# Higher FOC or speed?



## Cephas (Sep 7, 2010)

If you have a few pounds of draw weight to work with, would you opt for the lower draw weight with higher FOC or the higher draw weight and gain a little more speed if you're working with the same shaft length? I hope that makes sense. Do I opt for higher foc with a slower arrow or lower foc to gain about 7-8% more speed?


----------



## theminoritydude (Feb 11, 2013)

Are we talking recurve here? Indoor? Outdoor?


----------



## chrstphr (Nov 23, 2005)

high FOC if you are shooting outdoors at any distance. Speed is not an issue really. You can shoot great scores with 175 fps or 205 fps. 

You will be thanking FOC in the wind.


Chris


----------



## anmactire (Sep 4, 2012)

Having both rocks if you can manage it. I have ~16% foc and a bow that kicks those arrows at 220 fps. Border limbs helped acheive the speed but the foc can be done by going with a heavier point on a lighter shaft.


----------



## Cephas (Sep 7, 2010)

I appreciate the responses. Is there a 'max' recommended foc for recurve or a point where there are diminishing returns chris? We are talking 29# otf give or take and foc of between 16-19% and speed increase of possibly 12-14 fps.


----------



## cc46 (Jan 22, 2005)

Cephas, at 29# otf, if I were you, I'd opt for the best FOC. Buy the lightest shafts possible (MKIIs) and heaviest points that will tune. 

Don't get obsessed with the numbers.


----------



## chrstphr (Nov 23, 2005)

16% FOC is a good spot. Its not too aggressive where your arrow will die at a further distance, but its enough that it will pull your arrow in the wind. 

16-18% if your shaft is heavier. I have heard Vittorio say 20% FOC or higher is perfect, but i have never personally shot that high an FOC.

My arrows are 385ish gr total with 120 gr point, Gives me 16%. I get 205 fps, but have shot 195 ish for years as well with same results. 

Chris


----------



## Cephas (Sep 7, 2010)

Thanks cc46. This is for a fairly proficient young lady if it makes any difference. Is 19% foc too much or still acceptable?


----------



## chrstphr (Nov 23, 2005)

Cephas said:


> Thanks cc46. This is for a fairly proficient young lady if it makes any difference. Is 19% foc too much or still acceptable?


if she can shoot the furthest she will shoot with her sight normal, then its acceptable. The only downside is the the heavier the FOC there is a point where the heavy point will drop the arrow and you will lose trajectory near the end of the shot. 

Best to have her shoot it at the distances she will shoot and see if her sight marks are doable. 

Chris


----------



## lksseven (Mar 21, 2010)

chrstphr said:


> 16% FOC is a good spot. Its not too aggressive where your arrow will die at a further distance, but its enough that it will pull your arrow in the wind.
> 
> 16-18% if your shaft is heavier. I have heard Vittorio say 20% FOC or higher is perfect, but i have never personally shot that high an FOC.
> 
> ...


Chris,

My arrows are 317grain, 120grain points, 29.5" from point tip to nock throat, and FOC is 14.02% (I'd like it to be higher). How can you get 16% FOC with 385grain arrow and the same 120grain point? Maybe I'm not calculating correctly.


----------



## w8lon (Jun 2, 2012)

A handy calculator; http://archerycalculator.com/arrow-front-of-center-foc-calculator/


----------



## chrstphr (Nov 23, 2005)

lksseven said:


> Chris,
> 
> My arrows are 317grain, 120grain points, 29.5" from point tip to nock throat, and FOC is 14.02% (I'd like it to be higher). How can you get 16% FOC with 385grain arrow and the same 120grain point? Maybe I'm not calculating correctly.



My arrow is shorter. 27.75 from inside of nock to end of shaft. You also dont use the tip of the point. You measure from inside of nock end to end of shaft. this gives better results. 

Some points are 1 inch long, some 3/4, some 1/2. That shouldnt change the FOC if the point weight is the same. 

I would not include the X10 point, The 120 gr stainless steel point is longer than the 120gr tungsten point. I bet you are over 15% if you dont use the point. 

My arrow is 27.75 L, and the balance point is 18.5 "B" FOC 16.6666666% using the FOC calculator above. If i include the tip, then my FOC is 15.486%.

Chris


----------



## lksseven (Mar 21, 2010)

ok, thanks for the explanation. I'll re-calc.


----------



## Fury90flier (Jun 27, 2012)

some reading on FOC...don't always assume more FOC is better...

http://www.tap46home.plus.com/mechanics/


----------



## lksseven (Mar 21, 2010)

Fury90flier said:


> some reading on FOC...don't always assume more FOC is better...
> 
> http://www.tap46home.plus.com/mechanics/


The takeaway from Joe's analysis seems to be:

Upside: Having a high FOC for an arrow provides two principal benefits - better arrow groups and reduced wind sensitivity.

Downside: The downside to a higher FOC is because the offset angle between the arrow axis and the direction it's going will in general be smaller, the drag on the pile will increase; lift from shaft drag will be reduced and probably the arrow will be heavier and hence going at a lower speed. All these factors result in 'loss of sight mark'.


----------



## chrstphr (Nov 23, 2005)

lksseven said:


> The takeaway from Joe's analysis seems to be:
> 
> Upside: Having a high FOC for an arrow provides two principal benefits - better arrow groups and reduced wind sensitivity.
> 
> Downside: The downside to a higher FOC is because the offset angle between the arrow axis and the direction it's going will in general be smaller, the drag on the pile will increase; lift from shaft drag will be reduced and probably the arrow will be heavier and hence going at a lower speed. All these factors result in 'loss of sight mark'.


pretty much what i said in my posts. 




chrstphr said:


> 16% FOC is a good spot. Its not too aggressive where your arrow will die at a further distance, but its enough that it will pull your arrow in the wind.





chrstphr said:


> if she can shoot the furthest she will shoot with her sight normal, then its acceptable. The only downside is the the heavier the FOC there is a point where the heavy point will drop the arrow and you will lose trajectory near the end of the shot.


Chris


----------



## theminoritydude (Feb 11, 2013)

I would attribute the apparent decrease in range by a high FOC, to higher mass. Strictly speaking, a theoretically ideal arrow is one with 100% FOC. Imagine a hypothetical arrow with a point mass (pick any number) that has zero volume, with a hypothetical shaft that has the required draw length, stiffness, and zero volume and zero mass, and attached to the tail of it, a fletching that has zero mass, with a total volume required to tune the arrow sufficiently such that it allows airflow to travel straight down its entire length at the moment it leaves the string

We know that such an arrow does not exist. But you can be certain that it will outperform any arrow that exists in the real world, given it's perfect FOC. It's mass will control it's trajectory, exclusively, though one may question the need for fletching, let's just say that the rule of the sport is for the arrow to strike the target at an incident angle, instead of a random theoretical face of such a hypothetical point.

In the real world, we have limitations. We could only add mass to manipulate the FOC, some might argue that the FOC can be increased by reducing component weight at the back of the arrow, but that's besides the point. We could only add point weight until the arrow rest bends and gives way under the crushing weight of the point, and even then it would not reach anywhere near the theoretical ideal FOC, so good luck with trying to push it out of the bow.

Lift, is a double edged......no actually, for a projectile, lift is a grenade. For lift to extend the distance that the arrow travels, it also is susceptible to the random nature of the outdoor winds. This sport isn't about how much distance one can dump an arrow over, that's shot put, or discus throw. This sport is about accuracy. Any top archer would gladly sacrifice speed and range for consistency. No extra points will be given for 2 out of 6 shots that shoots further or faster.

In any case, given that drag occurs downrange, from the top of the trajectory all the way down, mass combined with Earth's acceleration seems to be the ONLY thrust available to the arrow (What kills the speed in the beginning, give it back during the drop). How much mass to use, depends on the angle of the arrow on impact. By the rules of geometry, the ideal angle to impact the target, would be 90 degrees. 10- 15 degrees is the range of the angle of tilt of the target board. Think about it, suppose a target board is located 70m away from the shooting line with a 12 degree tilt, at the point of impact, what your arrow is exposed to, should be the MAXIMUM impact zone available. That only happens when the arrow lands on the board at 12 degree elevation from the horizon.

I'm not suggesting that everyone should go out and start finding out the angle at which your arrows impact the target face. I'm trying to provide a perspective to archers out there trying to find the elusive "ideal FOC". If anyone of you is crazy enough to find out the mass/impact angle relationship, please let me know the results. It will delight me. It will also tell you that FOC is just another number, one that you could probably ignore. Probably.

Thank you all for your kind attention.


----------



## Dacer (Jun 10, 2013)

As far as trajectories go - the mass of the point doesn't have any effect on the arrow in the X component vector after the initial acceleration. Its only effected by drag, which slows the horizontal X component vector. The Y component vector is the only part effected by gravity. 

The FOC isn't that complicated. The further forward the center of mass the greater the leaver arm due to the drag of the fletching is - - which helps make an arrow more accurate and forgiving. Which is why big feathers are very forgiving - slower - but they induce a greater effect on the center of mass from the greater drag. 

That said: the 10-20% range seems to be working pretty well for the elite level shooters.


----------



## HikerDave (Jan 1, 2011)

Cephas said:


> If you have a few pounds of draw weight to work with, would you opt for the lower draw weight with higher FOC or the higher draw weight and gain a little more speed if you're working with the same shaft length? I hope that makes sense. Do I opt for higher foc with a slower arrow or lower foc to gain about 7-8% more speed?


I wrote an unpublished ballistic simulator and in testing this was surprised to find out that arrow speed doesn't affect wind drift as much as I thought.

The reason is that drag increases as the square of the speed. Wind drift is predominately caused by drag, because an arrow always turns into the wind (provided that the front of center is good enough). The speed increase of the light arrow gives the wind less time to act on the arrow, but the greatly increased drag negates most of this advantage.

Higher draw weight suffers from diminishing returns in the same manner -- the faster arrow suffers more drag force but less time for that force to act, so for a youth archer I would always choose the lighter draw weight -- which results in more practice time and a healthier archer.


----------



## w8lon (Jun 2, 2012)

Here is a depiction of trajectory of two arrows the first at 58 meters per second the second at 65 mps. Both will impact at same point in elevation at 70 mtr the angle of impact should be the same as where they left the bow. Drag is not taken into effect with these calculations.


----------



## chrstphr (Nov 23, 2005)

w8lon said:


> Here is a depiction of trajectory of two arrows the first at 58 meters per second the second at 65 mps. Both will impact at same point in elevation at 70 mtr the angle of impact should be the same as where they left the bow. Drag is not taken into effect with these calculations.


pretty much what i said here


chrstphr said:


> Speed is not an issue really. You can shoot great scores with 175 fps or 205 fps.
> Chris


and here



chrstphr said:


> My arrows are 385ish gr total with 120 gr point, Gives me 16%. I get 205 fps, but have shot 195 ish for years as well with same results.
> Chris



Chris


----------



## Bob Furman (May 16, 2012)

Also check out Joe's Arrow Weight and Downrange Energy write up:

http://www.tap46home.plus.com/mechanics/

Under Appendices|Arrow Weight and Downrange Energy


----------



## w8lon (Jun 2, 2012)

Not a very dramatic difference other than launch/impact angle. Time of flight does have some effect on wind drift though I would think as well as attaining the extra sight angle with slower speeds. The link to trajectory calculations:
http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html


----------



## Fury90flier (Jun 27, 2012)

If you really want to understand the various aspects of arrow flight, tuning, efficiency etc...read through his pages- quite informative.

Regarding FOC...and "ideal"
I'm sticking with results testing.

I can go through all the formulas I want and all that will do is give me an idea of what weight range to play with…kind of like DL


----------



## HikerDave (Jan 1, 2011)

w8lon said:


> Not a very dramatic difference other than launch/impact angle. Time of flight does have some effect on wind drift though I would think as well as attaining the extra sight angle with slower speeds. The link to trajectory calculations:
> http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html


This article is mostly about sight angle. Best way to reach the distance is with sight angle -- the sight can be moved closer to the bow, or a sight of the opposite hand can be mounted inboard on the bow instead of outboard.

Best way to achieve forgiveness to poor releases or resistance to gusty winds is with high front of center achieved with light shafts with heavy points ACE or McKinney.

Best way to achieve low absolute wind drift is with small diameter heavy arrows Nano Pro or / X-10 respectively or for those lucky few with just the right size, the oddly skinny Medallion XR 1300-2000 shafts.


----------



## Joe T (Apr 5, 2003)

Somewhat late addition but re another forum discussion I put together a spreadsheet to illustrate a possible process for coming to a conclusion about this arrow speed/FOC debate.
You can download the spreadsheet here: FOC for arrow selection.

The suggested sequence is this:
1. define the acceptable range of arrow speed (e.g. 185-200 fps). This is on the basis things like having an acceptable sight mark position for all distances with the same side bar extension.
2. Do a simple ballistic calculation which gives you the range of arrow weights that will give you the acceptable arrow speed defined at step 1.
3. Select the arrow options available from the manufacturers' charts (draw weight and draw length).
4. Enter the alternative arrow options into a table which includes shaft gpi and appropriate nock and fletch weights.
5. The table calculates the point weights required (from the all up weights derived at step 2) and also the arrow FOC.

So you have a table of arrows giving the FOC values for arrows that meet your arrow launch speed criteria. Basically you select the highest FOC available. The tiebreaker if need would be the arrow diameter.

This approach at least gives you some arrow options to to physically test.


----------



## lksseven (Mar 21, 2010)

Joe T, you're a treasure here. Be sure to look both ways before crossing the street!


----------



## limbwalker (Sep 26, 2003)

Having draw length and weight to spare, in 2004, I followed the Frangilli's lead and opted for maximum FOC, obtaining custom 125 grain tungsten points for my A/C/E's. All I got for it was a spot on the Olympic team after a week of shooting in strong, steady winds, and a 4th place national ranking after my first abbreviated outdoor season. So yea, if you have the option, I'd always suggest a higher FOC in the wind.

The other evening, I was watching two of my students - one being the #1 ranked Junior female recurve archer in the U.S., and another, a top 5 Cub recurve archer, shooting 70 and 60 meters in a strong wind. They were both consistently breaking 50 points/end using 900 and 1000 spine arrows with 100 grain points. FOC for each of them is off the chart. Arrows weathervaned wildly in that wind, but always tracked straight.

I think sometimes folks see that weathervaning and think their arrows are getting blown all over the place, when the contrary is true. That heavy point is guiding that arrow just fine.


----------



## Sosius (Feb 5, 2014)

limbwalker said:


> The other evening, I was watching two of my students - one being the #1 ranked Junior female recurve archer in the U.S., and another, a top 5 Cub recurve archer, shooting 70 and 60 meters in a strong wind. They were both consistently breaking 50 points/end using 900 and 1000 spine arrows with 100 grain points. FOC for each of them is off the chart. Arrows weathervaned wildly in that wind, but always tracked straight.
> 
> I think sometimes folks see that weathervaning and think their arrows are getting blown all over the place, when the contrary is true. That heavy point is guiding that arrow just fine.


Wow, that's really interesting. Out of curiosity, what brands of arrows/points were they shooting? My 10 year-old daughter will soon outgrow her Easton Tributes.


----------



## Cephas (Sep 7, 2010)

I would venture a guess that at least one of them is using CX Nano SST's.


----------



## limbwalker (Sep 26, 2003)

Good guess.  The other is using CX NPXtreme prototypes. Best outdoor arrow ever made IMO - same batch I shot a 341 with at the trials in Chula. They have magic dust in the carbon 

Sosius, what these girls are shooting is irrelevant to your daughter. At 10, she's best served shooting 1214 Jazz or Tribute arrows until she can comfortably shoot 22# or more, in which case CX Medallion XR 2000's will be the next step.


----------



## Sosius (Feb 5, 2014)

Thanks, limbwalker.


----------



## Vittorio (Jul 17, 2003)

FOC is the dominant factor in the wind, and those 125 gr tungsten custom points John has mentioned were a fantastic solution. 
What really makes me crazy is the lack of understanding manufactures have about this. X10 and Nano Pro X-treeme are rather heavy by themselves, so 120 gr tungsten points are not giving a really good FOC to them, as they should get >130/140 gr tungsten points to really perform at best, in my opinion, but manufacturers don't want to make them, no one knows why. Soon or later I will have these points made just to show that results can really change with them. Same as we did with ACE's special points. 
I can get 140 gr tungsten points for Nano Xtreme >600 spine size made in a couple of months. PM me if you would like to join, as I need to make 300 pcs at least and money involved is not small..


----------

