What arrow spine means, why it makes or breaks accuracy, and exactly how to choose the right deflection for your bow.
Spine is the most misunderstood number in archery — and the most common reason a perfectly good bow “won’t group.” Here is the whole topic in plain English.
What Spine Actually Measures
Static spine is how far a shaft deflects under a standard 1.94 lb weight: a “340” bends 0.340″. Lower number, stiffer arrow. Dynamic spine is how the arrow actually flexes when shot — affected by draw weight, arrow length and point weight.
The Three Variables That Matter
- Draw weight: more pounds need stiffer (lower) spine.
- Arrow length: every extra inch makes the arrow act weaker.
- Point weight: 25 grains more up front ≈ one spine step weaker.
Find Your Spine in 30 Seconds
Skip the chart-reading: our Arrow Spine Calculator takes your draw weight, arrow length and point weight and returns the spine range to buy.
Symptoms of Wrong Spine
- Under-spined (too weak): erratic flight, left tears for RH shooters, broadheads planing.
- Over-spined (too stiff): generally forgiving but groups drift right and bareshafts kick nock-left.
Frequently Asked Questions
What happens if arrow spine is too weak?
The shaft over-flexes, fishtails and won't recover before reaching the target — broadheads amplify it into misses.
Is it better to be over-spined or under-spined?
Slightly over-spined (too stiff) is the safer error; it costs a little tune but stays predictable.