Originally Posted by feta_mgp
It is disputable by anyone who knows anything about aerodynamics and how it affects a 3200lb car going 60-70mph... you will NOT see a noticeable dip in fuel economy with a roof rack. Especially the Aeroblade (and I don't even have one!) first of all a roof rack is not a sheet sticking straight up catching wind and producing much more drag... it's a rack, usually now designed with "flat" bars across, and a purposefully (and aesthetically cool/customizable) designed "shield" up in front to deflect the air up and over just like your windshield does. So... you know, it's not going to do a damn thing to your fuel economy.
As for slamming your bikes into your garage door and damaging your car, all I read in that paragraph was that you're telling yourself you're going to be one of those people and apparently you don't know how to handle your bike or pay attention. If you're too fatigued to realize your bike is on your roof rack and drive it into your garage, you shouldn't be driving anyway. And if you know a lot of those people maybe you should tell them what I just said.
Just my .02.
Do some research on the matter before you spit out "indisputable" facts.
A roof rack without bikes on it will impact fuel economy a significant bit, perhaps a special aerodynamic one will do so less than a conventional one. Put some bikes up there in the air flow over the top of the car and you're talking a major MPG hit. A hitch rack without bikes on it will impact fuel economy a tiny bit at best and a small bit with bikes on it. It's been documented many times and I just don't have time to go around educating you obstinate deniers, look it up yourself.
As far as running your roof racked bikes into an overhang, no one thinks they will do it but I've seen it happen so often that I know it's a very real concern. It's extremely expensive when it happens.
he Roof Rack MPG Experiment
He compared the gas mileage of his car at 54.7 mph (88 kph) with 1) no roof racks, 2) an empty roof rack, and 3) a mountain bike on the roof rack.
He found that compared to the baseline of no roof rack, the empty rack reduced his MPG by -12.7% and the roof rack with a bicycle reduced it by a whooping -27.3%. And since air resistance increases exponentially with speed, the difference would have been even bigger at 70 mph (many people drive at that speed).
While the methodology isn't 100% scientific, and every vehicle will be affected differently by a roof rack, it gives a good idea of how big a difference a roof rack (empty and full) can make.
So please, if you're not using it, take the roof rack off your car (and forward this tip to your family & friends)! It's such a simple trick, like inflating your tires properly, that could save millions of gallons of gas.