How does increasing or decreasing brace height affect arrow spine?

Decreasing BH = stiffening spine because the arrow is on the string longer and transfers more energy into the arrow.

Increasing BH weakens the arrows because it is not on the string as long thus less energy transfer.

It won't change the static spine at all. It changes the dynamic spine due to the point being closer to center with a higher brace ht.

MP

It won't change the static spine at all. It changes the dynamic spine due to the point being closer to center with a higher brace ht.

MP

Yes and if a few twist of the string gets you in tune,you are just that close to being out of tune. It is better to make a change in point weigh,spine,or strike plate to get closer to the middle of the tuning bracket so the least little change,like a tiny bit of string stretch doesn't throw you out. Tune for the middle. Hope that makes sense. >>----> Ken

2 bears,

"It is better to make a change in point weigh,spine,or strike plate to get closer to the middle of the tuning bracket so the least little change,like a tiny bit of string stretch doesn't throw you out."

So how does a static difference like point weight,spine or strike plate react to a dynamic change like a "tiny bit" of string stretch, which can still occur? You make it sound like the tuning bracket is somehow wide enough to remain tuned despite that "tiny bit", which is why the string is adjusted to begin with. How would you determine the string is finally done with stretching and thus allow your static differences to move the tune to a finality(or bracket)?

Are you assuming string adjusters do not consider point weight, spine and strike plate settings before adjusting the string?

Of course brace will affect tuning, but if your static spine is pretty solid, a few twists won't change the dynamic spine that much. I can change my brace by half an inch without affecting spine enough to cause bad or suspect arrow flight. I adjust brace for feel and quietness, not for correcting flight. Ken is saying if just a few twist change arrow spine where you need different arrows, you likely picked the wrong spine to start with. At least I'm assuming that.

Mdph and 2bears are both on the money. With aluminum and wood you have about a 5lb window. Both of those materials are pretty forgiving of spine. Twisting the string isn't gonna change spine much so if that makes your flight good you're still borderline so a slight stretching of the string or even a bad release can throw the spine off too far.

Brace height adjustment (assuming you aren't way of with it), in reality is simply a fine tuning practice to an already fairly closely tuned setup.

Once the brace height of a bow is set within the optimum window of it's preload, changing of the brace height within that window of setting has no significant effect on performance, therefore has no significant effect on the spine requirement of the arrow due to performance shift.

Going outside that brace height window of optimal preload (either up, or down) will decrease the performance of the bow, so if changing the brace height does have some significant enhancement to performance, it is highly likely you were way off with the brace height to begin with. 8^)

The only power stroke length, that has any significant effect on bow performance, and arrow spine requirement is draw length, and obviously the longer the better.

What changing brace height "does do", is change the angle of the arrow in relation to the strike plate, which in effect has the same outcome as changing the center shot of the bow.

The lower the brace height, the lower the spine requirement of the arrow will be, which is similar to moving the arrow more outside of center. SO, if your arrows are shooting a bit weak, lower the brace height. If a lot weak, then you need to revisit your arrow build.

The higher the brace height, the higher the spine requirement of the arrow will be, which is similar to bringing the arrow closer to center shot. SO, if your arrows are shooting a bit stiff, raise the brace height. If a lot stiff, then you need to revisit your arrow build.

Rick

Wild Bill. Please read what George,GLF, and Rick said. They said it much better than I. If a few twists fixes things you are very boder line. I could shoot holes in each of your statements but I just don't feel like being baited to day.I usually enjoy it so thanks any way.>>>-----> Ken

2 bears,

"They said it much better than I."

And that is why I understand what they said.

I didn't understand what you said, and so I posted to try and learn something. I learned you can be snotty.

Rick,

"Once the brace height of a bow is set within the optimum window of it's preload"

Is that something determined by the design/maker, or is it different for every bow? And, how would someone determine that setting?

Bill,

almost all bows have unique characteristics about them. Even those bows that are supposed to be "the same" will be different. Sometimes only slightly different, sometimes a lot, but seldom exactly the same.

You have to learn the bow to find it's behavior, and discover that "sweet spot". Then, and only then does the science of it start getting more pointed.

Without the tools to measure/gauge those settings, you are left with only the age old practice of shooting the bow, and paying attention to what it is telling you, which (if you are really being attentive) will often get you right where you want to be. 8^)

Rick

This is kind of off the topic, but does have it's place.

Your input to the bow will have a direct impact on the output of the bow.

How well you know yourself as in how you are handling the bow, and how well you understand how it wants to be handled goes a long way in getting the most out of it.

Kinda like a lover. <--- I know. Corny analogy, but it's true. 8^)

Rick

I'm going to disagree with most! Nothing you do to your bow will change the arrows spine!!! It might effect the tuning of the bow but the arrow is unchanged.

Bob

Bob - think on the lines of "required spine" then you'll be on board. 8^)

Rick

Sorry, left our a word,, it's supposed to be spine needed, not just spine.

Rick: Go back and read the posts, they are saying it changes the arrows spine, when it doesn't. It might effect how the arrow comes off the bow, and how the arrow reacts to the bow, but the fact remains it doesn't change the spine.

Bob

I did Bob, and you are correct. I hope changing the phrase to "required spine" cleared that up some.

Rick

This picture (not my picture by the way) shows the differences in the angle of the arrow in relation to the strike plate as brace height is changed, and is used to explain why there is a weaker spine shaft requirement at lower brace heights,

BUT

how could this be relevant at resting brace height?

The arrow is, or should be clear of all contact long before the arrow returns to this spot during the shot.

Rick

Wild Bill I apologize. If you are sincerely seeking to learn I will discuss those things till the cows come home. You used my handle and quoted me several times like what I said was wrong,not like you were asking a question. I see using quotes is just your way. Again, I apologize. The 3 named and I are almost always in agreement. If we are not then I usually have something else to learn. Yes a string may stretch the temperature can change. The point is if you are so barely on the edge of tune those little things can throw you off. If you are well tuned (in the middle) a tiny change won't hurt you. The brace height should be set first. Like Rick said we don't have access to that kind of equipment. I rely on sound and vibration or feel before any thing is added to the string,then measure the brace and record it. On recurves it is usually very close to where the string first starts leaving the groove on the curves. If you mark your arrows you will have a visual check avaiable, ever time you knock an arrow. Then you tune for flight and accuracy. A minor tweek of the string is O.K. but you don't want to lose the sweet spot in the brace height.Good luck <-----<<< Ken

2 bears,

Apology accepted.

I've never heard before, that the brace is where you start the tune. I started shooting traditional with Bear bows and I was told that a higher brace, such as, 8"+ was normal. Do you rely on charts to establish the arrow you use when searching for the sweet spot? When you say," before any thing is added to the string", do you mean only silencers or do you include center serving and nock point?

Vibration - I once had a wide limbed Bear that I hated because it shook so much after the arrow had left the bow. Is that the vibration you mean? I believe the brace was too low on that bow and the arrow speed was pitifully slow.

Sound - Does the twang pitch go up or down, above and below the sweet spot?

2 bears,

Apology accepted.

I've never heard before, that the brace is where you start the tune. I started shooting traditional with Bear bows and I was told that a higher brace, such as, 8"+ was normal. Do you rely on charts to establish the arrow you use when searching for the sweet spot? When you say," before any thing is added to the string", do you mean only silencers or do you include center serving and nock point?

Vibration - I once had a wide limbed Bear that I hated because it shook so much after the arrow had left the bow. Is that the vibration you mean? I believe the brace was too low on that bow and the arrow speed was pitifully slow.

Sound - Does the twang pitch go up or down, above and below the sweet spot?

I appreciate your observation on the sweet spot being near the point where the string starts to leave the limb grooves. Now maybe that accounts for why I consider longbows easier to shoot.

Thank you. Well my explanations got me again. I am afraid us old foggy s just take too much for granted. Just the silencers. They will tend to mask things. Get it as quiet as you can with out the silencers then they will help it even more. Make sure you are using enough arrow weight. At least 8 grains per pound of bow weight 10 is considered the norm for a hunting bow. That is a 400 and 500 grain total weight for a 50 pound bow.The heavier the quieter but too much really increases the arc of the arrow. Too much lighter, stresses the bow. I guess I never payed much attention to the pitch just how loud it was. The vibration you mentioned was pretty extreme but brace height surely would have helped. It may also have had a tillering problem. Since the string on long bows don't touch the limbs they tend to be quieter even though as a rule they have a slightly harsher feel.There is less mass weight in the bow. I have done it so long that I pretty well know what arrow I want for my bow weights + I make arrows from shoots and cane also.The charts and calculator do give a good starting palace.The charts tend to recommend a little on the stiff side. The times I have compared with Stu's calculator it has been right on. It is a little tricky to get all the information entered correctly. Well I haven't seen the cows yet but I believe I covered it,at least I tried. If you have any more questions I am always around. >>>-----> Ken

Thank you 2 bears, I will now re-examine my gear and hopefully enhance my accuracy.

One more question, if you would, please. Is FOC something you use in constructing arrows?

Rick -

It's relevant because the string has to get to the "resting" brace height from the anchored position. The lower brace height has a similar effect as a taller rest (distance from center) just BEFORE the arrow disengages - that's due to the angle off at that point. The fact the arrow is no longer on the rest is irrelevant, because it's own inertia is still a factor.

And no, I didn't draw that picture to scale ;)

Guys -

Just for the record.

1. You BUY arrows (shafts) based on static spine, which doesn't change, unless you physically modify the shaft. It's measured by supporting the shaft a specified number of inches apart, hanging a specified weight from it's center, and reading the deflection. (Unfortunately, there are several methods of doing that.)

2. You shoot and tune the dynamic spine, and static spine is only one factor of a number of factors in that.

Think of it this way: static spine is where you start and dynamic spine is where you end up (shoot).

Viper out.

Thanks Tony !!!!!!

I wasn't doubting it. I just wasn't understanding it even though I totally agree with the end result.

Rick

You're changing the spine that your bow needs, just like when you tune your bow instead of arrows by changing side plate thickness.

Rick -

No problem buddy, I'm sure other people had the same concern. Kinda glad you brought it up.

Viper out.

Wild Bill I do check FOC but don't have need for heavy front of center. I don't hunt thick skinned game. I only shoot 40 to 45 pound bows and too much weight up front slows them and causes excessive drop.So 400 to 500 grain arrows. Normal arrows with 125 grain points usually always work out real close. 10% FOC is fine for me for hunting purposes and ever day use. I have gone a good bit lighter for 3D competition. It helped with my bad range estimation. Lighter= faster,flatter,but usually nosier. Heavier=slower,usually more penetration,quieter. It is all a trade off and folks have different needs.The same rig don't work well for Olympic type shooting,3D,and hunting Buffalo.Hope that helps. >>>-----> Ken

So static spine is a just a measured number on an bare shaft.

When the shaft becomes an arrow then it becomes part of the dynamic spine process?

D -

Yes.

Shaft length, point weight (and fletch/nock weight), heck even shaft diameter and degree of centershot/limb efficiently of the bow all factor in, as does the shooter.

Agree with Ken, FoC just doesn't really factor in for most circumstances, unless you going below 7-9%, so most of the time you can forget about it.

Viper out.

Thanks Viper. I have been in archery for more years than I like to count. I still gained volumes from your book.>>---> Ken

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