Yeah if the "cf picture (lol)" looks too cheap or whatever, I may end up returning it and getting the real cf one. Or just having the ebay one painted body color.

 

From a certain perspective, CF *is* plastic - fiber reinforced plastic is fiberglass just with a melted plastic vs epoxy.

 

Are there any aerodynamical advantages to these spoilers or is it more show?

 

I thought I remember someone saying recently that they did some kind of cheap airflow test off the back of their G but I can't seem to remember where I saw that. I would assume a lip spoiler has at least a slight aerodynamical benefit. That's not the reason I'm getting it though. I don't like the chrome piece on the trunklid and I feel like the bottom of the bumper sticks out too far in comparison to the trunk. I like the rear end to be more equal length top to bottom, if that makes sense. Also I'm getting my windows tinted this week along with some gloss black vinyl on the window trim, and I feel like a CF spoiler would compliment that and my wheels.

Here's another car that shows the "big butt" syndrome that I think looks so wrong:

 

That was Mike... right here in this thread. Literally 18 posts back.

I suspect it's almost always just a trim piece. However, there are street cars with active aero that's there for a reason. I remember reading how the active aero in the old Crossfire kept the car more stable on the highway than otherwise.

 

lol guess I didn't scroll up far enough

 

I’m surprised nobody tried to use filler and a lot of sanding to mold the chrome piece into the trunk to make it flow better and then paint the chrome piece (it’s plastic right?) to the body colour. I know what you mean about the big butt bumper syndrome.

 

I’ve debated molding in the chrome piece but the trunk release and camera are housed in the chrome trim. If either ever failed you’d just be doing without from that point on I believe. Never checked under the trunk lid to see if they are accessible that way though.

 

So the short answer is that spoilers and wings are almost exclusively a style item. For most OEM spoilers even more so. Spoilers generally increase drag and therefore fuel consumption so manufacturers make them as ineffective as possible.

Medium answer - coefficient of friction drag doesn't really become significant until about 45MPH - see where rain starts to bead and run off on your windshield with the wipers off. Since most cars average speed is below that, no effect whether you have a subtle trunk lip or STI wing. Above 45, things get interesting and complicated.

Longer answer: It depends. A trunklid-end spoiler or wing is likely not enough into the airflow at speed to affect downforce (or drag) much. But you can't really say for sure until you test it experimentally (more below). A roof-rear-edge lip likely *does* change airflow, by changing the laminar flow departure angle (and maybe smoothness) from the roofline. Good? Bad? Need to experiment. Depending on the overall shape of the car, and the speed, and any crosswinds, a trunklid spoiler *may* help with turbulent flow suction drag behind the car.

2 tests that us non-NASA connected folks can do: tuft testing and air pressure differential testing.

Tuft testing is even taught, to an extent, at the high school level by NASA outreach: https://www.grc.nasa.gov/WWW/K-12/ai...tunvsmoke.html To do this on a car, all you need is yarn, scissors, lots of scotch tape, a buddy who also has a car, and a buddy who can run a camera. Tuft the car (I'd recommend one surface only vs the entire plane as shown), drive between 50 - local limit on a straight, smooth 4-lane road, have buddy in chase car follow and/or be slightly in front or behind, have camera buddy film out rear side windows. It's actually really neat to see what the air is *actually* doing around mirrors and fold lines etc.

Here's another good article: https://www.autospeed.com/cms/a_111110/article

Second test comes from the homebuilt aircraft crowd. Water tube manometers are very simple: https://www.autospeed.com/cms/a_2159/article

The homebuilt folks would make a manometer backing board with a bunch of u-bends, and then put the multiple taps in different places - along the hood edge, middle of hood, etc. to see what the pressures were like relative to each other (not an absolute measurement). Good way to site hood vents and intake scoops. Also a good way to check for lift at the rear end of the car...

 

I'm also on the hunt for a spoiler but I want something that isn't CF (appearance-wise). If it could just fit without any modification to the holes for button/camera that is what I want.

Some older pics that show the spoiler well: