How to Choose Arrow Spine (Without Guessing)
Start from a manufacturer chart using your draw weight, arrow length and point weight, then verify with bare shafts before buying a dozen. Lower spine numbers are stiffer, and longer arrows, heavier points and higher draw weight all make a shaft behave weaker than its printed number.
Spine is the single most consequential arrow decision, and the one most often made by guessing from draw weight alone. Draw weight is only one of four inputs. Arrow length, point weight and bow type each move the answer by a full spine group or more, which is why two archers pulling the same poundage can need completely different shafts.
What the number means
Spine is deflection in thousandths of an inch. Support a shaft over a 28 inch span, hang a 1.94 pound weight from the middle, and measure how far it sags. A 500 spine shaft sags half an inch. A 340 sags 0.340 inches and is therefore considerably stiffer. Lower number equals stiffer shaft, which trips up almost everyone once.
That is static spine, measured on a bench. What actually matters is dynamic spine, which is how much the shaft flexes when your particular bow launches it. The printed number is a starting point for predicting dynamic behavior, not a description of it.
The four inputs
- Draw weight. More weight means more force at launch, so the shaft flexes more and behaves weaker. Spine requirements shift roughly one group per 10 pounds.
- Arrow length. A longer unsupported span flexes more. Each additional inch weakens dynamic spine by roughly one group, which is why draw length has to be settled before you order shafts. Measure it with the draw length guide.
- Point and insert weight. Weight at the front makes the shaft flex more around it. About one group per 25 to 30 grains. A brass insert plus a 125 grain broadhead can weaken a shaft by two full groups compared to a standard insert and a 100 grain point.
- Bow type and cam aggression. A hard cam accelerates the arrow more violently and effectively weakens spine. A recurve with a finger release is a different world entirely, because the string rolls sideways off the fingers and the shaft must bend around the riser.
Starting spine by draw weight and arrow length
Use this as a first pass for a compound with a 100 to 125 grain point, then confirm against your shaft manufacturer's own chart, since spine designations vary slightly between brands.
| Draw weight | 26 in arrow | 28 in arrow | 30 in arrow | 32 in arrow |
|---|---|---|---|---|
| 40 lb | 600 | 600 | 500 | 500 |
| 50 lb | 500 | 500 | 400 | 400 |
| 60 lb | 500 | 400 | 400 | 340 |
| 70 lb | 400 | 400 | 340 | 300 |
| 80 lb | 340 | 340 | 300 | 250 |
Shift one column stiffer if you shoot a heavy point above about 150 grains, and one column weaker if you shoot a light point under 85 grains. The arrow spine calculator handles these adjustments together rather than one at a time, which is more accurate than reading a static chart and mentally correcting.
Recurve and traditional spine is a different chart
Do not read a compound chart for a recurve. With a finger release the string pushes the nock sideways, and the arrow must bend around the riser to reach the target. That means recurve shafts need to be considerably weaker than a compound of the same marked weight, and the correct input is the bow's actual weight at your draw length, not the number printed on the limb, which is measured at 28 inches.
A recurve marked 40 pounds at 28 inches drawn to 30 inches is closer to 44 pounds. Add point weight and length on top and the difference from the marked number is substantial. Traditional bows shot off the shelf usually need weaker shafts still, because there is no plunger to absorb the sideways push.
Verify before you buy twelve
Charts predict. Bare shafts confirm. Buy three shafts, build them to your intended specification, and run them through bare shaft tuning at 20 yards. If they land with the fletched group, order the rest. If they are consistently off, you have learned something for the price of three shafts instead of twelve.
Leave your test shafts long. A shaft that is an inch too long can be shortened to correct a weak reading. A shaft that is an inch too short is scrap.
Spine, weight and the safety floor
Safety: whatever spine you land on, total finished arrow weight must be at least 5 grains per pound of draw weight. A 70 pound bow needs 350 grains minimum, a 60 pound bow needs 300. Very stiff, very light target shafts make it possible to fall under that floor while chasing speed, which damages limbs and cams and voids nearly every warranty. Confirm with the total arrow weight calculator. Also inspect carbon shafts before every shot by flexing them and listening for cracking, because a damaged shaft can fail on release and injure the bow hand.
How spine interacts with the rest of the build
Because point weight is the easiest spine correction, spine and front of center are effectively the same decision. Adding 25 grains of point weight to soften a stiff arrow also raises FOC by roughly two to three percentage points. Hunting builds generally want 10 to 15 percent, target builds 7 to 12 percent, and extreme FOC starts around 19 percent. Check where you land with the FOC calculator rather than assuming.
Heavier arrows also cost speed, at roughly 1 fps per 3 grains above the IBO reference of 350 grains, and gain kinetic energy and momentum. Run the trade with the kinetic energy calculator before deciding that a heavier build is automatically better.
Related
- Arrow building guide: turning the right shaft into the right arrow
- How to tune a compound bow
- Broadhead tuning: where spine errors show up worst
Frequently asked questions
What does arrow spine 340 or 400 mean?
It is a deflection measurement. A shaft is supported over a 28 inch span, a 1.94 pound weight is hung at the center, and the sag in thousandths of an inch is the spine number. A 340 shaft sags 0.340 inches and a 500 sags 0.500 inches, so lower numbers are stiffer. The scale is counterintuitive on first contact but consistent across every major manufacturer.
What spine do I need for a 60 pound bow?
With a 28 to 29 inch arrow and a 100 grain point, a 60 pound compound typically calls for a 400 spine shaft, and a 340 if the arrow runs longer or the point heavier. Those are starting points from manufacturer charts, not verdicts. Cam aggression, insert weight and draw length all shift the answer, so confirm with bare shaft testing before buying a full dozen.
Is it better to be slightly stiff or slightly weak?
Slightly stiff is the safer error. A marginally stiff arrow can be corrected downward with point weight, which is cheap and reversible and raises FOC at the same time. A weak arrow is harder to fix without shortening the shaft, which is permanent, and weak arrows behave worse behind fixed-blade broadheads because the extra flex gets amplified by the blade surface.
Do recurve and compound bows need different spine?
Yes, and the difference is large. Recurve charts are built around finger release and archer’s paradox, so a 45 pound recurve often needs a shaft that a 45 pound compound would find far too weak. Never read a compound spine chart for a recurve. Use the manufacturer chart for the bow type you actually shoot, and account for stated bow weight at your draw length rather than the marked weight.
How much does point weight change spine?
Roughly one spine group per 25 to 30 grains of point or insert weight. Moving from 100 to 125 grains weakens dynamic spine by about the same amount as adding an inch of arrow length. This is the most useful correction lever because it is reversible and it raises front of center at the same time, which most hunting builds want anyway.
What happens if I shoot the wrong spine?
A mismatched shaft leaves the bow oscillating and never fully recovers, which shows as erratic groups past 30 yards, broadheads that will not group with field points, and a bow that resists tuning no matter where the rest goes. Severely underspined arrows are also a safety concern, because a shaft that flexes far beyond its design can fail on release.
How we choose: we compare published manufacturer specifications, verified owner reviews, and pro shop guidance. We do not test gear in person. Draw weight and arrow spine affect safety, so follow your bow manufacturer's specifications and have setup work checked by a qualified pro shop.