Your mountain bike wheels are important for striking a balance between weight and performance. There are three common wheel sizes, 26”, 27.5” and 29”. The smaller of the wheel sizes was for many years the standard, but larger-diameter 29” wheels were introduced to offer improved speed, lower rolling resistance and a better fit for larger riders. Today the 27.5” standard is viewed by many as offering the ideal balance between speed, weight and handling. Before buying your new set of wheels, make sure the axles will match the frame and fork of your bike, as various standards are in use.