Bicycles have fat tires for a number of reasons. Firstly, fat tires provide more stability and grip on uneven terrain, making them ideal for off-road riding. They also absorb shock better than thinner tires, resulting in a more comfortable ride. Additionally, fat tires have lower air pressure, which creates a larger contact area with the ground, improving traction and reducing the likelihood of skidding. Finally, fat tires can also be used to carry heavier loads, as they distribute the weight more evenly across the surface of the tire.