stuntman - I agree. The more a car uses underbody aero to generate downforce, the more a fixed-floor wind tunnel will screw up the front and rear lift figures. The floor’s gradually thickening boundary layer is not a good simulation of the real world since there is no boundary layer on the road. For NASCARs with their deep front air dams and no underbody aero, that probably doesn’t make much difference. For Le Mans prototypes with their highly developed underbody aero, a fixed-floor wind tunnel may deliver pretty much worthless front and rear lift figures. Road cars traditionally use little underbody aero but recent Ferraris are starting to, so comparing the lift figures of a 360 Modena to an NSX-R in a fixed-floor wind tunnel can be problematic.
But the drag figures should still be pretty accurate. Wind tunnels measure the drag of a car and if you divide that by its frontal area, you can calculate the drag coefficient. If your estimate of the frontal area is wrong, you’ll get the wrong drag coefficient. But the overall drag index (Cd x A) is what was actually measured so that is not impacted.
Using the same wind tunnel, Sport Auto measured the drag indices (Cd x A) of various cars. Here’s a selection:
2005 Porsche 911 Carrera S (997) : 0.54
2003 Porsche 911 Carrera (996) : 0.56
2006 Porsche 911 GT3 (997) : 0.58
2007 Porsche 911 Turbo (997) : 0.59
2005 Corvette C6 : 0.59
1997 Honda NSX: 0.59
2002 Honda NSX-R: 0.60
1999 BMW M5 V8 : 0.62
2002 Mercedes SL 55 AMG : 0.63
2007 Corvette C6 Z06 : 0.65
2009 Corvette C6 ZR1 : 0.66
2003 Lamborghini Gallardo : 0.66
2008 Lamborghini Gallardo LP 560-4 : 0.67
2006 Ford GT : 0.67
2010 Ferrari 458 Italia: 0.67
2004 BMW M5 V10 : 0.68
2006 Ferrari 430 : 0.70
2007 Audi R8 V8: 0.70
2009 Nissan GT-R : 0.71
2004 Porsche Carrera GT: 0.72
2009 Audi R8 V10 : 0.73
2004 Dodge Viper : 0.75
2009 Aston Martin DBS : 0.76
2010 Lexus LFA: 0.78
2004 Pagani Zonda S: 0.84
Recent Porsche 911s have less drag than an NSX, but a Nissan GT-R has a lot more.
