When buying arrows, you must consider their length, fletching, point weight and “spine.” All those factors affect accuracy and arrow flight, but the arrow’s stiffness – its spine – is especially important.
“Spine” is the measurement of the arrow’s flex or bend. Arrow shafts are sorted by spine measurements, and manufacturers designate them with a number.
You’ll find the spine number on the arrow’s label. Some common numbers are 350, 400, 500 and 600, but they vary by manufacturer.
How do arrow manufacturers measure spine?
The Archery Trade Association standard for measuring arrow spine requires this test: Suspend a 1.94-pound weight at the shaft’s center, and use a machine to measure the deflection or bend at that point. Deflection is measured in inches. Some typical deflection measurements are .500, .400 and .350. These measurements correspond to the spine sizes most manufacturers use to mark arrows.
Why Spine Matters
When you shoot an arrow, it flexes as it leaves the bow, and then straightens out as it flies. That flexing is called “archer’s paradox.” If an arrow doesn’t flex enough, or if it flexes too much, it will fly poorly. Finding the right spine requires factoring in your draw weight, arrow length and point weight. All three factors affect the arrow’s spine.
- Bows with high draw weights need arrows with stiffer spines than do bows with low draw weights.
- Short arrows require weaker spines than do long arrows.
- Heavier arrow points need stiffer spines than do lighter points.
Arrows that are too stiff won’t bend enough. That creates an unforgiving setup, which usually causes the arrow to shoot left. Arrows with too soft of a spine shoot like wet noodles and won’t recover from paradox. That is, they keep flexing all the way to the target.
How do you know which spine is right for your bow?
Arrow manufacturers supply charts that give you a starting point, but the most certain way to find the right spine is to visit an archery shop and shoot different spines to see which one works best for your setup. A pro staff’s knowledge and experience are invaluable when selecting arrows.
Once you find the arrow spine your bow likes best, stick with it unless you change your draw weight, arrow length or point weight. When buying new arrows, tell the archery pro the spine size and arrow length. Or simply provide one of your arrows so they can replicate it.
To find an archery shop to help you with arrows, click here.