Explain why the mass of the vehicle does not affect the calculated maximum or minimum velocities for cars on banked curves.

The friction forces are proportional to mass, and so are the centripetal forces required and the weight. The mass cancels out of all equations that determine the maximumand minimum speed without slipping.

For mildly banked cuves, there is no minimum speed. Static friction of the tires will prevent slowly moving and stationary cars from slipping sideways on most banked slopes.