Arrow Spine
Arrow spine is the shaft's stiffness rating — how much the shaft deflects under a standardized load. The ATA static spine test measures deflection at the center of a 28-inch span with 880 grams hanging from it; the result expressed in thousandths of an inch gives the spine number (340, 400, 500, etc.).Details
Static spine is the number stamped on the shaft and listed in manufacturer charts. It is measured by suspending the shaft between two points 28 inches apart and hanging 880 grams from the center. A 340-spine shaft deflects 0.340 inches; a 500-spine shaft deflects 0.500 inches — so a lower number means a stiffer shaft. Easton, Gold Tip, and Victory each publish spine charts that cross-reference draw weight, arrow length, and point weight to recommend a starting spine.
Dynamic spine describes how the arrow actually bends during the shot cycle — and it rarely matches static spine exactly. Cam aggressiveness, draw length, point weight, and release type all influence dynamic spine. A heavier point effectively weakens the arrow's dynamic spine; a longer cut length does the same. Conversely, a shorter arrow or lighter point stiffens dynamic behavior. This is why two archers with the same draw weight can require different static-spine shafts depending on their setup.
Reading a spine chart correctly requires three inputs: peak draw weight (not holding weight), cut-to-length measurement, and intended point weight. Most charts assume a standard 125-grain point; if you're shooting 100 or 150 grains, adjust one step stiffer or weaker accordingly. When in doubt, the conservative recommendation is to err toward stiffer — weak-spined arrows are harder to tune and more affected by release inconsistency than slightly stiff ones.
The symptoms of a spine mismatch are diagnostic. For a right-handed compound archer using a release aid: a weak-spined shaft (too flexible) causes the tail to kick left on release and the arrow to impact left of the point of aim. A stiff-spined shaft produces the opposite — tail right, impact right. These observations assume reasonable form; significant technique errors can mask or mimic spine problems and should be ruled out first. Recurve and finger-style shooters follow different directional rules due to the archer's paradox — the arrow's flex around the riser reverses the weak/stiff impact directions.
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Common questions
- What spine do I need for my draw weight?
- Spine selection depends on draw weight, cut arrow length, and point weight together — not draw weight alone. Start with the manufacturer's spine chart using your actual peak draw weight (not holding weight) and your finished arrow length. As a rough guide, a 60 lb compound shooting a 28-inch arrow to a 100-grain point typically lands in the 340–400 range, but always verify against the specific shaft brand's chart.
- What is the difference between static spine and dynamic spine?
- Static spine is a lab measurement: a fixed load applied to a fixed shaft length. Dynamic spine is how the shaft actually behaves during the shot — influenced by cam type, draw length, point weight, release style, and even arrow rest design. Two arrows with identical static spine can behave very differently dynamically. Tuning (paper tuning, walk-back, bare-shaft) is the practical method for verifying dynamic spine is correct for your specific setup.
- How do I know if my spine is too weak or too stiff?
- Watch where your arrows impact relative to your point of aim at 20 yards with good form. For a right-handed compound archer using a release aid, arrows hitting left indicate weak spine; hits right suggest too stiff. Paper tuning confirms this more precisely: a nock-left tear indicates weak spine, nock-right indicates stiff. Recurve and finger-style archers follow reversed directional rules. If your groups are tight but simply off-center, consider form or rest position before blaming spine.