# Brace height effect on arrow spine



## hooktonboy (Nov 21, 2007)

Lowering is usually the way to go - it lengthens the power stroke of the bow a little (the distance the string travels from full draw back to its resting position). Although like most things in archery, experimentation may produce different results ;-)


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## Mika Savola (Sep 2, 2008)

I think you'd weaken your arrow more just by turning limb bolts in a quarter more, than playing with your brace height and probably ending up out of tune...


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## crolla (Feb 3, 2011)

higher=weaker/lower=stiffer


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## Viper1 (Aug 21, 2003)

far -

Raising the BH will -

Weaken the dynamic spine
Slow the arrow speed (slightly) 
Increase the draw weight (slightly) 

Lowering the BH will do the opposite.

Viper1 out.


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## farsight (Apr 8, 2012)

I'm not sure but I think I just got both answers. I would like to agree with viper since that makes sense to me. I still see people however claiming that the increased power stroke of a shorter brace height weakens the arrow more. It also bothers me that OT2, which is fairly detailed software, weakens the projected dynamic spine when I lower the brace height.


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## Sanford (Jan 26, 2009)

Farsighted, it's not hard to test and then there's really no question in your mind. Viper is correct.


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## lksseven (Mar 21, 2010)

Viper is most definitely correct. His book, Shooting The Stickbow (one of the archery world's 'bibles') says so.


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## Bean Burrito (Apr 20, 2011)

farsight said:


> I'm not sure but I think I just got both answers. I would like to agree with viper since that makes sense to me. I still see people however claiming that the increased power stroke of a shorter brace height weakens the arrow more. It also bothers me that OT2, which is fairly detailed software, weakens the projected dynamic spine when I lower the brace height.


I think the shorter brace = stiffer spine requirement in OT2 comes from modelling compound bows


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## limbwalker (Sep 26, 2003)

As usual, Viper is right. 

The other thing that raising the brace ht. does is change the angle of the arrow on the rest, creating an arrow that's closer to centershot, which is another reason it softens the dynamic spine.

So much of this used to be "common knowlege" among traditional longbow and recurve shooters. Things like this were one of the few ways we had to properly tune our bows. Now that target bows are almost infinitely adjustable, and so many spine arrows are available, the fundamentals of setting up and tuning bows shot with fingers are being forgotten. 

John


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## farsight (Apr 8, 2012)

Thanks all for helping to clear that up.


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## Jim C (Oct 15, 2002)

another way to weaken the spine slightly is to use the forward plunger hole. the greater the distance between the arrow's contact with the bow's plunger and the bow string, the more the DynaSpine will be weakened. think of a pencil. If you want to break a pencil in half is it easier to grab it at both ends or put both hands next to each other.

its why a 34" ACE 550 is too weak for a 50 pound recurve but a 26" one is not


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## atjurhs (Oct 19, 2011)

+1 for the Viper


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## farsight (Apr 8, 2012)

Thanks for the reference LKS. 
Just ordered a copy of "Shooting The Stickbow".


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## massman (Jun 21, 2004)

As Jim C points out, "Brace Height" as we measure it has nothing to do with the distance from the hollow of the grip to the string. Rather it is the distance between the plunger and the string that are the tuning points. We use the grib as an easy reference. However when we talk about this or that "Brace height" it really is all relative to the positioning of the plunger in relation to the hollow of the grip.

Modern riser designs has gravitated to a plunger location somewhere close to the hollow of the grip. Not having measured every riser on the market I'd presume that there are suttle variances, manufacturer/riser to manufacturer/riser.

Testing as previously pointed out is the only definative answer to how your bow/arrow combination needs to be adjusted.

Regards,

Tom


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## Viper1 (Aug 21, 2003)

Tom -

Think that goes into the overly splitting hairs category. Since most plunger holes are directly above the throat of the grip and since conventional wisdom is that a stick-on rest (without a plunger, for example on traditional bows) should be placed over the deepest part of the grip, the point becomes moot. 

Further, for any given shooter, the brace height can be any distance on a given bow. For example, if a guy decides that he wants to call "his" brace height the distance from the string to the face of his riser, that's fine, since it will always be a constant on that bow. It won't make any sense when comparing different bows, of course. 

I typically use a marking on the arrow in relation to a landmark on the riser or rest and don't need to pull out a bow square - on my bows. 

Viper1 out.


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## gairsz (Mar 6, 2008)

In this video we adjusted the BH a little at a time from 9 1/4 down to 8 7/8. We needed to stiffen the arrow so it would bend a little faster to help with the clearance away the plunger. You can see the progression, and there was a definite an improvement.


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## Greysides (Jun 10, 2009)

Great video. Thanks.


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## hooktonboy (Nov 21, 2007)

Always here to learn, that's why I visit. Having re-read the Easton tuning guide, I can do nothing but agree with the far more experienced posters - so now you don't have opposing answers  

But the Easton guide (for example) is conditional - there are other changes that go with raising the brace height - suggests you will get increased bow poundage but also a loss of arrow speed, and also suggests that the slight increase in draw weight does not equally compensate for the reduction in the power stroke. Soooo (thinking out loud) - the only certain way to get the result you want is to experiment (in both directions presumably, from your current setting, raising and lowering), until you produce the right result or admit the arrows is the wrong spine and buy some more 



gairsz said:


> In this video we adjusted the BH a little at a time from 9 1/4 down to 8 7/8. We needed to stiffen the arrow so it would bend a little faster to help with the clearance away the plunger. You can see the progression, and there was a definite an improvement.


That's a really interesting video, but I'm not sure that what it shows is that the arrow reaction has been stiffened (in the way I understand it - i.e bends more/less /faster/slower). What I think I'm seeing is a very similar amount of bend in each shot, but the arrow is detaching from the string progressively closer to the button / rest, until you reach a point where the bend happens at a place when it ceases to cause a clearance issue...? I admit it's hard to be sure without measuring...


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## limbwalker (Sep 26, 2003)

Jim C said:


> another way to weaken the spine slightly is to use the forward plunger hole. the greater the distance between the arrow's contact with the bow's plunger and the bow string, the more the DynaSpine will be weakened. think of a pencil. If you want to break a pencil in half is it easier to grab it at both ends or put both hands next to each other.
> 
> its why a 34" ACE 550 is too weak for a 50 pound recurve but a 26" one is not


Great point Jim. Rarely do you ever see the forward plunger hole used for this purpose, but it's there and folks should take advantage of that!

John


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## limbwalker (Sep 26, 2003)

Gary, that's a great piece of work right there. Thanks for sharing.

John


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## hwjchan (Oct 24, 2011)

I do this! Haha... Been using the forward plunger hole for my Nanos because the 830s I have spine a little bit stiff. Definitely helps with weaking the dynamic spine a bit.


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## Sanford (Jan 26, 2009)

Courtesy of Viper1:


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## Gurn (Jul 25, 2007)

So are ya sayin in the video the lower the BH the stiffer ya need??


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## limbwalker (Sep 26, 2003)

Gurn, the lower the brace ht, the weaker arrow you need (or more point weight, or longer arrow).

John


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## kshet26 (Dec 20, 2010)

Based on the image posted above, does that mean that if I have a stiff arrow I could change my arrow from being just outside of centershot to being at true center?


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## limbwalker (Sep 26, 2003)

Maybe not "true" center, but certianly very close to true center.


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## Abriz (Nov 2, 2017)

limbwalker said:


> Gurn, the lower the brace ht, the weaker arrow you need (or more point weight, or longer arrow).
> 
> John


I'm still confused then. Why in the Easton arrow chart does it have you add 5lbs for lower brace height which would be requiring a stiffer arrow for a lower B/H?


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## limbwalker (Sep 26, 2003)

That is referring to compounds.


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## erose (Aug 12, 2014)

I would like to address this again somewhat, from some testing I did this weekend concerning brace-height. I shoot a W&W CXT 25" riser, with the WiaWis NS Graphene 34lb longs. These are 37lbs on the finger at anchor for me.

Over the weekend I did some brace height tuning, under the suggestion of a few books I read, because I just haven't had consistent grouping at 70m like I was expecting. My brace height that I used through indoor season was 232mm, and for indoor I averaged in the 270s; but out to 70m I just wasn't getting very good groupings. At 232mm my grouping was all over the place. So I increased my brace height to 235mm which is what I shot last year for outdoor, and my grouping got better, but when I missed the red/yellow the arrows nearly always drifted left. Even when bareshaft tuning, I noticed that if I had a errant bareshaft it always appeared stiff.

Anyway the books, Simon Needham, _Archery the Art of Repetition_, and Richard Cockrell, _Modern Recurve Tuning_ suggested that adjusting the brace height will affect the release point of the arrow, and that if the brace height was too low that the arrows would appear stiff, and if too high the would appear weak, albeit they were not truly weak or stiff. 

So I decided to see if there was some truth to that. I tightened my string 4 turns which moved my brace height from 235mm to 241mm, checked my tune at 30m, and sure enough my bareshafts shot center to center right of the fletched group. I backed up to 70m and shot a 36 arrow round, and two things happened. 1) When I missed the red/yel the arrows missed right instead of left and 2) my arrow speed increased some I'm assuming, because even though my sight marks didn't change at 18m they did change from 79 to 76 at 70m on a Shibuya. 

I'm going to take two turns out of my string today, and drop my brace height down to 238mm (split the difference) and see what happens today.


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## lksseven (Mar 21, 2010)

erose said:


> I would like to address this again somewhat, from some testing I did this weekend concerning brace-height. I shoot a W&W CXT 25" riser, with the WiaWis NS Graphene 34lb longs. These are 37lbs on the finger at anchor for me.
> 
> Over the weekend I did some brace height tuning, under the suggestion of a few books I read, because I just haven't had consistent grouping at 70m like I was expecting. My brace height that I used through indoor season was 232mm, and for indoor I averaged in the 270s; but out to 70m I just wasn't getting very good groupings. At 232mm my grouping was all over the place. So I increased my brace height to 235mm which is what I shot last year for outdoor, and my grouping got better, but when I missed the red/yellow the arrows nearly always drifted left. Even when bareshaft tuning, I noticed that if I had a errant bareshaft it always appeared stiff.
> 
> ...


Increased brace height will slow arrow speed, not increase it (with the increased brace height, the arrow is now not on the string for as much of the power stroke, thus not gaining that ending bit of acceleration). But the extra twists may have moved your nock point lower, thus increasing arrow elevation angle and overcoming the diminished arrow speed.


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## erose (Aug 12, 2014)

lksseven said:


> Increased brace height will slow arrow speed, not increase it (with the increased brace height, the arrow is now not on the string for as much of the power stroke, thus not gaining that ending bit of acceleration). But the extra twists may have moved your nock point lower, thus increasing arrow elevation angle and overcoming the diminished arrow speed.


When I changed the brace height, I went back and checked nock point to make sure that it didn't change. I'm wondering if there is an optimum efficiency point on (these) limbs that may change this. I was not expecting the results I got to be honest.


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## lksseven (Mar 21, 2010)

erose said:


> When I changed the brace height, I went back and checked nock point to make sure that it didn't change. I'm wondering if there is an optimum efficiency point on (these) limbs that may change this. I was not expecting the results I got to be honest.


How about it, engineering types on here? Along with erose, I'd also love to know if his notion (optimum efficiency point) is a possibility. That would be cool!


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## chrstphr (Nov 23, 2005)

limbwalker said:


> Great point Jim. Rarely do you ever see the forward plunger hole used for this purpose, but it's there and folks should take advantage of that!
> 
> John


Hyejin Chang has used the front plunger hole for at least 5 years. She won Rio doing it as well. She shoots 38 lbs off the fingers. I dont know her arrow spine, but she is able to make 70 meters and have the sight extension all the way out and not bottom out her aperture block.


Chris


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## stick monkey (Mar 9, 2015)

just to clarify... if we lower or raise the brace to compensate for spine issues do we readjust centershot with plunger...Limbwalker, I am well versed in traditional wood risers with a fixed shelf and there the centershot doesn't change...But...with a metal riser cut past center do we adjust plunger centershot or are we leaving the changed departure angle as we would on the wood riser?


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## erose (Aug 12, 2014)

stick monkey said:


> just to clarify... if we lower or raise the brace to compensate for spine issues do we readjust centershot with plunger...Limbwalker, I am well versed in traditional wood risers with a fixed shelf and there the centershot doesn't change...But...with a metal riser cut past center do we adjust plunger centershot or are we leaving the changed departure angle as we would on the wood riser?


The answer to this from my experience is that it depends. Normally I don't have to, but occasionally I do have to. When you make a change to your bow, you should look at it as a process, in that any change may or may not effect the rest of your tune. Draw weight, brace height, center shot and plunger tension are interrelated; and changing one may or may not affect the others.


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## erose (Aug 12, 2014)

lksseven said:


> How about it, engineering types on here? Along with erose, I'd also love to know if his notion (optimum efficiency point) is a possibility. That would be cool!


From other archers that shoot the same limbs that I do, they have given me brace heights between 228mm to 232mm as optimum for them. When I shot at 228mm, my bare shafts were all over the place (mostly left though), just couldn't control them at all. It got better at 230mm and at 232mm I did get more consistency, but I had issues with clearance. Every 3 to 10 shots I would have a mark on the rear of my arrow from the plunger. I also out of about every 30 to 60 shots depending on how good I was shooting, one or two arrows that would jam so hard down on my Shibuya rest that the wire would be pushed in to the point that I couldn't get the next arrow to rest on the wire without having to readjust the wire position. I figured that this was due to me, and have been working on trying to figure out what I was doing technique wise, with little to no explanation. 

Anyway after 4 months of fighting this frustration, and retuning my bow about 30 times with different methods and techniques, I revisited the brace height question, and said hell with it. Lets see what this thing does when I drastically increase brace height. I adjusted it to 235mm, and got better results, but at 70m my arrows were everywhere and I was still getting occasional clearance issues, albeit not as bad as at 232mm. So I went to 240mm and then it was like shooting a different bow. No more clearance issues, and where the arrow grouping was center left before, the new grouping was center right now, but better grouping. When I checked my bareshaft planing, my arrows were actually showing weak, where before, no matter what I did they showed stiff. 

Anyway yesterday I backed my brace height down to 238, thinking that if at 235mm my arrows showed stiff and at 240mm they showed weak, then let's split the difference and see what would happen. But yesterday wasn't a very good day to test, as we were having 25 to 35 mph gusts that were all over the place. So on that part I will get back to you when I have a chance to shoot on a calmer day. 

Anyway, I'm curious on what the optimum brace height for a bow is based upon. Is it due to the riser/limb combination, or just the limbs, or archer's technique, or draw length, or tune, or string, or all of these? Why am I getting more consistency at a higher brace height than other archers?


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## PregnantGuppy (Jan 15, 2011)

lksseven said:


> How about it, engineering types on here? Along with erose, I'd also love to know if his notion (optimum efficiency point) is a possibility. That would be cool!


It's a pretty clear possibility. Let's boil it down to an incredibly simple case and consider only power stroke and draw weight. Increasing brace height decreases power stroke, but it also puts more load on the limbs. Since the total energy going into the arrow is effectively proportional to the product of the power stroke and the peak draw weight, if you assume the draw weight increases linearly with the brace height then you end up with a quadratic expression for the total energy going into the arrow, which has an optimal value.

Of course, that's only two factors, and under very debatable assumptions. But the point is that it is quite unlikely that there _isn't_ an optimal value, since all of these factors interact non-trivially in different directions. Which is why I think it's not really reasonable to ask whether increasing brace height increases or decreases spine; there's way too many factors that depend on many other aspects of the bow, arrow, and shooter to be able to derive a practical answer.


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