It is the heart of every bicycle: the frame. Small changes in the length, height and angle of the bicycle frame have an enormous influence on the handling and fit of a bicycle. Various standards for the head tube, bottom bracket, brake mount and axle width of the bicycle frame dictate the choice of components. The frame materials used also have an influence on the weight and riding characteristics. Steel, aluminium and carbon are among the most commonly used raw materials for bicycle frames. Road bikes and touring frames are often sold as a set with a suitable rigid fork. The suspension fork is always available separately for mountain bike frames. With full suspension bike frames, the damper is usually included.