Picking The Correct Arrow Spine For Longbows & Recurves

Traditional ArcheryBy Doug Besherse

One of the most common asked questions I receive is “what spined arrow should I shoot out of my bow.? 

This is a very important question because to achieve good arrow flight having the correct spine is a necessity Picking the correct spine can be confusing and down right frustrating at times, but once you understand the variables involved it is much easier.

In the following article, I will focus on those variables and how they affect the spine of the arrow. After reading this article you should be able to pick a spine range that will be a good starting point in your quest for proper arrow flight.

Correct Arrow Spine

A statement that I have made before and will probably make again is 

“I have never helped someone correct arrow flight problems by going up in spine weight.” 

This statement has more bearing when it comes to tuning the arrow to the bow, which is something that I will discuss in the following article, but it is something that should be brought up now in the early stages of picking a spine. The problem I see most people make is they start with a spine that is border line to stiff. When they can’t get the arrow to fly correctly they automatically think the spine is too weak and therefore proceed to make the problem worse by going up in the spine.

When picking a spine you should consider that most of the shots you will take while hunting is not going to be in the best of situations. Things such as cold mornings, extra clothes and awkward positions will not allow you to draw the bow as far as you normally would under more perfect conditions. When you don’t draw the bow back as far it does a couple of things that in effect make the arrow stiff. The conditions that are faced while hunting has always made me advise a person to go a little light when picking spine.

The Most Common Variables That Affects Spine. 

There are many variables that affect the arrow spine. I will list the most common variables and tell how they affect the spine. Keep in mind that some of these variables do not drastically affect the spine but when several of those variables are added together it can drastically effect the spine. 

1. Fast Flight Strings affect spine probably more than anyone factor. 

Fast Flight may only add 5 or 6 feet per second in the speed when compared to a Dacron string however it’s effect on the spine are enormous. Fast Flight has virtually no give and literally “hammers” the arrow, conversely, Dacron has to give and acts as somewhat of a shock absorber on the arrow. As a general rule if you use Fast Flight you will have to increase your spine weight by 15# with wooden arrows or go up two shaft sizes on aluminum arrows. 

2. Weight Of Broadhead: 

Weight Of Broadhead

This is not near as big a factor as what most people would make it out to be but it can make the difference between an arrow flying good or not flying good. When trying to pick a spine weight to consider that if you use a heavier broadhead it will in effect weaken the arrow and therefore you will need to increase your spine. If you use a lighter broadhead you will in effect stiffen the arrow and therefore need to decrease your spine. 

How much should you increase or decrease? 

Well, that is more or less an educated guess. Over the years this is what I have found, the vast majority of people prefer a 125gr broadhead and when I recommend a spine that is what I have in mind.

  • If you have the perfect spine for your bow you can probably shoot a 110gr to a 140gr broadhead and get acceptable results.
  • If you go down to a 100gr or up to a 150gr I would suggest adjusting your spine weight by #5 on wood or by 1 size on aluminum.
  • If you are going to use a 190gr broadhead you will probably need to go up in spine weight another #5 on wood or go up another size on aluminum.

You will have to adjust the above suggestions if you are shooting an arrow that is borderline too stiff or too weak. 

3. Draw Length also comes into play when selecting spine. 

Keep in mind that draw length and arrow length are two separate things. Most bows are marked certain poundage at 28″ (50#@28″). When selecting the spine you need to know your exact draw length and the poundage you are pulling at your draw length. The best way I have found to determine exact draw length is to actually shoot the bow you are getting arrows for.

  • Loosen up by shooting a few times then have a friend grab the arrow at the back of the bow while you are at full draw,
  • then ease down on the string and let your friend take the arrow off the bow.
  • Now measure the arrow from the nock to the spot on the arrow that he is holding.
determine exact draw length
Recurve Draw Length

The most effective way to do this is to let the friend grab the arrow without you knowing when he is going to grab it. Most of the time when a guy gets his draw length checked he will overdraw the bow as to make sure his arrows are long enough, this only gives you a false draw length. When a person grabs the arrow when you are not expecting it the results will be more accurate.

For most people, the above exercise is an eye-opening experience. I have found that most guys overestimate their draw length which can really mess things up. If you do this your draw weight calculation will be more than it should be and you will have to add spine for the extra length. What you will end up with will be a grossly over the spined arrow.

When I deal with someone on the phone I have a test I give them to find out if they are giving me their correct draw length. To do this I ask them in a very casual way how tall they are and if they wear a “regular” or “long” in a jacket. I am positive some people have scratched their heads upon hearing these questions but the test has never failed me.

Here is how it works.

It is no coincidence that a bows weight is marked at 28″, the vast majority of guys out there have a draw length within 1/2″ of this. In fact, most guys have this draw length. The reason for all this is that the average Joe is 5″10′ tall. If you are 5″10′ and you wear a “regular” jacket you have a draw length of 28″ whether you believe it or not. I have proved this to so many people I am extremely confident that you are no exception.

If you do not have that long of a draw you are probably short drawing the bow by not spreading your shoulders. If this is so you need to work to correct that because you are losing a lot of performance by short drawing a bow when you don’t have to.

  • To take this test a step farther to adjust for every 1″ in height add or subtract 1/2″ in draw length.
  • If you are 5″8′ your draw length should be very close to 27″.
  • If you are 6″ tall your draw length should be close to 29″.

Give this formula a try you’ll be amazed at how accurate it is. 

4. Draw Weight: 

Once you have determined your exact draw length you can now discover what your draw weight is at that length.

  • The best way to do this is to put the bow on a bow scale and draw it to that length.
  • Make sure you measure it to the back of the riser because this is the way you checked the draw length.
  • A bow scale is the best way to check the poundage because sometimes, and I stress sometimes, the bow is marked wrong and the bow weight is something other than what you think it is.
  • If you do not have access to a bow scale you can take for granted the bow is marked correctly and use this formula.
  • For every inch of draw above or below 28″ add or subtract 5% of the draw weight. An example is 50# x 5% = 2.5# per inch, if you drew this bow 30″ the draw weight at your draw length would be 55#.
  • On the other side if you only drew the bow 26″ the draw weight would be 45# at your draw length. 

5. Arrow Length: 

When you lengthen the arrow it weakens the spine when you shorten the arrow it stiffens the spine. This is very simple to understand, like taking a stick and breaking it in two then taking one of the two pieces and trying to then break it. The short piece is very hard to break because it is stiffer. 

How much will length affect spine? 

Again this is a guessing game but this is what I have found. The average guy shoots a 281/2″ arrow, for every 2″ over that you will need to increase the spine weight by 5# in wood or by 1 size in aluminum. For every 2″ under that, you will need to decrease that same amount. 

6. Off-Set In The Riser is another big factor in determining correct spine. 

You can shoot a stiffer arrow out of a more center shot bow and you have to shoot a weaker arrow out of a bow with more offset. This, in fact, is the reason you can shoot a stiffer arrow from the average recurve than you can from the average longbow of the same draw weight. 

How much does it affect the spine? 

You know the answer, it’s an educated guess. All bows are different and the amount of off set varies but here is the general rule. For longbows shoot one step weaker in the spine than the average center shot recurve. There is a difference between a center shot and a past center or true center shot. The true center shot is cut 1/2 the diameter of the arrow shaft past the centerline of the bow rather than just to the center line of the bow. On a bow cut past center go up one step in spine compared to an average center shot recurve.

7. Bow Quivers are probably the most overlooked variable when it comes to picking spine. 

They do however have the effect of stiffening the spine. The ones that bolt to the riser section are not as noticeable as the ones that slide on the limbs but you should take them into consideration. When you are going to use a quiver that slides on the limbs of the bow you definitely need to go down one step in spine. 

8. The Way You Shoot A Bow has an affect on the spine. 

If you pause before you release or for whatever reason let the limbs ease forward just before you shoot you will hurt the performance of the bow.

If this is the way you are comfortable shooting, by all means, do it, but keep in mind this has the effect of stiffening the arrow. Of course, the amount it stiffens the arrow is relative to the amount in which you do these two things. At any rate, it is something to keep in mind and it is not out of the question to have to drop down a size in spine if you do these things. 

9. Feather Size has an effect on arrow spine also.

Bigger feathers have the effect of stiffening the shaft. You have heard that if you shoot a big heavy broadhead you need to shoot a big feather to stabilize it. Most people don’t realize that the reason it stabilizes the arrow is because of the stiffening effect it has rather than the ability the bigger feather has to stabilize the arrow through rotation. This may be a little hard to comprehend but I have come to this conclusion through much experience and evaluation. I have no set rule for this variable I only figure it into the mix when I am trying to pick a spine. 

10. Crown Dipping has a stiffening effect on arrows also. 

The reason is that you are adding weight to the back half of the arrow. This is another “figure it into the mix” variable. 

11. String Silencers add weight to the string and slow it down. 

This has a stiffening effect on the arrow as well. Some of the more noisier bows need a couple of sets of silencers to quieten them down. Some of the material that string silencers are made from is heavier than others also.

While we are on the subject of making the string heavier, if you are using more strands in your bowstring than usual (having an 18 strand string when you could be using a 14 strand)you will also slow down the bow a little. Take these variables and figure it into the mix. 

With all the variables that make an arrow stiffer as opposed to those that make it weaker is it any wonder why so many people come to me with an over spined setup. 

I believe now you are starting to understand why I feel it is better to under spine a little when picking a spine. After reading all the things I have just said you are probably thinking “I need to be shooting a 30/35# arrow out of my 55# bow.”

Don’t panic it isn’t as bad as it sounds.

I only listed all the variables to show how many things can and do affect the arrow spine. A lot of the variables are figured in already when you are picking a spine as you are about to see. The spine recommendations that I’m about to make take into account that you are going to have an average set up. 

What is an average set up? 

The arrow is 28 1/2″ long (or within 1/4″ of that) it has 5″ feathers and a 125gr point. The bow has a dacron string with one set of silencers on it and no bow quiver. With that in mind use the above information to adjust for your particular set up.

  • Remember the poundage of the bow needs to be taken at your draw length so on this set up the poundages listed are at 28?.
  • The wooden recommendations are for cedar arrows(all wood does not shoot the same, I discuss that some other time).
  • I personally do not like shooting aluminum arrows off of dacron stringed longbows because you have to shoot such a weak spine to get them to fly good. The weaker spined aluminum shafts do not have a lot of mass weight and therefore the bows will generally have excessive hand shock.
  • If the longbow has fast flight the spine weights you shoot will have more mass weight and will help absorb the hand shock.

The spines listed below for a longbow are for dacron strings remember to adjust for the fast flight.

@ 28″
4035/40 40/451813, 1816,191335/401716, 1813
4540/45 45/501816, 1913,191640/451813, 1816
5045/50 50/551913, 1916, 201345/501816, 1916
5550/55 55/602013, 2016, 201850/551916, 2013
6055/60 60/652016, 2018,211755/602013, 2016
6560/65 65/702215,2117,221660/652016,2018

I’m sure you noticed that the recurve has more options, that is because of the center shot riser. The longbow is not that hard to tune but it does have tighter tolerances. The suggestions I have made above are that, suggestions. They have worked well for me and my customers in the past though and I hope they help you as well.

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