You are not politically correct enough for all those lip-less cars out there! It's discrimination!

Just call it a bumper cover. That's what it is.

But it doesn't cover 90% of the bumper.

The bumper is 100% covered.

Are you guys talking about the valence?

Subaru technically calls it a diffuser and in the official BRZ brochure Subaru claims the channeled roof and diffuser both reduce drag.

Low .28 Coefficient of Drag2
To a sports car, wind is like weight—the more of
it you have to move, the more it takes from your ability to perform. Features like a channeled roof and rear diffuser help the BRZ cut through the air, sharpening the performance you’ll feel.

All the rear bumper cover acts like is a parachute.
Put an actual diffuser on it and you'll notice the difference.

The suitcase oem muffler has an angle to it that persuaded air under the bumper cover.

I have a velox diffuser and yes it’s better but that’s not to say the oem one is a parachute

norcalpb: oem one is parachute depending on what catback is used, as it works together with catback-s muffler. If there are different shaped aftermarket mufflers, eg. longitudinally placed or at angle, then they would benefit from extra diffuser or in general some aero element to to direct flow around stock bumper cover's edge.

He said the OEM muffler. Your reading comprehension skills need a tune up.

No need to. Like some spellchecker clippy, you'll always stick around and will correct any mistakes.

To expand on this, if you don’t have a muffler you can still buy these for pretty cheap to maintain the flow that the stock muffler creates. I agree that a car without a muffler is creating a parachute due to the openness behind the bumper.

Apexi:
http://www.ft86speedfactory.com/medi...diffuser-4.jpg

Trd:
http://www.evasivemotorsports.com/mm...S342-18003.jpg

Borla:
https://sep.yimg.com/ay/yhst-8488678...ion-fr-s-3.gif

Is it?
Show me how the diffuser covers 100% of the bumper?

There is no diffuser.
There is bumper cover, and that bumper cover covers 100% of the bumper.
A bumper cover being what lay people call a bumper, and a bumper being what lay people call a crash bar.
Does that explain it for you to understand more easily?

Oh cool, a lay person. I must be a lay person.

Feel free to educate Subaru too, but feel free to place blame on their marketing department.

https://parts.subaru.com/a/Subaru_20...10-591-01.html