vis wrote:
I found this aero-data for Ferrari P4/5 by Pininfarina:
Cx 0,340
Czf -0,123
Czr -0,025
Frontal Area (m2) 1,906
I was impressed and don't know why such a supersleek car has a Cx that high. It is not the first coupè I found with higher drag figure than common saloon cars. With my rudiments of aerodynamics I would state a coupè to have definitely less drag because of the smaller vacuum area at the rear, due to the sleeker silhouette than a saloon.
So, what I'm missing?
Maybe is some sort of "induced drag" caused by negative Cz (downforce)...
The need to counteract the lift (or even generate downforce) is certainly an aspect, particularly because as other said the car’s stylists, even if sometimes they brag about it being the case, usually don’t really take in account aero requirements on the basic design, so the aero work is more often than not a second stage fix leading to not optimal solutions (Audi TT anyone ?)
Still there’s a more important factor that leads invariably to increment of drag, and that’s the fact that the powerful engines typically fitted in sportcars generate lot of heat. The required cooling causes conspicuous increment of the drag, in particular because, even if these cars have everything needed to go really fast, they are still road cars so the dimensioning has to take in account that most of time it will run at low speed and possibly in traffic.
Also considering the same car model, say a normal saloon car, the version fitted with the most powerful engine often suffers a not negligible increment of drag compared with the base version, less powerful, exactly because of increased cooling requirements.
