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How to Tell if an Arrow Spine is Too Weak or Too Stiff


Choosing the right arrow to achieve the best accuracy can be challenging sometimes. If you notice your arrows are all over the place, and you’ve already checked your form, your technique and your equipment, then arrow stiffness (or lack thereof) may be the problem.

This stiffness, called the arrow spine, is crucial in the flight of your arrow and the accuracy of your shot. If the flight of your arrow is consistently wobbly, or veering to one side or the other, an incorrect arrow spine may be at play.

So how can you tell if your arrow spine is too weak or too stiff?

The best way to tell if an arrow is too stiff or too weak is to videotape the flight of the arrow. Watching the flight of your arrow, you’ll be able to see if the arrow is veering to the right (too weak) to the left (too stiff). Based on the results, you can take steps to correct the flight of your arrow. This process is called “arrow tuning”.

An “over-spined” arrow can lose energy and velocity as it veers off-target. An under-spined one is less tense, or weaker, and may wobble and stray off-course. Knowing more about arrow spine will go a long way in correcting the problem.

The Significance of Stiffness

Now that we know that spine is a measurement of an arrow’s stiffness., let’s talk about what “stiffness” actually means to an arrow. 

Put simply, it is the opposite of “flex.”

An arrow that is flexible is less stiff. When an arrow is shot, it necessarily flexes as it leaves the bow. As it catches the air and flies, it straightens out.

How much it flexes and how much it straightens out – well, that is the product of its spine rating. An arrow with a weak spine will flex easier than an arrow with a stiff spine. And an arrow with a stiff spine won’t allow for much flex.

What Gives an Arrow Spine?

You’re probably already envisioning that a spine like limp spaghetti won’t help an archer reach the target. And, if an arrow has little to no “give,” that won’t do much good, either.

But why exactly is the stiffness of an arrow important to the shot?

The stiffness interacts with other aspects of the arrow to determine the spine. “If an arrow doesn’t flex enough, or if it flexes too much, it will fly poorly, “ says Archery360.com.

Here are a few other factors that figure into an arrow’s spine:

  • Arrow length
  • Arrow weight
  • Point weight

The Archer’s Paradox

An understanding of the Archer’s Paradox helps to explain why an arrow might need the right balance of flex and stiffness.

As explained by realworldphysics.com, the Archer’s Paradox is: “When an arrow is released to the left (or right) of a bow its trajectory follows a path that is different from its expected trajectory.”

This means that, to get around the bow and the archer’s fingers, an arrow must bend to clear the bow and hit the air. The paradox is that the arrow must bend in order to shoot straight. Watch this video to see several  slow-motion examples of the Archer’s Paradox in action.

How Arrow Spine Straightens the Shot

Arrow spine comes back in play here. If the arrow’s spine is too weak or too stiff, the arrow will not correct itself as soon as it should while in flight.

If that arrow is weak and continues to flex (has a low spine rating), it’s going to veer off target. Likewise, if the arrow is unforgivingly stiff, it also won’t follow the path the archer intends. 

Optimizing the flight of your arrow is key to accuracy. While an arrow will necessarily twist and turn in flight, what you don’t want it to do is wobble.

Less wobbling, less fishtailing, means your arrow straightens out and flies toward the target.

Straight flight means your arrow isn’t losing its energy to the wobbles – and it’s going to get maximum force into that target.

How do Manufacturer’s Assess a Spine Rating?

There are two widely recognized standards of measurement: The Archery Trade Association (ATA) and the ASTM (the American Society for Testing and Materials). Each organization has a similar test for determining spine rating.

The ATA Test

An arrow is attached to two supports, 26 inches apart, and pressed in the middle with a weight of 2 pounds/907 grams. The deflection in the arrow determines its spine rating.

According to targetcrazy.com, the ATA rating is primarily used for wooden arrows, while the ASTM test varies slightly and is used for arrows of carbon fiber or aluminum construction.

Using Arrow Spine Measurement to Buy an Arrow

So, now you know that manufacturers tend to adhere to certain standards, designating their arrows with a number and marking their arrows accordingly. But how do you use the ratings to choose an arrow?

To help simplify the process, just about every large manufacturer produces calculators and charts, such as these found on huntersfriend.com. Some of these charts get pretty complex. And not all producers use the same numbering system to mark the rating.

In fact, arrow selection can get so complex, that some companies have created software for it. A shooter enters the specs or their gear, such as the type of bow, arrow shaft and other details, and the software searches its database for appropriate arrow choices.

When in Doubt, Ask a Pro

The complexity of arrow selection is why the pro staff behind the counter is invaluable to you. Their knowledge and experience can go a long way in helping you select and purchase arrows. 

What about hunting arrows?

If you’re into bowhunting, you have probably asked yourself, “What are the best hunting arrows?” In bowhunting, you want to know that your arrows are good enough to consistently make the shot every time. So why not trust what the Pros are using?

Luckily, I’ve done all the research and have the definitive list of the Top 4 Best Hunting Arrows Used by the Pros right here.

Other Variables to Take into Consideration

On many charts, you’ll see more than one column for arrow specs. This is because other factors figure into determining the correct arrow spine. Make sure you know this when you go to the shop:

Arrow point weight The calculated weight of your arrow, in grains per pound (GPP)
Draw length of bow The length of the bow at full-draw, from grip to arrow nock.
Draw weight of bow The amount of force pushing the arrow, measured in lbs.

Can Arrow Spine be Adjusted?

Yes and no. First, it’s important to differentiate between the two types of spine: static and dynamic:

Static Spine

The measurement of an arrow itself. This is the spine of the arrow in its stationary state, or it’s static state. It’s solely a metric of the physical arrow itself and is unchangeable.

Dynamic Spine

This is the spine an arrow has during a shot. It’s affected by other that are part of the act of shooting and the other elements at work, so dynamic spine can be adjusted by manipulating those other factors:

  • Tip weight
  • Nock weight
  • Arrow length
  • Bow’s draw weight

How to Test the Spine

Maybe you’ve got some arrows around the garage and you want to know their spine rating. If your arrow is unmarked, there are ways to find out what you’ve got.

  • Buy a spine tester. Purchase your own measuring equipment.
  • Make a spine tester. Set up your own measurement tool at home. Many enthusiast websites have directions for putting one together, like this one at shootingtime.com.
  • Take them to an archery shop. Odds are, your local shop has a spine tester on-hand. Many pros will be able to determine the arrow spine just by looking up the manufacturer and name of the arrow.

Peter Sontrop

I live in Alberta, Canada where I enjoy field archery and target shooting with traditional bows and compound bows. On this site, I share everything I’ve learned about archery along the way.

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