arrow's actual spine deflection is
the arrow's measured resistance to bending. Basically ... an arrow's actual
spine deflection tells you how stiff the arrow is. For proper safety and best
performance, the arrow spine must be matched to the output of the bow. Arrows
which are too stiff or too limber will not fly well and will degrade the
accuracy of your bow. Arrows which are dramatically underspined (way too
limber) can even present a failure hazard. So selecting the proper arrow spine
is very important, but it can be confusing. Manufacturer spine sizing
systems may be arbitrary (100, 200, 5575, 45-60) and may or may not reflect the
arrows' actual spine deflections. And some manufacturers list spine sizes
in ascending order of stiffness - others in descending order. So you must
often cross-reference the arrow's
advertised spine size with the actual spine deflection your bow requires.
According to the modern standards (ASTM F2031-05) an arrow's official spine deflection is measured by hanging a 1.94 lb. weight in the center of a 28" suspended section of the arrow shaft (not to be confused with the old AMO standard of 2 lb. and 26"). The actual distance the 1.94 lb. weight causes the shaft to sag down is the arrow's actual spine deflection. For example, if a 1.94 lb. weight causes the center of a 28" arrow to sag down 1/2 inch (.500"). Then the arrow's spine deflection would be .500". Stiffer arrows will, of course, sag less. More limber arrows will sag more. So the stiffer the arrow is, the LOWER its actual spine deflection measurement will be. The more limber an arrow is, the HIGHER its spine deflection measurement will be. See actual arrow specification data before selecting an appropriate spine stiffness for your bow. If you need help, call our pro-shop at 877-410-7811 or email us for assistance.
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