 

[ODWms]

These roof boxes look very aerodynamic. I‘m sure it’s been mentioned somewhere, but what range reduction numbers have you experienced?

 

[ghume]

Has anyone tried mounting the roofbox backwards and testing your efficiency? I remember reading reports that it helped a fair bit but have only seen anecdotal evidence of that.

I have a Thule Ascent 1600 that I tested mounted with the pointed end forward and the flat side forward (backwards?). With the flat side forward the car was on average 12% more efficient on the same freeway runs. I also tested this driving from Portland to San Francisco. The box was perhaps slightly more noisy, but the efficiency improvement was well worth it.

 

[PNWLeccy]

I have a Thule Ascent 1600 that I tested mounted with the pointed end forward and the flat side forward (backwards?). With the flat side forward the car was on average 12% more efficient on the same freeway runs. I also tested this driving from Portland to San Francisco. The box was perhaps slightly more noisy, but the efficiency improvement was well worth it.

Wow, that's quite an improvement! It makes me wonder why roof boxes are designed the way they are if turning them around increases efficiency so much