When it comes to consistent accuracy, archers worry greatly about the straightness of their arrow shafts. And they should. But just as important – perhaps even more so – is using a shaft with the correct spine.
There are actually two types and . To measure static spine, an 880-gram (1.94 lbs.) weight is suspended from the center of a 29-inch long arrow that is supported by two points 28-inches apart. The number of inches x 1000 the arrow deflects (bends) is the spine size of the arrow. For example, if it bends .340-inch, the spine size is 340. Dynamic spine describes an arrow’s reaction to a bow’s stored energy at the shot. A nearly unlimited set of variables determine dynamic spine, including the method of release; a bow’s cam system; the amount of energy stored by the bow’s limbs and cams; arrow weight and length; nock weight; fletching weight; and more. Because of this, for simplicity’s sake arrows are usually selected using static spine.
