(e-mail address removed) wrote in @q75g2000hsh.googlegroups.com:
Does anyone know how cg for a car is determined?
Is car during testing in the windtunnel placed on a treadmill
running at the speed of the airflow to account for the effect of the
rotating
tires or it's completely stationary?
How does 08 impreza frontal area compare to 07?
Not sure how Cd is calculated/determined but I do know that windtunnel
time is typically not done with the wheels turning. I personally have
always seen this to be a serious shortcoming in windtunnel testing. F1
cars sometimes use a moving "road" surface during testing but this is
EXTREMELY expensive and, for the typical passenger car manufacturer, not
worth the cost.
As a former bicycle racer, I know that spinning wheels have a profound
effect on the aerodynamic drag of a vehicle. Witness the "smoothie" wheel
covers of the Bonneville racers and the disc wheels on racing bicycles.
Now, look at the wheels on any street car. Do you see any real
aerodynamic considerations? I don't. Wheels could be designed so that
they help pull air out from under the vehicle, thus improving
downforce/stability at high speeds, as well as improved engine and brake
cooling and potentially lower drag. As far as I know, the only
aftermarket wheel ever made with this in mind was the Enkei 81 (or maybe
it was the 82). I'm not sure Enkei even makes that wheel any more. I
thought it looked really nice though...like a thick fan.
~Sh0ck~
