Arrow Spine & Length

You set up your new compound, pick an arrow that “looks about right,” and head to the range. Your groups are scattered — three inches here, five there — even though your form feels solid. The culprit is almost never the archer. Most of the time, it’s an arrow with the wrong spine: flexing too much or too little to ever fly straight.

Quick recall

Quick recall from Choosing Your Bow — what does 'draw weight' actually measure on a compound bow?

Quick recall from Choosing Your Bow — what does 'draw weight' actually measure on a compound bow?

The peak pulling force, in pounds, at full draw The weight of the arrow, in grains The arrow speed, in feet per second

Check answer

What spine actually is

Spine is the stiffness of an arrow shaft — how much it resists bending under load. It is measured by a standard test: suspend the arrow, hang a 1.94-lb weight at the center, and measure how much it deflects (sags). The sag in thousandths of an inch is the spine number.

Here is the part that trips up beginners: a lower spine number means a stiffer shaft.

• 340 spine = very stiff (deflects only 0.340 inches) → for heavier draw weights
• 500 spine = more flexible (deflects 0.500 inches) → for lighter draw weights

The number is not a rank where bigger is better — it is literally the amount of flex. Less flex = lower number = stiffer.

The why The archer's paradox: why arrows flex at all

When the string releases, it pushes the nock end of the arrow forward — but the arrow’s tip is still resting against the rest or shelf. For a brief instant the shaft has to bend around the bow’s riser before it clears and straightens. This bend-and-recover is called the archer’s paradox. A correctly spined arrow flexes just the right amount to clear the riser cleanly and then straighten out in flight. Too much flex (under-spined) and the arrow whips side to side all the way to the target. Too little (over-spined) and it doesn’t clear cleanly, deflecting off the riser unpredictably.

Compound bows use a center-shot rest that reduces how much the arrow must bend, so compounds need stiffer spine than a recurve of the same draw weight. Your spine chart accounts for this automatically.

What happens when spine is wrong

Under-spined (too flexible for your draw weight):

• The arrow over-flexes when launched.
• For a right-handed archer, it usually flies right and groups are strung out horizontally.
• At heavier draw weights the arrow can shatter on release — a real safety hazard.

Over-spined (too stiff for your draw weight):

• The arrow under-flexes and deflects off the riser.
• Groups typically string left (right-handed).
• Flight and accuracy suffer, but there is less safety risk.

How to pick the right spine

Every major arrow maker (Easton, Gold Tip, Victory, Carbon Express, Black Eagle) publishes a spine selection chart specific to their arrows. The chart is your tool — not a rule of thumb.

To use it you need two numbers you’ve already measured:

1. Your actual draw weight — measured with a draw scale at your real draw length, not the bow’s label.
2. Your draw length — measured correctly (see the Draw Weight & Draw Length lesson).

Find your draw weight on one axis and your draw length on the other. The chart intersection gives you a spine range. When in doubt, choose the stiffer option (lower number) — a slightly over-spined arrow flies better than a slightly under-spined one.

Arrow length should be 1–2 inches longer than your draw length so the tip clears the rest at full draw. Beginners start at the longer end; experienced archers may trim to exact length once their form is locked in, but only after a qualified bow tech measures them.

Edge case Four things that change which spine you need

• Point weight — heavier broadheads or field points add forward weight, which requires a stiffer (lower-number) spine. Many charts have a column for “added point weight.”
• Arrow length — a longer arrow is effectively weaker than the same shaft cut shorter. Adding an inch can drop you a spine class.
• Cam aggressiveness — fast, aggressive compound cams deliver energy sharply and may need a stiffer spine than a mellow single-cam at the same peak weight.
• Release aid vs. fingers — finger shooters (recurve, longbow) put a side-load on the nock that requires weaker spine than a release aid on the same bow. Charts specify which.

The spine selection map

The diagram below shows a simplified spine selection grid. Heavier draw weights and longer arrows move you toward stiffer spines (lower numbers); lighter draw weights and shorter arrows allow more flexibility (higher numbers).

Heavier draw weight → stiffer spine (lower number) Longer arrow → stiffer spine needed Lighter draw weight → more flexible spine (higher number) Shorter arrow → can use slightly weaker spine

Make the call

Knowledge check

You're shooting a compound bow at 60 lbs draw weight with a 29-inch draw length. You're choosing between a 340-spine and a 500-spine arrow of the same brand. Which should you consult first?

You're shooting a compound bow at 60 lbs draw weight with a 29-inch draw length. You're choosing between a 340-spine and a 500-spine arrow of the same brand. Which should you consult first?

The manufacturer's spine chart for that arrow, using your measured draw weight and length Pick 500-spine because it's a bigger number and sounds stronger It doesn't matter much for a compound, just pick one

Check answer

Knowledge check

A right-handed compound shooter finds that their arrows consistently group several inches to the RIGHT of the aim point. The most likely culprit is…?

A right-handed compound shooter finds that their arrows consistently group several inches to the RIGHT of the aim point. The most likely culprit is…?

Under-spined arrows (too flexible for the draw weight) Over-spined arrows (too stiff for the draw weight) Arrows cut too short

Check answer

Take it to the woods

Before you shoot another arrow at game, confirm your spine is matched to your setup.

Spine check before hunting season

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Reset

• Use a draw scale to measure your bow's actual draw weight at your draw length — not the label on the limb.
• Confirm your draw length (wingspan ÷ 2.5, or measured at a pro shop).
• Pull up your arrow brand's spine selection chart (manufacturer website or pro shop).
• Find the intersection of your draw weight and draw length and confirm your current arrow is in the recommended spine range.
• Measure arrow length — it should be 1–2 inches longer than your draw length so the tip stays on the rest at full draw.
• ⚠ Safety Inspect each arrow shaft for cracks or damage before shooting. Cracked carbon shafts can shatter on release — flex-test each shaft by rotating it against slight pressure before every session.

Sources

• Easton Archery — Making Sense of Arrow Spine: https://eastonarchery.com/2014/07/making-sense-of-arrow-spine/
• Easton Archery Arrow Selector tool: https://eastonarchery.com/selector/
• Nock On Archery — Arrow Spine Chart guide: https://nockonarchery.com/choosing-the-correct-arrow-spine/
• Bowhunter-Ed — Spine and the Archer’s Paradox: https://www.bowhunter-ed.com/national/studyGuide/Spine-and-Archer-s-Paradox/301099_185407/
• Archery Supplier — Arrow Spine Chart Explained: https://archerysupplier.com/arrow-spine-chart-how-to-pick-right-arrows/
• SC archery regulations: verify current SCDNR regulations before hunting — https://www.dnr.sc.gov/hunting.html