27.5-inch wheels, also known as 650B wheels, are a popular size used in mountain biking. They offer a balance between the agility of smaller wheels and the stability of larger ones, making them suitable for various terrains. This size provides a good compromise for riders who want both speed and control. These wheels are designed to fit specific bike frames and are compatible with a range of tires. 27.5-inch wheels are often favored for their ability to roll over obstacles while maintaining a responsive feel, making them ideal for both casual and competitive riders.