A spoiler directs airflow, not improves it - it's chief use at the
rear of a car is to increase downforce; to make the air push down on
the car. A high speeds, the air moving under the car can create enough
lift to make the car unstable and hard to control, since you're
essentially creating hurricane-speed winds under and around the car. A
front air-dam reduces the air moving under the car, while the rear
spoiler interrupts the flow and causes it to push down on the car,
counteracting the lift.
So, do you need one? Definitely, if you're regularly driving at
over 120 mph. At normal US traffic speeds, not so much. Lowering the
car to Euro specs (are they different anymore?) would make the car
stable up to Autobahn speeds, since that's what the car was designed
to handle. You might notice a slight improvement in handling with a
rear spoiler at such speeds, but you still wouldn't *need* a spoiler.
2003 BMW 325i Black/Black
2003 BMW Z4 Black/Black
Yes. I'm referring to the roof spoiler. Maybe the two spoilers work together
for optimum airflow? Could it be that they "engineered-in" an aerodynamic
flaw so they could sell an accessory "fix" later ( to increase the bottom
line)? Shrewd marketing perhaps? Does it extend very far over the rear
window and act as a sun visor?
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