What does arrow spine really mean?

Leigh Hauck – August 28, 2025

Arrow spine is one of the first numbers you will face when buying a new arrow, and the most important. Yet, this number is so often misunderstood and purchasing arrows without a complete understanding of what arrow spine actually is and means can be detrimental to your down range success. In fact, more than half of the arrow flight issues that archers come to me with can be traced back to an error in arrow spine selection – (most of the rest are form issues, but surely you don’t want to read a blog about that!)

Most of us have looked at spine charts before. They look like Excel spreadsheets and are the starting point for selecting your arrow spine. Unfortunately,  many archers consider spine charts to be the only factor in selecting your arrow spine, and some don’t even consult spine charts at all.

What is arrow spine?

Arrow spine basically means arrow stiffness. Bows which exert more energy (through both draw weight and length) require stiffer arrows. Lower numbers equal stiffer spine, so a 300 spine is stiffer than a 400 spine.

Spine selection is as crucial as selecting the right size when you are picking out a new pair of hunting boots. You wouldn’t walk out of Cabela’s with a pair of boots 3 sizes too small just cause you like the laces, right?

Why does arrow spine matter?

Your bow exerts a precise amount of energy on every shot, with your draw weight, draw length, and cam design being the main factors that determine this amount of energy. You need to have an arrow which is built to handle precisely that amount of energy that your bow is producing. Too stiff or too weak, and your arrow flight will suffer as there is either too much energy being exerted on the arrow and it can’t handle it all, or there isn’t enough energy being put into the arrow for it to get out of the bow properly.

What is the difference between arrow spines?

As spines get stiffer (stronger), the wall thickness increases. Basically, the arrow is getting stiffer because it is being built with thicker walls, and more material. This also translates to stiffer spines being heavier. Arrows are measured in GPI (grains per inch), and stiffer arrows have higher GPI’s. This leads us to the most common error made when it comes to arrow selection.

The most common arrow selection error:

Many archers look at spine selection only in terms of arrow weight. If they want a heavier shaft, they will select a stiffer spine just to attain that weight with zero regards to what spine actually means, and the crucial energy matching component that we discussed earlier. This would be like buying a pair of boots that are 3 sizes too small for you, just because they are lighter weight than the ones that fit. It makes zero sense.

A recent spine selection case came  across my desk, where an archer was having difficulty getting his fixed blade broadheads to fly. He said the flight was completely erratic – a dead giveaway that incorrect arrow spine is the culprit.

The first thing I will always ask is for the customers draw weight, carbon to carbon arrow length, and current arrow spine. This gives me at least a baseline for assessing whether or not they are in the right spine range. This particular archer replied back, stating that he was trying these broadheads with both a 250 spine and a 400 spine shaft, and the flight was terrible with both.

To come back to the boot analogy, this would be like trying on a size 6 and a size 12 boot, while you have size 9 feet. Of course, neither the 6 or 12 are going to fit, they are not your size.

Presumably, this archer was selecting spines based on arrow weights, and he was trying to achieve certain arrow weights by changing up his GPI.

What if you want to target a certain arrow weight?

There are many ways to do this without getting out of your correct spine size! First of all, different manufacturers will make the same arrow spine but in different weights. Just like how you can buy a size 9 shoe from Nike, Reebok, or Adidas. You can start by finding a brand which makes a shaft in a GPI that you like.

If you aren’t sure where to start, I recommend going with a higher GPI shaft like The Arrow from Tooth of the Arrow. You’ll get a better penetrating arrow at a more forgiving speed, and naturally stronger arrow because of the increase in wall thickness. If you want to target a certain arrow weight, do so by changing your front-end weight – never your arrow spine.

This is a lot of information, what now?

Yeah, I know, it can be a bit overwhelming. It’s really important to keep things simple at first. As long as you select the right arrow spine, your arrows will never cost you a hunt. Many bowhunters scrutinize over every detail of their arrow setup, while ignoring their form.

If your arrows hit their mark, you will find success in bowhunting. As long as your spine is correct, all the rest is up to you and how many hours you spend on the range! Remember, bowhunting is a primitive art. Don’t overcomplicate it, I promise your grandfather wasn’t worried about FOC and arrow clocking!

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If you have any questions or would like to discuss the topic further, please feel free to reach out to us at sales@toothofthearrowbroadheads.com

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