Postby underworld1001 » Sun Dec 29, 2019 11:20 am
They're crossbars. They're not going to drop your mileage by any margin even if they were squared. Now if you add a roof rack or one of those enclosed roof carriers on top, then yes.
As far as handling, I can possibly see the crossbars acting as miniature spoilers, but anytime I've been behind a semi my vehicle was a bit wobbly due to the airstream being created by the tractor trailer and not my vehicle. This was with crossbars or not.