Brace Height and Tuning

[Curtis Haden]

Will increasing brace height (within reasonable limits) increase a bow's draw weight at a given draw length, and make an arrow act weaker in spine?

-or-

Will decreasing brace height (again - within limits) produce a longer "power stroke" and make the arrow act weaker in spine?

Obviously, there are dissenting opinions on this, but if you know the answer, please enlighten me!  I've heard reasonable "sounding" arguments both ways, but both obviously can't be true...

[Bob Sarrels]

No to the first,  yes to the second.  Bob

[Curtis Haden]

Ok, so I'm reading this book, which prompted my question in the first place...  I get a little farther along, and the author seems to answer my question.

He says, (paraphrasing) that a higher brace height increases draw weight, and weakens the dynamic spine of the arrow.  He goes on to say that a lower brace stiffens the dynamic spine, but also increases arrow velocity, due to the longer power-stroke or string contact.

Quote: "A taller brace height increases the poundage but decreases speed, and a lower brace height reduces the draw weight but increases speed or cast."

So... If I need to "tune" my bow to shoot a slightly stiffer arrow, I should increase the brace height.  But if I want a little gain in arrow velocity, I should lower the brace, keeping in mind that the arrow will actually act a little stiffer... Right???

Anyone disagree with this, and if so, why?

[Curtis Haden]

Thanks for the input, Bob.  I was busy writing my second post while you were answering.  I'm still chewing this one over...LOL!    

[Old York]

From Easton's Tuning Guide - 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.

Although you may note a small loss in velocity when increasing brace height, do not let speed be the deciding factor when selecting the best brace height for your bow. As is often said, "Better to have a slow bull's eye than a fast miss".  *******

I've found that adjusting brace height works for "tweaking" arrow spines and if you're way too stiff or weak in spine to begin with, adjusting BH does not always yield the expected results.

[Curtis Haden]

Thanks York.  Easton seems to agree with the author I'm reading.  It's a bit confusing.  My interest is not so much in tuning a specific bow, but just to understand all the aspects of the process.

[Old York]

Well best of luck, Curtis. It's awfully complex to me, trying to determine which parameter comes out on top. Changing BH is changing more than one thing at a time. Some chrono testing might show small differences in arrow velocity, dunno.

Easton does not mention BH changes and degree of offset/centreshot, either.

Throw it all together & you've got yourself a fine kettle of at least eight simultaneous equation-fishes, eh?  

[Boom Stick]

Who woulda thunk that a simple stick 'n string could be so complicated!?    

So what's this fancy "sweet spot" all about?  

Tuning the bow to the arrow or having the bow quiet to a tuned arrow?

[Curtis Haden]

Originally posted by Boom Stick:
Who woulda thunk that a simple stick 'n string could be so complicated!?        

So what's this fancy "sweet spot" all about?  

Tuning the bow to the arrow or having the bow quiet to a tuned arrow?

I'm in total agreement with having a tuned arrow and a quiet bow, brother!  Don't mean to confuse or complicate things.  I just want to know, and more importantly, understand the process as well as I can.  I think there are some misconceptions, or at least, opposing opinions about brace height changes in regards to arrow and spine behavior.  That's what prompted my  post.

Thanks for everyone's input.

[Boom Stick]

Originally posted by Curtis Haden:
 

Originally posted by Boom Stick:
Who woulda thunk that a simple stick 'n string could be so complicated!?        

So what's this fancy "sweet spot" all about?  

Tuning the bow to the arrow or having the bow quiet to a tuned arrow?

I'm in total agreement with having a tuned arrow and a quiet bow, brother!  Don't mean to confuse or complicate things.  I just want to know, and more importantly, understand the process as well as I can.  I think there are some misconceptions, or at least, opposing opinions about brace height changes in regards to arrow and spine behavior.  That's what prompted my  post.

Thanks for everyone's input. [/b]

Don't get me wrong,  I wasn't taking a shot at you.  I'm just learning about brace height myself.  Until a few days ago I always just put the string on as is and never thought anything of it.  I always thought that a proper lenght string to a bow's AMO was all you needed!  I'm still not sure how to tell if I have it set right or not.

[4D]

Regarding Brace Height.... would a person with a shorter draw length say 26.75" lean to a higher Brace Height ? Appreciate any feed back on this .

[moebow]

Since this is an older post that was done before this became the "Form" forum. I'll answer but this question is better addressed in the Pow Wow.

For shorter draw lengths, you MIGHT do better (slightly higher arrow speed) with a lower brace height to get a longer (relatively) power stroke but that will be minimal.  Best to find the "sweet spot" and just shoot.

Arne