Road bikes are indeed faster than mountain bikes and hybrids. It's a known fact that the wheels on a road bike are lighter, narrower, and have higher pressure. This alone gives significantly less rolling resistance. Then, there's the taller gearing of a road bike, as compared to a mountain bike with much lower gear sets that are designed to take on the steep upgrades demanded of them. Obviously, wider tires are required to cover loose surfaces that a road bike tire will sink into. Hybrids are the jack of all trades, master of none. They are designed for a variety of roads, from tarmac to loose gravel. A mountain bike is designed more for fire roads and trails, which the more aggressive knobby tires are designed for. Any of the three varieties can ride on pavement, but road bikes are best suited for the smooth surfaces due to their lower rolling resistance and taller gearing. Then, there's the question of aerodynamics, where the rider sits in a crouched position, giving less wind resistance. With either a mountain or hybrid, the rider sits upright, and efficiency is further reduced due to the wind pushing back on the rider and equipment, providing more resistance against the rider and bike's forward motion. There is a big difference in speed and efficiency between the three, and each type of bike is designed for its specific purpose.