Spine is the first thing you get right or wrong when you build an arrow, and it is the one most people guess at. Get it right and your arrows group tight and steer broadheads like they are on rails. Get it wrong and no amount of tuning fully fixes it. Here is how to pick spine without the mystery.
What arrow spine actually is
Spine is how much an arrow flexes. Every arrow bends when you shoot it: the string shoves the back of a stiff carbon shaft forward, and the shaft bows around the riser before it recovers in flight. Static spine is the shaft's stiffness measured on a bench. Dynamic spine is how that shaft actually behaves off your bow, with your draw weight and your point weight. Dynamic spine is what matters, and it is what the numbers below are really chasing.
Lower spine numbers are stiffer. A 300 spine is stiffer than a 400. That trips people up, so keep it simple: heavier, faster, higher-poundage setups need a stiffer (lower-number) shaft.
The four inputs that decide your spine
You need four things before anyone can spec an arrow for you:
- Draw weight. More poundage bends the shaft harder, so you need more stiffness. A 70-pound bow needs a stiffer arrow than a 60-pound bow, all else equal.
- Arrow length. Longer shafts flex more (like a longer diving board), so a long arrow acts weaker. Cutting an arrow shorter effectively stiffens it.
- Point weight. More weight up front makes the shaft flex more on the shot, acting weaker. Jumping from a 100-grain to a 125-grain point moves your dynamic spine.
- Bow type and cam aggression. Fast, aggressive cams load the arrow harder and can push you toward a stiffer spine.
Change any one of these and your correct spine can change. That is why an off-the-shelf dozen labeled for your poundage is a rough guess, not a fit.
How the inputs interact
Two shooters both pulling 70 pounds can need different spines. One shoots a 27-inch arrow with a 100-grain point; the other shoots a 30-inch arrow with a 125-grain point. The second setup flexes far more and needs a stiffer shaft. This is the whole reason a real build beats a stock dozen: your length and point weight are dialed in, not averaged.
A quick rule of thumb, not a substitute for a chart: at 60 to 70 pounds with a normal hunting arrow length and a 100-grain point, most compound shooters land around a 340 to 300 spine. Lighter poundage or shorter arrows drift toward 400. But rules of thumb miss individual setups, which is exactly what tuning exposes.
Why the wrong spine shows up with broadheads
Field points forgive a lot. A slightly weak or stiff arrow still punches paper fine with a field point because the point is inline and low-drag. Bolt a fixed-blade broadhead on that same arrow and the blades act like little wings on a poorly flexing shaft, and your groups open up or your broadheads plane away from your field points. If your field points hit but your broadheads do not, spine and tune are the first suspects. Read more in our broadhead guide and check flight with the BeeReal paper tuner.
The easy way: let the shop spec it
You can run spine calculators and charts, and they work. But the fastest way to get it right is to give us your draw weight, draw length, arrow length, and point weight, and we will spec the shaft for you. That is the point of the Custom Arrow Builder: pick your shaft and spine, add vanes, wraps, inserts, and nocks, and we cut every arrow to length and fletch it by hand. If you already know you want a proven hunting shaft, the Victory RIP TKO is a strong place to start.
Bottom line
Spine is set by draw weight, arrow length, point weight, and your bow, not by the sticker on a box. Nail those four and the rest of your build has a foundation. Guess at it and you will chase tune all season. When in doubt, send us your specs and start a custom build.