Nissan Murano tail light aerodynamic detail

[MetroMPG]

Just got back from biking with a friend and noticed an aero detail (I believe) of the tail light of his Nissan Murano (like this):




Note the 90 degree step in the edge of the plastic, which I assume is there to promote clean separation (in the same way Daimler uses vents on its rear tail lights for the same purpose and GM added a pronounced "step" at the trailing edge of the Volt's bodywork:







Of course Nissan only applied a small aero band aid on the Murano. For styling reasons (I guess), the large presumably aero-unfriendly radius in the greenhouse transition from the side to the rear in the hatch area is left un-creased.

The Firefly/Metro has quite a lot of curvature at its side-to-rear transition from the hatch, through the tail lights down to the bumper cover. Zero attempt to fix a clean separation point. Hopefully addressing this soon with the boat tail...

[Frank Lee]

I think it's a place to put the reflector.

[gascort]

I see that too, but I have to wonder how much attached air there is there, right after the giant wheel well about .4m to the back of the car.
Sometimes I wonder if engineers are trying to prepare "us" for design to come. Aero ideas not taken the whole way out, but ideas that could transition easily if people dig the gradual style change. I think the back end of the Pontiac Aztek was too much for people... I bet it would get better mpgs because of its shape if it didn't have the dumb roof rack on it.
For "preparing" of the public, take a look at the 2010 Honda CR-V:
Follow that window line and you have a nice aero shape.

[Frank Lee]

I've long wanted to see the Cd values for the Aztek and an otherwise equivalent mini-van. Chevy Venture is the GM Aztek twin- same chassis + running gear- fuelecondotgov says they have identical fe.

[MetroMPG]

Originally Posted by gascort

I see that too, but I have to wonder how much attached air there is there, right after the giant wheel well about .4m to the back of the car.

But the tail light is interacting with flow that is mostly above the wheel arch.

Originally Posted by Frank Lee

I think it's a place to put the reflector.

I wondered that too.

But note that the rear facing reflector in the tail light assembly isn't in the step; it's incorporated into the curved plastic. It's the trapezoid at the bottom (not currently reflecting the camera flash in my photo.)

Demonstrating there's no functional reason they couldn't have done the same with side reflector (incorporated it behind the compound curves of the assembly). They didn't have to build the "step" just for the reflector.

I'm betting they killed 2 birds with one stone: airflow detachment was bird #1. Bird #2 was the stylists using the structure as a nifty place to house the side reflector.

[MetroMPG]

Originally Posted by gascort

Sometimes I wonder if engineers are trying to prepare "us" for design to come.

I think Ben was more or less wondering the same thing when he wrote this for Autopia:

Ugly Becomes Beautiful As Efficiency Reigns | Autopia | Wired.com

[NeilBlanchard]

Hi,

I think the edge is there to help the air separate cleanly. Similar to this bit on the rear quarter of the Toyota/Scion iQ:



There is a little wedge on the rear quarter window, and the bit behind the rear tire look similar...