I believe the wind tunnel tests proved the rear spoiler didn't work, the coupé needed the squared off rear end to prevent the body from creating lift.

good stuff CC

Here's another:





Well no, they did extensive windtunnel experiments on the Coupe (even with long 917-style tails - according to Mr Bangle ). It's true they settled on the "boot"-rear cos the slanted hatchback-rear created too much lift. And they got rid of so much lift they didn't need additional spoiler. That said, a small lip/spoiler like the one pictured will probably work very well, and reduce lift even further.

I thought that the hatchback rear boot was creating lift, which is why they went for the squared off rear (Technically called apparently a termed a Kamm Tail, end or back)
http://en.wikipedia.org/wiki/Kammback http://en.wikipedia.org/wiki/Wunibald_Kamm

I was originally quite opposed to rear spoilers on the Coupe but having recently seen both an M3, M5 and Cada I am starting to wonder if they don't add some visual impact to the rear of the Coupe.

Does the Coupe really have a Kamm Tail? I know the Alfa GTV certainly does...

More on the design of the Coupe, just in case you haven't seen it before.

Not really Per, you want the air to separate from the rear of the car cleanly, a spoiler (unless its a wing giving down force) will just make the air more turbulent at the rear which can actually slow the car down.

So that's why this kind of spoiler is so frequent on high-end cars like Audi RS-series, BMW M-series and Mercedes AMG-series..? That they're originally too fast..?
No really, it helps!

My M3 spoiler ... fitted for aesthetic purposes only

My two pennies, I think that the M3 is the most aesthetic and tempting.
The ones at the beginning of the post, look like they have fallen off, just not right.
When you see a Supra without a rear wing it just looks odd. So maybe its conditioning, if the coupe came originally with a wing fitted I wouldn't be saying that I think the coupe is one of the sports cars that really dont need a rear wing. Maybe they got it right! unlike the TT?
As an aside without going way off THIS is very interesting to watch on its own, but look at the wings front and back about half way through.

There's a difference between a spoiler and a wing

A spoiler is designed to interrupt (or spoil) the airflow over the rear edge of the bootlid. This helps to reduce the partial vacuum behind the rear of the car, which in turn reduces drag

A wing is designed to provide downforce, and doesn't care too much about drag

The vast majority of spoilers / wings are NOT designed to create downforce (or even to reduce lift) - they are designed to LOOK like they create downforce

Actually, I tell a lie - a wing that weighs 10kg will, by its very nature, produce 10kg more downforce. However, so would ten bags of sugar in the boot AND the sugar in the boot would be aesthetically more pleasing

Diffusors are nicer aswell.

Per,
The designers of these cars will do wind tunnel testing to make sure the spoilers have the correct effect, they don't just go to Halfords and glue on a spoiler or select one from another make of car and hope it will have the desired effect.
Look at the Bugatti, the spoiler is retracted in standard mode and that's speeds up to 137mph, it deploys to give downforce in handling mode and in high speed mode it's flush with the chassis.

Each to their own, I personally don't like the look of a wing or spoiler on the coupé but that's a styling choice and it's personal.

I know someone involved with design of Mk1 RS Focus and they told me that when they wind tunnel tested those, that the car needed 3BHP less power at 100MPH when fitted with the rear spoiler.

However, each spoiler needs to be wind tunnel tested for the coupe to indicate whether it would aid the Coupe

Also didn't they have to retro fit the little spoiler to all Mk1 Audi TTs together with ESP due to lift off oversteer accidents?

Well, there are some basic aerodynamic rules which applies to most 3-box cars (which the Coupe essentially is). The release at the end of the Coupe trunklid is a typical situation where you don't really need tests in windtunnels to make some estimations, if you like me, has seen a few before (I work at Volvo Cars, exterior design).

Wings however, can do with some testing on the specific car to see if they add downforce or just drag..

But surely the lip at bottom of rear bumper fulfils that role?

rAzOr_20vt I like that spoiler, can you post some more pics as I am considering the M3 spoiler for my Sprinty. It looks good, very good in fact!

Yeah no problem mate, i'll post some pictures later tonight.

The lower lip is mostly hiding the screws + stiffens the bumperskin. It's possible that it helps release..

Mine's here (M5-spoiler):
http://sfk.ibk.se/depa/showfile.php?carpic_no=2442&type=picture
http://sfk.ibk.se/depa/showfile.php?carpic_no=2441&type=picture
http://sfk.ibk.se/depa/showfile.php?carpic_no=2440&type=picture

Per, that looks great, your coupe looks pretty awesome, can you post a photo from straight behind? As if being followed by another car?

.. i would like to point out these are old pictures minus some mods; coil overs, exhaust and rear wiper arm removed etc

rAzOr_20vt That's made my mind up for me, I will be getting an M3 spoiler! Cheers for the photos, that looks awesome

very good choice and thanks very much lol

sorry to bring this up from the dead, i never knew the spoiler was fitted wrong

still the same to this day, 4 years on