To get arrows with the correct spine for your bow, you first need to know your exact draw length and the weight that you are pulling from your bow. The standard measurement for a bow is based on 28″, but many of us fail to draw to that length; most of the time we draw less. A rule of thumb is to add five pounds of spine for each inch over 28″ as well as an additional five pounds for the broadhead. For each inch under 28″, you will subtract five pounds. For example, if you are drawing 65 pounds at 29″ you would add five pounds for the inch over 28″ and another five pounds for the broadhead, ending up needing an arrow spined at 75#. I would also err on the high side, adding another five pounds. In this case, I would opt for shafting that is spined 75# to 80#.
A recurve bow will generally accept a wider range of spine in its arrows because of the near centershot design of the bow. A longbow, on the other hand, will require a tighter tolerance due to the arrow having to bend farther around the bow’s riser when shot. But this is not true for all archers. Bow weight, bow design, release, and numerous other individual shooting characteristics will all play a part in what spine arrow will work best for you.
The chart below shows the recommended arrow spine for any given bow weight and draw length. But these are not set in stone; rather, you should use these figures as starting points.
This tip is an excerpt from T.J.’s book The Traditional Bowhunter’s Handbook.