[mwilliamshs]

Originally Posted by aerohead

1) the majority of the central portion of the airdam can be as straight as the bumper and valance,but the outer edges should roll into a radius,then extend straight back to the edge of the outer tread line to kick the air onto the sidewall of the tires,leaving as small a gap as will accommodate wheel flop from lock to lock.
2) The rocker panel extensions should pickup where the sides of the airdam leave off,at the outer edge of the tread at the tires rear,again,minimizing the gap.You want the tire face essentially even with the new 'sides' of the van.
3) If the rocker panel extension behind the tires begin at the outer tread edge,then gently taper inwards,they become the vertical equivalent of a diffuser,allowing the air to decelerate without separation,and by the time this flow breaks away at the rear,it's imparting a higher pressure to the wake region,reducing pressure drag.
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Later on,if you add a belly and diffuser,you could add actual wheel fairings below the diffuser to streamline the turbulence behind the tires,as land speed record cars,SAE and Shell Eco Marathon racers,and Solar race cars use.

THANKS A TON!!! EXACTLY WHAT I WANTED TO KNOW AND THEN SOME.