a boring bit..
a body travelling through air will always generate lift..
lift is dependant upon the shape of the body..
lift in aerodynamic terms is force acting in any direction.. up.. down.. sideways.. anything..
a cannon ball generates lift in all directions equally.. therefore it flies straight..
(forget the gravity bit.. that's something else)
half a cannon ball will generate lift in one direction.. (if you can find a way to stop it from rotating in flight)
and you miss what you're shooting at..
the generation of lift requires energy which has to come from somewhere..
In a car that's the engine..
Most cars generate upward lift..
which requires energy..
which comes from the engine..
A spoiler reduces upward lift by disturbing / spoiling the airflow..
therefore more engine energy available to do what its supposed to be doing and not lifting the arse end of the deck..
The CD will increase a tad but but more gained for the above reasons..
So I reckon they go faster..
And we can all feel good about spoilers because they also look the dogs b*****s..
The idea that a formula one car can be driven flat out accross the ceiling is a myth..
A way of testing a 'Chav wing' is to pile bags of cement onto it until the suspension compresses a couple of inches.. in most cases the wing will either snap off or the boot lid will implode.. Try it.. not on an Alfa..
I tend to go on because unlike Turtle I've been married for a long, long time..