# Brace Height and its impact to tuning



## toxoman (Sep 10, 2004)

Disagree with point 2. Physics can't be changed. If you shorten the string (increase brace height) then the draw weight has to go up (unless you draw shorter). The string is shorter thereby causing the limb tips to be pulled farther. Not only is preload higher but full draw weight has to be higher as well.


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## Brandeis_Archer (Dec 20, 2006)

toxoman said:


> Disagree with point 2. Physics can't be changed. If you shorten the string (increase brace height) then the draw weight has to go up (unless you draw shorter). The string is shorter thereby causing the limb tips to be pulled farther. Not only is preload higher but full draw weight has to be higher as well.


Are you telling me that
"You cannot change the laws of physics, Jim?"

But the string angle is changed also, along with the position of the limbs at full draw. You're not only changing one variable. Course, I'm not saying I've tested this myself and that either one of you is right, but it's not out of the question.


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## chrstphr (Nov 23, 2005)

toxoman said:


> Disagree with point 2. Physics can't be changed. If you shorten the string (increase brace height) then the draw weight has to go up (unless you draw shorter). The string is shorter thereby causing the limb tips to be pulled farther. Not only is preload higher but full draw weight has to be higher as well.


yes, but what you are missing is the limbs can not go back beyond the preload so you are shortening the cast of the limbs and equalizing the change in brace height. 

and the way i explain it is you have a 60 inch bow with normal string. it will cast a certain distance and the beginning pull will be light. now put a one foot string on it. the limbs will be preloaded all the way back to one foot and look like a U, but they wont be able to cast very far. What has gone up is the pre load, but not the real poundage as the one foot string wont cast the arrow very far, since the limbs are prevented from moving by the shorter string. 

this is an exaggeration of course.

if i draw 28 inches, it doesnt matter where the tips of the limbs start, its still only to 28 inches and to the poundage at that. its the bottom of the limb angle that changes the poundage, not the tips. Pre load and nothing to do with cast or poundage. 


also i would put out that the high speed compound bows all have shorter and shorter brace heights, the brace heights are not increasing. 

Chris


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## gig'em 99 (Feb 1, 2008)

I appreciate the feedback gentlemen!

I won't argue with physics. But, we're talking fractions of an inch in the final locations of the limb tips. So for the sake of the descriptions, the impact to real draw weight is miniscule, or fractions of a pound. Possibly more if you went from say 8.0" to 9.5"...but that is a pretty extreme jump in brace height. But really, this is intended for general tuning understanding. When an archer is adding/subtracting 4 or 8 twists, it could easily impact the brace height by 1/8" to 1/4". But that isn't going to perceptibly change the draw weight.

So, maybe rather than me saying that brace height does not change draw weight, a better description would have been "not significantly."


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## c3hammer (Sep 20, 2002)

gig'em 99 said:


> I see very often, that there is a common misconception regarding brace height   <SNIP>
> 2. Does increasing brace height mean that the poundage is heavier? No, it does not. If you do not change the limb bolt, the poundage will remain the same by adding or removing twists. All you've done is change the pre-load on the limbs at rest. But the amount force that builds in the limbs will be the same once you get to your draw length.<SNIP>


This is completely false. Shortening the string to get a higher brace height changes the poundage by shortening the distance from the nock to the limb tip at full draw, thus increasing the bend of the limbs which increases the poundage.

Your post also completely ignors the most important aspect of brace height. That being at what angle the nock leaves the string at the end of the first bending cycle.

Setting of brace height is exclusively a process of finding the spot where the nock leaves the string with little or no sidways force. All other factors of brace height pale in comparison of import to this function.

Cheers,
Pete


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## Seattlepop (Dec 8, 2003)

*You betcha*



toxoman said:


> Disagree with point 2. Physics can't be changed. If you shorten the string (increase brace height) then the draw weight has to go up (unless you draw shorter). The string is shorter thereby causing the limb tips to be pulled farther. Not only is preload higher but full draw weight has to be higher as well.


Agree, if you shorten the string and keep the draw length the same, the limbs have to bend more to reach the DL. And here's the proof: I just measured the holding wt on my set-up w/ the Easton digital and got 39.4#. I added 10 twists and repeated the holding wt test and immediately got an increase to 40.1#. 

Gig: I otherwise thought your description of the effects of changing brace height on tuning quite good.

5c


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## gig'em 99 (Feb 1, 2008)

Seattlepop said:


> Agree, if you shorten the string and keep the draw length the same, the limbs have to bend more to reach the DL. And here's the proof: I just measured the holding wt on my set-up w/ the Easton digital and got 39.4#. I added 10 twists and repeated the holding wt test and immediately got an increase to 40.1#.
> 
> Gig: I otherwise thought your description of the effects of changing brace height on tuning quite good.
> 
> 5c


Great that you did the digital scale...I hope that maybe you did it a few times for an average...but I think that you helped prove my second post, which was for general tuning, a few twists will have a fraction of a pound impact. So on your set up, it was .7 pounds with 10 twists...did you check to see what impact the 10 twists did to your brace height?

I'll then add that even if we're talking a full pound, which I venture to guess would take a lot of twist, and a significant change in BH, generally you'll still be within the arrow's recommended draw weight ranges.


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## Old Sarge (Sep 9, 2008)

Wow! Never knew that brace height was so technical or controversial.

I do know that after my post yesterday I went from a brace height of 22.5 cm to 23.5 cm and my bareshafts stopped showing stiff and impacted with the fletched shafts every time. In the 40 years I've been shooting I had the direction to twist the string backwards the entire time. Somehow though I always managed to get all the bows I've owned to shoot well but it was truely only a matter of trial/error, and apparantly dumb luck. After reading all of the above posts it seems that there is still some debate about why or how it works. At this point I'm just happy it does.


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## chrstphr (Nov 23, 2005)

Seattlepop said:


> Agree, if you shorten the string and keep the draw length the same, the limbs have to bend more to reach the DL. And here's the proof: I just measured the holding wt on my set-up w/ the Easton digital and got 39.4#. I added 10 twists and repeated the holding wt test and immediately got an increase to 40.1#.
> 
> 5c


yes you have gained a slight amount of poundage at full draw but you lost limb recoil so it evens out. the limbs cant go back to rest as far as when it was 39.4. reduced cast, you need higher poundage to equalize. 

chris


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## toxoman (Sep 10, 2004)

Old Sarge said:


> I do know that after my post yesterday I went from a brace height of 22.5 cm to 23.5 cm and my bareshafts stopped showing stiff and impacted with the fletched shafts every time. In the 40 years I've been shooting I had the direction to twist the string backwards the entire time. Somehow though I always managed to get all the bows I've owned to shoot well but it was truely only a matter of trial/error, and apparantly dumb luck.


So from the outside looking in, this means that you raised BH and got more velocity from the shaft. (Went from stiff to perfect). Isn't this is the opposite of what g99 postulated?

Perhaps they weren't stiff at all. I think that you went from a badly tuned situation, where the nock was not releasing from the string cleanly, to a situation where the nock released cleanly.


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## chrstphr (Nov 23, 2005)

or now he doesnt have contact and his arrows have better clearance since he raised his brace height. 

Chris


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## Old Sarge (Sep 9, 2008)

Toxo, 

No, in his reply to me yesterday he said to increase brace height since it made the spine effectively weaker. That's what I did and the arrows shot much weaker than before and corrected the problem. It sounded backwards to me also but when I increased the brace height it worked. 

Viper1 also mentioned that he thought the arrows were to stiff for my set up but didn't the brace height issue. 

Whatever happened it worked.


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## gig'em 99 (Feb 1, 2008)

toxoman said:


> So from the outside looking in, this means that you raised BH and got more velocity from the shaft. (Went from stiff to perfect). Isn't this is the opposite of what g99 postulated?
> 
> Perhaps they weren't stiff at all. I think that you went from a badly tuned situation, where the nock was not releasing from the string cleanly, to a situation where the nock released cleanly.


No, I'm sorry. His post proves my point exactly. His arrows were impacting left, which is indicative of a stiff spine for a right handed shooter. A few of us recommended him increasing his BH to weaken the shaft, or move the bareshaft to the right. He increased the brace height and voila, now his bare shafts are grouping with his fletched arrows.

Christopher rightly describes this as cast shortening. Which in my initial post, I described as the duration of acceleration. This duration is now less on his set up, so he is getting less velocity, a weaker and better tuned arrow.


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## toxoman (Sep 10, 2004)

Physics has to prevail. If arrows are truly stiff, the way to "weaken" them is to put more energy into them (there are other ways but that's not what we're discussing). If you put more energy into a shaft and don't change the mass of the shaft, then you are making them faster, NOT slower. Therefore, if his shafts were truly stiff, raising the BH would have increased his speed.

I contend that they weren't stiff at all, but instead, severely mistuned.


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## cc46 (Jan 22, 2005)

this is how i think of brace height

Most important is to find the sweet spot for the string position so that when the nock leaves the string it avoids hitting the bow.

and
--a low brace height means lower preload of the limbs and lower poundage at draw
--a high brace height means higher preload of the limbs and higher poundage at draw
but because the brace height moved from say 8" to 9" then the power stroke is 1" shorter
and
The energy delivered to the arrow may be the same or it may not. This is what determines the velocity.

But who cares about that. It's the tune you want. Funny the word "tune" is used, the sound of the bow is very telling. Some never measure brace height, just tweak the string...probably muscians in a past life...ok g2g i'm trying not to think too much...cheers


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## Old Sarge (Sep 9, 2008)

Not being an expert of any kind I can't argue the laws of physics but I know my arrows are flying better. I really don't think the set up was that much out of tune because I was right in the middle of the mfg recommended brace height to start with and if I only shot fletched arrows the groups were good and the flight was straight. It was only the bareshafts that shot poorly. I did increase the point weight 25gr. which also had some impact. Normally when I tune I only adjust one factor at a time but yesterday I was getting so frustrated I changed both the point weight and brace height at the same time.

Because of that it's hard to say which had the bigger impact but both were positive and should have weakened the shaft.


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## gig'em 99 (Feb 1, 2008)

Well I went to my archery shop and had my bow tested 4 times. Twice at 8.25" brace height, and twice at 9" brace height. Now they didn't have a digital scale, they have a spring scale, but it is in 1 pound increments. In order to make the .75" of change it took me 30 twists.

Here were brace heights and corresponding draw [email protected] 8.25 = 1. 44 lbs, 2. 44 lbs, @ 9" 1. 44 lbs, 2. 44 lbs. 

Now, I'll accept that spring scales accuracy is difficult to measure to the 1/10th pound level...but based on the above, a 3/4" difference in brace height didn't have more than 1/2 pound of impact to the draw weight. So, based on this and the one other test that was posted here, and trying to take into account that different set-ups will respond differently, the difference in draw weight is negligible.

Regarding the physics of all of this, I'm not an engineer and I don't claim to be. But archery publication after archery publication agrees that a shorter brace height increases velocity, and a higher brace height decreases velocity. This isn't a new idea that I just drummed up. There isn't even any discussion about this amongst the elite in archery.

In the end, the general ideas presented in my opening quote are good for the beginning and intermediate archer, and those items are what generates the nock position at departure. But this was never intended to be a discussion on the intricacies of archers paradox and brace height. Just a basic discussion about this very misunderstood topic.


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## toxoman (Sep 10, 2004)

Perhaps this can make it more basic and maybe we can agree on this:
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If your arrow is acting stiff, raise the brace height.

If your arrow is acting weak, lower the brace height.

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As for the reasons the above is true, well, we'll just have to agree to disagree. 

(For now, we'll just ignore all the other things one can do to change dynamic spine.)


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## jwalgast (Aug 7, 2005)

As Pete said:

Setting of brace height is exclusively a process of finding the spot where the nock leaves the string with little or no sidways force. All other factors of brace height pale in comparison of import to this function.

This is what all the books teach us. But to me, finding the correct brace height is a matter of trial and error. My question is "is there a scientific way to find the exact brace height?????"

John


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## gig'em 99 (Feb 1, 2008)

Most of the items discussed with regard to my original post are the back ground that gets us to when the nock leaves the string. 

I'll quote Kisik Lee in "Total Archery" page 187 and 188, chapter 10-2-d "...as basically the brace height determines when the arrow nock will leave the string at a certain point in the arrow's bending cycle." He then goes on to explain how the sound of the shot is a good indication that the arrow is leaving the string at the correct time, and that "A high or harsh sound is usually an indication of incorrect brace height or an incorrectly spined arrow."

The previous points that I make, lead to the arrow leaving the string at the right time. If the brace height is too high and shaft too weak, the lateral force imparted on the arrow by archers paradox (recurve), will not be dealt with efficiently. The opposite is also true. If your spine is stiff (and not too stiff), you can increase the brace height to accomodate. Thereby effectively weakening the spine and allowing the arrow to leave the string at the appropriate point to allow for a proper tune.

Gentlemen, with the exception of a negligible difference in draw weight due to an adjusted brace height, we are all in agreement here. Brace height is extremely important to good performance, and this is the reason I started the thread. Too many times on this forum, people are shooting stiff and lowering their brace height with no success. Hopefully threads like these will give them the proper guidance they need to solve their issues.


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## Stans_Recurve (Dec 4, 2006)

I bought a digital fish scale for ~$25.00. Not only is it good for weighing fish, but it can answer brace height difference questions. Pretty good deal for that amount of cash relative to the price of a dozen arrows. 

Increasing brace height increases the draw weight at constant draw length. The higher poundage acts to make an arrow behave 'weaker' at release. But, the velocity is less because the arrow has less time in contact with the spring. 

Conversely, lowering brace height reduces the draw weight for a constant draw length. The lower poundage acts to make an arrow behave 'stiffer' at release. The velocity goes up compared to a higher brace height because the arrow is in contact with the string longer. 

So, to confirm these statement one needs a digital fish scale, a chronograph, and the ability to shoot groups. I have confirmed the above, but don't take my word. For $150.00 and some persistence you too can find out an answer to these mysteries!

But, as mentioned before, the best brace height gives the lowest vibration and cleanest arrow release. The only way I know to find this is by shooting at various brace heights.

Stan


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## omega_archer (Aug 25, 2008)

Turns out my bow was shooting really weird the last two days. At 18 m my groups were non existent and my bareshafts were going way right (I'm a lefty). To make a long story short, the brace height was off by 0.75" and I didn't check it when I assembled the bow. Made all the difference in the world. I guess you're supposed to check it every time you assemble the bow eh.

Sorry to beat this to death but I'm sort of an engineer and in order for the draw weight to change, something physically needs to be different at your "normal" full draw. When you change the brace height you only change the preload on the limbs and starting point at which you draw, nothing more (I am not considering arrow release here). The draw weight physically can not change at same full draw because the pivot points are fixed and nothing has changed. My 2 cents.


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## ZephyrSoul (Nov 12, 2007)

Funny, can't seem to re-edit my last post. Anyway, I originally posted some calculations but realised I made a mistake in it and have editted it here.

Its simple math if you make a few reasonable assumptions.

1) The draw weight at full draw is proportional to the angle the limbs are pulled back to.

2) The string doesn't stretch appreciably as you draw.

Draw a diagram of the top half of the bow as a simplified schematic i.e. a right-angle triangle with the limb as the hypotenuse, brace height as base and half the string length from top limb tip to nocking point as the vertical.

Setting first condition as:
brace height = 9"
half string length = 33"
Length of limb from pivot to limb tip can be calculated as 34.21"
At 28" draw, calculate the angle between the arrow and the limb (Theta) using:
A^2 = B^2 + C^2 - 2(B)(C)cos(Theta)
You get Theta as 63.1 degrees.

If brace height is reduced to 8.25",
Half string length is calculated to be 33.2"
Using the same calculation as above, Theta at full draw has been increased to 63.59 degrees. Meaning the angle between the limbs and the arrow is bigger. i.e. the limbs are not bent as far back and draw weight at full draw HAS decreased with the decrease in brace height.

Edit: But as for how big of a change it makes to the full draw weight, that's another matter. =)


And yes, I was bored.


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## omega_archer (Aug 25, 2008)

ZephyrSoul said:


> Funny, can't seem to re-edit my last post. Anyway, I originally posted some calculations but realised I made a mistake in it and have editted it here.
> 
> Its simple math if you make a few reasonable assumptions.
> 
> ...


Agreed, I guess I should have stated "significant" changes in the setup. As you noted a decrease in almost half an inch (0.2*2) only changes the draw angle 0.5 a degree.


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## bis (Feb 2, 2005)

Just in case you haven't seen this ... http://www.goarchers.org.uk/mechanics/
go on Bow Mechanics, than Bracing Height.


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## Vittorio (Jul 17, 2003)

It seems everybody forgetting that the brace height is not a parameter that can be changed by itself without changing all other parameters involved.
Supposing we are talking about a perfectly tuned Olympic style recurve bow for a certain arrow, with a certain sytring, following parameters are interrelated:
- Tiller
- Poundage
- Button position
- Button spring precharge
- Angle of the arrow to the rest
- Nocking point
- Brace height
- Position of the cliker
- Masses and distribution of them on stabilizers 
- Point of pressure on the grip

A tuned bow has found the best possible interrelation among all above settings, but everytime you change one of them, some or all others can be effected in different amount. 
The matrix of adjustement coming out from all possible combinations is sometime so complicate that explains why nobody has been able to write the final "Bible" for tuning, yet. 
Think to add to the matrix all parameters of the possible arrow spine and its spine distribution ober its lenght, as well as all parameters of the different draw curves of different kind of limbs, and the relationship of your specific draw lenght to your specific pair of limbs, and understnding interrelations among parameters may bring to a nightmare. 
In THA I have clearly explined that the approach to tuning, even to fine tuning, has to be done considering several parameters as costants and forgetting about them until there is aneed to touch one of them to correct situations thta can't be corected in other way. 
One of the parameters I suggest to consider as a constant, in addition to my standard suggestion of using zero tiller, is the brace height. You decide it, check it with maximum precision every time, and you tune considering it a constant. 
But, reading all coments above, I can see that many of them are false or true depending from the real parameters involved. 
For instance: 
- poundage is ever incresing with brace height, but depending from the draw length involved, increase can be negligeable. Surely increases if you are close to the stacking, but may also show almost nothing if you are in a flat area of the drawing curve. 
- Speed can only increase shortening brace heigth if you are going to be close to perfect tuning by that change. Otherwise, arrow speed may even decrese (perfect tuning is the one that looses less energy on the botton)
- Increasing brace makes the arrow acting weeker because of the different angle of the first bending, ant it should come out from the bow slower, but again, the speed can instead increase if the angle becomes better than the previous one
- Each change in the angle of exit because of the change in brace is related to the pressure of the botton, its position and the relative angle of the rest. It means that you can change instead one or more of the other parameters to get the same result (as we all know), so why to act on the brace?
- Finally, the brace is interrelated witht he vertical stability that is interrelated with the tiller, the pressure point and mass distribution... 

OK, I'm already dropping into the infinite matrix... time to stop...


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## gig'em 99 (Feb 1, 2008)

bis said:


> Just in case you haven't seen this ... http://www.goarchers.org.uk/mechanics/
> go on Bow Mechanics, than Bracing Height.


bis - That was a very interesting article, and thank you for posting that link. It certainly parallels my original post on many levels.

I want to thank everyone again for their input, as this has become a very informative thread. And I'll say one more time, that my intent was never for this discussion to get into a level of advancement that the novice and intermediate archer gets discouraged from learning about brace height. Only to help that archer understand the basics of what is happening to the arrow at different brace heights, all other parameters being constant on their specific equipment set up. It is difficult, to say the least, to boil down a complex topic into a general understanding for everyone.

Vittorio is correct, that the interrelation between brace height and all other equipment settings is quite complex, and yes an entire book could be written about it, but this is not the place for that book to be written.

I think that I should have titled this thread "Brace Height and its effect on Dynamic Spine". That might have been a clearer description of what I was intending to discuss.


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## Arrowinten (Apr 9, 2009)

*Brace hight*

I have made the following test while shooting at 70 m:
- set brace hight at 23 cm
- shoot 2 ends
- decrease brace hight by 2 twists
- shoot 2 ends etc.
I got to 22,6 cm and the groupings were constantly the size of the 8-7 ring. I decreased another 2 twists and the group got smaller; then I decresed another 2 twists and I grouped all 7 of 9 arrows in the gold, very close to eachother. So, I can say that 4 twists in the string decreased the goup from the size of the 7 ring to the size of gold.

Did any of you experienced such a change?


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## midwayarcherywi (Sep 24, 2006)

I have not been so diligent about brace height tuning. All though seeing your results, I'd better get at it! 
I think I've gone for a quiet set up with brace height and fine tuned with nock height and plunger pressure.
The truth be told, I don't believe my consistency at 70m is at the point where I could discern if the difference in my groups were due to a change in BH.
I'll not be so lazy as to not give it a go though!


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## Greg Bouras (Nov 17, 2006)

gig'em 99 said:


> I see very often, that there is a common misconception regarding brace height and its effect on arrow spine. So I'm starting this thread to hopefully set the record straight.
> 
> 1. What does increasing brace height mean exactly? Depending on your view, it is either the measurement between the string and the pivot point on the grip, or according to my view, the measurement between the string and the plunger. I prefer to measure to the plunger, because it does not move, if you change grips. And, it is the true span of contact points when the arrow departs the string. You'll all agree that many risers have a forward and rearward plunger location. If you move to the forward plunger, you will weaken the spine...In effect by increasing the brace height.
> 
> ...




The original question you poised you did not answer. How does brace height effect arrow spine?

For a very good treatment of this subject see 
http--www.tap46home.plus.com-mechanics-

Mr. Vittotio was kind enough to share this link with all several weeks ago when he replied to a F.O.C. discussion.


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## Viper1 (Aug 21, 2003)

Guys - 

Pete posted this LAST year. It was correct then, and to the best of my knowledge, still is. 



c3hammer said:


> This is completely false. Shortening the string to get a higher brace height changes the poundage by shortening the distance from the nock to the limb tip at full draw, thus increasing the bend of the limbs which increases the poundage.
> 
> Your post also completely ignors the most important aspect of brace height. That being at what angle the nock leaves the string at the end of the first bending cycle.
> 
> ...


The last point has to do with (dynamic) arrow spine. As Vittorio said, you change one parameter, and everything else technically changes - the trick is to find the best compromise.

I'm also a little surprised that folks are find a couple of MM's in brace height (or less) making noticeable differences. Something is amiss. Like being at one end of the spectrum or the other vs. close to center.

Viper1 out.


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## gig'em 99 (Feb 1, 2008)

Viper1 said:


> Guys -
> 
> Pete posted this LAST year. It was correct then, and to the best of my knowledge, still is.
> 
> ...


The intent of this thread, when I started it, was to give a basic understanding of brace height to newbies. Prior to my post last year, and frankly even since, I've seen numerous posts where people argued that increasing the brace height would STIFFEN the dynamic spine and lowering would WEAKEN it. Or increasing the brace height adds to poundage and therefore must increase speed, or the opposite. These statements are not true.

Greg, right in between items 1 and 2 in my original post, I answered the question. "More twists = higher brace height, therefore a weaker spine and visa versa."

Pete's old post is correct, from a mathematical standpoint. But in practice, small changes in brace height up or down, do not make enough of a a draw weight change to be concerned with. I wasn't the only one to post on this thread with actual tested data that illustrates that point quite nicely. Measurements within a 1/2 pound are within margin of error on almost any normal commercial scale, and you'll get that type of ranging data without ever touching the brace height. But I will add or concede that small changes in brace height on bows under 68" are more noticeable than the same changes on bows 68" and up. But we're digging in, and possibly confusing beginners.

I still stand by my original post, as good for a beginner to start with. But since this thread has gone far beyond the general newbie's understanding...

In fact, when you read Joe Tapley's descriptions and review the draw force curve diagram, you'll clearly see that any mathematical increase in draw weight is completely negated by the loss in draw force from the increased brace height. So you lose draw force, but still dynamically weaken the spine. This is why people get confused. This is also why I tried to simplify the concept for the newbies. It isn't that there is a mathematical (and fractional at that) increase in draw weight that leads to the subsequent weakening in the dynamic spine of the arrow. Which could be easily misunderstood to be true, for a beginner.

On to a more advanced level, as Vittorio and others points out correctly...far more is impacted by a change in brace height. This is why a couple MM change in brace height (1/8" is 3MM) absolutely can and often will make a big difference in groups at 70M+. Nothing is amiss in that statement. Certainly not on an Olympic style set up. This is where a significant discussion of the bending cycle of the arrow comes to play, as well the interrelation of all other components. For example, a couple mm change upward in brace height, given an archers particular set up, arrow, release style, plunger button tension, nock height etc..may actually increase the arrows speed.:mg::mg::mg: How is this possible if increasing brace height reduces the amount of draw force? Well, that very small change would decrease draw force mathematically, very slightly. But because of the point at which the arrow leaves the string, a higher percentage of that energy under the draw force curve could be transferred into the forward motion of the arrow. (ie, it leaves the string at the perfect time in its bending cycle) This could even be measured by an additional 1 - 2 FPS or so on a chronograph. The opposite could also be true. But this is because the archer is fine tuning. By now, they better have the right arrows for their draw weight, they'll already be at or very near the correct brace height, and hopefully they are VERY consistent in their form.

In the end, the science and math behind all of this only has a limited value. As soon as you add a human variable into the equation, it can make the math almost worthless. For example, the 4MM change in brace height might have been exactly what the bow needed...or it could have been exactly what the archer's confidence needed. Either or both, in the end having a positive or desired effect.

Gig'em


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## Viper1 (Aug 21, 2003)

gig - 

Not sure what you're point is, but for the sake of _beginners_ you're trying you're trying to help, here's the deal:

Increasing brace height

1. Increases draw weight
2. Softens dynamic spine
3. Decreases arrow speed

Decreasing brace height

1. Decreases draw weight
2. Stiffens dynamic spine
3. Increases arrow speed

The extent to which any of these actually factor in is directly related to the magnitude of the change being made. 

The rest really is a waste of time by making things more complicated than they have to be, IMHO of course. 

Viper1 out.


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## gig'em 99 (Feb 1, 2008)

Viper1 said:


> gig -
> 
> Not sure what you're point is, but for the sake of _beginners_ you're trying you're trying to help, here's the deal:
> 
> ...


Viper1, I don't disagree with you...I guess my point is this...

The change in draw weight due to normal brace height adjustments is normally so miniscule, stating that it increases/decreases draw weight only leads to confusion. For all practical purposes, the change in draw weight is imperceptible. Now, I'm NOT talking about changing a 68" bow from 5" brace height to a 10" brace height...that of course would be quite perceptible. But for the sake normal adjustments, say 3/8" in either direction, within the recommended range, draw weight really isn't a factor that is big enough to list or be concerned about. So I modify the list to read:

Increase brace height
1. Weakens dynamic spine
2. Slows the arrow

Decrease brace height
1. Stiffens dynamic spine
2. faster arrow

Everytime I've talked about draw weight and brace height with a beginner, it always leads to, "well if the draw weight goes up, then the arrow has to go faster..." The ensuing conversation, is never a fun one. And "Trust me...increasing the brace height slows the arrow" for some reason is a difficult concept for many to grasp. As everyone has an aversion to "Because I said so" type comments. :wink: I'd bet you can relate to that. 

My original post was an attempt to explain, in a simple way, why the above list is true. As I said before, I wish I had titled this thread, "Brace height and its impact to dynamic spine." I also wish that I'd just left item 2 out of my post altogether. As the marginal increases in draw weight are negated by the reduced overall energy under the draw force curve.

Gig'em


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## Viper1 (Aug 21, 2003)

gig - 

We are definitely saying the same thing. 

And yes, of course minor changes in brace height will be imperceptible without a very good bow scale, and I think we've both been in that situation trying to explain it to a new shooter. I do however use a fairly large jump, like the one you described and a bow scale to prove the point when necessary 

I do think that not stating the draw weight factor can and has lead to misconceptions concerning basic Physics (as can be seen in the above post). I use it as an alternate meaning of the "archer's paradox", ie more weight, but less speed. Most people I've worked with do get the principle, if you take the time explain it/demonstrate it. It's doesn't take that long - so it's worth a shot, at least in my teaching experience.

I do like to keep it as simple as possible though 

Viper1 out.


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## Jim C (Oct 15, 2002)

toxoman said:


> Perhaps this can make it more basic and maybe we can agree on this:
> ---------------
> If your arrow is acting stiff, raise the brace height.
> 
> ...


a higher brace height makes an arrow react weaker not because of more poundage but because the the distance between the nock and the plunger increases


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## alish (Jan 31, 2018)

I know this is a very old thread, but just thought I'd add some additional real-world data for those trying to understand how brace height can change the dynamic spine of an arrow. I increased my BH from the lower sweet spot (based on sound and vibration on the hand) of 8 1/2" to the upper sweet spot of about 9 3/16". Long limbs on 25" riser, 29 1/8" DL, 34.5# OTF, RH archer. No significant difference in DW with the change in BH (<1/2# on a digital scale, measured twice); but my bareshafts went from hitting about 4" right of my fletched group to hitting 14-16" right of my fletched group at 18m. And my fletched group size increased compared to what I had been shooting previously (even though the higher BH might be more forgiving of slight inconsistencies in release / finger tension due to shortened arrow contact time with the string).

So I guess the standout point for me was that although there is a mathematical increase in DW as BH increases (as shown in an earlier post), for my DL on a 70" bow the DW was minimal enough that dynamic spine would not be impacted. Yet, the dynamic spine of the arrows was significantly weakened by the increase of 11/16" in BH. I'm going to play around with adjusting by a couple twists each direction because there is the tiniest bit of vibration that I didn't have at the lower BH. And as has been pointed out, this may be slightly contributing to the arrow being pushed off-line due to lateral pressure on the nock as it breaks contact with the string. However, the limbs are far from out of tune with regards to BH (based on sound and hand feel), so I feel confident that the major rightward shift in bareshaft impacts is (almost) entirely a result of the increased BH weakening the dynamic spine. 

This would also suggest that, as most tuning guides say, determining the right BH should be a very early step in the tuning process, with tuning arrows to the bow being a later part of the process. Until now I didn't realize just how much the order of the steps in tuning could effect the process and result. Intuitively the order made sense, but seeing the data really hit it home for me.

[Just a side note, to achieve the higher BH I bought a new string because my other string already had a lot of twists in it, so the results are not due to the string itself (e.g. the lower BH having too few twists, or the higher BH having too many twists). Nock height was maintained constant with the new string (9/16" on both strings), and this was supported by no vertical shift in bareshaft impacts.]

I hope there will be more posting of real data on AT, and a little less opinion. I love the AT community, and have gotten a ton of helpful info from folks here. But so often I have to read through a lot of contrasting, unsupported opinions and dogma to find the helpful data / facts. One of the many reasons for the Koreans' high level of success is that they are very data driven. Let's emulate them in that regard...

Aaron


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## lksseven (Mar 21, 2010)

Moving plunger to forward hole doesn't increase the brace height (which is truly just a representation of the power thrust travel and the point in space where nock/string separation occurs), but it does change the arrow angle against the rest, thus encouraging a 'weaker' arrow presentation/behavior.

Increasing brace height (more twists) will increase preload OTF at full draw (shorter string). But also, as Chris pointed out, a shorter power thrust, so you actually lose arrow exit speed at nock-separation-from-the-string. In most circumstances, that's the worst of both worlds.

At outdoor distances, for many archers, increasing an extra inch of brace height to accommodate/compensate-for a 'too stiff arrow' results in losing a few fps and often times means the archer does not now have enough cast to aim at the middle and hit the middle. 

As many have said, brace height tuning is ideally about finding that perfect distance at which the nock separates from the string at an effortless angle such that the arrow 'wants' to go straight to the bullseye. A couple of twists can truly make a noticeably difference in a bow setup's forgivability


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