Quote Originally Posted by NickRally View Post
Couple of other thoughts after my first post on aero:

1. Double diffuser on the Ford – it was mentioned on this forum and also such thought crossed my mind when I first saw the Fiesta small diffuser at the launch. I thought there was no way that was all the diffuser they have designed in and it also appeared like the original road car “diffuser” on top is used as an additional extraction device, though it wasn’t clear where on the underfloor this particular air would have been taken from, even though there are plenty of openings on the underside as it would appear. Nevertheless looking at images a bit later on, I couldn’t see an air passage between the dedicated WRC diffuser and the road car one so I discarded that thought, but once again none of the images I have seen so far is clear enough to say for certain what’s what and I haven’t seen one in person. Maybe people that have seen the real car with their own eyes can comment?
Regarding double diffuser. I don't really think it is double. I was reading this book about aeordynamics (by Simon McBeath) and CFD analysis shows that efficient angle of diffuser is somewhere between 8-12 degrees. Now 8 degrees is quite shallow, any road car has this angle. And, as I understand primary function of diffuser is to balance downforce between front and rear (same as rake). So in Fiesta case it could be that front-end has enough downforce thus large difusser angle is not needed.