Why do 250 mph (400 km/h) supercars have 0.40+ Cds?

[Big time]

Originally Posted by ERTW

It's not so much that they need that much downforce at 250 mph. They want usable downforce at 100 mph and they happen to have enough hp to go 250. The faster you go, the lower the Lift coefficient you need. ie. 100 lb will keep the car on the ground regardless of speed.

So right.
I guess that explains it all.

Race regulations forbid actively variable aerodynamics.
Many supercar manufacturers race or provide extensive help to those who race.

While there are no rules limiting active aerodynamics on road cars I think the designers are psychologically stuck with racing rules requiring fixed aerodynamics.

In the 90s I was a little kid who was astonished with the Lamborghini Countach successor the Diablo.
If it had a rear wing it couldn't reach the record breaking 202 mph. I just couldn't believe Lamborghini designers were so stupid as not to place a retractable wing on it.
The fact that retractable wings took about 20 years to be widely used in supercars shows how much designers are focused on fixed aerodynamic regulations.
Maybe they still expect supercars to be modified and raced?
Maybe they are pressured to leave room for racing mods for Marque bragging rights?
This happens despite the fact that most top-end supercars are deemed to expensive to race.
Only the McLaren F1 raced. AFAIK no Bugatti Veyron ever raced at least not in really competitive races with tight rules.

[aerohead]

Originally Posted by Big time

So right.
I guess that explains it all.

Race regulations forbid actively variable aerodynamics.
Many supercar manufacturers race or provide extensive help to those who race.

While there are no rules limiting active aerodynamics on road cars I think the designers are psychologically stuck with racing rules requiring fixed aerodynamics.

In the 90s I was a little kid who was astonished with the Lamborghini Countach successor the Diablo.
If it had a rear wing it couldn't reach the record breaking 202 mph. I just couldn't believe Lamborghini designers were so stupid as not to place a retractable wing on it.
The fact that retractable wings took about 20 years to be widely used in supercars shows how much designers are focused on fixed aerodynamic regulations.
Maybe they still expect supercars to be modified and raced?
Maybe they are pressured to leave room for racing mods for Marque bragging rights?
This happens despite the fact that most top-end supercars are deemed to expensive to race.
Only the McLaren F1 raced. AFAIK no Bugatti Veyron ever raced at least not in really competitive races with tight rules.

It may be that only recently,automakers have had the confidence that serious active aerodynamics were 'bulletproof' enough to outlive the lifespan of the host vehicle,and in so,not jeopardize the safety of the owner/driver.
Fatalities are not the sort of thing an automaker wants their product associated with.GM 'rolling sarcophagii' would be a contemporary example.
As confidence grows with certain technologies we'll probably see more and more active structures.
In failure mode,the car may fail safe,staying within a performance envelope unaffected by the loss of a components function.