Arrow Spine: The Archer's Guide

Arrow spine is a measure of stiffness, or how much an arrow bends when weight is applied. It is an important aspect of archery because it affects the accuracy of your shot. The spine rating of an arrow is measured by 'deflection', which is the amount of bend in the arrow shaft when force is applied. The lower the number, the stiffer the arrow. For example, a 300 arrow is stiffer than an arrow with a spine rating of 500. There are two types of arrow spine: static and dynamic. Static arrow spine measures flexibility in a static state (at a standstill), while dynamic arrow spine describes how the arrow reacts to the stored energy transferred upon release of the bowstring.

Static spine

The 'spine' of an arrow refers to its stiffness or backbone. The static spine is the measurement of an arrow's stiffness when stationary. It is calculated by suspending an 880-gram (1.94-pound) weight from the centre of a 29-inch arrow supported at two points 28 inches apart. The amount of deflection or bend in the arrow, measured in thousandths of an inch, is the spine size. For example, if an arrow bends by half an inch with the weight applied, it has a static spine of 0.500.

The static spine is solely measured on the arrow shaft. It does not take into account other arrow components such as field points, broadheads, fletchings, and nocks. The static spine is an important first step in selecting an arrow shaft, but it is not the only factor. The dynamic spine, which describes the arrow's behaviour when shot from a bow, is also critical.

The static spine is a standardised measurement. The Archery Manufacturers Organisation (AMO) published a booklet in 1968 that set out the standard for measuring the spine, among other standards for archery and archery construction. The AMO standard for measuring the static spine is slightly different for wooden arrows, which are supported at two points 26 inches apart, with a two-pound weight suspended from the centre.

The static spine is used to predict the dynamic spine, which is the reaction of the arrow shaft when pushed at one end by a force. The dynamic spine is influenced by the static spine as well as other factors, including the power stroke of the bow, the weight of the arrow, the length of the arrow, the point weight, the nock weight, the fletching weight, and the nock relationship with the string.

The dynamic spine is the actual goal of spine tables, which help archers select the right arrow shafts. The static spine is a means to this end. Once the archer has specified their draw weight, draw length, and point weight, they can refer to the table to find a static spine that will help them find the right arrow shafts. However, the dynamic spine cannot be measured precisely until the arrow has been built.

Dynamic spine

The dynamic spine of an arrow is crucial to achieving optimal accuracy and consistency in archery. If the arrow does not have the correct spine for the specific bow setup, erratic arrow flight and poor shooting groups may occur. A proper balance of flex and stiffness is necessary for the arrow to clear the bow riser and fly straight.

Archers can manipulate the dynamic spine of an arrow by making adjustments such as decreasing the peak bow weight, using heavier bowstring material, or changing the arrow length. However, due to the numerous variables involved in determining dynamic spine, arrows are typically measured and sold based on static spine, which is the spine of the arrow at rest.

To summarise, dynamic spine in archery refers to the arrow's behaviour when shot and is influenced by various factors related to the bow and the arrow itself. It is essential to understand and adjust the dynamic spine for optimal accuracy and performance in archery.

Arrow weight

There are three weight categories for arrows: light, midweight, and heavy. A light shaft weighs 5 to 6 GPI, a midweight shaft weighs 7 to 9 GPI, while a heavy shaft weighs 10 or more GPI. However, the weight of an arrow is not the same as its spine, which refers to the stiffness of the arrow and how much it flexes when shot. A stiffer arrow will have a lower deflection number, while a weaker arrow will have a higher deflection number.

The weight of an arrow is influenced by various factors, including the arrow shaft, point weight, and additional accessories. Arrow shafts can vary in weight depending on their material and diameter. The point weight, or the weight of the arrowhead, can also impact the overall weight of the arrow. Additionally, accessories such as nocks, inserts, and fletchings can add weight to the arrow.

When choosing the weight of an arrow, it is important to consider the type of game being hunted, the expected hunting conditions, and personal preferences. For example, bowhunters may opt for lighter shafts when hunting thin-skinned game like pronghorn, while heavier shafts are chosen for larger, tougher game like elk and bears. It is also crucial to ensure that the arrow weight matches the specifications of the bow to avoid damaging equipment and endangering the archer.

Overall, understanding arrow weight and its impact on arrow flight is crucial for optimizing archery performance. By selecting the appropriate weight category and considering factors such as GPI, point weight, and accessories, archers can improve their accuracy, consistency, and effectiveness in different hunting scenarios.

Arrow length

The relationship between arrow length and spine is that a shorter arrow will have a stronger spine than a longer arrow of the same type. This is because a shorter arrow shaft can withstand more tension and resist outside forces better than a longer shaft. Therefore, for a given arrow spine, a shorter arrow will require a less flexible shaft than a longer arrow. For instance, a 60-pound bow with a 24-inch arrow would need a more flexible shaft than the same bow with a 30-inch arrow.

Additionally, the arrow length affects the dynamic spine of the arrow, which is how the arrow reacts when shot from the bow. The dynamic spine is influenced by factors such as the peak bow weight, arrow point weight, and the point/insert combination. Due to the numerous variables involved in determining the dynamic spine, arrow manufacturers typically rely solely on static spine measurements, which are standardised to a 28-inch shaft length.

In conclusion, selecting the appropriate arrow length is crucial in ensuring the correct spine for your arrows, which in turn improves consistency and accuracy in your shots.

Arrow stiffness

There are two types of arrow spine: static and dynamic. Static spine is the measurement of the arrow's stiffness at a standstill. It is calculated by suspending an 880-gram (1.94 lbs.) weight from the center of a 28-29” arrow supported at both ends, 28” apart. The amount of deflection, or bend, of the arrow shaft is then measured and multiplied by 1000 to give the spine rating. A stiffer shaft will have a lower deflection number, indicating less bend.

Dynamic spine, on the other hand, describes the arrow's reaction to the stored energy transferred from the bow when shot. There are numerous variables that determine how an arrow will react when shot, including the human executing the shot, the power stroke of the bow, arrow weight, static spine of the arrow, length of the arrow, point weight, nock weight, and fletching weight. Due to these nearly unlimited variables, arrows are typically measured and sold based on static spine alone.

Having the correct arrow stiffness, or spine, is crucial for achieving consistent and accurate shots in archery. An arrow that is not stiff enough, or an arrow with too much flex, will struggle to straighten and fly straight. Conversely, an arrow that is too stiff will not be able to clear the bow properly and will not be as forgiving during flight. The correct amount of flex helps the arrow clear the bow riser and achieve pinpoint accuracy.

To find the correct arrow stiffness, or spine, for your setup, you need to consider several factors, including draw weight, draw length, arrow length, and arrow point weight. Using an arrow selection chart from the manufacturer can help determine the proper spine rating for your specific bow and arrow combination.

Frequently asked questions