# Optimizing Brace Height (Recurve)



## sevanseriesta (Jul 7, 2017)

"Without exception, every one of them performed best, were the most stable, and the quietest when the brace height was set where the inline load of the string (preload) was at it's highest point."

The above quote was very interesting to me, as I have been trying to make my bow quieter for some time. Every time I adjust the BH it never changes sound. I am within the manufacturer recommedations, is it possible to go below or above that to get the Optimal Brace height. Does the arrow make a difference in BH setup.

I'm using x-tour 42lb limbs, with MCKinney II 725's cut to 26.5" I believe that the arrows might be slightly stiff, would I decrease or increase BH to counter the stiffness?

What exactly is does the above quote mean. Does it infact mean shoot my bow through a chrono till I find the BH that yields the fastest speed?


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## erose (Aug 12, 2014)

sevanseriesta said:


> "Without exception, every one of them performed best, were the most stable, and the quietest when the brace height was set where the inline load of the string (preload) was at it's highest point."


 I’m curious where you got this quote?



sevanseriesta said:


> The above quote was very interesting to me, as I have been trying to make my bow quieter for some time. Every time I adjust the BH it never changes sound. I am within the manufacturer recommendations,


 Adjusting braceheight doesn’t always change the sound of the bow where you can discern it. If you are looking at making a quieter bow the two best ways of doing this is: 1) Shoot a heavier arrow; and/or 2) add dampeners and/or silencers. 



sevanseriesta said:


> is it possible to go below or above that to get the Optimal Brace height.


. Yes, depending upon the quality of the limbs. Going below recommended brace height isn’t an issue; going above it, may be an issue for long draw lengths.



sevanseriesta said:


> Does the arrow make a difference in BH setup.


 Yes it does. Brace height tuning is a important part of tuning, especially micro-tuning.



sevanseriesta said:


> I'm using x-tour 42lb limbs, with MCKinney II 725's cut to 26.5" I believe that the arrows might be slightly stiff, would I decrease or increase BH to counter the stiffness?


 It can some, but not as much as adjusting the tiller bolts, which is the best way of adjusting the dynamic spine of the arrow. 



sevanseriesta said:


> What exactly is does the above quote mean. Does it infact mean shoot my bow through a chrono till I find the BH that yields the fastest speed?


I’m not sure but it is an interesting idea. If I had a chrono I would give it a try.

Brace height when it comes to tuning, dictates when during the shot cycle that the arrows releases from the string. Since the string oscillates due to a finger release, adjusting the release point adjusts the horizontal release of the arrow. So adjusting the brace height affects the horizontal impact of the arrows. Lower the brace height the stiffer the arrow will act, and weaker for higher adjustment. 

What I have found there is a correlation between the plunger setting and brace height. So the optimal braceheight for a specific bow/arrow configuration is dependent upon plunger setting, tiller adjustment, and center shot.



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## john kristian (Dec 31, 2005)

Thanks for the detailed question and reply. 

I am new to recurve tuning, but need to learn more to help son and wife. It seems that a brace height (BH) is a function of tiller and string length. IOW, tightening/untightening limb bolts and twisting/untwisting the string gives a matrix of many possible BHs. It seems possible that a single (absolute) BH could be the product of many different tillers and twists. For example, 8.125" could be found with lighter limb settings (tiller) and fewer twistsn (longer string); 8.125 could also be reached with heavier tiller settings (bolts further in) and more twists (shorter string). Clearly there is much experimentation and interplay with plunger and center shot to figure out, but has someone ever done a detailed study on the effects of many tillers vs. twists? There would seem to a minimum number of twists needed to get the string to act as a single unit, and a minimum poundage to absorb the force from the archer. Any comments?

Thanks,
JK


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## nuts&bolts (Mar 25, 2005)

john kristian said:


> Thanks for the detailed question and reply.
> 
> I am new to recurve tuning, but need to learn more to help son and wife. It seems that a brace height (BH) is a function of tiller and string length. IOW, tightening/untightening limb bolts and twisting/untwisting the string gives a matrix of many possible BHs. It seems possible that a single (absolute) BH could be the product of many different tillers and twists. For example, 8.125" could be found with lighter limb settings (tiller) and fewer twistsn (longer string); 8.125 could also be reached with heavier tiller settings (bolts further in) and more twists (shorter string). Clearly there is much experimentation and interplay with plunger and center shot to figure out, but has someone ever done a detailed study on the effects of many tillers vs. twists? There would seem to a minimum number of twists needed to get the string to act as a single unit, and a minimum poundage to absorb the force from the archer. Any comments?
> 
> ...


You pick the limb poundage that works for you (adjust limb bolts).
Next, after you have the pounds on the fingers where you want, then, you experiment with BRACE, to get the quietest shot (yes, decibel level). There will be TWO brace heights, that give you the quietest sounding shot. There will be a low brace that works. There will be a high brace that also works. If you cannot tell the difference in the sound of the shot, then, just experiment with brace until you get the tightest group size. The LOUDNESS of the shot, when you release the bowstring on a recurve, tells you via SOUND level, the efficiency of that brace height. So, the QUIETEST sounding shot, is the brace height that provide maximum energy transfer to the arrow (less wasted energy, wasted energy means was used to create vibration in the system, which you can HEAR as a loud sounding shot). When you find the brace height that gives you a very QUIET whoooooosh sound (like a whisper), then, play with centershot (plunger extension) and play with plunger spring pressure, for tightest group size.

You also forget another variable. Recurve string material. BCY 8190 is very "SPRINGY" bowstring material, resulting in a "soft" shot. I also make recurve bowstrings from BCY Trophy, which is basically 452X with a tiny amount of gore material (less fuzzy). Very "crisp" shot.


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## sevanseriesta (Jul 7, 2017)

Erose, first thanks for your response it is greatly appreciated. I have a chrono so I will try doing some testing. here is my issue and correct me if I’m wrong, if I increase brace height wouldn’t the FPS just continue to go up due to the tension on the string?

I’m not experienced in tunning and I’m trying to learn so if this is extremely false let me know. 

When using the chrono is it simply just adjust the brace height and shoot through the chrono and record all the ratings. Should I shoot strings on 3 to get an average or should I shoot more.

I also completely agree on plunger and brace height. I have already noticed as I changed brace heights that my plunger setting had to change. 


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## sevanseriesta (Jul 7, 2017)

nuts&bolts said:


> You pick the limb poundage that works for you (adjust limb bolts).
> Next, after you have the pounds on the fingers where you want, then, you experiment with BRACE, to get the quietest shot (yes, decibel level). There will be TWO brace heights, that give you the quietest sounding shot. There will be a low brace that works. There will be a high brace that also works. If you cannot tell the difference in the sound of the shot, then, just experiment with brace until you get the tightest group size. The LOUDNESS of the shot, when you release the bowstring on a recurve, tells you via SOUND level, the efficiency of that brace height. So, the QUIETEST sounding shot, is the brace height that provide maximum energy transfer to the arrow (less wasted energy, wasted energy means was used to create vibration in the system, which you can HEAR as a loud sounding shot). When you find the brace height that gives you a very QUIET whoooooosh sound (like a whisper), then, play with centershot (plunger extension) and play with plunger spring pressure, for tightest group size.
> 
> You also forget another variable. Recurve string material. BCY 8190 is very "SPRINGY" bowstring material, resulting in a "soft" shot. I also make recurve bowstrings from BCY Trophy, which is basically 452X with a tiny amount of gore material (less fuzzy). Very "crisp" shot.


I use a very aggressive string I believe, I’m using brownell Rhino with 14 strands. Is it possible that I never get the whisper sound that you speak of. Tomorrow I will be testing different brace heights through the chrono and recording all of the shots. I will then discuss the results. If I had a way to record decibel the. I would add that to the test. I might look for one on amazon and test it best on the results.


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## john kristian (Dec 31, 2005)

@sevanseriesta:

I am very interested too and thanks for looking at this. For a dB meter there are apps for iOS and Android, and Walmart is selling ones for +/- $15.00 and there are others that look pretty inexpensive. dB is good, but I would like to measure actual vibration. A quick search finds:

VibroChecker PRO is a fully-fledged vibration and spectrum analyzer, developed for use on iPhones and iPads. The app uses the optional integrated acceleration sensor or gyroscopes and also allows the connection of an external, high-resolution and professional piezo-electronic sensor (DIGIDUCER 333D01) via the lightning interface. In fact, the app is a joint development by the companies ACE, Fabreeka Inc. and Tech Products Inc. (Kaydon – Motion Controls Group)."

at this URL: https://www.motioncontroltips.com/a...ces-professional-vibration-measurement-tools/

It looks a bit costy, though. Any ideas on an option?

Thanks,

JK


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## sevanseriesta (Jul 7, 2017)

john kristian said:


> @sevanseriesta:
> 
> I am very interested too and thanks for looking at this. For a dB meter there are apps for iOS and Android, and Walmart is selling ones for +/- $15.00 and there are others that look pretty inexpensive. dB is good, but I would like to measure actual vibration. A quick search finds:
> 
> ...


Most of what you said is way over my head. Lol

However, with that said, I did purchase a decibel meter, I will be testing both speed and sound tonight. I will see what I can go about getting vibration recorded as well. Would you like to see vibration sound with or without stabilizers or do you think it matters. I currently run 3, 1 on each rod.


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## john kristian (Dec 31, 2005)

If I were doing this test I would run it both ways, with and without stabilizers. I would also use the same exact individual unique arrow in all the tests. I know it might sound excessive, but I would want to know that different arrows didn't contribute a measurable effect upon the decibel level (that is, controlling for variances in arrow weight by using just the same arrow each time). Depending on the variance of the measured decibel levels per shot (how different each measurement is from one shot to another using the same arrow with all the other settings the same per shot) I might shoot as many as 10 or 15 times for each brace height setting (combination of tiller and string length) just to make sure that there was/wasn't a difference between each brace height setting. I'll do some more research and see if I can find out what the trade-off might be in terms of repetition versus accuracy, but if the objective of the whole adventure is to determine if there is a real difference between brace height settings, and the dB range for each shot swings between +/- 5dB (this is just a pure guess) then one would need more trials at each specific brace height with the same arrow to be able to determine if there is any real difference (that is, not due to chance). Even given the same decibel level (that is, no real differences between brace height settings) it could very well be that the quality of the sound (sharp versus soft) is the determinant factor I'm very interested in a very careful statistical analysis because I've never ever seen carefully controlled comparisons.

I don't really have any experience in competition shooting and just used a long stabilizer for literally a couple of weeks. But conceptually, because we can't get around F = MA, and if we draw back the same distance each time for every shot (that's putting the same energy) then a big stabilizer increases the mass which would have to decrease acceleration. I suppose one way to look at it is if a stabilizer weighed 10,000 pounds then 60 lbs. of pull might cause very little measurable acceleration and transfer more kinetic energy to the arrow. All this is meant to say that I don't know if decibels are an accurate proxy for vibration, and I might even have the conservation of energy concepts twisted around. What I do know is that there just aren't a lot of cited studies that archers point to which carefully track interactions and effects of all the multiple variables that make up accuracy for a bow. That's all I know for the moment; please add any thoughts anyone. K.


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## sevanseriesta (Jul 7, 2017)

Interesting information so far, I have already found that maximum FPS is reached somewhere between 8 1/8 and 8 1/4. This is quite a bit under the recommended BH. I also recorded vibration, I was not able to record decibels (kids were screaming in the pool). I’m not sure my phone will ever be the same after that many shoots and vibration. RIP iPhone 6plus. As soon as I can figure out how to post the data I will. I was able to reach a maximum of 213 FPS on 42lb limbs at a draw of 28.5”

Now tell me I’m crazy but the lower BH seemed much easier to get through the clicker. Is that just crazy or could it be true. I know it’s a hell of a lot easier to string that’s for sure.


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## sevanseriesta (Jul 7, 2017)

john kristian said:


> If I were doing this test I would run it both ways, with and without stabilizers. I would also use the same exact individual unique arrow in all the tests. I know it might sound excessive, but I would want to know that different arrows didn't contribute a measurable effect upon the decibel level (that is, controlling for variances in arrow weight by using just the same arrow each time). Depending on the variance of the measured decibel levels per shot (how different each measurement is from one shot to another using the same arrow with all the other settings the same per shot) I might shoot as many as 10 or 15 times for each brace height setting (combination of tiller and string length) just to make sure that there was/wasn't a difference between each brace height setting. I'll do some more research and see if I can find out what the trade-off might be in terms of repetition versus accuracy, but if the objective of the whole adventure is to determine if there is a real difference between brace height settings, and the dB range for each shot swings between +/- 5dB (this is just a pure guess) then one would need more trials at each specific brace height with the same arrow to be able to determine if there is any real difference (that is, not due to chance). Even given the same decibel level (that is, no real differences between brace height settings) it could very well be that the quality of the sound (sharp versus soft) is the determinant factor I'm very interested in a very careful statistical analysis because I've never ever seen carefully controlled comparisons.
> 
> I don't really have any experience in competition shooting and just used a long stabilizer for literally a couple of weeks. But conceptually, because we can't get around F = MA, and if we draw back the same distance each time for every shot (that's putting the same energy) then a big stabilizer increases the mass which would have to decrease acceleration. I suppose one way to look at it is if a stabilizer weighed 10,000 pounds then 60 lbs. of pull might cause very little measurable acceleration and transfer more kinetic energy to the arrow. All this is meant to say that I don't know if decibels are an accurate proxy for vibration, and I might even have the conservation of energy concepts twisted around. What I do know is that there just aren't a lot of cited studies that archers point to which carefully track interactions and effects of all the multiple variables that make up accuracy for a bow. That's all I know for the moment; please add any thoughts anyone. K.


The same arrow was used the entire time. And speed and vibration was recorded at the same time (again no decibels at this time). I believe just from the ear lobe test that sitting at 8 1/8 is significantly quieter and less vibration then the 8 3/4 i was at.


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## nuts&bolts (Mar 25, 2005)

john kristian said:


> I don't really have any experience in competition shooting and just used a long stabilizer for literally a couple of weeks. But conceptually, because we can't get around F = MA, and if we draw back the same distance each time for every shot (that's putting the same energy) then a big stabilizer increases the mass *which would have to decrease acceleration*. I suppose one way to look at it is if a stabilizer weighed 10,000 pounds then 60 lbs. of pull might cause very little measurable acceleration and transfer more kinetic energy to the arrow. All this is meant to say that I don't know if decibels are an accurate proxy for vibration, and I might even have the conservation of energy concepts twisted around. What I do know is that there just aren't a lot of cited studies that archers point to which carefully track interactions and effects of all the multiple variables that make up accuracy for a bow. That's all I know for the moment; please add any thoughts anyone. K.


More mass for the bow system, increases inertia. More inertia for the bow system, more energy transferred to the arrow. Energy losses, meaning energy not absorbed by the arrow, during launch. HEAT, vibration, translation (movement). Low inertia bow system, you might see the bow jump into the finger sling. High inertia bow system, you see less bow jump into the finger sling. Bow riser jump also has to do with limb pocket angles and the rigidity of the riser (more flex or less flex by design). Vibration in the riser, bowstring harmonics translate into SOUND. So, SOUND is an excellent vehicle for assessing wasted energy.


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## john kristian (Dec 31, 2005)

Thanks Nuts&Bolts,

So, would the quietest shot equate to the optimum brace height--not counting plunger and rest issues for the moment? It would seem that arrow speed would be another indicator (of optimum KE transfer), along with deflection (variance of the distance between each shot). All else being equal, could a faster shot be louder or a quieter shot slower?

Thanks,

JK


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## sevanseriesta (Jul 7, 2017)

I just got done testing with decibels and my fastest shot is my loudest shot. As the speed goes down (brace height was increasing) the decibels also went down. As I lower the BH the sound continues to go up. I will put all this in a spread sheet to be reviewed but at @ 8 3/4 fps was measured at an average of 203 and 76db. At 8 1/2 it goes to 209fps and 79db and at 8 1/4 it’s at an average of 211fps at 81db. I believe I have only shot my bow ever at 8 3/4. Tomorrow I’m going to try 8 1/2 and 8 1/4 and see how they group. I will then decide if it’s sound or speed that is optimal.

Going back to my original quote, I’m curious if it’s going to be speed. Although I’m fairly surprised that there was never a point where speed and sound ever ended up being the fastest and the quietest.


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## john kristian (Dec 31, 2005)

Cool. Are you increasing BH with more string twists? I am thinking back to N&B's July 6th, 2019, 02:21 AM post (above) when he writes about there being two 'nodes' (my term) where there is optimum poundage and string length (no. of twists). Just so I am thinking clearly, the objective is the best accuracy by getting the (assumed) highest speed (a function of the amount of power a single, unique human can put into the system) that in turn is a function of poundage and string length? I have seen bare bow shooters that have remarkably quiet bows, so there is a lot of practical application out there. Interested to see how it works out and be careful. Thanks, JK


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## sevanseriesta (Jul 7, 2017)

Yes, BH was adjusted by twisting the string only. My limb bolts are all the way in so there isn’t any additional adjustment there.


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## nuts&bolts (Mar 25, 2005)

sevanseriesta said:


> I just got done testing with decibels and my fastest shot is my loudest shot. As the speed goes down (brace height was increasing) the decibels also went down. As I lower the BH the sound continues to go up. I will put all this in a spread sheet to be reviewed but at @ 8 3/4 fps was measured at an average of 203 and 76db. At 8 1/2 it goes to 209fps and 79db and at 8 1/4 it’s at an average of 211fps at 81db. I believe I have only shot my bow ever at 8 3/4. Tomorrow I’m going to try 8 1/2 and 8 1/4 and see how they group. I will then decide if it’s sound or speed that is optimal.
> 
> Going back to my original quote, I’m curious if it’s going to be speed. Although I’m fairly surprised that there was never a point where speed and sound ever ended up being the fastest and the quietest.
> 
> ...


Sound and speed also depends on how clean you release the bowstring, or whether you pluck the string. If you pluck, you are twanging the bowstring like a guitar. Find the brace height that gives you the TIGHTEST groups...this is your defining variable...not just pure arrow speed. If the lower brace heights give you more SPEED, but you cannot control the speed (you get larger groups...then, who cares about the higher speed). Plot GROUP size versus brace height and find the more forgiving brace height (that means tightest groups).


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## erose (Aug 12, 2014)

john kristian said:


> Thanks for the detailed question and reply.
> 
> I am new to recurve tuning, but need to learn more to help son and wife. It seems that a brace height (BH) is a function of tiller and string length. IOW, tightening/untightening limb bolts and twisting/untwisting the string gives a matrix of many possible BHs. It seems possible that a single (absolute) BH could be the product of many different tillers and twists. For example, 8.125" could be found with lighter limb settings (tiller) and fewer twistsn (longer string); 8.125 could also be reached with heavier tiller settings (bolts further in) and more twists (shorter string). Clearly there is much experimentation and interplay with plunger and center shot to figure out, but has someone ever done a detailed study on the effects of many tillers vs. twists? There would seem to a minimum number of twists needed to get the string to act as a single unit, and a minimum poundage to absorb the force from the archer. Any comments?
> 
> ...


Tiller doesn’t play a roll in brace height adjustment. Only string length.


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## erose (Aug 12, 2014)

sevanseriesta said:


> Interesting information so far, I have already found that maximum FPS is reached somewhere between 8 1/8 and 8 1/4. This is quite a bit under the recommended BH. I also recorded vibration, I was not able to record decibels (kids were screaming in the pool). I’m not sure my phone will ever be the same after that many shoots and vibration. RIP iPhone 6plus. As soon as I can figure out how to post the data I will. I was able to reach a maximum of 213 FPS on 42lb limbs at a draw of 28.5”
> 
> Now tell me I’m crazy but the lower BH seemed much easier to get through the clicker. Is that just crazy or could it be true. I know it’s a hell of a lot easier to string that’s for sure.
> 
> ...


It would be easier because you would have less stacking.


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