Arrow Spine Selection: How to Choose the Right Spine for Your Bow

Watch: Arrow Spine Selection Guide

Arrow Spine Is Not Arrow Weight

Before we go any further, there's one thing we need to clear up because we see this all the time in the shop:

Spine does not mean arrow weight.

A 300-spine arrow does not mean the arrow weighs 300 grains. Those are two completely different measurements.

Numbers like 250, 300, 340 and 400 refer to the stiffness of the shaft. With the common carbon-arrow spine system, the lower the number, the stiffer the shaft.

So a 250 is stiffer than a 300, a 300 is stiffer than a 340, and so on.

Finished arrow weight is typically going to be a completely different number from the spine printed on the shaft.

Static Spine vs Dynamic Spine

This is another place where understanding the terminology makes the whole process easier.

Static Spine

Static spine is the measured stiffness of the shaft. That's the 250, 300, 340 or 400 number printed on the arrow.

If I shorten a 300-spine shaft, it is still a 300-spine shaft. I didn't magically turn it into a 250.

Dynamic Spine

Dynamic spine is how that finished arrow behaves when you actually shoot it.

Arrow length, front-end weight, bow energy and the rest of the setup all influence that reaction.

The Four Variables That Actually Determine Arrow Spine

There are four big variables I want to know before recommending a shaft:

1. Draw weight
2. Draw length
3. Actual arrow length
4. Point and front-end weight

Guys call us and say, "I shoot 70 pounds. What spine do I need?"

Our answer is always the same:

We need more information.

1. Draw Weight

More draw weight means more energy is being applied to the arrow. As draw weight increases, the spine requirement generally moves toward the stiffer side.

But draw weight by itself does not determine the correct spine.

This is where people get into trouble.

2. Draw Length

Draw length has to be considered along with draw weight.

Two guys both shooting 70 pounds do not automatically need the same arrow setup.

A 27-inch draw shooter and a 30-inch draw shooter aren't identical. Same draw weight does not automatically mean the same spine.

3. Actual Arrow Length

This is another mistake we see all the time:

Your draw length and arrow length are not automatically the same thing.

If your draw length is 29 inches, that does not automatically mean I want to cut your arrow to 29 inches.

Actual arrow length depends on the bow itself, where the rest sits, the components we're putting on the front and how much broadhead clearance we need.

My own draw length is 28.5 inches, but that doesn't mean every arrow I shoot is 28.5 inches long. Depending on the bow and setup, my actual shaft length can be shorter.

That's exactly why we don't automatically cut somebody's arrow to their draw-length number.

A longer shaft behaves dynamically weaker. As we safely shorten that same shaft, the finished arrow behaves dynamically stiffer.

Again, the static spine number printed on the shaft does not change. The dynamic reaction does.

4. Point and Front-End Weight

This is probably the variable that gets overlooked the most after somebody has already selected a shaft.

Let's say I've got one arrow with a 100-grain head. Another has a 100-grain head with a heavier insert. Another has a 125-grain head and an even heavier insert.

Those are not all the same setup anymore.

Adding more weight to the front makes the finished arrow behave dynamically weaker.

So you may initially fall inside the manufacturer's recommendation, then add substantial insert or broadhead weight and push that original spine selection in the wrong direction.

You can't choose your arrow spine and then completely ignore everything you're stacking onto the front of that shaft.

Whether you're building around a 4mm arrow, 5mm arrow or a standard-diameter shaft, those relationships still matter.

Start With the Manufacturer's Spine Chart

So where do we actually start?

We start with the manufacturer.

We're not throwing the spine chart away. The chart is our baseline.

Different manufacturers structure their charts differently, so use the chart or selector for the exact shaft you're considering.

Example: Easton's Hunting Spine Chart

Easton has a good spine chart because it gives you guidance for how additional front-end weight can affect the spine recommendation.

Easton's current hunting chart uses a baseline that includes a 100-grain point. When point weight increases beyond that baseline, Easton instructs you to adjust the calculated bow weight used in the chart.

For each additional 25 grains of point weight above the baseline, Easton's chart adds 3 pounds of calculated bow weight. Easton also gives separate guidance for heavier inserts and outserts.

The point here isn't that every arrow company uses this exact formula.

The point is that the components you're putting on the arrow matter, and you need to follow the guidance from the manufacturer of the shaft you're actually using.

What Happens When You Get Arrow Spine Wrong?

Here's where this stops being a chart on a website and becomes something we actually see come through the shop.

Some of the most common issues are pretty simple:

• Somebody chooses spine based only on draw weight.
• They ignore draw length.
• They confuse spine with arrow weight.
• Or they choose the correct shaft initially and then add a bunch of weight to the front without reconsidering the spine.

Now the arrow can end up dynamically weak.

The setup becomes harder to tune. Rest adjustments start getting chased. Broadhead flight can become inconsistent and groups can start opening up downrange.

Spine isn't the only thing that can cause a tuning or broadhead-flight problem—we know that.

But it's one of the foundational things I want correct before I start chasing other adjustments on the bow.

What If Your Arrow Is Too Weak?

If we end up a little weaker than we want, we've got a few things we can look at.

If It's Marginally Weak

First, we determine whether the shaft can be safely shortened.

If we can shorten it while maintaining proper broadhead and component clearance, that will stiffen the dynamic reaction.

We can also look at reducing excessive point weight.

One thing I'm not going to do is change your proper draw length or dramatically reduce the bow just to get the wrong arrow to work.

We're not doing that.

If It's Excessively Weak

If it's excessively weak, stop trying to force the setup to work.

Move to the stiffer shaft.

Chalk those arrows up as a loss, give them to your buddy if they fit his setup, and rebuild the arrow correctly.

I'd rather start over with the right shaft than spend all season chasing a tuning problem created by the wrong one.

What If You're Between Two Arrow Spines?

This happens all the time with modern compound bows.

If both options fall inside the manufacturer's recommendation, you've got a choice to make based on what you're trying to accomplish with the complete arrow.

The weaker spine will often have a lower GPI, which can help keep finished arrow weight down.

The stiffer shaft is generally going to have a higher GPI and give you a heavier finished arrow.

In our experience here at the shop, if a modern compound setup genuinely falls between two appropriate recommendations, I generally prefer the slightly stiffer option.

We tend to see fewer problems during tuning, and I'd rather end up a little stiff than clearly weak—especially once we start adding broadheads and hunting components.

Our Step-by-Step Arrow Spine Selection Process

If you're trying to choose your next arrow, here's the process I'd go through.

1. Know your actual draw weight.
   Measure what the bow is actually pulling rather than assuming the limb sticker tells the whole story.
2. Know your draw length.
   We need draw weight and draw length together to understand the setup.
3. Determine your actual finished arrow length.
   Don't automatically make it the same number as your draw length.
4. Know how much weight you're putting on the front.
   Insert, outsert, field point and broadhead weight all matter.
5. Use the manufacturer's spine chart or selector.
   Follow the instructions for that specific manufacturer and shaft.
6. If you're between spines, evaluate the entire build.
   Look at GPI, finished arrow weight, front-end weight, intended use and where you want the finished arrow to land.
7. Build the arrow and verify it through tuning.
   Retune the bow, put the arrow back through paper, confirm clean arrow flight and then reconfirm your sight marks.

I can't say that last part enough.

When you make a meaningful change to the arrow, go back and check the bow.

Your draw weight, draw length, arrow length and point weight all work together.

Start with the manufacturer's recommendation. Build around the arrow you're actually going to shoot. Then verify everything through the tuning process.

Arrow Spine FAQs

Is a 300-spine arrow 300 grains?

No. A 300-spine designation describes shaft stiffness. Arrow weight is measured separately in grains.

Is a 300 spine stiffer than a 400 spine?

Yes. With common carbon-arrow spine ratings, the lower number represents the stiffer shaft. A 300 is stiffer than a 400.

Does adding point weight weaken arrow spine?

It makes the finished arrow behave dynamically weaker. That's why heavy inserts and broadheads need to be considered before finalizing your shaft spine.

Does cutting an arrow shorter make it stiffer?

Cutting the shaft shorter does not change the static spine number printed on it, but it makes the finished arrow behave dynamically stiffer. Never shorten an arrow beyond what is safe for your bow and broadhead setup.

Should I choose the stiffer spine if I'm between two sizes?

Both options first need to fall within the manufacturer's recommendation. If I'm genuinely between two appropriate spines on a modern compound hunting setup, I generally prefer the slightly stiffer option rather than ending up dynamically weak.

Can the wrong spine cause broadhead tuning problems?

It can contribute to them. Incorrect spine can make consistent arrow flight harder to achieve, and broadheads often make those problems more noticeable. Spine isn't the only possible cause, but it's one of the first foundational variables I want correct.

Bottom Line

Don't pick an arrow spine from draw weight alone.

I need your draw weight, draw length, actual arrow length and the amount of weight you're putting on the front of the shaft.

Start with the manufacturer's chart. Use it as the baseline. Then build around the arrow you're actually going to shoot.

And once you've built a new arrow, retune the bow, confirm that it's shooting that setup correctly and reconfirm your sights.

Get the foundation right before you start chasing everything else.