In the very first hi-jacking scene, before they enter the construction zone, you can clearly see that there are 2 sets of wheels (8 total tires) in the back of the semi-trailer, but as soon as they get in the construction zone, and one of the Honda's has to go under the trailer, there is only 1 set of wheels(4 total tires), and then after it leaves the construction zone, there are 2 sets again.