The straps you're attaching the top of the Kammback to the car with will create some drag when wind gets under them, like a bike rack strap does. They are going to negate a big part of the aero benefits, and at 60 mph they'll vibrate like a guitar string. It would work a little better with a different attachment up front.
The Kammback itself looks awesome, nice work if it will hold up! Maybe a little aggressive on the side curvature, but it looks a ton better than the one I put on the Festiva that was actually made for the car! Give it a couple of tanks to see if it has a positive affect on mpg. Mine actually gained me about 2 mpg from what I could tell.
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