I have recently acquired a set of Yakima 50" CoreBar crossbars for use with my existing Yakima BaseLine towers bare-roof, roof rack set up. My previous set up consisted of Yakima 60" JetStream on Yakima BaseLine towers. I've had the opportunity to test out the two different set ups and their effect on the Prius' MPG this past few weeks.
The set ups included a Yakima 46" Windshield fairing.
The 60" JetStream set up yielded an average fuel efficiency of 48.3 MPG over the course of two weeks, two fill-ups.
The 50" CoreBar set up yielded an average fuel efficiency of 53.1 MPG over the course of 1.5 weeks, one full and one partial fill-ups.
My average commute fuel efficiency between fill ups these days is 54.6 MPG. A noticeable dip in fuel efficiency is expected, but the 60" JetStream took the biggest hit. While the JetStream is designed with aerodynamic in mind, the extra 10" of bar (5" each side) on two cross bars is enough to drop the MPG down by a good 6.3 MPG. The 50" CoreBar set up on the other hand took a meek 1.5 MPG dip in MPG.
For now, I will shelve the 60" JetStream until I have use for them, i.e. carrying bikes, snowboards, etc. in addition to the SkyBox. For our road trips, we'll be primarily hauling the SkyBox Carbonite 16 and the 50" CoreBar crossbars will suffice.