[basjoos]

I debated both approaches when I did my car, but figured the side skirts would help to keep the airflow travelling straight and parallel under the car, unaffected by the presence of any crosswinds, that could slant and redirect the airflows under the car, possibly increasing the drag. I'm containing the turbulence created by the wheels into a "pod" running down each side of the car with a straight, parallel airflow underneath the car in between the "pods". I recall discussing it with Aerohead on another site, who recommended the approach I took. Adding the side skirts made a noticable reduction in the dust trail kicked up by my car when driving on a dirt road.

My side skirts are made of coroplast and are designed to flex out of the way when scraping on bumps in the road. I deliberately made them overlong, sprayed them with black paint, and then after several days of driving, noted how far up them the paint had been scraped off, and trimmed them appropriately.