Using Spine Deflection Measurements to Select Published Arrow Sizes
OK! Let's choose an arrow spine! We strongly suggest you learn this system, as using actual spine deflection data is the only universal system for comparing arrow spines from model to model and manufacturer to manufacturer. The next section is technically exhaustive, but worth the read. Once you know about spine deflections measurements, picking arrow shafts will be easy from now on.
To understand the issue of arrow spine deflections and why they matter, you must understand something about the history of the arrow industry. The gold standard for rating arrow spine has always been Easton's fitment charts. Before carbon arrows hit their stride in the 1990's, practically every archer in the world had at one time studied the little blocks on the Easton chart, trying to decide if the 2219's, 2413's, or 2315's would be better (remember?). The basic rating system wasn't really hard to understand. The first two numbers were the arrow's diameter (in x/64th's of an inch) and the second two numbers were the shaft's wall thickness (in x/1,000th's of an inch). So a 2315 was an arrow shaft with a 23/64" diameter and a wall thickness of .015". Easy enough. But what did that really mean? The rating system had nothing to do with arrow spine, directly anyway, and the numbering system wasn't necessarily sequential. A 2315 arrow was actually heavier and stiffer than a 2413 arrow. A 2219 was surprisingly heavier than a 2512, but not as stiff. And a 2314 and a 2315 oddly weighed the same but had different deflections. Ok. So it wasn't so easy. But Easton's engineers crunched all the numbers and the handy aluminum arrow charts solved all the woes with their nice little organized blocks.
Then carbon arrows came along and made things easier ... almost. Since carbon arrows had a much broader ranger of application, there was no need for 10 to 15 sizes of the same arrow. For most carbon arrows, 3 to 5 sizes covers virtually every application. So Easton simplified the sizing system by basing the sizes on actual spine deflections. Easton's familiar carbon arrow spine sizing system (500, 400, 340, 300) is basically the arrow's spine deflection x1000. So a 500 shaft is a .500" deflection. A 340 Easton shaft is a .340" deflection ... and so on. So forgiving the shift of the decimal, the Easton spine sizing system matches up nicely with actual spine deflections.
Unfortunately, the system is somewhat counterintuitive. For Easton/Beman arrows, the lower numbered shafts are actually the stiffer heavier shafts, and the higher numbered shafts are the more limber and lighter shafts. This naturally goes against the bigger is more line of thinking. Since most people don't know how spine deflections are obtained, or why they matter, some archers will simply buy the "larger" size for heavier bows and "smaller" sizes for lighter bows. Of course, this is completely backwards. So everyone ended up back at the Easton charts studying the little blocks. And why not? No archery pro-shop is complete without a big Easton chart on the wall. So why mess with tradition?
Turns out, Easton wasn't the only player in the carbon arrow game. In fact, they were one of the last to join-in when they purchased Beman in 1995. By that time, Gold Tip already had a five year head start with their popular graphite arrows. And Gold Tip had really simplified things with an easy 3 size system ... the famous 3555, 5575, and 7595. The system was intended to be self-explanatory. The 3555 roughly fit a 35-55# bow, a 5575 fit a 55-75# bow, and a 7595 fit a 75-95# bow. At least that's how most archers understood the sizing. But it didn't always work out. The Gold Tip arrows had spine deflections of .500" (3555), .400" (5575), and .340" (7595) respectively. So for example, a 53# bow shooting a 30" arrow actually required the 5575 spine (per the Easton gold standards anyway) instead of the 3555 that Gold Tip's sizing convention might suggest. So it wasn't long until Gold Tip published their own charts (yes, with the little blocks), based essentially on the Easton spine deflection data.
To be fair, Gold Tip's system really wasn't so bad ... comparatively anyway. There was worse to come. Not to be outdone, Carbon Force Arrows, a division of PSE, decided to really simplify things and make their sizes completely sequential ... 100, 200, 300, and 400. So the larger the number, the heavier and stiffer the arrow. Fine! But this scrambled all of our brains even worse because their arbitrary sizes actually overlapped the actual arrow deflections. The Carbon Force 100 has a .500" spine, the 200 has a .400" spine, the 300 has a .340" spine, and the 400 has a .300" spine. Try to wrap your noodle around that!
And just as our grey matter started to congeal from Carbon Force, Carbon Express reinvented their generally understandable 30/50, 45/60, 60/75 system (similar to Gold Tip's system but with the same drawbacks) to a system that's not just arbitrarily sequential (150, 250, 350), but varies from shaft to shaft. Their Maxima 250, for example, has a spine deflection of .404", but the Maxima Hunter (camo) 250 has a spine deflection of .417". Oh boy!
It boils down to this. Whether you like Easton arrows or not, Easton is the big dog in the arrow market (biggest by far). And Easton's competitors don't want to be seen as "copycatting" Easton by following Easton's sizing format. They want to be unique and develop their own marketing and sizing system for their products ... even if it ultimately leaves us all confused. There are well over a dozen popular carbon arrow manufacturers who sell carbon arrows in the U.S., and all of them are trying to sing their own tune. For archery enthusiasts this is both good and bad. Competition and innovation will continue to keep prices low and product quality high, but we'll all have to continue to put our thinking caps on when we shop for arrows. There are no universally agreed spine sizes among the various arrow manufacturers.
But the system of actual spine deflection is universal, because those measurements are guided by industry standards. That's the only apples-to-apples system that applies to every brand and model of carbon arrow. As long as the various carbon arrow manufacturers provide their spine deflection data (and they test using the industry standard method), manufacturers can size and market their arrows by any system they like ... and we can still reference the proper application to the gold standard Easton charts using actual spine deflections (see below).
Jon Henry is an avid outdoorsman who enjoys both hunting and fishing. He has been shooting and competing in archery for almost 40 years, and began competitive archery in the NFAA at age 12 as a youth. He was a sponsored PAA pro archer for several years, and before that competed for 15 years in both the NFAA and NAA. Jon retired from competition about 8 years ago, due to a series of shoulder injuries that impacted my ability to sustain competitive performance.
Jon is in his mid 50's, and still very much enjoys shooting his bow and now crossbows as well. He is taking a great deal of his experience gained from building and tuning archery equipment and applying it to crossbow shooting, since they are very similar in many respects.
Jon's goal is to help as many new shooters gain a solid knowledge of their equipment as possible, so that we can continue to grow the sport of target shooting and hunting with a crossbow, until it becomes as popular as the other traditional forms of archery.
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