Arrows Series – Part 4: Spine, Flex and Stiffness

Before we discuss the topic of arrow spine, for proper safety and best performance, arrows need to match your entire bow setup. If you change draw weight, draw length, limbs, riser size, etc. this will affect you arrows. You may need to adjust the arrow length or require different arrows.

Arrow Myth:  An arrow is always straight.

Arrows SHOULD be perfectly straight when not in motion. However, when an arrow is released the force applied from the string causes the arrow shaft to be compressed against the resistant static weight of the arrow point and therefore bends.

Newton’s First Law of Motion: Every object in a state of uniform motion (rest) tends to remain in that state of motion (rest) unless an external force is applied to it.

Since the force applied is greater than the  resistance (weight of the tip), the arrow is propelled forward, and the shaft continues to flex and oscillate as it straightens itself. Arrow shafts that are either too stiff or too flexible will not fly well and will impact the accuracy of your shots or fail causing damage and/or injury. Therefore, we need to manage the flex properly so the arrow does not make any contact with the bow, or your arrow flight will be affected.

Important Tip: Arrow spine refers to the arrow shaft’s degree of stiffness (how much the arrow resists being bent) and is called spine deflection.

Basic Rule 1:  Shorter arrows act stiffer and longer arrows act more flexible.

Basic Rule 2: Powerful bows require stiffer arrows and less powerful bows require shafts that are more flexible.

Basic Rule 3: The heavier the tip equals greater the resistance, therefore the greater amount of compression.  So, a heavier tip causes the arrow to flex more and a lighter tip increase the stiffness.

According to the American Society for Testing and Materials (ASTM) the modern standards (ASTM F2031-05) an arrow’s official spine deflection is measured by hanging a 1.94 lb. weight in the center of a 28″ suspended section of the arrow shaft and is used for aluminum and carbon fiber arrows. (I believe original AMO standard has a basic guide to use for wood arrows spine determination and uses of 2 lb. and 26” section for standard measurement.) The actual distance the 1.94 lb. weight causes the shaft to sag down is the arrow’s actual spine deflection

For example, if a 1.94 lb. weight causes the center of a 28″ arrow to bend down 1/2 inch (.500″) the spine deflection would be .500″.  Stiffer arrows will bend less and more flexible arrows with bend more.

Almost every arrow manufacturer has its own numbering system and there are no universally agreed spine sizes among the various arrow manufacturers. Simply, the lower the deflection measurement equates to a stiffer arrow and higher the deflection measurement the more flexible the arrow. Manufacturers can number, size, and market their arrows anyway they want, as long as they provide the deflection data and test using the industry standard method.

Fortunately for us the engineers have already done the math for us and manufacturers provide spine selection charts. You are able to select an arrow based on your draw length and draw weight.

So when selecting arrows a good rule of thumb is that lighter draw weight, shorter draw length and/or lighter tip weight equals LESS arrow spine OR heavier draw weight, longer draw length and/or heavier tip weight equals MORE arrow spine.

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Follow the Arrow: Adjust your sights

Unless you are a traditionalist, one of the first things you will need to do as an archer is adjust your sight. Unless you are a compound shooter with the same setup for ever, you will need to make adjusts again and again. For recurve archers there are many reasons why you will need to make adjustments including…

Environmental Differences : Every location is different, wind, rain; check out my earlier blog about Weather Conditions here.

New Distances : As you develop and change categories, distances change. Junior women need to shoot 70M and junior men 90M, if you are not there yet, do not worry, you will be.

Growth : As you get older, your body changes, you get taller and stronger and your draw length changes, using a clicker can help with consistency, so check out my Clicker blog.

Equipment Changes : As you get stronger and you are required to reach longer distances you need to change equipment, such as higher poundage limbs. Eventually equipment wears outs and we all want the latest and greatest technology.

Archery Form Changes : As you develop as an archer, you will perform better as an archer and your archery form will get better.

For young recurve archers adjusting a sight is a frequent event and is actually quite easy, the hard part is resisting the temptation to adjust it after every shot. Remember that consistency is your ultimate goal, so track your arrows before making any adjustments. You can do this on paper or there is an awesome free application for your IPod Touch called Archery Score Free by Yakoob Ali.  Once you are warmed up begin to track your arrows and determine the centre of your arrows grouping and then move the sight accordingly. Remember, if your groups were good yesterday and are not today, evaluate your form first. Also, if you have one arrow consistently out of group, check the arrow for defects.

When you are ready to adjust your sight, apply this simple rule, “Follow the arrow” or in this case the centre of the group of arrows. If the centre of your arrow grouping is to the left, then move your sight towards the left or opposite if your group is to the right.  The same principle applies for the group’s height; move your sign up or down if the group is not centered.  By moving the sight towards the arrow, the trajectory of the bow is altered to better centre the arrows on the target.

Remember, consistent form is essential to archery, and before you start micro-adjusting be sure you are grouping consistently first. Otherwise, if you are always making changes to your sight you will never truly know if you will consistently hit the bulls-eye.

Practice can be Fun

In the seasons between indoor and outdoor, it is time to practice. In an individual sport like archery, practicing can be boring, for target archers we are spending a lot time doing the same thing over and over again.  It can be hard to track your progress since all athletes experience growth and development like the NASDAQ industry average with lots of peaks and valleys.

Practicing is an absolute must if any athlete wants to improve however you can help yourself keep focused and motivated by changing things up, working towards the future and adding a little fun.

Different Distances

It is always a good idea to practice all the distances that you need to compete in for a tournament; however, there are several reasons why an archer should practice at longer distances. First, practicing to shoot longer distances will automatically improve shorter distances.  Second, it helps develop strength and endurance since you need to hold your arm up higher and longer. Lastly, especially for younger archers, it prepares you for the future, since every older age category moves further and further back.

Change Targets

For target archers, the smaller the grouping of arrows the better. You can help develop tighter groups by shooting at smaller target faces. Indoors, try a 3 spot target or 5 spot field face for target practice. Try novelty target faces or make your own target using an old catalogue. To this day, my favourite is to shoot balloons, much like a carnival. You can set up different sizes and shapes. Small balloons are great for accuracy and long thin ones help with groupings since you often need 3 arrows to pin and pop the balloon.

Noise

In most individual sports, like archery, athletes practice by themselves which allows them to focus without distractions, however tournaments are rarely completely quiet. A lot of archers end up shooting lower scores simply because of the noise, so why not have some practice with noise and distractions. Invite friends over to shoot with you, play loud music or have friends TRY to “safely” distract you while shooting. Since you cannot predict or avoid distractions at a tournament; prepare for it.

Scoring

A lot of young archers get stressed out at tournaments when they have to score OR when they are score watching. When you are young and still developing your math skills, it can be very stressful to keep score with everyone looking over you.When you are at home, practice quickly adding scores together to become good at it. Score watching is can be very stressful no matter your age or experience, sometimes you get caught up in the score for each end, how far behind you might be, or even focusing on one bad arrow.  Practice focusing on consistency and grouping ; ignore the score because if the group is good you can always move your sight.

By keeping focused, practicing, keeping it fresh and fun and being prepared for all types of tournaments you can enjoy the sport for the long term and reach your goals with a smile on your face.