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In Formula 1 they have the Drag Reduction System (DRS). This reduces the drag on the straights to optimise speed and increases the downforce in the corners to increase handling. This makes sense to me.

I sometimes find myself following a posh car, usually a porsche, that has a retractable spoiler. These generally seem to have the opposite action, in that when the car is cruising on the motorway the spoiler will be up, presumably increasing drag and reducing fuel efficiency, and when the car turns off the motorway, slows down and approaches a roundabout the spoiler drops, presumably reducing downforce and roadholding.

What is the logic behind these systems?

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  • I think their main use is extracting greater amounts of cash from gullible buyers.
    – Glen Yates
    Commented Feb 9, 2022 at 22:36

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In a way you have answered your own question.

The DRS wing is there to keep there vehicle planted on the road to allow the vehicle to maneuver bends at high speed. At certain straight 'safe' locations, the wing can be changed to lower the down force and increase speed. If the vehicle was travelling very slowly (for a race car) there would be no need for the wing, since it wouldn't need the extra traction.

The spoiler on a Porsche is not needed at slow speeds since the tyres are providing enough traction and there isn't a large amount of turbulence at the rear of the vehicle that can cause drag, so the spoiler can drop to keep the familiar shape of the Porsche (see wikipedia where the 911 is mentioned). When the vehicle is moving fast, turbulence increases, so the spoiler raises to remove some of turbulence, which decreases fuel consumption and increases stability.

The Porsche (for example) spoiler doesn't increase drag, it actually lowers drag by changing the way the air flows over the rear of the vehicle, so reducing turbulence and drag. Not all spoilers are functional however, many are just for cosmetics.

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  • Thank you for the answer. I think the core of my misunderstanding is captured by "The Porsche spoiler doesn't increase drag, it actually lowers drag". Do you have a link for this? It was not my understanding at all, and is somewhat unintuitive but would make the behaviour totally logical.
    – User65535
    Commented Feb 9, 2022 at 10:40
  • You're welcome. See the Wikipedia link in my answer.
    – HandyHowie
    Commented Feb 9, 2022 at 14:43
  • You don't mention it, but there are vehicles like the Bugatti Veyron which has a retractable wing, not necessarily for aerodynamics, but for braking. When going above a certain speed, the wing is flapped straight down during hard braking to help increase drag and thus slowing the vehicle down faster. When going above 250mph, wide tires and big carbon fiber brakes can only do so much to slow a vehicle down. Commented Feb 10, 2022 at 14:20

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