Brace height effect on arrow spine & tune

[DRT]

Exactly. It kind of makes a few things that I sensed but didn't pay attention to come into the light. Maybe another tool to put in the bag.

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[Perkins7581]

Good info I've been telling my brother in law for weeks same info I'll pass it on to him. He will be able to understand it better the way u worded it. Thanks Rick

[RickBarbee]

Gary, if I am understanding your question correctly, then the answer is no.

Gaining, or losing "power stroke" within the brace height optimal adjustment window does nothing significant for speed. The only area where "power stroke" has any significant impact on performance is draw length, and as I said in my initial post, the longer the draw length is, the better the performance will be.

You are looking for that brace height which gives you the optimal preload. That particular brace height could be higher, or lower depending on the bow.

Rusty, you're doing it right. When you don't have the tools to take the measurements/readings, you shoot the bow, and let it tell you where it needs to be set. You make your adjustments until you get to that "sweet spot".

Time, and again I have seen shooters trying to get their brace height as low as possible, because they thought it would enhance performance due to the additional power stroke, when in reality it was doing just the opposite, and making their rig more difficult to tune & shoot.

The belief, that lowering the brace height in & of itself will make a bow shoot faster is one of those old wive's tales. The optimal brace height (the "sweet spot") can just as easily be higher than lower.

Rick

[DRT]

Okay.

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[Shiloh]

What's interesting also is - two otherwise identical bows will sometimes require a different brace height to achieve their best performance.


I've experienced the above for sure. I have two Bob Lee recurves that are both 60" set up exactly the same. One of them shoots perfectly at an 8 & 1/16" BH. The other will shoot the exact same arrows erradictly with that same BH setting.

[DRT]

So what that tells me is there is no exact science to it. Trial and error is the course.

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[RickBarbee]

So what that tells me is there is no exact science to it. Trial and error is the course.

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Yes !!!!!

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.

Rick

[DRT]

That's kind of discouraging. I would lay odds many bows get sold or traded because an archer without the tools or resources to get it shooting to peak performance just let's it go.

Or maybe even let's the discipline go.

Good thread Rick. Knowledge is good.

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[RickBarbee]

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.

Rick

[Bisch]

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.

Rick

This is the only part of this whole thread my little pea brain can comprehend!!!!

Bisch

[SwampRabbit]

This picture is an over illustration, yet good explanation of what happens to the angle of the arrow, and it's deflection due to brace height changes.

Note, that the lower the brace height, the more the arrow will need to flex (be weaker in spine) to come back on center when shot.

Rick

There is a problem with your picture Rick.

The arrow shouldn't be in contact with the riser by the time it reaches brace.

Look at any slow motion video of a finger released arrow (properly tuned) and you should notice that the initial deflection starts at initial release, builds, until the arrow deflects back... upon which the arrow shaft loses contact with the riser. The riser and the pressure it provides to help create the initial deflection now no longer plays a role... and this occurs well before the string returns back to brace.

Initial deflection should occur during the first portion of the power stroke after the release and the full power cycle, especially the tail end, should really have a minimal affect on dynamic spine requirements.

[SwampRabbit]

But the dynamics do get interesting at full draw and how much arrow is sticking out... and where that riser pressure actually exists along the shaft during that initial time where the shaft is in contact with the riser... how much and how far the weight is out in front of the point, releative to the force of the string at the nock... and how much lateral movement of the string exists (archer dependant) etc all play into alot of variability in how much an arrow will deflect and how much "spine" is needed to properly dampen that impulse and correct the arrow flight (over damp, under damp, etc.)

I'm guessing in order to really do the math on it... you'd be solving some differential equations and having to rely on Fourier transforms to really get down to it. Gotta love rules of thumbs though in times like this

[Bisch]

Ugh!!!! My head hurts after reading all that, Scott!

Bisch

[RickBarbee]

When within an acceptable spine match to the bow, and assuming a decent release/loose, the shaft will flex three times during the power stroke.

First flex - Occurs at release/loose of the fingers from the string, and forces the shaft inward toward the strike plate. This flex is initiated by a combination of the roll of the string from the fingers, and the forward force applied to the tail of the arrow.

Second flex - Occurs during mid power stroke, and is simply recovery from the first flex, and springs the shaft outward, and away from the strike plate.

Third flex - Is a recovery from the second flex, and once again is forcing the shaft inward toward the strike plate. This flex occurs right at the point where the arrow is exiting the string. The lower the brace height is at this point, the closer the proximity of the shaft is to that of the bow/strike plate during the pass, thus the stiffer the shaft the more likely it, and/or the fletching will make contact at this point.

Side note to this point:
Aside from dragging the string & limbs forward creating shock, and vibration, one of the reasons why nocks that are to tight create arrow flight problems is they straighten out the 3rd flex, and jerk the arrow back into contact with the bow.

Rick

[DRT]

Uh . . . I'm a hunter not a lover. I just want to make sure I build the right arrows for my bow.

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