As it happens, today Rob Palin (ex Tesla, Bentley and F1 aerodynamicist) has been in communication with me about lift (giving me feedback on that chapter in my book).
As always, what he has to say is fascinating. He states that one car company (that I am not going to name here) has these requirements:
- Front coefficient of lift greater than rear coefficient of lift up to 15 degrees yaw
- Actual forces need to be less than 10 per cent of each axle weight at top speed
He also emphasizes what I have been saying, in that steady state wind tunnel (and, he adds, short-run CFD) often doesn't capture the actual quick variations in lift. He writes:
In research I did back at MIRA, we saw easily 100% fluctuations in lift forces, on all manner of vehicles, with the associated spectrums varying wildly between vehicle shapes, and with individual modifications. A rear spoiler, for example, may have zero net effect on the mean lift, yet reduce the standard deviation of the forces away from that mean quite dramatically - and vice versa.
I just wish I'd had his feedback before I wrote my book, not afterwards!