roof-rack crossbar aero effect

Someone recently posted about the vacuum by the wagons at highway speeds, and it was suggested to use the old style crossbar at the rear position to alleviate this. I can't find that post now, but I meant to get back to it.

I had never heard of that vacuum effect on the wagon or recommendation before. I've been leaving the crossbars off my caprice because I always assumed it probably helped mpg, even if it's a minute amount. Has anyone done any comparisons with/without/with just one crossbars ? Doesn't need to be super scientific.

The thread referred to high speed affects...over 180 MPH. Depending on the shape of the rack it may or may not help/hinder the aerodynamics. Someone would have to put it in a wind tunnel with smoke to see what the air is actually doing. I think the difference between having the roof racks on or off would be too small to measure, except for over a long time span. The other changes in the car over the time necessary to get usable results could throw the whole research initiative off.

Fred Kiehl wrote:

over 180 MPH. Depending on the shape of the rack it may or may not help/hinder the aerodynamics. Someone would have to put it in a wind tunnel with smoke to see what the air is actually doing. I think the difference between having the roof racks on or off would be too small to measure, except for over a long time span. The other changes in the car over the time necessary to get usable results could throw the whole research initiative off.

fair enough.