Arrow Spine: Stiffness, Selection & Spine Charts

Arrow spine is the measure of an arrow shaft's resistance to bending. Choosing the correct spine is one of the most consequential decisions in arrow setup — an underspined or overspined arrow will fly erratically regardless of how well the bow is tuned.

Static Spine vs. Dynamic Spine

Static spine is a standardized lab measurement. An 880-gram (1.94 lb) weight is suspended from the center of a 29-inch arrow shaft supported at two points 28 inches apart. The amount the shaft deflects — measured in inches — is the static spine value. That deflection is then expressed in thousandths: a shaft that bends 0.500 inches carries a spine rating of 500, while one that bends only 0.300 inches is rated 300 and is considerably stiffer. The lower the number, the stiffer the shaft. This measurement standard was originally developed by Easton founder Doug Easton in the 1940s.

Dynamic spine describes how an arrow actually behaves during the shot. Bow cam system, draw weight, release type (fingers vs. mechanical), arrow length, point weight, nock weight, and even serving material all influence dynamic spine. This is why shaft stiffness in real shooting conditions rarely matches the static number alone — the selection chart bridges that gap.

Using an Arrow Spine Chart Correctly

Spine charts are only as accurate as the data entered. Two mistakes are especially common:

• Guessing draw weight. Always measure peak draw weight with a scale — an estimate of even a few pounds shifts the recommended spine.
• Confusing draw length with arrow length. Charts reference arrow length, measured from the back of the point to the throat of the nock — not your draw length, which can differ by several inches depending on rest position and riser design.

Understanding how draw weight affects arrow selection is equally critical, since heavier bows require stiffer shafts.

Point Weight and Arrow Length Adjustments

Spine charts assume a 100-grain point as a baseline. Heavier points weaken effective spine; lighter points stiffen it. As a practical rule, add 3 lbs to your charted bow weight for every 25 grains your point exceeds 100 grains, and subtract 3 lbs for every 25 grains below 100. The weight of arrow points and their effect on balance is easy to overlook but directly shifts which spine column applies.

Arrow length also matters: shorter arrows are effectively stiffer. Cutting a shaft changes its dynamic behavior, which becomes especially critical when shooting fixed-blade broadheads. Arrow inserts add small amounts of forward mass that similarly affect dynamic spine and should be factored into your total point-end weight.

The Archer's Paradox Connection

Proper arrow spine selection is directly tied to the archer's paradox — the bending and recovery cycle an arrow undergoes as it clears the bow. A shaft with mismatched stiffness will not complete that cycle cleanly, producing inconsistent groups even from a mechanically sound setup.