What effect does changing brace height have on tuning? I saw a byron Ferguson video and he was tuning his arrow flight by changing brace height but didn't give a good explanation on what raising and lowering does . Can anybody fill me in?
Raising the brace height will make the arrows act weaker, and lowering the brace height will make the arrows act stiffer. It can be used for minor tuning, but I prefer to find the best brace height for each bow arrow combination. (least vibration), and then bare shaft tune. That is what works best for me.
A weak shaft can be tuned stiffer by increasing brace height and a stiff shaft can be weakened by decreasing the brace height. This is fine tuning to me after getting the best arrow combo that I can come up with. It has to be really close before changing brace height factors in for me.
By tuning this way it is possible to get better arrow flight but the sweet spot of the brace height may be affected causing more noise.
As an exaple I shoot 195 gr field points and 195gr magnus 1 broadheads. They both weigh the same but if I have the string set up for my broadheads to hit dead center in my 3D vitals the field points will shoot slightly weak and impact in the right hand side of the kill zone.
To get the field points to hit dead center I have to put two twists in the string and that will put my field tips dead center in the vitals.
QuoteOriginally posted by Friends call me Pac:
A weak shaft can be tuned stiffer by increasing brace height and a stiff shaft can be weakened by decreasing the brace height. This is fine tuning to me after getting the best arrow combo that I can come up with. It has to be really close before changing brace height factors in for me.
By tuning this way it is possible to get better arrow flight but the sweet spot of the brace height may be affected causing more noise.
As an exaple I shoot 195 gr field points and 195gr magnus 1 broadheads. They both weigh the same but if I have the string set up for my broadheads to hit dead center in my 3D vitals the field points will shoot slightly weak and impact in the right hand side of the kill zone.
To get the field points to hit dead center I have to put two twists in the string and that will put my field tips dead center in the vitals.
Duh! ............ Now that's and idea that I never thought of. Thanks, PAC
Heh--
Only three posts and you get to see the great brace height debate exemplified.
I'll go ahead and throw mine in:
Raising brace height weakens the arrow, and lowering the brace stiffens the arrow. The simple explanation is that yes, the lower brace height imparts more velocity to the arrow, but the higher brace height bends the arrow around the riser more easily.
Byron will tell you the opposite, as will the 50% of shooters who believe that to be the case.
For once everyone got it right - let us celebrate!
Raising the BH stiffens the arrow, lowering it weakens the arrow. Pac is right on with this.
Thanks guys.Man I learn so much on here. This site shortens the learning curve a lot.
Why does lowering the BH weaken the arrow?
OK here is the real answer - If you reduce the brace height (causing the arrows to increase speed) it will require a weaker spined arrow and vice-versa. Shooty1 answered it correctly - kind of like moving the plunger in and out (makes it weaker the farther it has to go around bow) If you don't believe me try it for yourself. Take your tuned bare shaft and raise your brace height by 1/2" - shoots weak - longbow shooters will notice it more than center shot recurves - it is what it is. And I have only been shooting traditioal for 4 years - man I'm a quick study!
JOJOTATER - it doesn't
Good job Shooty1 (Dan)
OK we have two different opinions. I started a thread a while ago asking why Byron Fergusons brace height is so high. I got no satisfaction out of the answers at all.
Point of fact - Byron is a trick shooter; he shoots better than most of us here; and look at the brace height of his bows. When he puts on an arrow the fletch comes no where near the back of the bow; the string hits about three inches from the inside of his elbow; he hits his hat with the string every time he draws back ----
If two twists make a bow shoot better; then a newer string still stretching could throw off your shooting really bad.
And using a specific brace height might mean nothing at all - it may come down to tuning your bow by adjusting your brace height until the arrow shoots perfectly.
If we came to that conclusion; seems like we could toss out half the tuning threads on record.
WHY is it that Byron has a longer brace height; and can out shoot everyone?
If two twists make it perfect; what would three do; and what would ten twists do: compared to 12?
:help: :confused:
I disagree with some. Raising BH will make your bow gain poundage which in some cases will weaken an arrow (to a point) because now, you have lost power stroke. Its a give and take balance. At some point raising BH stiffens an arrow.
Think about it, your at full draw, holding effectively 60lbs, what would happen if you shortened the string at that point .5"? Your making your limbs bend more and raise poundage. That inpulse right when you let go of the string is greater that point. But your stroke is less.
Raising the brace shortens the power stroke and gives less energy to the arrow, therefore it acts like a stiffer arrow. Lowering the brace increases the power stroke and provides more energy making the arrow act like a weaker arrow. Those of you familiar with a draw force curve will understand a low brace will allow more energy to be stored in the bow, a high brace will allow less. The area under the curve is the energy stored. Less energy stored in the bow less energy provided to the arrow. Less flex as the arrow is shot makes it act like a stiffer spine.
Your bow will only start higher on the curve not gain poundage across the curve, however the slightly lower starting poundage times the 1/2 inch lost in power stroke is energy lost. A 50#@28 bow will weigh 50# @ 28 wither its braced 7" or 8".
Well stated spike
QuoteOriginally posted by Spike:
Your bow will only start higher on the curve not gain poundage across the curve, however the slightly lower starting poundage times the 1/2 inch lost in power stroke is energy lost. A 50#@28 bow will weigh 50# @ 28 wither its braced 7" or 8".
Totally false and totally impossible. Go out to your bow shop raise the BH to 10". Yes your limbs can handle it. Wiegh it at 28". Lower it to 3" BH and see what happens. If your at full draw, and you take 1" of string length off, your limbs are going to bend more, your wieght will increase.
Read TBB vol 1 on energy curve and preload. Starting out with higher preload will have more energy than lower preload. This is of course if the power stroke is the same which is not.
Before you reply, go out and do the test on a bow scale. What your saying is impossible in the physics.
Every selfbow I have built so far has said different.
QuoteOriginally posted by Spike:
Your bow will only start higher on the curve not gain poundage across the curve, however the slightly lower starting poundage times the 1/2 inch lost in power stroke is energy lost. A 50#@28 bow will weigh 50# @ 28 wither its braced 7" or 8".
Ok, so those fimiluar with the intregation of area under an energy curve clearly knows starting out higher preload will increase area.
"If two twists make it perfect; what would three do; and what would ten twists do: compared to 12?"
Since the two twists was from me I'll try to answer that. If 2 twists gets me in the center of the vitals 3 twists would start to move my impact to the left. kind of like clicks on a rifle scope.
Does it work for everyone I don't know. But it works for me.
I started trad last July and thanks to tradgang there has been much experimenting on my part. I think I have tinkered with just about every way I can think of with my bow.
All this brace height conflict eventually ends up in the middle east, you know.
Shooty1 - LOL
I Wonder if a bow is efficient at lets say 6 " more than 6 1/2 - and then again at 9 but not 9 1/2.
B-E-C-A-U-S-E ole Byron is shooting a brace height that is really high; and well...he is shooting really well to perfect.
Before our swords are so sharp we start accidentally cutting each other; there is the apples to oranges factor. A reflex deflex shooter may experience a different reaction to BH than a 'D' longbow shooter and ditto on the recurve shooter.
Without those factors included- everyone could be right: with a different answer.
Will it harm a bow to increase the BH to find out the answers ????
:confused: :campfire:
Sorry I am just an engineer, I will defer to those who obviously know integral calculus better than I and its application. Also if compounds only hold at 15# at 30 draw where does the energy come from, must be FM :-)
You can harm a bow by raising a BH too much and shooting it. Most Mfg will ok a bow up to 31.5" of draw. So you can figure from that whats safe and whats not.
An easy way to do this is to draw a force curve at 4 points, starting at 0 draw, and ending at 28". Take that and put it in excel sheet and find the linear equation that goes with it thru excel. If its not linear than use a 2nd order polynomial to get a curve fit. Then integrate that (sorry for the calculus) linear equation from 0 to whatever your max stroke is at 28" draw. Thats your total energy.
QuoteOriginally posted by Spike:
Sorry I am just an engineer, I will defer to those who obviously know integral calculus better than I and its application. Also if compounds only hold at 15# at 30 draw where does the energy come from, must be FM :-)
Nope, thier energy curve is not linear like ours. Actually ours is not perfectly linear either (recurves for instance). Thier energy curve starts low, and within 2-10", shoots up to 70lbs (depending on how extreme the cam is) and stays at that high energy until 2-4 of full draw and comes down to 15lbs. Thats why they can capture so much energy. Its hard for me to draw a 70lb compound now, because you are holding so much wieght at 10" of draw. Where our (trad bows) wieght is not near that until we almost get to full draw.
If your an engineer, the intregation stuff like this is freshman calculus.
The Z bow compnay says that Byron has two different bows that he shoots; one he has a 6 1/4 to 6 3/4 inch BH ; and on the 'Radical' bow he shoots he has a 6 3/4 to 7 1/4 inch BH.
How does that compare with the BH you have ?
Okay, just did a test, 20# @24" solid glass bow 6 3/4" brace. Twisted up to 9 3/4" (3 inch higher brace) guess what still at 20# @ 24". Draw is measured from depression of grip +1.3/4" per amo standards ie 28" draw is 26.25" from the grip depression.
Longbows and Recurves are fairly linear with a bit of a rise early on on fast designs. Old round wheels stored energy looking like a parabola, the fastest compounds have energy storage curves that approximate a square wave.
Class Dismissed!!! :-)
QuoteOriginally posted by Spike:
Longbows and Recurves are fairly linear with a bit of a rise early on on fast designs. Old round wheels stored energy looking like a parabola, the fastest compounds have energy storage curves that approximate a square wave.
Class Dismissed!!! :-)
I agree whole heartly as I just told you this answer, but if you truely believe that you wouldn't have asked that question a few posts back when you said it must be FM if compounds are only holding 15lbs. Did you change your mind or was it FM :)
Now class is dismissed.
QuoteOriginally posted by Spike:
Okay, just did a test, 20# @24" solid glass bow 6 3/4" brace. Twisted up to 9 3/4" (3 inch higher brace) guess what still at 20# @ 24". Draw is measured from depression of grip +1.3/4" per amo standards ie 28" draw is 26.25" from the grip depression.
Ok, I just did a test, and my selfbow I am building right now, I put on a long string, with 0BH, and drew a total of 28" and got 45lbs, I then put the original string on and set it to 6" and got 55lbs.
I too am an engineer, and would like to know what FM physics you studied in school.
My head hurts. If you lower brace height, it puts more energy into the arrow. Raise it, and you get less. For me it's a moot point, because I will shoot my bow at the best brace height for the string that's on it. That's how it will perform best.
I'm no engineer, but I used to have one of those striped hats.
Don, I agree, if people on here stays within the Mfg recommended BH they most likely will weaken an arrow at its lowest BH. But we are just having a conversation about what is really happening. If you stay withing manufactures recommendations, then the energy gained from power stroke increase of 1" will be more than the starting preload and wieght increase.
It was just a friendly conversation.
Bigcountry, do a test on the Easton Bow Mapper device if you have a shop near you that has one. Let me know what you see. I just tried a widow PLV 47"@28 with 7.25", lowered to 6.25" brace and saw no detectable change in # at the measured 28".
QuoteOriginally posted by Spike:
Bigcountry, do a test on the Easton Bow Mapper device if you have a shop near you that has one. Let me know what you see. I just tried a widow PLV 47"@28 with 7.25", lowered to 6.25" brace and saw no detectable change in # at the measured 28".
I don't need a mapper. I can just use a bow scale and excel and some calculus. Thats all that machine is doing. We are both engineers here. We don't need no stinking mapper.
I doubt you would see a detectable change in lbs with only 1" of change.
To see a huge change go from 1" BH and then go to 9"BH. YOu will see it. As I said to Don, for 95% of the folks on tradgang, its a moot issue if they stay within Mfg specs.
Ok, can we agree on this Spike? If you shorten your string, your limbs are bending more? Can we start there? Think about an exaggerated 50" string put on a bow that requires a 60" string.
I will concede that you may see a small increase even though my home tests with a calibrated Hanson analog bow scale and steel tape don't show it over a range of useful interest. I did the Easton bow mapper on a Kanati LB I had and it gives really great resoultion of data, no parallax reading errors, uses a calibrated digital scale etc. but unfortunately I did not change the brace and repeat the curve.It outputs a Excel data file. I may still have it around if you would like to see it I could send it by email attachment. My point is I don't believe any increase in # will overcome the energy lost in power stroke, at least over the range of interest. Guess us engineer types are good with numbers but don't do well with communicating and spelling!
Here is a quote from SHOOTING THE STICKBOW, by Anthony Camera 2008, page 76,
"To correct for a stiff arrow...Increase the brace height by adding twists to the bowstring. This slightly increases the draw weight of the bow, typically one to three pounds per inch, and decreases the angle of offset as the arrow leaves the string, thus making the arrow weaker."
He also later states decreasing brace corrects for a weak arrow.
page 79,
"As can be imagined, the shorter the string, the higher the brace height and the heavier the draw weight at any given length. That is because with the shorter string, the limbs will need to bend into a tighter arc...most home and Pro Shop bow scales aren't accurate enough to show that amount of weight change...The lower the brace(longer string length) the faster the arrow leaves the bow. This is due to the longer time the arrow is in contact with the motive force-the string."
I certainly agree with these statements and will add that a higher brace will normally yield a more forgiving bow as there is less time for the archer to torque the bow throwing the arrow off target. The trick is to find the correct balance for you, play around with it, it is easy to adjust and observe the results.
What Katman says....thats the way Ive always understood it.
Dang now I don't know if I got it backwards or not. When I know for sure I think I'll write it down on a cheat sheet.
Maybe something like tighty righty, loosey left or right loose, left tight whichever is the correct way. :)
Perfect explanation Spike
Short version -
Arrow shows too stiff, raise BH.
Arrows shows too weak, lower BH.
Long version -
Easton Tuning Guide, 2nd edition
Brace Height
For recurve bows, another way of altering arrow spine is
with the brace height. By increasing or decreasing the
distance from the bowstring to the pivot point of the grip,
the dynamic spine of the arrow can be made slightly
weaker or stiffer. Increasing brace height will make the
arrow shoot weaker, and decreasing brace height will
make the arrow shoot stiffer.
Brace height affects arrow spine by increasing or
decreasing the amount of energy delivered to the arrow
at the moment of release. Raising the brace height
(shortening the bowstring) compresses the limbs,
increasing stress (prestress or preload) in the limb material.
The more preloading of the limbs, the greater the
actual bow poundage at full draw. The reverse is true
when lowering brace height. A lower brace height
(lengthening the bowstring) reduces the prestress in the
limbs and reduces bow weight at full draw.
However , raising brace height produces some small loss
in arrow velocity as the slight increase in draw weight
does not equally compensate for the reduction in the
bow's "power stroke". When the power stroke is reduced,
the amount of time the arrow stays on the bowstring is
also reduced, in turn, decreasing the length of time the
arrow has to absorb the bow's energy.
----------------------------------------
It does not mention the offset effect, IMHO this also has a significant influence.
Might not see much change in arrow flight when changing BH on centre or past-centre cut riser.
Yep, the easton guide says that. Lots of people here posting stuff they read. I am more of a experimenter. My old grandfather told me once, don't believe nothing you hear and half what you see. It was good advise.
But has anyone actually tried to go to the extremes to find out what is happening? I am not talkig about reading what another man has done. I am talking about trying it yourself? I have. I know one thing, you take a straight longbow down to 3" BH and you just lost 5-9lbs. No stroke is going to make that up. There will be a sweet spot for every bow where where speed is optimal or noise is lowest, or both.
Power stroke, schmower stroke.
Since raising the BH increases poundage, the reason an arrow "acts" weaker is because it actually becomes weaker to that bow. It's not playing pretend.
what Katman AND old york says...this has always worked for me.
glad I got rid of my wheel bows this tradional stuff is so much simpler.
LOL JIM :)
Well, I will see about testing my bow on the Easton mapper this weekend, it gets data every 0.10 inch of draw. I will test at 6.5" brace and 7.5" brace.
Till then guess I should twist up to 20" brace and shoot telephonepoles. :-)
The language used is driving me bananas- The arrow spine does not change, no matter what you do to your brace height! Saying that doing this or that makes the arrow stiffer or weaker just confuses the issue. The BOW is changing, not the arrow!!
I know, I know. My wife says I'm too sensitive.
In spite of all that's written, indeed test for yourself.
I've found Easton's information accurate, if
I'm close in spine to begin with.
BH tuning is for minor tweaking,
when one has already found the sweet zone.
I have played with this some, on my black widow PSA recurve. The specs say to brace it between 8.25 and 9 inches. But it just seemed too loud to me, and then I read on another forum where a guy had the same thoughts I was having, and raised his BH up past the 9 inches. His bow shot great, and got alot quieter.
So I moved mine up to 9.25 and it was quieter, then 9.5 and WOW........still shot great, didn't move my impact that much, but oh man, it is ever a much quieter bow.
So many variables go into the setup, shooter form, release, and so on. I keep my widow braced at 9.5 now, a full half inch higher than they recommend, but hey, it is what it is, and it works great for me. I dont think I lost any measurable speed either. The arrow seems to be flying just as sweet, and just as fast.
Just my experience.
QuoteOriginally posted by Spike:
Well, I will see about testing my bow on the Easton mapper this weekend, it gets data every 0.10 inch of draw. I will test at 6.5" brace and 7.5" brace.
Till then guess I should twist up to 20" brace and shoot telephonepoles. :-)
Spike, your an engineer, just use your hanson and carefully take data and you can make a mathcad or matlab routine to do the calculation licked split.
The shop owner is at the IBO worlds this week so it will be next week to get the data. Can't get the necessary accuracy using the Hanson. The mapper I have used before gets a nice smooth curve with no hysterisis effects until you do the letdown part of curve if you draw nice and smooth.With the hanson as someone pulls it to the mark you may get some bouncing around and a reading showing the hysterisis giving you scatter, plus hanson is only 1# increments so good to 1/2 # at best. I will follow thru with this as I now NEED to KNOW.
**Disclaimer**
IBO hillbilly, and I heard the Hanson bros sing once. I got me a map, but no mapper. Do have a wife with some nice, smooth curves and a lot of hysterisis. Draw Force Curves are completely applicable to cast iron skillets. I ain't no engineer, but I can spot other peoples' typos lickity split!
My experience has shown me that a higher brace has the effect of weakening an arrow. Lower brace height has the effect of making an arrow stiffer.
AAArrrrggggghhhhh!!!
I just twisty or un-twisty the string until the arrows fly where I need them to go. But then again what do I know? I'm just a cook!
:bigsmyl:
One other thing...it really helps understanding
all this if you're cross-eyed and dyslectic :p
Hell, throw in the plaid boxers too [grin]
Simple explanation. No complex physics, mathmatics or gadgets few of us have. Start with 10 lb draw weight bow with 5 inch power stroke.
10 lb bow with 5 inches of pushing (stroke).
Total power = 10 + 10 + 10 + 10 + 10 = 50 lbs.
Max thrust at release = 10 lbs.
Raise BH, which increases draw weight & decreases power stroke (11 lb bow with 4 inch stroke).
Total power = 11 + 11 + 11 + 11 = 44 lbs.
Max thrust at release = 11 lbs.
Lower BH, which decrease draw weight & increases power stroke length(9 lb bow, 6 inch push).
Total power 9 + 9 + 9 + 9 + 9 + 9 = 54 lbs.
Max thrust at release 9 lbs.
The arrow bends the most at release and then continues to bend less & less as it is leaving the bow. Higher draw weight from higher brace slams the arrow more at release and makes the arrow react weaker.
Lower brace height slams the arrow with less thrust upon release and makes the arrow react stiffer. But, while the lower BH pushes the arrow with a lower initial thrust, it pushes it longer so it leaves the bow faster.
I remember it this way, for a right handed shooter, LOWER/LEFT...lower the brace, the arrow goes left. Just remember VIPER never gets it wrong....
Jim,
back to your original question,
In my experience with my bows, when I have an arrow that's showing weak, I lower my brace height.
When I have an arrow that's showing too stiff, I raise my brace height until the bare shaft flies/groups correctly.
hope this helps,
sammy
And what about the fact that since the arrow is on the string longer with a lower fistmele, it has moved farther to the left for a right-handed shooter by the time it clears the string, but which also keeps the nock end of the arrow from moving freely during the second half of the paradox, keeping it closer to the riser and requiring less actual spine to compensate?
I made that up all by myself! I'll be quiet now.
the greatest effect changeing brace height has for me is,it helps me find the sweet spot on a given bow ,and shoots the quiest,smoothest,and most consistant,with what ever weight and spined arrow i am shooting at the moment,out to a minimum,maximum distance.regards,robert :thumbsup: :campfire: :coffee:
What's raising or lowering brace height got to do with hitting one's hat? That happens because the bow is drawn back to an anchor where the string touches the hat. Nothing to do with brace height. I shoot several bows with different brace heights and at full draw I still touch my hat brim, I can't shoot with a ball cap without twisting it around because of that. If you are to reach that particular anchor point your going to draw that far back regardless.
:coffee: