Altairs right about that. Its an aerodynamic phenomenon that basically results in an air cushion or 'pillow' that forms allowing airflow to slip over the entire bed in a smooth arc which is maximally effecient for that case.

With the tailgate down, the airstream is pulled down believe it or not in a concave curve into the bed space, which created slight suction or draw. This acts as a pulling force not unlike a parachute. This is the same principle used on open wheel race cars like indy cars and F1 cars, where the majority of downforce is generated by the shape of the undercarriage not by the wings. THe undercarriages are scooped upward toward the middle creating that concave airstream sucking the car to the ground. Sometimes with force close to equalling the weight of the car itself. Which is pretty cool since in a perfect theoretical scenario you could drive upside down @ 240mph.

Sry if too geeky, just super cool stuff.

I'll drive w/ tailgate down when taking bike to track and stuff, or carrying long loads but not otherwise.

Thanks for listening to me ramble...

 

oh i forgot about that whole debate... yah

 

Just thought I'd post an update after my first trackday w/ the truck and bed extender.

I'm SOOOOO sold on the quick release thing. Latch, latch, pop... the extender is out. Set up ramps, load up bike, tie it down... pop, latch, latch... ready to roll. Takes five seconds and is sooooo damned handy. Didn't sweat the rest of my gear back there in the bed a bit.

Totally worth the 200 smackers and 30 minutes of assembly.