Arrow spine vs. arrow weight: Don’t be confused

In the Lancaster Archery Supply Pro Shop, we hear it all the time.

“I want to switch to a lighter arrow to get more speed.”

That’s usually not a problem, as long as you don’t confuse arrow weight with arrow spine. Too often, that’s exactly what archers do. Someone shooting a bow with a 70-pound draw weight and a 29-inch draw length will grab a 400-spine arrow to replace the 340-spine arrow they’ve been shooting. They think that’s the right way to reduce arrow weight.

It’s not.

When we talk about an arrow’s spine, we’re talking about how much it flexes. We’re talking about its stiffness. Every arrow should flex when it leaves the bow. But it should only flex a certain amount. If it flexes too much – weak spine – then its flight will be erratic. If it doesn’t flex enough – stiff spine – then the arrow will have no forgiveness. Consistent accuracy usually suffers in either case.

Choosing the correct arrow spine for your setup depends on your draw length and draw weight. Draw length is important, because that determines how long of an arrow you need to shoot. And the longer a shaft is, the more it’s going to flex. Draw weight is factored in, because that determines the amount of force pushing the arrow.

Every arrow manufacturer has a spine-selection chart, so you know which shaft to choose for your draw weight and arrow length. (Some even factor in the bow’s speed rating, since faster bows exert more force on an arrow.) And every shaft bears its manufacturer’s spine rating.

Unfortunately, the numbering system for spine ratings is not uniform from manufacturer to manufacturer. So don’t assume the numbers you see on shafts across manufacturers are comparable.

Beside or below the spine rating, most shafts usually also are stamped with their weight in grains per inch. And this is where archers can get confused.

Let’s take the Easton Bowfire, for example. The 330 shaft weighs 9.6 grains per inch. The 400 shaft weighs 8.5 grains per inch. Logic might tell an archer that, in order to lighten their arrows, they should switch from a 330 to a 400. Bad move. The 400 arrow is lighter, but it’s also weaker, and so tuning could be a real problem.

If you want a lighter arrow, stick with the recommended spine rating, but switch to a lighter shaft. Again, that 330 Bowfire shaft weighs 9.6 grains per inch. A 330 Easton Hexx, however, weighs 7.9 grains per inch. Same spine – lighter shaft.

Just for comparison, take a look at these arrows. All measure 29 inches from the insert-end to the bottom of the nock throat. All include 100-grain points, and three Blazer, 2-inch vanes. And all are the correct spine for the archer shooting a 70-pound bow, according to the manufacturer’s chart.

Shaft                                Weight

340 Easton Full Metal Jacket     482.2 grains

330 Easton Bowfire              433.6 grains

330 Easton Hexx                 382.1 grains

So you can see here, there are opportunities to change the weight of the arrow, without deviating from the spine chart.

What size recurve bow is right for me?

So you want to get a bow, and the first thing you noticed when checking out a few recurve models is they come in different lengths. And you asked yourself, “What size recurve bow is right for me?” If the target archer chooses one that’s too long or too short, you won’t be as accurate – or have as much fun – as you could with a bow that’s a perfect fit.

And let’s be clear here. We’re talking about recurve bows for the target archer – those who want to get into competitive shooting, or who want competition-style bows for recreational shooting. When choosing a bow for hunting or for traditional shooting, other criteria would apply.

Here’s how to determine the correct bow size for you. Stand with your arms extending out to either side of your body at shoulder height. Don’t stretch. Just extend your arms naturally. Now have a partner measure the distance from the tip of one middle finger to the tip of the other. Take that number and divide by 2.5. This is your calculated draw length, which should be pretty close to your actual draw length, if it doesn’t hit that figure right on the head.

Optimized-measure photo

With your draw length in hand, you can now determine the length of the bow you should be shooting. That length, incidentally, is measured from tip to tip, following the curve of the limbs and along the back side of the riser, while the bow is unstrung.

Here’s a basic chart to follow:

DRAW LENGTH……………..BOW LENGTH

14-16 inches……………….48 inches
17-20 inches……………….54 inches
20-22 inches……………….58 inches
22-24 inches……………….62 inches
24-26 inches……………….64-66 inches
26-28 inches……………….66-68 inches
28-30 inches……………….68-70 inches
31 inches and longer…………70-72 inches

What happens if you go too short? Well, recurve bows are designed for peak performance at the proper draw length. For example, the sweet spot for the 62-inch bow is going to be when it’s drawn 22-24 inches. The draw weight increases at a consistent curve up to those lengths. If you draw that bow 28 inches, you’re going past the peak performance point, and the draw weight will increase sharply. Accuracy will suffer.

Conversely, if you only draw a 70-inch bow to 26 inches, you’re never getting to the peak performance spot. That’s not as big a problem as overdrawing a short bow, but you’ll be sacrificing arrow speed, which is critical for target shooters.

(Below is a sequence of photos which show, from top to bottom, the tip of a recurve bow in the underdrawn, correct and overdrawn position.)

Optimized-length1 (2)Optimized-length2Optimized-length3

When it comes to determining the proper draw weight for your new bow, that’s going to vary from archer to archer. Physical strength, coordination and stamina all play a role. Selecting the proper draw weight is important. Too often, archers start with a draw weight that’s too heavy, which leads to the development of poor shooting habits. Call the Lancaster Archery Supply TechXperts at 1-800-829-7408 for help in choosing a proper draw weight – or with any other questions about choosing the right archery equipment – or ask a coach or your local pro shop technician.