Why are NASCAR tracks slanted?

Answer 1

The term is called "Banked" not slanted. The drivers use the banking to keep the car planted thru the turns via the force pushing down on the car.

They go much faster than on a flat track.

Answer 2

A race track is tilted because of centripetal force pulling the vehicle to the center of the circle.

Answer 3

Banking allows the cars racing on the track to go faster in the corners. It does so by increasing a car's downforce while turning and preventing it from slipping during the turn.