Archery is a sport with many different details to learn and understand. The science behind it includes physics, energy, and aerodynamics. In addition to science, there are plenty of human factors to consider as well. Your archery form, mental toughness, and decision-making ability all come into play. There’s no denying how technical archery can really be. One specific and important thing to understand is arrow spine. Whether you have heard of this or not, we’ll be diving in so you can understand and determine the right arrow spine for you.
What is Arrow Spine?
The spine rating of an arrow is simply a measurement of its stiffness. The same arrow comes in a variety of stiffness: the lower the number, the stiffer the arrow. For example, a 330 arrow is stiffer than a 500 arrow spine. Depending on your draw weight, draw length, and arrow material, you’ll adjust your arrow spine accordingly. Arrows bend and flex when shot, so having the correct arrow spine will help improve your consistency and accuracy.
The Two Types of Arrow Spine
When discussing arrow spine, there are two types to consider, static and dynamic. While both are important, we’ll only really be concerned about one of them.
Static Arrow Spine:
Static arrow spine measures flexibility in a static state (at a standstill). It’s measured by applying an 880-gram weight to the arrow, suspended from the center of the shaft. The arrow must be 28” in length and supported at each end of the arrow. Spine is measured by the number of inches a shaft deflects (bends) X 1000. For example, a 500 spine arrow bends .5 inches when the weight is applied.
Dynamic Arrow Spine:
Dynamic arrow spine describes the way an arrow reacts to stored energy, transferred upon release of a bow string. Many different factors determine the way an arrow reacts upon release. Increasing or decreasing peak bow weight, arrow length, arrow point weight, or the point/insert combination can all affect your arrow spine. Because of these variables, arrows are measured and sold based solely on static spine.
Why is Arrow Spine Important?
Now that we know what arrow spine is, why is it important? If you don’t have the correct arrow spine, you’ll most likely experience inconsistencies. Erratic arrow flight and inconsistent impact are two major signs that you’re shooting an incorrect arrow spine. Correct arrow spine is key to improving consistency and accuracy in your shots. In general, an under-spined arrow will stray to the right, while an arrow that is too stiff will veer to the left. Just the right amount of flex helps your arrow clear the bow riser and impact with pinpoint accuracy.
The Archer’s Paradox
This leads to an important aspect of arrow spine called, The Archer’s Paradox. “The archer’s paradox is the phenomenon of an arrow traveling in the direction it is pointed at full draw, when it seems that the arrow would have to pass through the starting position it was in before being drawn, where it was pointed to the side of the target. The bending of the arrow when released is the explanation for why the paradox occurs and should not be confused with the paradox itself.”
The definition is a little confusing, so let’s simplify things a bit. Arrows bend and flex when shot. In order for them to be accurate, they must have the correct about of flex. This allows an arrow to flex away from the bow riser and return to the correct path as it leaves your bow. An incorrect spine results in unpredictable contact between the bow and arrow, reducing accuracy.
If an archer shoots several arrows with different dynamic spines, they will all deflect and react differently. This will affect arrow flight and create inconsistencies in impact. All your arrows must be 100% consistent and properly spined to fit your setup. Doing so will keep you consistently on target.
How to Find Your Arrow Spine
So how do you find the correct arrow spine for you? Thankfully, many arrow manufacturers make it extremely easy. They provide charts to help you determine the correct spine for their arrows. There are, however, a few simple measurements you’ll need to take in order to use them.
- Draw Length: In order to find your arrow spine, you must first find your draw length. This can be measured a number of ways and easily determined at your local archery shop. If you’re looking for a quick at home measurement, you can find it by measuring your arm span and dividing by 2.5. So, if your arm span is 70 inches, your draw length would be 28 inches (70 / 2.5 = 28) No matter which method you choose, you must first find your draw length.
- Arrow Length: The next step is to use your draw length to find your arrow length. If you have already found your draw length, you can simply add roughly an inch to this to find your arrow length. So, taking our previous example of a 28 inch draw, your arrows would be about 29 inches in length. This is just a ballpark estimate, however.
- Poundage/Draw Weight: The last step is to find your draw weight or poundage. This can easily be measured with a scale at your local archery shop. If you’d like to determine this at home, you can simply purchase your own archery scale. They are relatively cheap and very easy to use. If you plan on doing any adjustments/tuning at home, I would highly recommend picking up a digital scale because it will save you time and money in the long run.
- Using an arrow spine chart: Once you’ve determined your arrow tip weight, draw weight, and arrow length, you’re ready to determine your arrow spine. The charts below give you a simple way of finding the proper arrow spine for your particular bow setup. They use point weight, draw weight, and arrow length to determine your correct arrow spine.
To use these charts, simply take your point and draw weight and correspond it with your arrow length. Where these two numbers meet on the chart should provide your proper arrow spine.
Note* Arrow charts vary from company to company. These reference Goldtip arrow charts, reference charts from your preferred arrow manufacturer to find the correct spine.
There you have it! Arrow spines may seem complicated, but as long as you refer to the charts, you’ll be fine. It’s very important to have a properly spined arrow with your bow setup. Once you find the proper arrow spine for your bow, stick with it. It should change only if you adjust your draw weight, arrow length, or arrow point weight. When you order new arrows, be sure to let the archery shop employee know your spine and arrow length. You can also just provide one of your existing arrows to replicate. Once your set up with the correct arrow spine, you’ll be shooting every shot with consistency.