How To Determine Arrow Length And Weight. For example, a 500 spine arrow bends.5 inches when the weight is applied. Units of energy are often measured in joules.
With a recurve, the best way to find your draw length is to use a measuring arrow. 20 inches x 13 grains/inch = 260 grains. The number of inches the arrow deflects or bends due to the weight, is the spine size or measurement of an arrow.
Choosing the correct arrow spine for your setup depends on your draw length and draw weight.
For example, a 500 spine arrow bends.5 inches when the weight is applied. Spine is measured by the number of inches a shaft deflects (bends) x 1000. These three things need to be matched so that you, the archer, have the best chance of hitting their target. For each draw length, record the draw weight on the fingers and the resulting arrow speed.