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Arrow Straightness vs. Arrow Stiffness
Ever since you started bowhunting, arrow straightness was probably the number one factor that indicated arrow quality. The straighter the arrow, the better it was (at least in theory) and the more it cost. That was sound reasoning in the days of aluminum, but the same assumption doesn’t apply to carbon arrows. Yes, arrow straightness still plays a role in determining accuracy, but now other issues are even more important.
The processes used to make aluminum tubes automatically produced arrows with consistent weight and consistent spine stiffness. You didn’t have to hand select aluminum arrows to achieve these objectives – they were built in. No one ever talked about arrow spine stiffness tolerances or arrow weight tolerances in the days of aluminum because it was automatically good. Unfortunately, these qualities are a given with carbon arrows, but still no one is talking about them. Hopefully, this will help get people thinking and maybe even talking.
Carbon arrows are made differently. Not only is arrow stiffness and arrow weight more variable in carbon arrows than in aluminum construction, these aspects have a much greater affect on group size and accuracy than the one thing everyone does talk about: arrow straightness. Here’s why you should consider more than just arrow shaft straightness when buying your next dozen carbon arrows.
Arrow Straightness vs. Arrow Spine Tolerance
Arrow straightness is the measure of how much the arrow deviates from perfect as you turn it. Commonly, arrow straightness is measured as +/- .003 inch or +/- .005 inch, etc. That means that an arrow will deviate by as much as .003 inch or .005 inch in either direction from perfectly straight as you turn it and still be accepted.
Conversely, you measure arrow stiffness by hanging a weight from the arrow and measuring how far the arrow bends. Spine tolerance is a measurement of how much the stiffness measurement changes within a dozen arrows. Finally, spine around the arrow shaft (called SAS) is the measurement of how much the spine stiffness changes as you turn the arrow. If the arrow were stiffer on one side than another, a dial indicator attached to the weight would go up and down as you turned the arrow.
When you shoot arrows with poor stiffness tolerance (either within a dozen shafts or around a single shaft), you have problems. Each arrow flexes differently when you shoot it and therefore, your dozen arrow shafts will hit the target at different spots. When you place a broadhead on these arrows, the problem gets worse and the groups spread even wider.
Arrow stiffness tolerance, once a given with aluminum arrows, is more important than arrow straightness tolerance in determining the impact point of your carbon arrows. When ranked, the most important characteristic of a dozen carbon arrows is its arrow stiffness tolerance. The second most important is its arrow weight tolerance (how closely the arrows weigh to the same amount) and the third most important characteristic is arrow straightness. All qualities matter, but some matter more than others.
In other words, if you are buying aluminum shafts, low-grade arrows with a straightness tolerance of +/- .005 are nearly as accurate, at typical hunting distances, as those with super low tolerances of +/- .001 inch that cost more. However, when you get into carbon arrows, you have to be more careful. You can’t just buy the bargains and expect to enjoy consistent accuracy. In truth, you end up getting what you pay for in carbon. When you pay more, you generally get better arrows.
The only way to hold tight tolerances in carbon arrows is to hand select these arrows based on the chosen tolerance range. When intense hand labor is required, cost goes up. For the manufacturers to recoup that cost they must charge more for high-grade arrows.
How Bad Can It Be?
Ted Palomaki, an engineer at Easton has tested nearly every carbon arrow on the market. He bought them off the shelf, the same way you do. He was asked him how bad the worst dozen was. It was bad. Ted said that at Easton they hold the stiffness of a dozen arrows within roughly +/- .005 inch deflection of the target stiffness. The worst dozen arrows he tested had a stiffness range that was .090 inch wide. That translates into a range of three full stiffness sizes at most companies. Can you imagine having a bow quiver full of arrows that span three stiffness sizes? That can’t be good.
Some other companies also make high quality carbon shafts. For example, after testing arrow shafts from PSE, Carbon Tech, Carbon Express, Beman, Gold Tip and Blackhawk and their top grades were all excellent arrow shafts. And of course there are some that we haven’t tested that are also very good.
However, there are also companies that make arrows that are way below par. Also, it is hard to know what goes into a dozen low-grade shafts even at some of the bigger arrow companies. You need good arrows if you are going to consistent. Unfortunately, it is hard to tell them apart. We need a way to test arrows in the pro shop so we know what we are getting.
Sorting Arrows Based On Arrow Stiffness
If you’ve ever made your own fishing rods you know that you have to roll the rod blank on a table top as you apply pressure on the center to find the stiffest axis, or “spine” as it is called. That way you can properly locate the line guides to produce a stable rod. Unfortunately, the amount of spine difference needed to throw an arrow off target is so small that most people can’t feel it when they roll the arrow on the table. Additionally, the difference from one arrow shaft to the next is also just as important. A more sophisticated test is necessary.
You can test the arrow stiffness of a dozen arrows by suspending a weight at the center of a 28-inch span of arrow shaft (the industry standard is 1.94 pounds or 880 grams) and carefully measure how far the weight sags. Easton actually uses this measurement in its arrow shaft sizes (for example, a size 300 shaft flexes.300 inch). Other companies use different conventions to specify size.
Presumably, as you turn the arrow shaft, you will notice the indicator changing. But it is not a very accurate test when you turn the arrow by hand. All of this may seem a bit much. You just want to shoot a whitetail deer at 20 to 30 yards. But even at that distance, arrow stiffness tolerance plays a role in your success. It is worth worrying about.
Hopefully someday arrow stiffness tolerance will become a more important issue in the minds of bowhunters when they search for new arrows. Everything else will follow: dealers will start to do the kinds of tests that separate the good from the bad and manufacturers will respond by improving their arrow shafts.
In the meantime, the best thing you can do is ask the pro shop attendant for the arrow stiffness tolerances of the carbon arrows they sell. If they don’t know it, ask them to call customer service at the arrow company to find out. You might even get a dial indicator and try a few tests at the local pro shop. If enough bowhunters start making informed buying decisions, quality will improve all across the boards.
Arrow Straightness vs. Arrow Stiffness Conclusion
Arrow straightness, within reason, should not dictate which carbon arrows you buy. At typical bowhunting distances, arrow shafts with a straightness of +/- .005 inch will shoot just as well as those with a straightness of +/- .001 inch. However, the arrow stiffness tolerance (consistency of stiffness within a dozen arrows) should be a very important part of your buying decision.