Arrow spine ratings are a vitally important number when building the right arrow setup for your bow, but they can often be very confusing. Arrow manufacturers often don't use a universal standard rating system, so a 350 in one arrow can be the same as a 400 in another, and to complicate the matter further, some arrows (like the Carbon Express Maxima Reds) have different spine strengths in different parts of the arrow. So, what do we do?
First, you need to get your bow build's numbers. Specifically, you need to know your bow's draw weight, the length of your arrow shaft (not your draw length), and your desired point weight. These three numbers can be used to reference an arrow selection chart from your favorite arrow manufacturers (we particularly like what Black Eagle has going on), to select your arrow. Generally, the lower the number, the stiffer the arrow's static spine. The arrow's static spine is measured simply by weighting down the center using a spine testing machine. It's old school, for sure, but it is effective!
However, the stiffness you select there is only the static spine of your arrow- the spine of the arrow at rest. When you begin to alter the length of the arrow shaft, add weight to the front or rear of the arrow, or alter the arrow in any other way, you change the dynamic spine rating of the arrow. Adding point weight increases your arrow's FOC (front of center balance), but it decreases the dynamic spine rating, whereas shortening your arrow can increase the dynamic spine of an arrow that is too weak, but be careful not to cut too much! So, for example, if you had a Black Eagle Deep Impact Arrow with a 350 spine, but you add 185 grain broad heads to it (like a German Kinetic) your 350 spine is now going to perform at a spine rating more like a 400-450, even though the static spine rating is the same. If I then cut the arrow down to 27", I can increase the dynamic spine of that arrow back toward it's static spine rating. There's no perfect formula for this calculation, but talk to your local pro shop, or confer with experts online like John Dudley's "Knocked and Ready to Rock" segments for support.
In later weeks, we will get into building arrows, tuning arrows, and more detailed on arrow selection, but for this week, you are armed with the knowledge of how to select arrow shafts using the spine rating, and the knowledge of how arrow components can affect an arrow's dynamic spine. See you on the range!
What is this?
Deer Creek Archery will use this to archive articles and videos with tips from our team and the professionals on how to shoot and set up your bow more effectively.