First, Fifth Gear needed to find out how fast he needed to go to hit the 40-foot-tall full-size Hot Wheels loop. The physics equations are pretty simple for finding what the minimum speed the car can have at the top of the loop to perform a successful loop. The answer, in this case, given the car's weight and the size of the loop, was 36 MPH.
A bigger issue, however, was the question of what that gravitational forces would exert on the car given that forward momentum. Given speed and weight, we can expect to see a sizable gravitational force — say, six G's — upon the occupant. So, will Fifth Gear's stunt driver be able to overcome that gravitational force? Well, yeah, duh. But let's watch it anyway.