"Bruce" wrote in message

On Sat, 31 Jul 2010 19:55:31 +0100, "Recliner"
wrote:
"Tim Woodall" wrote in message
e.uk

Obviously, this breaks down for high performance cars at very high
speeds. I doubt that any road-legal car generates signficant down
force at speeds much below about 100mph due to the dire effect it
has on fuel consumption.

What about the sports cars which have retractable rear spoilers that
pop up at, say, ~75mph?


Some of them pop up at much lower speeds - I think the Porsche 911 and
Audi TT spoilers pop up at 40 mph.

I think it's 75 mph by default with both of those cars, but may be lower
in other cars. It can also come up at lower speeds to cool a hot engine
in the case of the Porsche. Of course, they can usually be deployed
manually, which is especially useful in countries with speed limits 75
mph, like the UK!