# Brace Height Tuning?



## JParanee (Oct 13, 2009)

For me no 

Arrows are cheap....I tune my bow to its optimal performance and than adjust the arrow to it 

But yes brace height will effect arrow spine


----------



## Bender (Dec 6, 2006)

Yes, I myself do use it. 

It can be used with bows that are before center, on center and past center.

It isn't about whether or not the arrow points one or another at brace. Immediately after release, the arrow should never touch the riser, shelf, rest, plunger again. Rather, adjusting brace is about timing the point that the arrow separates from the string. Altering brace height (BH) assists in timing the oscillations and flex that is induced in the arrow shaft so that contact does not happen.


----------



## rraming (Aug 5, 2006)

If you have to fine tune for broadheads you can do it - that is the only time I would use it for tuning


----------



## Bowmania (Jan 3, 2003)

I think everyone who really wants to fine tune their bow uses string length, but not to start out (unless your very luck and hit the spine, arrow length, and point weight by accident).

Start with impacts - www.acsbows.com/bowtuning.html click 'download printable version'. Towards the end is the best broadhead explanation I've ever found.

Bowmania


----------



## Easykeeper (Jan 2, 2003)

rraming said:


> If you have to fine tune for broadheads you can do it - that is the only time I would use it for tuning


That's how I look at it too. I've found that the better my tune the less likely I'll need to tweak anything for broadheads. I've always found that a good bare shaft tune, three bare shafts and three fletched shafts grouping together at 25-30 yards lets me simply swap out the field points for same weight broadheads and be good to go with just a confirmation shot for each arrow.

I think the effect brace height has on tuning has more to do with stored energy than the geometry of the arrow and bow, although the relative position of the arrow should have an minor effect too. A high brace height comes from a shorter string which results in more limb deflection at full draw and more acceleration placed on the arrow at release. The slight increase in stored energy and acceleration results in a slightly weaker dynamic response from the arrow. 

A low brace height will have the opposite effect since there is slightly less limb deflection and stored energy at full draw. 

I do like JP, get my bow as quiet and vibration free as possible and then tune the arrow to the bow. For me the quietest bow usually comes at the top or slightly over the highest brace height recommended by the bowyer. Brace height is always there as a minor tuning factor but I can't say I've ever used it.


----------



## emrah (Aug 28, 2012)

Easykeeper said:


> I think the effect brace height has on tuning has more to do with stored energy than the geometry of the arrow and bow, although the relative position of the arrow should have an minor effect too. A high brace height comes from a shorter string which results in more limb deflection at full draw and more acceleration placed on the arrow at release. The slight increase in stored energy and acceleration results in a slightly weaker dynamic response from the arrow.
> 
> A low brace height will have the opposite effect since there is slightly less limb deflection and stored energy at full draw.
> .


That's impossible. Your draw length is what it is regardless of brace height. The limbs will still get to the same deflection at full draw. The only thing different is the power stroke being a little longer or shorter.

Emrah 


Sent from my iPhone using Tapatalk


----------



## emrah (Aug 28, 2012)

I think the video I watched was trying to illustrate why a shorter or taller BH would need different spines. Not only from the power stroke but also from the tip pointing left (for a right handed shooter). An extreme example would be a 1" brace on a shelf less selfbow. With the arrow nock clipped to the string, the tip would point pretty far left (assuming the string runs down the middle of the limbs). Now take that nocking point (brace) back to say 8", the tip doesn't point so far left.

That was the part of the video I was intrigued with because I'd never considered that. With a true centershot bow, that phenomenon is eliminated.

Emrah 


Sent from my iPhone using Tapatalk


----------



## Sanford (Jan 26, 2009)

emrah said:


> That's impossible. Your draw length is what it is regardless of brace height. The limbs will still get to the same deflection at full draw. The only thing different is the power stroke being a little longer or shorter.
> 
> Emrah
> 
> ...


There's several factors going on, and increase limb deflection is one of them. Yes, nothing changes with your draw length. But, for a given draw length the limbs have to move to move with it. A shorter string will move the limbs farther than a longer string for the same draw length. Remember, limbs are not fixed levers. They bend, bow, and deflect, which they will have to do more of to maintain that same distance with a now shorter third side (string side). The shorter power stroke will reduce total amount of energy finally delivered, but initial energy will go up, which is where initial bend happens, at max force.

To point, I can set my arrow on dead center to string and BH changes still have an effect on dynamic spine.


----------



## Bowmania (Jan 3, 2003)

AND the impossible becomes true.

Bowmania


----------



## JParanee (Oct 13, 2009)

Brace height can definetly effect preload and even though you are effectively increasing weight you will get a slower arrow speed the higher the brace height 

Think about it


----------



## emrah (Aug 28, 2012)

I understand the different levels of preload at brace vs full draw. I just don't see how a fully drawn bow, with fully deflected limbs, delivers more or less initial energy at the shot based on brace height.

Example:
A 7" brace has "x" amount of stored energy.
An 8" brace has "y" amount of energy.
A fully drawn bow has "z" amount of energy.

I don't see how either "x" or "y" has any bearing on how much energy is transferred to the arrow at "z".

Help me understand here. I'm not wrapping my head around it.

Emrah 


Sent from my iPhone using Tapatalk


----------



## Viper1 (Aug 21, 2003)

Guys - 

Tuning by sound uses the same dynamics as paper or bare shaft tuning. Only difference is that the latter two are more easily quantifiable. 

e- 

Easy and Sanford are correct. 
The draw length doesn't enter into that part of the equation.

Viper1 out.


----------



## Sanford (Jan 26, 2009)

emrah said:


> I understand the different levels of preload at brace vs full draw. I just don't see how a fully drawn bow, with fully deflected limbs, delivers more or less initial energy at the shot based on brace height.
> 
> Example:
> A 7" brace has "x" amount of stored energy.
> ...


Think as it a triangle. The limbs make up two sides and the string makes up one. If you shorten any side of that triangle, one or both of the others have to change length to connect ends again to make a new shaped triangle. That's exactly what happens when you change the string length. If you shorten the string side of the triangle, the other sides, the limbs, have to bend down more to meet it. Since they cannot change length to meet it end for end (they need to be be shorter as well), they bow and deflect more, more at brace and more at full draw. The whole geometry of the triangle was changed.


----------



## emrah (Aug 28, 2012)

I get all that. I still don't understand how there is more initial energy transfer at the point of release depending on where brace height was.

I'll get there, I'm just not there yet...

Emrah 


Sent from my iPhone using Tapatalk


----------



## emrah (Aug 28, 2012)

So with a higher brace, the string is shorter, meaning the limb tips started in a more preloaded position. 

Does that also mean the limb tips then travel back farther at full draw? Or is it the same position in space? Would poundage go up too then?

Emrah 


Sent from my iPhone using Tapatalk


----------



## Sanford (Jan 26, 2009)

emrah said:


> I get all that. I still don't understand how there is more initial energy transfer at the point of release depending on where brace height was.
> 
> I'll get there, I'm just not there yet...
> 
> ...


The greatest force applied to the arrow is going to be the instant the string starts moving, at finger release. That's max force of the applied energy of the bow. It never gets stronger. Not total energy, just max. With a shorter string, for the same draw length of the bow, the limbs had to deflect more and stored a higher initial energy.


----------



## Ringlight (May 5, 2015)

Most bowyers have a recommended brace height or brace height range. Start at the recommendation or middle of the range and work up or down according to how well the bow shoots.


----------



## Easykeeper (Jan 2, 2003)

emrah said:


> So with a higher brace, the string is shorter, meaning the limb tips started in a more preloaded position.
> 
> Does that also mean the limb tips then travel back farther at full draw? Or is it the same position in space? Would poundage go up too then?
> 
> ...





Sanford said:


> The greatest force applied to the arrow is going to be the instant the string starts moving, at finger release. That's max force of the applied energy of the bow. It never gets stronger. Not total energy, just max. With a shorter string, for the same draw length of the bow, the limbs had to deflect more and stored a higher initial energy.


Sanford has it right.

Think of it this way, like you said your draw length remains the same and it will be the same regardless of the brace height of the bow. But, changing brace height requires either lengthening or shortening the string by a small amount. 

With the same draw length, and a longer string, what happens to the limbs? They are not deflected as far and there is less stored energy and a lower maximum weight on the fingers.

With the same draw length and a shorter string, the limbs are deflected farther, there is a more stored energy and a higher weight on the fingers.

Keep in mind that these differences are small, you probably wouldn't even be able to feel the difference but a good scale and draw board would show the difference is there. When we are talking about the dynamic spine of an arrow, which is what "tuning" is all about, the dynamic response is the result of many variables and one of them is the initial force applied by the bow at release. Since the brace height has an effect on stored energy and maximum draw weight (held at full draw, weight on your fingers) there is more or less force applied to the arrow on release depending on brace height.

Force is defined as mass x acceleration (Newton's second law, F=ma), when the force is increased or decreased (due to a higher or lower brace height) the initial force felt by the arrow will increase of decrease. Since the mass of the system is unchanged (same bow, same arrow), the change in force results in a change in acceleration, and acceleration is a variable that affects dynamic spine.

Once again, the effect is relatively minor. In my opinion playing with brace height should be considered a fine tuning variable and only done at the very last stage to tweak what is already a good tune.


----------



## emrah (Aug 28, 2012)

Sanford said:


> The greatest force applied to the arrow is going to be the instant the string starts moving, at finger release. That's max force of the applied energy of the bow. It never gets stronger. Not total energy, just max. With a shorter string, for the same draw length of the bow, the limbs had to deflect more and stored a higher initial energy.


I got it now! I had to physically pull out my bow, look at it in profile and manually deflect the limb tips in and out to get the picture right in my head. 

Once I concentrated on the shorter string part of the problem, it made more sense. The limb tip-to-tip distance would be shorter with a shorter string. That could only result in more deflection, hence more preload.

Emrah 


Sent from my iPhone using Tapatalk


----------



## Sanford (Jan 26, 2009)

For me, the mechanics of it all are too complicated to just knowing and accepting that it changes dynamic spine and is related to timing the exit point and oscillation factor of the arrow. Think of this aspect as well. Under the same applied tension, a longer string will exhibit more flex than a shorter one. That should translate to greater lateral exertion on the end of the arrow with a shorter string as the string will give less. 

As said, it's a combination of factors of which are out of curiosity and my experimentation have shown me that it will still affect a true center aligned arrow.


----------



## Bowmania (Jan 3, 2003)

Here's the simple way to look at it. The limbs aren't changing, the draw isn't changing, the string length IS changing. Something else has got to friggin' change. LOL, Not scientific but true.

Bowmania


----------



## emrah (Aug 28, 2012)

Simple. Right?

Emrah 


Sent from my iPhone using Tapatalk


----------



## Bender (Dec 6, 2006)

emrah said:


> That's impossible. Your draw length is what it is regardless of brace height. The limbs will still get to the same deflection at full draw. The only thing different is the power stroke being a little longer or shorter.


Stop and think about it for a minute.

Let's take it to an extreme using an imaginary bow that you can't break. String up a bow like normal. Measure the angle between the string and the limb at anchor. Now put on a string half as long. Brace height just went through the roof. Measure that angle again. I assure you that it will be significantly different. The limbs will be nowhere near the same deflection in this extreme example. 

Although not as blatant as our extreme example, this exact same change in geometry, the exact same changes in limb deflection take place even when we diddle with brace height within normal ranges. That's why final draw weight at anchor also changes as you change brace height.


----------



## George Fedelski (Nov 13, 2015)

I want to say something about this but I don't know where to start.
So let's assume (inference) that your draw length is 28 inches.

How much does the force/power change if the brace height is 3 inches vs 8 inches.

The draw length remains the same and the limbs flex the same amount .

Does a higher brace height really store more energy in the limbs?

I would think that the higher the brace height, the less power the bow would have to push the arrows.

I tuned my bow with a higher brace height just so it would be quieter.

Physics tells me that there would be no difference with extreme differences with the brace height.
But experience has show me that a new string and a different (slight) brace height does cause my arrows to go off target.

After a year and a half I have my bow tuned.
The 300 target, 42% are in the 4 ring and 18% are in the 5 ring.

I know there is science involved here but there is also some voo-doo.


----------



## Sanford (Jan 26, 2009)

George Fedelski said:


> I want to say something about this but I don't know where to start.
> So let's assume (inference) that your draw length is 28 inches.
> 
> How much does the force/power change if the brace height is 3 inches vs 8 inches.
> ...


By the same physics your limbs had to flex more to create a higher BH when the string was twisted shorter, they are flexed more when at 28" full draw. Basically, because you twisted the string shorter the limbs are now flexed more at every point from brace to full draw. The arrow will come off slower because, as well, the length of stroke was lowered while the power of stroke went up.


----------



## bigfoot522 (Jan 27, 2013)

Cut an old string in half and tie in a scale.
Brace bow to 7" read scale then brace to 9" and read scale. They are the same limbs but the scale reads a bit different. The voo Doo is in the string tension and the length of stroke. The thrust and end of travel point dictate arrow clearance. 
Like Bender said the ocillation.


----------



## kegan (Aug 28, 2006)

I usually have about 1.5" of brace height range to tune. However, I refuse to cut my arrows since already have two boxes of arrows too short for me to shoot anymore. Adjusting brace height, strike plate, silencer placement, and tip weight if necessary have been enough for me to get broad heads flying straight to the mark.


----------



## emrah (Aug 28, 2012)

So had anyone calculated just how much final poundage at anchor changes with, let's say a 1" brace height difference?

Kegan, you may be able to answer this. When a bow is built to draw say 50# @28", what brace height is used for that calculation? Like what is the actual poundage at (the same) anchor if the brace is 6.5" vs. say 7.5"?

Emrah 


Sent from my iPhone using Tapatalk


----------



## Sanford (Jan 26, 2009)

emrah said:


> So had anyone calculated just how much final poundage at anchor changes with, let's say a 1" brace height difference?
> 
> Kegan, you may be able to answer this. When a bow is built to draw say 50# @28", what brace height is used for that calculation? Like what is the actual poundage at (the same) anchor if the brace is 6.5" vs. say 7.5"?
> 
> ...


In addittion to 28" marked draw weight, there's an AMO Standard for marking the bow so that a string made to match it will produce the proper intended brace height for the bow. The standard for the brace height according to AMO is "Bows made to AMO Specifications should have string height indicated to a plus or minus 1/2 inch." 'Indicated' here means a suggested range in the manual, as don't see on any bows I have seen. Personally, I have scaled one at bh changes once but did not see any noticeable gain on the manual scale, but I knew dynamic spine changed. That tells me it's a compounded issue in dynamics happening.


----------



## kegan (Aug 28, 2006)

emrah said:


> So had anyone calculated just how much final poundage at anchor changes with, let's say a 1" brace height difference?
> 
> Kegan, you may be able to answer this. When a bow is built to draw say 50# @28", what brace height is used for that calculation? Like what is the actual poundage at (the same) anchor if the brace is 6.5" vs. say 7.5"?
> 
> ...


I can change the brace height from 6" to 8" and measure no difference in draw weight. I built a "kid's bow" for my wife when we started dating and went from a 5" brace height up to 9" (so she didn't smack her arm) and though the draw weight didn't measurably change, she lost quite a bit of cast.


----------

