At a certain speed, a race track could be any shape and the cars would stay on the track.

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If you've ever looked at a Formula One car, an Indy car or a Champ car, you know that a big part of the car's body is the aerodynamics package. At the front and back are wings. However, these wings are mounted upside down. Their purpose isn't providing lift, like the wings of an airplane. Instead, they are meant to force the car down onto the track to provide better traction and a more stable ride. Once a car gets above about 200 mph, the car is glued to the track by the aerodynamic forces from the wings. At this speed, the car could travel upside down on the ceiling of a tunnel if it wanted to.

What this means is that, as long as the car is always moving at 200 mph, you can make the track just about any shape you want. For example, you could make the track circular and make the walls completely vertical. You could also make it loop-the-loop, or have the cars drive upside down. It doesn't really matter because the car will stick itself to the road.

As long as the shape of the track doesn't expose drivers to more than 4Gs (but preferably no more than 3Gs), and there's enough force on the tires to keep them stuck firmly to the ground, the cars and drivers can handle most any shape.