What makes an arrow dynamically softer or stiffer?

Several factors can cause an arrow to react dynamically softer or stiffer.

The simple rule of thumb

Longer arrow - dynamically softer

A longer arrow will generally be dynamically softer than a shorter arrow with the same shaft and components. Arrow length is therefore an important parameter when choosing spine. However: An arrow must, of course, have sufficient length for your specific setup. One should not shorten an arrow solely to change the spine without considering safety and manufacturer recommendations.

Heavier point - dynamically softer

A heavier point increases the load on the shaft during the shot and generally makes the arrow react dynamically softer. This also applies if you install a heavier insert or other components in the front.

Higher draw weight - dynamically softer

When the draw weight and thus the force accelerating the arrow increases, the arrow will generally experience greater load. A setup that works with, for example, 45 lbs., therefore cannot necessarily use the same spine if the bow is subsequently adjusted to 55 lbs.

Shorter arrow - dynamically stiffer

A shorter arrow is generally dynamically stiffer than a longer arrow of the same shaft type and static spine.

Lighter point - dynamically stiffer

A lighter point reduces the load on the front of the arrow and generally makes the arrow react dynamically stiffer.

Lower draw weight - dynamically stiffer

If you reduce the draw weight, the force the arrow is exposed to during acceleration is reduced, which generally makes the dynamic reaction stiffer.

These are general tendencies and not a complete tuning formula. The overall setup determines the actual reaction.

What happens if the arrow is too soft or too stiff?

One often talks about under-spined and over-spined arrows. When the arrow is under-spined, it is too dynamically soft for your setup, which can lead to challenges with tuning, arrow flight, and grouping, among other things. If the arrow is over-spined, it is dynamically too stiff, which can also make tuning more difficult and affect the arrow's flight and grouping. But be careful with overly rigid rules. A poor result on the target does not automatically mean that the arrow has the wrong spine. Shooting technique, release, nock fit, tiller, centershot, cam timing, and other tuning parameters can also affect the arrow's reaction. Spine should therefore be considered as part of the overall system.

How to choose the right spine?

When choosing a spine, you should at least know:

You can then use the manufacturer's spine chart or shaft selector as a starting point. However, a spine chart is precisely a starting point – not a guarantee that a specific arrow will be perfectly tuned in your particular setup.

Spine for compound, recurve, and longbow

Spine is relevant across bow types, but the way the arrow reacts and how it is tuned varies. For compound bows, the cam system, let-off, and release aid play a role, among other things. For recurve and longbows, finger release and archer's paradox are central factors. Here, the bow and arrow move through the shot in a different way than with a compound bow. Therefore, spine recommendations from one bow type should not be automatically transferred to another.

Spine and point weight

For the experienced archer, point weight is an interesting tool. If you change from, for example, a 100 grain to a 125 grain point, you do not change the arrow's static spine. But you change its dynamic spine. At the same time, you change:

• the arrow's total weight

• F.O.C.

• balance point

• speed

• kinetic properties

It is therefore important to consider point weight as part of the entire arrow's construction – not just as "the point I like best."

Spine and F.O.C.

Spine and F.O.C. are not the same. Spine describes the arrow's stiffness. F.O.C. (Front of Center) describes how far forward the arrow's balance point is in relation to the arrow's total length. But these two things often go together in a practical arrow setup. If you increase the weight in the front with a heavier point or a heavier insert, you typically increase the F.O.C. while also making the arrow's dynamic spine softer. It is therefore important to look at the entire arrow's construction rather than a single number.

Spine and hunting arrows

For bowhunting, spine becomes particularly interesting because the broadhead is an important part of the arrow's overall setup. Although broadheads and practice points often have almost the same weight, differences in weight, shape, and aerodynamics can affect the arrow's dynamic reaction and arrow flight. Broadheads also place high demands on stable and consistent arrow flight. Therefore, your hunting arrows should, as far as possible, be tested and tuned with the actual broadhead setup you will use for hunting. An arrow that flies perfectly with a field point is not necessarily optimally tuned with a broadhead. This is especially important if there is a difference in the weight or construction of the points.

Is a lower spine better?

In short, no! A 300 spine is not automatically better than a 500 spine. Spine primarily indicates the stiffness of the shaft. A good arrow also depends on, among other things:

- straightness tolerance
- weight tolerance
- diameter
- weight
- components
- durability
- F.O.C.
- consistency from arrow to arrow

For serious archers, consistency from arrow to arrow is precisely important. The less variation there is between your arrows, the more consistent your setup will be.

In short

If you are completely new to archery, remember:

But if you want to choose the right spine, you need to look further than the number on the shaft. The arrow's spine must match your entire setup. Bow, draw weight, draw length, arrow length, point weight, components, and your shooting style all work together to determine how the arrow reacts. And that is precisely why choosing arrows is not just about finding an arrow with the right spine number.

Get help choosing the right arrow

At Bowgear, we have many years of experience with archery and help both beginners and experienced archers find the right equipment. Book a free and non-binding consultation here
We help you find the perfect arrow for your bow.

Frequently asked questions about spine

What does spine mean on an arrow?
Spine is a measure of the arrow's stiffness. The lower the number, the stiffer the arrow.

Which spine should I choose?
It depends on your draw weight, draw length, and arrow length. Use a spine calculator or contact us.

Can I use the same arrows for recurve and compound?
Not necessarily – the two bow types often require different spine and arrow types.

See more questions and answers here.