Those lips or flaps are under most newer cars now a day. Their purpose it to cut down on turbulent air flow under the car, specially around the tire. This cuts down the noise and forces felt by the turbulent flow under the car.

 

Hey I have the same question. One of mine is missing and I want to order a new one(or pair) but can't find them ANYWHERE on the net. Someone please help me get these "wind deflectors" ordered!

 

I have a set in liquid silver brand new in a box.
For a g37 sedan sport

 

I need the black rubber flaps that go in front of the rear tires, like pictured above. Can anyone help me out?

 

Are you saying they are painted? If so, they will surely taking a beating underneath the car.
Mine is black rubber and was recently hanging due to me running over something in the road. Went to good ole Pep Boys and they put it on the lift and secured it with another screw.

 

I know it's been a while but I am looking for that plastic screw button that is holding that "flap" in place. I guess the dealer is the only place since I can't find any info online regarding this.

 

Bumping this topic since I unfortunately got a wooden pike shot through my rear passenger side deflector and spent too many hours online trying to locate the part number. For future googler's:
Part number:
76856JK000 - Right Rear (passenger side)
76857JK000 - Rear Left (driver side)
Known as a "wind deflector" in the repair manual