The gold standard for rating arrow spine has always been Easton's fitment charts. To understand the issue of arrow spine deflections and why they aren't just standardized, like tire sizes or plumbing fixtures, you must understand something about the history of the arrow industry. Once you know about spine deflection measurements, picking arrow shafts will be easy from now on. WHY HAVE SO MANY SPINE SIZE SYSTEMS? The next section is technically exhaustive, but worth the read. Look up the real deflections and base your choice on that. Never assume an arrow's published spine size matches the arrow's actual deflection. For example, a "Carbon Express Maxima 250" has an actual spine deflection of. Again, please note actual arrow spine deflections do not necessarily match the manufacturer's marketed spine sizes. Chart not applicable for traditional bows. For slower bows, read chart one block up and to the left. For faster bows, read chart one block down and to the right. These charts are normalized for modern compound bows with IBO speeds between 280-330 fps. STANDARDIZED SPINE CHARTS BASED ON DEFLECTION` We suggest it is far more reliable to reference the deflection data on standardized charts. For example, an Easton 340 (.340" deflection) is dramatically stiffer than an Easton 500 (.500" deflection) - not the other way around. Make sure you understand the relationship of spine deflection and stiffness. The more limber an arrow is, the HIGHER its spine deflection measurement will be. So the stiffer the arrow is, the LOWER its spine deflection measurement will be. Stiffer arrows will, of course, sag less. Then the arrow's spine deflection would be. weight causes the center of a 28" arrow to sag down 1/2 inch (.500"). weight causes the shaft to sag down is the arrow's actual spine deflection. 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. According to the modern standards (ASTM F2031-05) an arrow's official spine deflection is measured by hanging a 1.94 lb. Published spine sizes can be anything (a number system, color codes, letters of the alphabet, etc.) but an actual arrow spine deflection is expressed as a direct technical measurement. WHAT IS ACTUAL SPINE DEFLECTION? There is a difference in an arrow's published spine size and the arrow's actual spine deflection. It sounds a lot more complicated than it is. If you would rather not use the simplified method, then we suggest you get to know the concept of actual spine deflection. You might need to accommodate by choosing a little stiffer spine like the 3000 shaft, right? And what if you prefer a heavier 125 grain tip, what then? We appreciate the easy reference of simplified charts, but they're not always the best utility. Easy! But what if you shoot a very aggressive speed-bow with a 350 fps IBO Speed? In that case, your bow will have more output than the average 60# bow. If you know your bow is set for 60# and you use 29" arrows, you just follow the dots on the chart and choose the 2000 spine size.
For example, if you shoot a typical 310 fps compound bow, with normal 100 gr tips and 75% let-off, the simplified chart works fine. If you go by the simple chart method, then you'll need to apply a little common sense - particularly if your bow setup isn't exactly 'average'. But other arrow manufacturers offer a more simplified chart with an arbitrary number system, like the sample chart on the right which just references draw weight and arrow length. SIMPLIFIED ARROW SPINE CHARTS` Some arrow manufacturers have very complex charts which take many variables into account. Carbon Arrow Selection & Research Guide | Chapter 2
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