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Spine Considerations for Bowhunters

Spine Considerations for Bowhunters

Spine Considerations for Bowhunters

Arrow Spine, or calibrated stiffness of the arrow shaft, is one of the most important characteristics for any hunting arrow.  With the newest bows pushing arrows harder than ever, the importance of correct, consistent spine is more important than ever.  Not only do arrows need to be stiff and strong enough to withstand the tremendous forces involved in shooting and engaging game, they also need the tightest tolerances for stiffness from shaft to shaft for consistent results and tuning.  

Easton literally wrote the book on arrow spine- in fact, the industry standard for spine measurement is based on the method created by our founder, Doug Easton, in the 1940’s.  This “static spine” measurement is marked on many Easton arrows as the model number- for instance, a Deep Six Injexion 400 has a spine of 0.400”.  Aluminum arrows are identified with the dimensions of the diameter and wall, but there is also a specific spine value for these shafts as well.

Measuring spine

Spine is measured by suspending the arrow on supports 28” apart and applyimng 880 grams of load to the center of the shaft between the supports.  The amount of bend is measured in inches- 0.400 is 4/10ths of an inch.   A higher number, like 0.500, is therefore weaker- the arrow is bending more.

Easton ensures that every shaft has correct spine, 360 degrees around the shaft.  With Easton technology, you don’t need to worry about one side of the shaft being stiffer or weaker.

Static vs dynamic spine

So-called “dynamic” spine is a way to express how the arrow is influenced by broadhead and insert mass weight, fletching mass weight, bow acceleration and other variables.  The Easton Shaft Selection Chart takes into account these variables to yield the correct size arrow for a given setup.  That’s why, for example, there are different selection columns for different bow speed ranges.

Proper spine enhances good broadhead flight

With the aerodynamic characteristics (“steering effect”) of broadheads, correct and consistent arrow spine is of extreme importance- arrows that don’t have consistent spine will leave the bow with more variation, and this has a big influence on broadhead flight.  Even with mechanical blade broadheads,