If I recall reading a Motor Trend magazine, they said that stock spoilers basically do nothing for performance. They actually found that it hinders performance (I think). For it to have any effect, the spoiler would have to be higher than the roof to apply "real" downforce. And front spoilers are like that too. I read in an issue of Muscle Mustangs & Fast Fords when they were comparing the '93, '95 and '00 Cobra R, that the '00 ran faster in the 1/4 with the front spoiler and rear wing off because it created more drag during straight line performance. They gained one mph and nearly a tenth off the 1/4 time. Pretty good. I know that Porsche has that spoiler that comes up at around 50mph...but honestly do you guys think that stock spoilers do anything to help with downforce? Has there been a real test on it, besides straight linie performance?

 

the stock spoiler is just for looks. it may not serve any performance purpose but it looks good