That E46 roof spoiler

I asked this question a few weeks ago and got some good answers but no one answered my original question: Why the roof spoiler is there (E46. Maybe
others?). So, does anyone know why the engineers at BMW have added this feature? Seems to me that a smooth roof-line would create the best flow of air over that part of the body. I understand the theory and usefulness of the front air dam, side-skirts and rear deck spoiler. TIA!
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snipped-for-privacy@bigfoot.com sgfan3 says...

IIRC the theory behind roof spoilers is that the downforce is applied to the balance centre of the car, so if the car is nicely balanced then you get equal downforce at both ends.
It's all cobblers, of course, since unless you're on a race track and doing about 150 mph, it's going to make bog-all difference to the handling. You could try removing it and seeing what happens. If you immediately crash, I was wrong.
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sgfan3 says...

one
of
of
I think you''l find they start becoming effective at far lower speeds than that. ISTR it's at something like 50-60mph. Mike.
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snipped-for-privacy@lycos.co.uk Mike G says...

I doubt very much if 99 out of 100 drivers would notice at those speeds.
But since a blind test is unlikely, we'll never know.
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Thanks everyone.
sgfan3 says...

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sgfan3 says...

no
Maybe
this
flow
usefulness
to
you
than
And what has that got to do with my comment? I also think your explanation of their purpose is incorrect. AIUI they are intended to reduce drag, rather than contribute any downforce. Mike.
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snipped-for-privacy@lycos.co.uk Mike G says...

The inference was, by your use of the term "start becoming effective", that it would have a noticeable effect.

It may very well be. If you look, I said I wasn't sure.

So in other words, you don't know either.
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