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In Reply to: Why rear spoilers.... the facts posted by John Stein on March 31, 2002 at 18:00:05:
dear john,
i am of the understanding that a "FUNCTIONAL" rear spoiler increases downforce, which in turn raises the coefficient of drag. this increase of drag (less top speed) is usually accepted in exchange for improved high-speed stability. the added downforce is usually measured in pounds of force on the rear axle. I have owned several e30 M3's. BMW Motorsport manufactured a 3 position rear spoiler for these cars. in the highest position, the cars top speed is reduced, but the cars tendancy to oversteer is also reduced, enabling the car higher lateral accelleration (cornering power).
in the real world, a BMW's top speed is normally not reached that often. so it makes sense to play with the areodynamics and generate some down force. this discussion also applies to front spoilers (sometimes called splitters), except the add pounds of downforce on the front axle (used to tune out understeer...).
in my '90 M3 i have pulled 1.33g (thats not 1.04) on street tires (yokohoma AVS intermediates). this car has genuine BMW Motorsport DTM (german touring car) suspension. the front spring rate 684 lbs/inch 1026 rear. the car is terribly stiff, but handles like nothing out there.
best regard, todd
ps: your black buffalo armrests are in the mail.
Gents...
We all understand that BMW RARELY does things for cosmetic reasons.....
Like it or not... BMW had an engineering and performance reasons for adding the spoiler to the e23...
Put simply... It significantly reduced the coefficient of drag.
I cant remember the numbers exactly (but I promise I will find them..) but if memory serves me correctly it reduced the COD by about 28%.
So what does this mean in real world performance.... In Germany, where these cars regularly run at 140mph+ and fuel is REALLY expensive.... , the reduced drag relates to lower fuel consumption, faster acceleration, more down force at speed (better handling and stability), and last but not least, higher top end speeds...
So.... Like them or not... BMW did have their reasons for tail pieces...... and the reasons were performance oriented, not just to join the ranks of those manufacturers sporting psudo-effective rear fins
Just my .02....
Regards All
John Stein
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