# Finding Brace Height



## swagpiratex (Apr 8, 2012)

If you're looking for a mathematical formula where you plug in different parameters to spit out a perfect brace height for you...

I've never heard of one, and it's not written in Viper's book either.


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## icehaven (Nov 30, 2010)

what's wrong with trial and error?


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## dchan (Jun 29, 2004)

Sorry but no easy find for that sweet spot. Especially since every person shoots just a little bit differently.

The sweet spot on brace height can be affected by pretty much every thing you do. torque the bow, pluck the string, alignment, anchor, draw weight, draw length, plunger pressure, string count/diameter, serving length, string material, length of stabilizer, weight distribution of stabilizer.

If you find an APP or formula to get that BH every time, you could make a mint but because of the human factor, it's pretty much a trial and error thing. If your release gets better, or draw length changes because you are getting stronger, guess what, Your perfectly tuned BH may not be so perfect any more.

DC


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## ksarcher (May 22, 2002)

Today I spent close to 4 hours doing "Trial and error" with brace height...That was after a few hours last week getting the draw weight and bare shaft right...

Add 5 twist..shoot..measure...document add 5 twist...shoot...measure...document. after some point you reverse the process..evaluate documentation and wa-la you have the best brace height for the arrow setup...

It takes time..That has always been part of the fun of Archery especially with the Recurve...


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## Chris RL (Oct 30, 2011)

Dan, I'd start with the manufacturer's recommendations, also the recommendations of the limb makers, then, as everybody else has said, go from there.

Mostly on a Hoyt 25" medium (68") bow it's somewhere around 8-8.75", but be aware - on my 68" with Border Hex6H limbs, for instance, that's well outside the Border warranty limits, which run very low, as much as a couple inches lower than the Hoyt ranges. So start with what the bowyers say and tune from there.

Sorry I can't be more specific without more equipment information.


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## Joe T (Apr 5, 2003)

Trial and error is really the only method for brace height.

However if you are looking for an equation then a reasonable BH estimate is:

Brace Height = (arrow mass)*(arrow speed squared) divided by (twice the draw weight * gravity acceleration)

As you have to measure the arrow mass and draw weight and estimate or measure the arrow speed it's probably quicker to use the trial and error approach  .

PS on a side note having just watched Alverez at Lords his brace height (i.e. arrow speed) is so large I'm not sure his bow would be valid for bare bow even without stabilizers.


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## Joe T (Apr 5, 2003)

PPS re the parachuted in equation

The Relationship between Brace Height and Arrow Speed
If you make the assumptions that during the shot the time the arrow is on the bowstring equals the free-free shaft vibration time and that the arrow goes through 0.25 vibration cycles between the nock leaving the bow string and passing the pressure button then you get the relation that the bracing height equals the arrow launch kinetic energy divided by the peak draw force.

For example using data from Dennis Lieu 
A tuned bow system with an ACC 3L-18 arrow had the following measured properties:
Arrow mass 341 grain (23.01 grams)
Draw Force 169N
Arrow launch speed 57.9 metres/second
Using the KE/Draw force method with the above data gives a bracing height requirement of 22.8 cms
The actual measured bracing height was 22.5 cms


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## John_K (Oct 30, 2011)

Just a thought: don't forget to try the entire bracing height range.

When I bought my first ILF set up, I found a sweet spot very quickly at 9 1/2in bracing height (70in bow). Later, the manufacturer of the limbs advised me to try a lower bracing height. I found another sweet spot at around 9in, and gained a hell of a lot of arrow speed. I no longer had to bring my sight all the way in to hit 90m.


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## Greysides (Jun 10, 2009)

If you run with the idea that at an ideal BH the arrow leaves the string cleanly with max energy faster.....

1. Use a chronograph to find the BH with the max speed.
2. At a set distance, aim at the target, chart height of impact against BH. Reset NH with each change before shooting.
3. Use an instrument to measure noise levels. Min noise is max energy transfer.

Another school of thought is that BH is an element of tuning a bow-arrow-archer system and not fixed.


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## HikerDave (Jan 1, 2011)

The owner of our local shop told me once that the tiller bolts aren't for setting draw weight, but that they are used for setting brace height. This statement makes a lot of sense. With a Hoyt formula bow and medium limbs, 5 turns in on the tiller bolts move the bolt 1/4 inch. The limb tips are 20 inches away from the pivot point at the dovetail, so they move 1 1/4 inch out. I think that it follows that the optimal brace height would decrease by this same amount, provided that the arrow was properly matched.

I'm going to try my bow cranked in with a low brace height next time I get out to the range. The bow is already set up for this experiment.


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## dchan (Jun 29, 2004)

HikerDave said:


> The owner of our local shop told me once that the tiller bolts aren't for setting draw weight, but that they are used for setting brace height. This statement makes a lot of sense. With a Hoyt formula bow and medium limbs, 5 turns in on the tiller bolts move the bolt 1/4 inch. The limb tips are 20 inches away from the pivot point at the dovetail, so they move 1 1/4 inch out. I think that it follows that the optimal brace height would decrease by this same amount, provided that the arrow was properly matched.
> 
> I'm going to try my bow cranked in with a low brace height next time I get out to the range. The bow is already set up for this experiment.


The flaw in this thought process is that the string still does not change length so while you will bend the limbs more you will not get 1.25" less brace height. By cranking the limb bolts (or tiller bolts) in all the way, you will change the effective draw weight and thus change the dynamic spine of the arrow and then it's still back to trial and error to find that sweet spot brace height.

Let us know what you find with the experiment.

DC


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## icehaven (Nov 30, 2010)

dchan said:


> The flaw in this thought process is that the string still does not change length so while you will bend the limbs more you will not get 1.25" less brace height. By cranking the limb bolts (or tiller bolts) in all the way, you will change the effective draw weight and thus change the dynamic spine of the arrow and then it's still back to trial and error to find that sweet spot brace height.
> 
> Let us know what you find with the experiment.
> 
> DC


i agree. the distance between the limb tips isn't changing so neither can the brace height.


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## HikerDave (Jan 1, 2011)

dchan said:


> The flaw in this thought process is that the string still does not change length so while you will bend the limbs more you will not get 1.25" less brace height. By cranking the limb bolts (or tiller bolts) in all the way, you will change the effective draw weight and thus change the dynamic spine of the arrow and then it's still back to trial and error to find that sweet spot brace height.
> 
> Let us know what you find with the experiment.
> 
> DC


I will. I forgot to mention that I did make a new longer string in order to keep the bend in the limbs the same. Draw weight which was previously 36 pounds at the high brace height surprisingly only increased to 37 pounds at the low brace height -- these are Border Hex6 limbs that are only gaining about a pound and a quarter per inch out at 30 inches of draw so a different bow would probably have shown a greater increase in peak weight.


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## HikerDave (Jan 1, 2011)

icehaven said:


> i agree. the distance between the limb tips isn't changing so neither can the brace height.


I made the statement that the OPTIMAL brace height will change. Not the actual brace height. I will find the optimal brace height through experimentation. My hypothesis is that the optimal brace height for a bow is less with more preload. I will vary the string length and arrow point weight as necessary to keep the bow in tune.


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## lksseven (Mar 21, 2010)

_"3. Use an instrument to measure noise levels. Min noise is max energy transfer."_

Greysides,

I love a quiet bow. But what I've found lately is that with my current setup, 8-7/8" = super quiet, but 8-1/2" = tighter groups (but not drastically so) and a little more noise (a flat note, not a twang), so I'm putting up with a little more noise. 

So, that brings me to this question - does a flat note indicate slightly stiff, and a twang indicate slightly weak?


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## Greysides (Jun 10, 2009)

That I don't know. Not very good with musical notes. Hank De Thoreau has experimented in that area.

I'd be hypothesising but I wonder if the difference between your BHs is while one is more 'ideal', the other is better due to human input?

For Bareshaft Tuning, a slightly nock high BS is generally preferred i.e. impact below fletched; but whether that impact is best on the slightly stiff or slightly weak side seems to be down to hte individual archer.

I wonder if your BH experience is similar?


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## ksarcher (May 22, 2002)

I've tried that in the past.. It all depends on the string... strand count, number of twist, wax content and temperature... My son is a musician and I have a recording studio and my sound meters can identify actual notes..

Testing the same bow repeatedly of the course of a week, measuring the brace height with a bow square...then pluck the string with a credit card the not changes "flat to sharp" even into the next note sometimes...

I like the idea but rather tune for grouping and bow sound...


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## dchan (Jun 29, 2004)

By all means tune for groups however until you get close to the sweet spot meaning the nock is releasing from the string cleanly, the bow will not be very forgiving to very small form errors. Once your BH is near that sweet spot, then make small adjustments to get the best groups. Reminder that changes in form, good or bad will affect how the arrow releases from the string and where that sweet spot is as far as brace height. It may not be much but I have found it will change.


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## Rick McKinney (Mar 4, 2008)

dchan pretty much as it according to my research. Getting the nock ears to leave the string without any interference is optimal (least amount of noise). Then you can start to tune the bow. If your groups are better when the sound of the bow is louder than it's quietest setting, it means that your bow is not tuned at it's optimal. Yes, it takes time to do this, but once you find it, it is well worth the effort. Also, keep an eye on the brace height:wink: during practice to see if your string stretches a bit. If so, you will want to add a couple of strands to the string to eliminate the stretch. Once you do that, then you will have to retune.....it is never ending but what else do you have to do other than just shoot 500 arrows a day 24/7? :wink:


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## lksseven (Mar 21, 2010)

_"it is never ending but what else do you have to do other than just shoot 500 arrows a day 24/7? "_

Haha - if only!

Here's another question - how much of an impact will 3/8" of center serving make in my tune? I had my local shop center serve a couple of strings for me (to match one I'm shooting now which is shooting great), asked them to match that center serving which is 7-1/8". Well, one of the center servings is 7-3/8", and the other one is 7-7/8". Do I need to insist on both being redone?

After 2-1/2 years of trying to learn everything from big to small that I can, as quickly as I can, Strings are one area I'm only now starting to delve into.


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## Greysides (Jun 10, 2009)

It's very easy to serve a string. Thread, a cheap jig and a scissors are all you need. 

Youtube will show you how. The biggest issue is knowing what size thread to use.


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## dchan (Jun 29, 2004)

lksseven said:


> _"it is never ending but what else do you have to do other than just shoot 500 arrows a day 24/7? "_
> 
> Haha - if only!
> 
> ...


If I would hazard a guess that difference would be like replacing a brass nock point with a tied on one. It will affect the tune..


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## lksseven (Mar 21, 2010)

dchan,

Yes, I think you're right. Sigh .... the first time they served toward the wrong end, so the serving was more of an 'upper third' serving instead of 'center'. So they redid those, but couldn't get the length correct, even though the length requested was written on a tag on each string. Aaaaargh ... guess I'll be learning how to center serve ... under the 'if you want something done right...' hat.


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## grantmac (May 31, 2007)

Serving your own strings is a gateway drug to making them. Both are good things to do if you like to experiment and you want the best you can get.

-Grant


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## lksseven (Mar 21, 2010)

Greysides,

_"It's very easy to serve a string. Thread, a cheap jig and a scissors are all you need."_

Hmmm - a good friend of mine (old college roomie) is a heart surgeon now; he says that "it isn't as hard as it sounds - all you need is a sharp edge, a needle, and some thread." And yet ... 
Well, I'll let you know how it goes. And anyway, it'll give me an answer to Rick's question "what else have I got to do besides shoot 500 arrows a day 24/7?" Answer: Center servings!!!


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## Jim Colgate (Jun 12, 2012)

Hi Rick,
Thanks for posting.
If i can ask what tiller setting do you generally use, and what is your sequence of events for tuning, example Tiller, brace height, nocking point level, center shot, plunger tension, bare shaft, etc 
Thanks
Jim
:aero:


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## HikerDave (Jan 1, 2011)

HikerDave said:


> I will. I forgot to mention that I did make a new longer string in order to keep the bend in the limbs the same. Draw weight which was previously 36 pounds at the high brace height surprisingly only increased to 37 pounds at the low brace height -- these are Border Hex6 limbs that are only gaining about a pound and a quarter per inch out at 30 inches of draw so a different bow would probably have shown a greater increase in peak weight.


The best brace height didn't change with the limbs cranked in. The bow just wants to be shot with more than 8 inches of brace height.


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## rick11743 (Sep 20, 2010)

I thought that the optimum brace height would be the one that provides the best bareshaft tuning, and is within the limb manufacturers recommended range


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