Arrow tuning 102, a “next level” Olympic and barebow arrow tuning method

Over the last 20 years of my archery career, there as been one area that has held particular interest for me…tuning.

The physics of how to get an arrow to shoot “straight” are fascinating. There are numerous actions and reactions that all happen in a very short period of time once you release the string.  If all the variables do not work together appropriately we get less than ideal arrow flight, and consequently inconsistent results.

I have used many methods of tuning in the past with good results but until recently, my understanding of the physics was…incomplete.

Recently, I had the privilege of working with Tom Stevenson, and Wes Wilhelm, two of the most knowledgeable arrow tuning experts I have ever met.  With their help I was finally able to get scientific answers to all the questions no one before was able to answer!

My moment of clarity came to me when I realized tuning equates to “timing”. When an arrow is shot, the front, middle, and back end of the arrow go through a cycle of movements. If everything is timed correctly the arrow will have good clearance, good direction, and good flight. If the timing of any part of the arrow is off, the arrow will have poor clearance, poor direction, and poor flight.

Using your fingers to release the bow string results in the string following a path that oscillates left and right as it moves forward and returns to the brace height position.

Photo credit: meta-synthesis.com

These oscillations cause the arrow to flex horizontally in a cycle as it is shot. Many people erroneously call this the “Archers paradox”.

Photo credit: Bahamas Archery

At the front and the back of the arrow there are nodes. A node is a point on the arrow that stays stationary while the rest of the arrow bends and oscillates in flight.

During the first phase of the arrow’s initial “bending” cycle, the front of the arrow is pressed into the plunger. After a couple inches of travel the arrow disconnects and loses contact with the plunger.  If, at the moment of disconnect, the front node is too far behind the plunger, the front of the arrow will “jump” away from the riser. Conversely if the front node is too far in front of the plunger at the moment of disconnect, it can cause the front of the arrow to “jump” in towards the riser. Arrow length and plunger tension are two major considerations that have a large impact on the position of the node at the time the shaft disconnects from the plunger.

During the last phase of the arrows initial cycle, the nock will disconnect from the string.  If the timing of the disconnect is off because it cycled too fast by oscillating too quickly (high frequency), or because it cycled too slow by oscillating too gradually (low frequency), it will again cause the nock to jump in towards or away from the riser. Brace height and arrow weight are two major considerations that have a large impact on the timing of the disconnect of the nock.

***VERY IMPORTANT***
Before any successful tuning can be done, you need to be able to execute a proper release with an appropriate grip! Additionally your equipment needs to be set up properly and have sufficient arrow clearance so that there are no “contact” issues. If you are unable to execute a proper release, you have a poor grip, or your equipment is not set up correctly, you may not be able to achieve successful or accurate results.

Please note, this tuning method includes adjustments for a bow that has a cut past center riser and uses a cushion plunger. If you do not have these options, you can still achieve very good results by skipping over the steps that specifically address the plunger or center shot adjustments. To begin, make sure your bow is set up properly by following these steps:

Pre Tune Bow Set up:

1. Brace height.
Set brace height to the middle of the manufacturers recommended brace height range.

2. Tiller.
Set the tiller to accommodate your style of hook and finger pressure. If you are not sure, I recommend 1/4” positive tiller (1/4” greater on the top than the bottom) for split finger shooters, even tiller for three under shooters, and 1/4” negative tiller for string walkers.

3. Limb alignment.
Click here for my custom method of limb alignment.

4. Plunger tension.
Set the plunger tension to the middle setting i.e. medium spring set to medium tension.

5. Arrow alignment “center shot”.
In this step adjust the rest arm and plunger depth so the center of the arrow shaft runs directly down the center plane of the bow and visually aligned with the center of the string. YES,  you read that correctly… for this method you will NOT be setting the arrow “to the left” of the string (for right handed shooters) like you may have been told to do previously. Then set the rest arm height so the plunger contacts the center of the side of the arrow shaft.

6. Sight alignment.
Finally, if you use a sight, set the center of your sight aperture directly above the center line of your arrow shaft. This is also the final horizontal position of your sight aperture. After this point, making a major horizontal move to the sight is not recommended as it most likely means you are compensating for a poor head position/angle or poor string blur alignment. With a good tune, you should only have to make micro horizontal adjustments to account for lighting and environmental conditions as they change

Pre Tune Arrow Set up:

1. Arrow length.
To allow ample room for adjustment, you will need at least 3” of shaft length in front of the cushion plunger at full draw. For an appropriate starting arrow shaft length you can just add 3” to your actual draw length or 1.25” to your AMO draw length (Generally 1.25” in front of the riser). If you are unsure what your actual or AMO draw length is you can check out my article on finding your draw length.

2. Arrow spine.
To find an appropriate starting spine, use the total length of the arrow you just calculated and the draw weight on your fingers to look up the manufacturer’s recommended spine in their spine chart. It is usually more convenient (especially for your budget) to fix an arrow that acts “weak” than an arrow that acts “stiff” so I suggest starting with an arrow that is one group weaker than the chart recommends. I have found most of the charts tend to recommend an arrow spine that is too stiff anyway.

3. Arrow weight.
In regards to arrow weight, you will have to come back and check this after further tuning is completed. It is uncommon for the arrow to weigh too little but I would recommend you do a quick check of the completed arrow (after it has been cut down and components installed) post tuning. An arrow that is too light can cause the arrow to move too fast, not allowing it to complete its initial oscillation cycle, which can result in erratic/inconsistent flight due to the back end of the arrow contacting the riser, plunger, or rest. The arrow weight measurement we use is “grains per pound” (gpp). To find your gpp, measure the overall mass weight of your arrow (including all components) then divide that by the draw weight on your fingers at full draw. If your arrow weighs less than 8 gpp, I suggest using a heavier arrow. This will help to insure the arrow is traveling at a speed that will allow it to complete its initial oscillation cycle and have adequate clearance.

At this point you are ready to begin tuning  

Step 1 – Optimize Dynamic Spine

The first step in tuning is to optimize the dynamic spine. There is only a split second of time from the moment you release the string until the arrow clears the bow.  It is only during this split second of time that the arrow will be influenced by the plunger settings and the dynamic spine reaction. The first part of tuning is to make sure the dynamic spine (the amount the shaft flexes when shot) is optimized.

To check the dynamic spine you will need to shoot a bareshaft through paper at about 3 meters away. Shooting at a close distance allows us to capture the true flight of the arrow just as it leaves the bow. Shooting at greater distances can allow air friction and other environmental factors to influence the alignment of the bareshaft increasing the potential for false readings.

To build an appropriate bareshaft, use a grain scale to find the total arrow weight by measuring a bareshaft along with the fletching and all the arrow components. Now remove the fletching (if they were attached to the shaft) and wrap an amount of tape equal to the weight of the fletching around the bareshaft where the fletching would go. Basically, wrap tape around the shaft until the weight of the arrow equals the total arrow weight measured previously with the fletching. The weight of the fletching changes the dynamic spine, so you want to mimic the weight of the fletching with the tape on the bareshaft.

Next, set up to shoot your bareshaft through paper at 3 meters away. I do not recommend using anything other than a paper tuner to capture the nock position as the alignment of the arrow may unintentionally be altered by using a foam or bag target, giving you a false reading. Remember, interpreting the shaft angle from arrows shot at long distances can also cause false readings!

A note in regards to barebow and string walking…If you are shooting barebow you will have to decide on one particular string walking distance to tune from aka “crawl”. All other string walking positions will change the tune of the bow. If you are barebow tuning for field archery, I recommend tuning to your median crawl distance. If you are barebow tuning for outdoor target archery, I recommend tuning to your 50m crawl distance. If you are barebow tuning for indoor target archery, I recommend tuning to your 18m crawl distance.

At shoulder height, shoot your bareshaft through the paper with an effective and proper release then inspect the paper tear and/or the nock position of the arrow.

If a vertical discrepancy is discovered, fix that first.

If the nock of the arrow is higher than the point of the arrow you have “nock high” flight. To fix this issue, lower your nocking point on the string. If the nock of the arrow is lower than the point of the arrow you have “nock low” flight. To fix this issue, raise your nocking point on the string. Adjust your nocking point until you have level nock flight.

Now determine if there is a horizontal discrepancy.

If the nock is to the left of the point (for a right handed archer) your arrow is acting too “weak”.

If the nock is to the right of the point (for a right handed archer), your arrow is acting too “stiff”.

If the arrow is acting weak, you can shorten the arrow length, or decrease the point weight, decrease draw weight, or use an arrow with a stiffer spine to correct the issue.

If the arrow is acting stiff, you can increase the point weight, increase the draw weight, use a longer arrow or use an arrow with a weaker spine.

Once you are able to achieve decent flight with very little horizontal and vertical displacement at 3 meters (ideally there would be no displacement, meaning the arrow is exiting the bow perfectly straight and level) you have optimized your dynamic spine!

If you are having trouble deciphering which end of the tear was made by the point and which end of the tear was made by the nock end, you can simply add some colored pigment to the tip of the point of the arrow. You can use lipstick, a drop of blue or red loctite, or something else that would leave a mark on the paper.

If you are getting inconsistent results with a good release, or the adjustments you are making do not seem to change the results, you may be experiencing an arrow contact issue. It is always a good idea to conduct an insufficient clearance test to determine if the arrow is hitting the bow or plunger as it is shot. If during this test you revel there is a contact issue you will need to address that first! Two common ways to resolve contact issues are by further adjustment to the dynamic spine or increasing overall arrow weight.

Step 2 – Optimize Plunger Tension

This is the most fascinating part to me. Changing plunger tension is actually a timing adjustment! Adjusting the plunger tension changes where the front node is in relation to the plunger when arrow disconnects from the plunger.

Increasing the plunger tension lessens the amount of time the arrow is in contact with the plunger “advancing” the timing of the disconnect. Decreasing the plunger tension increases the amount of time the arrow is in contact with the plunger “retarding” the timing of the disconnect.

As I mentioned before the position of the front node in relation to the plunger determines if the front of the arrow will want to jump left or right. Ideally we want to find the optimal position where the arrow doesn’t want to jump in either direction.

To find the optimum setting, you will need to do a version of a “walk back tune”. Basically you want to shoot at the same spot on a target without changing your sight at multiple distances.  This will create a pattern of impact holes on the target. When all the holes line up in a perfectly vertical and plumb sequence without leaning at an angle, you have optimized the plunger tension setting. If the holes line up leaning at an angle you will need to adjust your plunger tension setting.

I suggest using the back of a vertical 3 spot FITA target face. Draw a vertical line down the center of the paper and draw a dot to aim at on the line somewhere close to the middle (it doesn’t have to be positioned perfectly in the middle).

Set the target face on a target 2 yards away. Set your sight for 18 meters and leave it at 18 meters the entire time. If shooting barebow, use only the one crawl position you are tuning for and aim at the dot at every distance. Using only a bareshaft, aim for the dot and take a shot. I recommend taking three good shots and averaging the impact zone. Disregard poor shots or shots executed with a poor release. Next move the target to 5 yards and repeat. Then do the same at 10 yards.

To analyze the results, draw a line connecting the average impact zones from all distances starting at the 2 yard group pattern and finishing at the 10 yard group pattern.

If the average impact line angles off to the left (right handed shooter) your plunger tension is too stiff, and the shaft is not in contact with the plunger for a long enough period of time before it disconnects. Reduce the tension and repeat the process starting again at 2 yards.

If the average impact line angles off to the right (right handed shooter) your plunger tension is too weak, and the shaft is in contact with the plunger for a period of time that is too long before it disconnects. Increase the tension and repeat the process.

Once the impact holes line up plumb, straight, and vertical, you have achieved an optimal plunger setting. If the holes are plumb, straight, and vertical but they are all off to the side of the line you drew, you need to adjust your string blur position, not your sight (if you have one). If the holes are to the left of the line, move your string blur to a position further left. If the holes are to the right of the line, move your string blur to a position further right. If you move your sight instead of your string blur to fix the problem, you are most likely compensating for a less than ideal head position.

Step 3 – Optimize Brace Height

Your brace height controls the timing of the nock departure from the string. I think brace height tuning is one of the most underrated and overlooked variables. The timing of the nock departure from the string can be just as important as the timing of the front node position! If the nock departure is too early or late the back end of the arrow can again “jump” in a way that makes consistent and repeatable arrow flight very difficult.

To optimize the brace height, first check your brace height and make sure it is in the middle of the manufacturers recommend brace height range. Write the current brace height on a fresh target face.

Pin the target face on a target at 18 meters (or 20 yards) away. Switch to using fletched arrows, shoot a group of 12 arrows at the target.

If you make a huge mistake while shooting an arrow, disregard that arrow and shoot another one in it’s place. Make sure to mark the hole from the bad arrow so it can be disregarded.

An arrow shot from a recurve bow will oscillate horizontally. Because of this, brace height tuning will only help the horizontal discrepancy of your group. Any vertical arrow discrepancies are from causes other than issues with the brace height.

To decider the results, find the two holes that are furthest away from each other “left to right”. Measure horizontally from outside to outside edge of the two holes and write that measurement down. This is your 12 arrow horizontal group size. To keep track of which holes I used for the measurement, I put a small number 12 next to each hole. Now discard the single worst hole (the hole furthest away from the center horizontally) and measure the distance between the remaining furthest two holes (you will always be using one of the holes from the previous measurement). Because you disregarded the worst hole from before, you now have an 11 arrow horizontal group size. Write that measurement down and then write the number 11 next to each of these holes to keep track. Again disregard the worst single hole from the 11 arrow group and find your 10 arrow horizontal group size and write that measurement down with the number 10 next to each of these holes as well. You should now have a horizontal measurement for a 12, 11, and 10 arrow group size for that one particular brace height.

Add all three measurements together and divide by three to get your average horizontal group size.

Now decrease the brace height by a 1/4”. With a fresh target face write the new shortened brace height down on the target and repeat the steps from above getting the average from a 12, 11, and 10 arrow horizontal group size using the 1/4” shorter brace height.

Finally increase the brace height by 1/4” from the original brace height and repeat the process again. This means you have to return the brace to the starting height and then increase it by an additional 1/4”

If you started with an 8 1/2” brace height, in the end you would end up with average group size measurements for 8 1/2”, 8 1/4”, and 8 3/4”  brace heights.

You can record the results in a matrix chart like I did here:

Of the three brace heights you just tested, the brace height with the smallest average group size is the best choice. If the middle brace height also happens to be the best choice you have found your optimal brace height. If however, your best choice of the three was one of the smaller or larger brace heights then you are only headed in the right direction but more testing is required. Continue to make 1/4” brace height changes and chart the results in the direction that produced a tighter average group size. Continue to do this until you find a brace height that produces a worse average group size. The optimal brace height will be the one just before it got worse. If you max out and reach one end of the manufacturer’s recommended brace height range, you can stop there, or continue at your own risk. Once you find the optimum brace height, make sure to check that your brace height is at its optimal measurement each and every time you string your bow.

At this point you have successfully optimized your spine, plunger tension, and brace height. You can be confident knowing your equipment is now working with you instead of against you.

An optimized tune will help you to achieve very good results. Personally, I am satisfied with an optimized tune, but depending on how serious you are about your equipment, you can continue to refine the results with a fine tune.

To fine tune your equipment repeat the entire process starting at step 1 with the following changes…

1. Adjust point weight, and/or arrow shaft, and/or nock point until your bareshaft is flying perfectly straight and can create a perfect “bullet hole” through paper at 4-6 meters.

2. Lengthen your “walk back” tune distances to 5, 10, and 20 yards and adjust your plunger tension accordingly

3. Instead of 1/4” changes, adjust brace height in 1/8” increments to find the perfect brace height.

I hope this information helps you to take your equipment tuning to the next level and achieve exceptional results.

If you have any questions, please feel free to contact me. Happy shooting!

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