You can't compare a car that is already seated in the ground by its natural configuration and a truck that is raised so high by its nature. It would take much less force to work on a truck then a car. Again, not saying they are functional but I would like to see some kind of proof. All the nascar trucks have had aggressive spoilers and travel at a much lower speed then the cars.
So read this...
So if air can have such an effect on a stock truck wearing a spoiler at highway speeds, why would a wing not work? Bottom line if wind is all over the spoiler, would it not be all over the wing, which is even higher?
I am just curios and I think this is a good discussion, keep the opinions coming.