What is front of centre (FOC) balance?

Front of centre (FOC) balance is the percentage of the arrows overall weight that is found in the front half of your arrow. The easiest way to understand this concept is to think of the balance point of an object. A blank arrow shaft, without the nock, flights, insert, or a broadhead will have an FOC of 0% – i.e. the weight is evenly distributed along the arrow shaft, and the balance point will be located directly at the centre point. By adding weight to the front end of the arrow shaft, such as a broadhead and insert, the FOC will increase in percentage, and the balance point will move forward with it. For the sake of this example, and without complicating it with measurements, we’ll call it a FOC balance of 9%. This means that 9% of the arrows total weight now sits forward of the centre point of the arrow. If weight is then added to the rear of the arrow shaft, such as a nock and flights, the FOC will slightly decrease – let’s say to a FOC balance of 7%. This has shifted the balance point slightly backwards towards the rear of the arrow. However, as it was not enough weight to fully counteract the broadhead and arrow insert, the arrow will still remain slightly “nose heavy”, which is a good thing.

Using the above example, if we are to look at the balance in terms of a ratio, the arrows weight distribution would have shifted from the original 50:50 even split (front/rear @0% FOC), to 59:41 (front/rear @9% FOC), to the final ratio of 57:43 (front/rear @7% FOC).

Why does FOC balance matter?

The FOC balance of the arrow will affect the arc of the arrows trajectory. A high FOC percentage will provide you with better stability in flight, meaning that it will be more resistant to outside influences, such as a crosswind, rain or snowfall. The trade-off for this added stability will be a steeper drop in an arrows trajectory over long distances. Conversely, a low FOC percentage will provide you with a flatter trajectory when shooting over long distances, however, it will be more susceptible to the environment factors listed above. These characteristics make lower FOC arrows better suited to target shooting activities, such as Fédération Internationale de Tir à l’Arc (FITA) events, where target distances can reach up to 90m. Hunters and 3d archery competitors will usually fall on the other end of the scale, and opt for a high FOC percentage. Beyond the added stability, an arrow with a heavier front end will produce additional momentum. The higher the momentum, the greater the penetration power of the arrow. This is a critical attribute for hunters to consider, especially when targeting larger game species with thicker hides (skin). 

What is the ideal FOC range?

Most arrow manufacturers recommend an FOC range between 10% – 15%. However, it should be noted that it’s more of a suggestion, as opposed to a hard-and-fast rule. When building arrows for the first time, it’s more important that you research the requirements (and limitations) of the activity that you will be undertaking, and match your arrow to the appropriate draw length, and the equipment you will be using. The best advice I can give you for arrow design is this – 

• Start by researching your chosen archery discipline online,
• Next, ask questions at your local club or archery store, and;
• Finally, build (or buy) a few different arrow combinations based upon this advice, and find out what works best for you.

How to measure FOC

The AMO method:

1. Build an arrow to your desired specifications. This should include all components of the arrow, including an arrow insert and a broadhead.
2. Measure the length of the arrow from the throat of the nock, to the end of the arrow shaft. 
   Do not include the insert or broadhead in this measurement.
3. Using a sharp edge – like the side of a ruler, balance the arrow across the edge of the object, and mark the balance point on the arrow using a lead pencil.
4. Measure the distance from the throat of the nock to this balance point.
   
5. Insert both numbers into the calculator below.