Lift. As you drive your car is shaped kinda like a wing with a greater distance across the top of the vehicle than the bottom. The air on top has to travel across a greater distance in the same time as the air that goes under the vehicle. The faster moving air over your car creates a low pressure zone wich allows the air under the car to "push" up on the car hence reducing the effective weight of the car on the road and in turn the size of the contact patch decreases. that is why your cars steering feels lighter at speed because in effect, it is.

Now, if you have an airdam it can provide downforce and maintain your contact patch.

As for weight of the 150, with a full tank of gas and me in the truck it weighs it at 3300 lbs. at the scales. I don't know what ford claims, but that there is what the truck weighs.

1966 VW bug, weighed 1700 lbs with me in it.

Justin