Basically, did anyone know, what is the theory or purpose of fixing a rear spoiler for car?

Apart from making the car look better,i think it does contribute to some downforce to the car when travelling at certain fast speed.

But, how the downforce theory work.

While I'm no expert, this is my grasp on spoilers:

Spoilers work as wings on an airplane, generating a pressure difference between the up and the downsize when the wing runs thru high speed air. Only that in a airplane wing, the pressure difference results in lift whereas in a car's spoiler, it generates down force.
The theory behind how the spoiler helps is that by generating down force, traction is gained in rear wheel vehicles as the wheels are pushed further against the road. So in essence, in the Lancer and any front wheel car, it does nothing, except maybe tighten the car's suspension at high speeds and reduce the gap between the road and the cars bottom, further increasing aerodynamics (don't ask me how though. I only know that it's better!!).

...Now let the flaming begin :P

^Pretty much what you said, but it also helps you corner better at higher speeds. The spoiler, in essence, is pretty useless for our car... cept for looks.

Do you thinks, installed the spoiler will also help to increase gas mileage and stable in high speed?

Yes it does help you corner at higher speeds (like when you power slide or drift.) on a front wheel drive car it would prevent you from spinning out due to too much oversteer by adding the grip to the back tires. in a rear wheel drive car it adds grip to the back tires which helps in acceleration, cornering (to a point). but it will lower top speed slightly due to the wind resistance added by the spoiler. thats where the downforce comes from.. in lamence terms. the air traveling at your spoiler is forced upwards. causing added drag and downforce due to the angle of the spoiler.

While I might be wrong, I don't think anything that adds drag and modifies the car's airflow will help with aerodynamics. I could be wrong though since the right spoiler in the right spot might help to improve the airflow and smooth air turbulence.

A spoiler is more effective the faster you go.

A car's shape is similar to a wing. Flat bottom, curved top. The higher speeds you go, the greater the change in air pressure between the bottom and the top of the car (greater pressure under the car)

This causes a lift effect, making the car unstable and want to slide/fishtail

A spoiler and front wings help counteract this by providing down force on the car that again, it proportional to the speed you're traveling

This doesn't really apply to our car. Were at the top of our cars limits when we get to a point where the effect of the lift/spoiler is functional. So they're basically just for looks.

Just for looks in our cars, as many people said. You'd need to be going pretty **** fast to obtain a significant amount of downforce. And even then it can't be much, as the angle of attack of the wing, is minimal. However it does create drag and probably does negatively affect your mileage.

Ok here is what I know from a huge physics paper on flight and wing design.

A car is essentially a wing like stated before, curved top flat bottom. This creates a low pressure area on the top because the same amount of air is moving over a greater distance faster than the underside of the car. This causes both a high pressue (on the bottom) and a low pressure (on the top) area. Thus creating lift. The spoiler does exactly what its name implies

It spoils the air. It causes the air passing over the top of the car to become spoiled and slow down creating a high pressure area above the back end of the car. This causes the downforce by counteracting the natural lift of the shape of the car.

And besides like stated as well our cars do not under normal circumstances experience a high enough speed to take advantage of the spoiler. The car would have to be going at minimum probably 90-100 MPH to actually take advantage of the spoiler.

But other than that just having a spoiler is +5 HP and +10 Ft/lbs Torque. :grin:

Yeah it does have so little impact on our car as our car does not goes as fast as those Formula 1 cars does on the track,as you can see how it affects the F1 cars when their gear spoiler is gone during an accident or so.if you want real specified details on those spoiler aerodynamics stuff,u need to consult those aerodynamics F1 engineers :D

As far as I understand, it also helps greatly for RWD cars in auto-x. I know some people who auto-x in RX-8's with some custom made GT wings and they say it makes a huge difference.

Sigh... Basically another word for spoilers is called an airfoil.

Our lancers are economy cars, having a spoiler or air dam or front fold or side skirt is going to do nothing significant to your driving or the car but instead will add on to the looks. That is until you decide to use your lancer as a track/drag car or for racing competitions, then the small extra downforce caused by those add-ons or kits will help a great deal. Then again, why choose a stock body kit?

Unless you're going some speed over 60mph on some turn, the spoiler isn't going to help much, and plus, 60mph is already going over most speed limits on local roads.

And no, adding on any of the accessories or body kits will not help your mpg. Actually, you'll tend to lose more and it is a psychological thing; the better looking the car, the heavier your foot becomes and thus you'll have a case of Lead Foot. :bwekk:

So adding on a Bugatti badge may give you some 1000HP boost, but you'll suffer some -17MPG loss :bwekk: