What is arrow spine?
Arrow spine is a measure of shaft stiffness, or how much an arrow bends under a load. On the common deflection scale, a lower number means a stiffer shaft. Choosing a suitable spine requires your bow weight, arrow length, and point weight, plus the correct manufacturer's selection chart.
Reading static spine numbers
Static spine comes from a controlled bend test. In the common carbon-arrow test, a 1.94 lb weight hangs at the center of a shaft supported 28 inches apart. Deflection in inches, multiplied by 1,000, gives the familiar spine number: a 500 spine bends 0.500 inches in that test.
A 400 spine therefore bends less than a 500 and is stiffer. These numbers describe stiffness, not arrow weight in grains. Different shaft models with the same spine can weigh different amounts.
Check which numbering system the shaft uses before comparing arrows. Aluminum size codes and traditional wood-shaft poundage ratings use other systems. A number printed on a shaft is not automatically a carbon-style deflection rating.
Why dynamic spine changes
Dynamic spine describes how the arrow bends during the shot. The bow accelerates the nock while the front of the arrow resists that acceleration. Shaft length, front-end weight, and the bow's delivery of energy all affect the response.
- A longer shaft generally behaves weaker than a shorter shaft of the same model and static spine.
- A heavier point or insert generally makes the arrow behave weaker during launch.
- Higher draw weight generally calls for a stiffer shaft, with cam design and release method affecting selection.
A heavier point leaves the factory spine rating unchanged, even though the arrow bends more during launch. This is why copying someone else's spine number can fail even when you both shoot the same draw weight.
Using a spine chart without guessing
Use the chart for the shaft model and bow type you intend to shoot. Check its arrow-length definition and point-weight assumptions. For a recurve, measure weight at your actual draw length. Compound charts generally use peak weight and may ask for the bow's speed rating.
Decide on a safe shaft length before reading the chart. The arrow length calculator explains the starting measurements, but clearance at full draw needs a physical check. Never cut an arrow shorter than your setup safely allows to make it behave stiffer.
Treat the chart as an initial selection, then check clearance and flight. Bare shaft tuning can help a recurve archer compare unfletched and fletched arrows. Avoid diagnosing spine from one left or right impact; release errors and contact can produce similar results.
Questions
Is a 300 spine arrow stiffer than a 400?
Yes, when both numbers use the same deflection-based spine scale. A 300 shaft bends less under the standard test load. That does not make it a better choice for every bow. Match the shaft to the chart inputs, including finished arrow length and the intended point weight.
Does a heavier arrow always have a stiffer spine?
No. Weight and stiffness are separate specifications. Construction, diameter, and wall thickness affect both, so a heavier shaft from one model may have the same spine as a lighter shaft from another. Compare the published spine rating and grains per inch separately when choosing a shaft.
Can a plunger fix the wrong arrow spine?
A recurve plunger gives you some adjustment of the arrow's lateral support and launch behavior. Its useful range is limited. A shaft far outside the suitable spine range usually needs a different shaft or a change in length or point weight within safe limits. Winding the button to its limit will not substitute for that match.