What are the main differences between a mountain bike and a regular bike?

The main differences between a mountain bike and a regular bike are the tires, suspension, and frame. Mountain bikes have wider, knobbier tires for better traction on rough terrain, suspension systems to absorb shocks, and a sturdier frame to handle off-road conditions. Regular bikes typically have thinner tires, no suspension, and a lighter frame for smoother rides on paved surfaces.