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The “spine” of an arrow simply refers to its stiffness.
While looking for the perfect arrows you need for shooting with your bow, you have to be aware of the basics of arrow spine.
You need to know how the spine is calculated and why you need to spend your time looking for the best arrow to shoot.
We will teach you about all these things along with the comparison between the arrow spine and arrow weight.
You will also be able to find a user guide chart at the end of this guide to choose the perfect arrows.
So, if you are still wondering what spine arrow do I need, then you are in the right place.
What is Arrow Spine?
Arrow spine is the measurement of stiffness of an arrow.
While a model of arrow can be available in a single spine stiffness, you can find some arrow models with different spine stiffnesses.
A stiffer arrow has a smaller spine rating.
If you own an arrow with 300 spine rating and your friend owns one with 500, then your arrow would be more rigid than your friend’s.
There are two different types of arrow spine rating out there. One of them is a Static Spine and the other one is Dynamic Spine.
Static Spine
A static spine is the spine measurement when the arrow is stationary, without including factors such as the arrow head and nock.
To be more specific, it is a measurement of how much an arrow bends when a two-pound weight is suspended from the center of an arrow shaft supported by two points 28″ apart.
This flex is measured in inches, specifically thousands of an inch.
So, an arrow that bends 0.3″ has a spine rating of 300.
This is the ASTM test method1. Some manufacturers use their own method.
Dynamic Spine
A dynamic spine defines the way an arrow responds from the release of stored energy in the bow after shooting.
In other words, how much the arrow flexes in real-world conditions.
While determining a dynamic spine, several factors such as draw length, bow weight, broadhead weight, nock weight, bowstring material, vanes/fletches, etc. affect how an arrow might bend after shooting.
Due to the difficulty of figuring out all of these factors, most arrows are represented with only a static spine.
However, you can calculate the arrow’s dynamic spine yourself with a calculator.
You can even adjust the stiffness yourself.
Increasing an arrow’s dynamic spine can be done by using a lighter bow, switching to a lighter point, using heavier bow strings, adding more strands on the strings, as well as using heavier vanes and nocks.
Shortening the shaft also contributes to increasing the arrow’s dynamic spine. A 26″ arrow will be stiffer than a 28″ arrow if both are marked with a 300 static spine.
Clearing the Confusion about Arrow Spine vs Arrow Weight
It’s easy to confuse arrow spine and arrow weight.
However, these things are totally different from each other.
For example, you might be thinking about replacing your 330-spine arrow with a 500-spine one to reduce the arrow weight in a 70-lb bow with a draw length of 29″.
However, everything you are doing incorrect.
Let’s look at why.
Let’s Look Deeper into the Difference
The spine rating of an arrow is related to its stiffness. It depends on how much it flexes, but not the arrow’s weight, though that is a factor.
When you are shooting with a bow, every arrow needs to flex a certain amount.
“Certain” is an important word because if your arrow is flexing too much then it will be inconsistent and likely hit to the right of where you’re aiming.
The arrows will form a larger group than they should, too.
Using an arrow the right spine rating, which doesn’t flex a lot after moving past the riser, can improve your consistency when hitting the target.
Past a certain amount of stiffness, however, you’ll find it harder to aim because the arrow will hit too far to the left.
This applies primarily to right-handed archers, mind you. The directions will be reversed for left-handed archers: Too little flex can send the arrow to the right and too much to the left.
But too-stiff arrows can be problematic, too, as they won’t flex around the riser and may strike it.
This can cause them to fly off target. It can also damage or even tear the vanes off your arrows!
Related: How to Shoot a Compound Bow
The Relation between Shaft Length & Arrow Spine
If you have a longer shaft, your arrow is more likely to flex too much.
While choosing the best arrow for your bow, you can take a look at the spine selection guide provided by the manufacturer to find out what shaft you need to select to meet your draw weight and arrow length requirements.
The shaft can be determined by the spine rating of your arrow.
The speed of your bow might also be useful to know because faster bows can exert a larger amount of force on the arrow, causing it to flex more.
When you are looking for spine ratings of shafts designed by different manufacturers, you will find a lot of differences since the spine rating system isn’t uniform.
Sometimes cases, the grains per inch are printed on the shaft instead of the arrow spine rating, which might put you into a dilemma.
Get it Clear with This Example
Let’s look at an example.
Suppose there are two shafts rated 330 and 400, which weigh 9.6 and 8.5 grains per inch respectively.
You might think about replacing your 330 shaft with the 400 one since this lets you use a lighter arrow, increasing velocity.
The arrow may weigh less, but it is also weaker and more flexible than the 330 one. If it’s too flexible for your bow weight and draw weight then the arrow will be less precise.
This is why replacing a 330-spine arrow with a 400-spine arrow can be a bad choice.
If you are really looking for a lightweight arrow, a better option may be to switch to a lightweight shaft with the same spine.
When there are two arrows of the same spine rating, their weight in terms of grains per inch can still differ from each other. This is due to different materials.
Here’s a comparison table which includes three different arrows, all cut down to measure 29″ from end to end without tip, nock, or vanes.
All of these arrows have a spine rating of 400.
With the information displayed in the table below, you’d be able to find out that there are still a lot of options available for you to switch the arrow weight instead of changing the arrow spine ratings.
| Arrow | Grains per Inch | Total Weight |
|---|---|---|
| Easton 6.5mm Match Grade | 8.4 | 243.6 gr |
| Easton 5mm Axis Carbon | 9.0 | 261 gr |
| Easton 5mm FMJ | 10.2 | 295.8 gr |
What Spine Arrow Do I Need?
With the above information, you should know the difference between arrow spine and arrow weight.
Now, it is time to find out what spine arrow you need.
There are several factors you need to look for to select the best arrow spine.
You can find a lot of information regarding the best spine arrow to choose with the selection charts offered by your arrow’s manufacturer.
While looking at the selection charts, the deciding factor may be to choose which arrow is lighter than the others of the same stiffness.
If you want to change the dynamic spine of your arrow, you can do so by switching the length of your arrow or adjusting the draw weight of the bow you are using2.
You might also want to consider changing the weight at the ends of your arrow.
Since arrows having broadhead-like tips are highly sensitive to the proper spine in comparison to the arrows containing field tips, it is recommended for you to figure out the best spine before you go hunting.
Stiffer Arrow Spine or Not?
Using a stiffer spine may stop your arrow from flexing3. With this condition, your arrow won’t be able to bend the proper amount past the riser, which results in an inconsistent arrow flight towards the target.
On the other hand, using a weaker spine might make your arrow flex too much, which can also result in an improper arrow flight.
Annoyingly, this might also lead the arrow to strike the riser.
This clearly means you need to look for a weaker spine rating in case your arrow too stiff. Also, if your arrow is very weak, you need to go for a higher spine rating.
Arrow Spine Selection Charts
All of the following charts are based on a 100 gr point.
Compound Bow Weight Arrow Spine Selection Chart
Traditional-style Bow Arrow Spine Selection Chart
Conclusion
Now that you’ve read this article, you should understand what an arrow’s spine rating means and how to select the right spine for your needs.
If you have any confusion regarding any of the topics discussed in this guide, feel free to write about your issue in the comments.
We’ll try to get back to you right away!
