E90 rear spoiler

[Megabucks38]

Does the rear spoiler improves stability of the car??

 

[astroboy]

yes.. at above 200kph.. more rear down force, better rear grip going thru turns.. the steeper the spoiler angle, the greater the down force. Trade off will be sacrifice of top speed. There really is no free lunch.. :smokin:

 

[peanut]

I put on rear Hamann roof spoiler and M boot spoiler and not really sure it helps the stability at 200kph! I think a lowered suspension like JIC Cross or KW2 plus a thicker set of ARB will probably help more.

 

[astroboy]

So sum it all, the boot lip or rear spoiler is more show off than stabilizes the car.

 

[MSport]

Fuyoh! Gaya ada, performance tarak!

 

[Schwepps]

Maybe they'll work if you put a row of shark fins on the roof to direct the airflow?

 

[Lefthanded]

The addition of the tiniest rear spoiler, however, did help produce downforce in the rear aka negative lift. For some, the look usually outweighs the actual effectiveness of the body changes.

 

[astroboy]

Unless you put in a GT wing that you even your mother can dry cloths on, with a 45 degree tilt angle, then sure got effect, even at 60kph.. and at 200kph, u can proly drive on the ceiling of a tunnel..

 

[valkryie]

The spoiler as it names suggest just spoils the air flow over the car.
This will reduce the uplift tendency of the car when the air flow over the car is not smooth.

But if i am correct you will need some wings to create downforce for the car and this is not what the spoiler is for.

 

[Schwepps]

You're very correct valkrie, but they don't even reduce the uplift tendency as you put it. Spoilers do not create downforce. They're meant to reduce drag and thus improve fuel consumption. The purpose of a spoiler at the trailing edge of the roof or boot is to reduce the tumbling of air over the roof/boot edge creating turbulence and a low pressure area (Bernoulli effect), which causes drag and instability.

Downforce can only be created by a wing with a cross-section similar to an aircraft wing, but fitted upside down. Then the low pressure area is the underside of the wing, pulling it down, the opposite of an aircraft wing. The majority of rear spoilers and wings fitted on cars out there are totally useless for anything but decoration.

A front spoiler or air dam CAN reduce the volume of air going under the car, thus stabilizing it. But to do that, the air dam has to have no more than 5cm of ground clearance, which won't be practical on a road car. To create downforce, you need diffusers on the underside of the car (note the double-diffuser issue in this year's F1) to speed up the air, create the Bernoulli effect and thus pull the car down. So the majority of front spoilers out there are also useless.

 

[valkryie]

Hi Schweep,

Thanks for the nice writeup. Spoilers like you say reduce drag and improve FC. I don't mean to imply that spoilers increase downforce just that they spoil the airflow based on an article i read long time ago about high speed accidents involving audi tt. After which audi fitted the tt coupes with rear spoilers to reduce uplift tendency something like aircraft spoilers do (reduce lift but not necessarily increase downforce).

But i am no expert and this is just my inference from my readings. Anyway as you said spoilers are generally for aesthetic purposes.

 

[Schwepps]

The article you read was a bit optimisitc. Spoilers are called that because they 'spoil' the laminar flow of the air at the trailing edges and delay air separation which turns into vortices, turbulence and a low pressure area just behind the car. Reduction of uplift would be very minimal, if at all. A front spoiler WOULD help to reduce uplift under the car by deflecting air to the sides, but it would have to be almost touching the road surface in order to do that.

To achieve a few percent of air flow effect needs a lot of calculation and testing. Aerodynamic design and wind tunnel testing take up the biggest chunk of F1 development cost. Just buying the nicest looking spoiler that fits on one's car isn't going to do much, except empty the pocket and boost 'feel good'.

 

[E46Fanatic]

Here's what BMW has to say about their BMW Performance Front Carbon splitters..

Important notice:
The installation instructions are not
included in the retrofit kit. Print out
the latest update of the instructions
from
the Aftersales Assistance Portal (ASAP)
and hand them over to the customer.
It is recommended that the attached
parts be installed in conjunction with
an original BMW rear spoiler, as this
improves the aerodynamics.

http://www.realoem.com/bmw/showparts.do?model=VB12&mospid=48482&btnr=51_6029&hg=51&fg=95

I guess there is also some function besides form afterall.