Cyclocross bike frames appear similar to road bikes, but there are key differences. Relaxed angles improve off-road comfort and handling and a higher bottom bracket offers increased confidence over rough terrain. Cyclocross frames will feature tyre clearances front and back to allow use of high-volume off-road tyres and prevent clogging with mud. The upright riding position and versatile nature of cyclocross bikes lends them to other disciplines including commuting. Aluminium and steel remain popular choices for frame material due to durability, but carbon is becoming a preferred material due to its light weight and shock absorption properties.