BowCast Blog

"Front and Center" for Front of Center 

Many of you may have heard Anthony or Aneal talk about "Front of Center" or "Forward of Center" when talking in relation to building an arrow that is efficient in flight, and maximizes the trade offs between arrow stability and arrow flight distance.

Front of Center ( FOC) may feel like some "mojo" calculation when you first hear it, but it is important to consider when building your arrows.  In this blog entry, we want to explain why Front of Center is an important consideration, how to perform the calculation, as well as highlight what is a generally acceptable range of values.

Why do we care about Front of Center?

First, let's look at why we even bother talking about calculating Front of Center for an arrow.  Front of Center (FOC) is a calculation used for tuning your arrow for effective flight.  By determining your arrow's FOC (measured as a percentage), you will be able to tune/adjust your arrow to help increase arrow flight stability as well as arrow range.  In layman's terms, the FOC percentage is a measure of where the balance point of your arrow is in relation to the center of the arrow shaft.  If your FOC is 8%, that means the distance between the balance point (which should be in front of the center of the arrow because your field tip/broadhead is heavier in the front than the vanes and nock are in the back) is 8% of the total arrow length.

Another way I like to describe this is think about holding a broom handle in your hand (just the handle, no broom bristles attached).  If you placed a 5lb weight on one end and a 10 lb weight on the other hand, what would happen if you tried to balance the broom handle with your hand placed directly in the center of the broom stick?  The 10lb weight would tip down, and the 5lb weight would tip up.  To truly balance the broom handle you would need to move your hand (balance point) towards the 10lb weight to compensate.  Therefore your balance point (your hand) would be closer to the 10lb weight to get the broom handle to actually balance.  Or, in other words, your balance point would need to be some percentage front (or forward) of the exact middle point of the broom handle.  The distance between the exact middle of the broom stick, and where your hand can actually acheive a balance would be how far "front of center" your balance point is.  Divide this distance over the total length of the broom stick, and you will get your FOC percentage.  But broomsticks don't help us kill game (at least I haven't heard of any instances of this), so let's apply this to our arrow shaft to calculate our FOC percentage.

Should I get out my Algebra text book?

 No!

There is a very simple procedure to calculate your arrow's FOC percentage.  These steps are outlined below:

Obtain Balance Point (BP) - Take one of your arrows.  We make an assumption that the arrows you are shooting are all consistent.  Meaning, they are the same brand, same length, same type of vanes, same weight of field tip/broadhead, and overall weigh relatively the same (within 5-10 grains).  When measuring, the arrow should be completely setup, meaning, the tip you will be using is screwed in and your nock is on the back of the arrow.  Place your arrow on a share edge (or if nothing else use your finger) and attempt to balance the arrow.  Once you are comfortable you know the location of the balance point, place some sort of mark on the arrow where the balance point is.

Measure Balance point (BP) - Once you have the BP marked, measure the distance from the bottom of your nock groove to the BP.  This is the Balance Point (BP) measure.

Measure Total Arrow Length (TAL) - Next, you need to measure the total arrow length.  You do this by measuring from the bottom of the nock groove, all the way down to the edge of your arrow shaft (NOTE:  Don't measure down to the insert, measure to the end of the arrow shaft - this is called the arrow's cut length).

Calculate Center Point (CP) - take the Total Arrow Length (TAL) and divide by 2.  This is where the Center Point (CP) will fall on the arrow shaft - TAL/2 = CP.

Calculate FOC Length (FOC L) - Once you know your center point, you want to subtract the center point (CP) from the balance point (BP) to get the FOC L - (BP - CP) = FOC L

Calculate FOC Percentage (FOC %)  - Once you have the FOC length, you simply divide the FOC L by the total arrow length value and multiply by 100 to get a percentage - (FOC L / TAL) * 100 = FOC %

Am I good?

So now that you have a FOC percentage calculation, what does it mean?  First, we need to caution that the ranges we publish here are based on our own personal experience.  Many others will have opinions on what FOC percentage works best for their particular setup.  Remember the goal of calculation FOC percentage - we want to balance the arrow's performance between stability in flight and distance down range.  So, the discussion below are some general guidelines.  You'll need to tweak/adjust your FOC based on your setup and your results on the range.

An FOC percentage between 7 and 10 percent is often what you hear as an acceptable range from many of the archery pros and arrow manufacturers out there.  Again, if your FOC percent doesn't fall into this range, it does not mean you necessarily need to make an adjustment.  If you are getting a good combmination of arrow stability, flight, and accuracy down range with an 18% FOC, then stick with it.  In general I would not recommend going below a 7% FOC because I feel you are giving up way too much arrow stability for distance down range. 

What if my FOC is below 7%?

Again, as a general guideline I would not recommend going below a 7% FOC.  A couple of quick things you could do to correct this and get your FOC into the 7 to 10% range:

1. Go with a heavier broadhead/field tip.  If you are using 100 grains for your point, maybe try out 125 grains and see how it performs and what FOC percentage you are calculating.
2. Without going to a heavier broadhead, many manufacturers have inserts that are weighted forward.  This could help get your FOC percentage within range.
3. I use Gold Tip 5575's, and Gold Tip sells screw-in inserts that can add weight to the front of your arrow.  I screw in 10 grains of weight into each of my arrow inserts, and am very happy with my arrow speed, stability, and distance down range.  My FOC % comes in right at 9% with a 26.5 draw length.

Carbon vs. Aluminum

I don't come across many hunters (under 40 years of age) still using Aluminum arrows.  But if you are, you still should calculate your FOC %.  One thing that I would point out is that Carbon arrows tend to have a higher acceptable FOC percentage.  So if you are using carbon arrows and you are up there at the 15-18% range, you may be OK.  But if you are using Aluminum arrows, I would definitely look at lightening up the front end of your arrow to get down into the 7-10% range.

As always, if there are any questions about FOC, feel free to drop Anthony and Aneal an email at info@bowcast.com.  Alternatively, feel free to use the forums on http://www.bowcast.com/ to get some other opinions and perspectives around front of center.

 Shoot Straight!

Aneal