[Richard O'Clery]

I don't have my copy of 'Competition Car Suspension' by Staniforth close by, but I remember him saying something like canards will produce a little downforce and lots of drag, but the performance gain of cars with them fitted seemed out of proportion with the expected results from the canards alone. He says that a massively beneficial by product was that the vortices created behind the canards would actively depressurise the undertray by pulling air out from under the car along the sides.

I guess the effect would be more pronounced with rounded sill cars like the MkIs, MkIIs, P4s and Lolas etc than the later square edged sill cars as the transition is smoother allowing the vortex to roll more easily down low along the side of the car, but I could well be wrong about this!