No one around have the time to model the XF aerodynamics? No I don't either. I agree that time to deploy must be considered, I would like to see some clever logic taken into consideration, ie current speed and rate of acceleration so the wing only opens at 60 if you are still accelerating with menace, that would stop the activation on UK 'A' roads, some of which are peppered with roundabouts or sub 40 mph corners bridges etc that mean I have to put the thing up or have a yoyo spoiler...you US guys don't want to see the fuel bill for that kind of drive at $3.785 a US gallon (first time I have seen £1 a liter in the UK so the conversion is easy).

40 lbs doesn't sound much and it would have to have more effect than that to be important. Imagine putting you arm out of a car window at 60 mph (as a passenger on a quite road etc) tilt you hand at 45 degrees, what's the opposing force feel like? Multiply that by five? Then remember that at 120 mph the effect is four times that at 60 mph. Lets say 40 lbs at 60 mph that's 160 lbs at 120 mph and 250 lbs at 150 mph.

...but it is all about balance, what does the back end weigh? Curb is 3200 lbs so perhaps 1400 lbs rear with 1800 lbs up front. All sorts of things happen, but say at 120 mph lift means you loose 200 lbs at the back, that leaves 1200 lbs. Now remember the XF has big fat tires (fatter than the SLK and TT), contact pressure is what important in determining grip and as the area increases the pressure reduces. Our 1200 lbs is split in two, now only 600 lbs downforce over an area 10% bigger than say a TT. An extra 80 lbs downward pressure per wheel would make me happier, but what if the lift is more than 200 lbs.

I think the danger area is the motorway starting at 90 to 120mph (depending on conditions and road) for the following reasons. Even shallow curves have reasonable G force at 120 mph, I have seen drivers belting down the motorway at over 100 mph in RAIN (must think the aqua tread tires are magic or something), and effects like overtaking a large trailer mean large negative pressures are available to further mess up aerodynamics.

Personally, I would never disable a safety system (that I paid for), just in case it came into my mind (or my wife's) to do 120 mph. (if Ian or others so want to disable a safety system perhaps they should put a blown fuse in the circuit for the accident investigators to ponder over).

I know my guess on lift might be way out but the spoiler effect must be considerable at 120 mph.