decklid spoilers

[mikejungle]

do decklid spoilers like the one that comes with the is's serve any purpose besides aesthetic enhancement?

if they serve a functional purpose, can anyone explain? thanks.

[Danny]

Downforce.

[e30pwr]

At the speeds your going to be reaching, not one bit of a benefit besides looking good.

well, no, at any speed they wont do anything.

[nando]

yes, they actually do offer an aerodynamic advantage - but the only real improvement you would see is a small (1-2%) increase in mileage, which is most likely it's intended purpose. It's not big enough to add much downforce. I have one in the garage I don't really want that bad, but I might do it just for that reason..

[Uber E30]

Nope... i doubt any true aerodynamic benefit is made with them, and they deffinatly arent making any downforce.

[sticksdaman]

same goes for front IS lips

[rThor432]

Top speed on a standard late model 325i is ~133 mph according to factory literature. The 325is is rated at ~137 mph. Aerodynamics are the only real difference that would affect that number.

If I remember correctly.

[gearheadE30]

Actually, I think I read in an old advertisement or something that the is lip (the trunk one) actually makes 15 lbs of downforce at something like 120 mph. Of course, the net aerodynamics probably still produce lift at that speed...

[NOMAD]

it's not for downforce, it is a spoiler, not a wing.
It "spoils" the airflow over the rear trunk lip which, in essence, "cuts" the airstream so that it releases from the rear of the car. A minute increase in mileage may be present when run at high speeds but it does help you slip through the air easier.

Without it the air comes off the roof, down the window and rear trunk lid and wants to curl down towards the rear bumper. A large swirling "tube" of air results that actually is some of the wind force that you have to overcome in order to move forward. Drag is more than just on the front of a car. So a good lip spoiler (not saying the BMW is the best) will interrupt (spoil) this air current and let it break off cleaner, sending it straight off the trunk behind you.

The front spoiler pushes air away from the front and keeps it from building under the car, so it reduces the "wing" effect of a car body going at high speeds (car gets floaty and grip decreases). Less air under the car = low pressure = more overall downforce from the air going over the car.

Just a little science.

[nando]

same goes for front IS lips

same deal - it's closer to the ground, meaning less air to swirl around all the crap and doo-dads underneath your car. So you net a small increase in fuel economy and a slightly higher top speed.

nobody is suggesting these offer downforce like the wings on an F1 car, it's a similar idea with a different purpose. These theories are well tested and proven - a lower front airdam and a sharper cut off on the trunk are both significant aerodynamic advantages.

[mikejungle]

yeah...i thought downforce was created by air flowing underneath the wing to act like an upsidedown airfoil
. Does anybody have a picture or something of how the spoiler works? Maybe how the airflow looks like with a spoiler and without?

Prior to this, i didn't even know the difference between a spoiler and a wing...

[Aptyp]

no one knows word VACUUM?

In case some people don't know, but all m-tech I goodies were designed in an air tunnel. If it had no effects, BMW wouldn't put them on.

All the aero goodies don't come into effect until 90mph though.

[Delphinitive]

can't imagine there are any crazy huge benefits or more people would know more about it.

that being said; the germans don't do anything without a purpose.

[BrewCity11]

Paging JasonC.

Didn't the Kamei spoiler and windsplits' brochure come with multiple comments about how it improved gas mileage? Windtunnel testing?

[JasonC]

Paging JasonC.

Didn't the Kamei spoiler and windsplits' brochure come with multiple comments about how it improved gas mileage? Windtunnel testing?

If i can find it again, i lose it everytime i go to look for it. But when i don't need it, there it is .

But i do recall it saying that about drag and gas mileage and so on. And i think they show a picture of them testing a car in a wind tunnel, but it's a 3rd gen Camaro.