Brace height effect on arrow spine & tune

[RickBarbee]

I actually posted this in a topic on another forum, but would love to see it discussed here:

"Brace height adjustment (assuming you aren't way off 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 the bow'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.

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."

Throw in your 2 cents.

Rick

[KenWood]

Very good info. That is exactly how I was taught to think about spine adjustment with brace height. I agree that a bows brace height dictates its performance. If mine has creep 3/16" I notice it. It's almost like it shoots every where when it has creeped out of its optimum "window".

[RickBarbee]

I've done a lot of testing of brace height effect on performance with a lot of different bows. Without exception, every one of them performed best, were the most stable, and the quietest when the brace height was set where the inline load of the string (preload) was at it's highest point.

You generally have some wiggle room/adjustment either side of that optimal point, but once you get outside that "window" of adjustment, the bow's performance, and overall behavior starts to degrade.

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

Rick

[Bisch]

I've done a lot of testing of brace height effect on performance with a lot of different bows. Without exception, every one of them performed best, were the most stable, and the quietest when the brace height was set where the inline load of the string (preload) was at it's highest point.

Rick

How would a person know where the inline load of the string was at its highest point???

An inquiring mind want to know!

Bisch

[RickBarbee]

How would a person know where the inline load of the string was at its highest point???

An inquiring mind want to know!

Bisch

I used a cable tensiometer, but they are expensive, and most folks won't have access to one,

BUT

through my testing I discovered, that a chronograph will get you close if not spot on, because the best speed will always be right at the point of highest preload. You may not know the exact preload measurement, but you'll know you are there, or very close.

Worthy to note: You're not always looking for big changes in speed. If you are already within an acceptable brace height for the bow, the changes of speed may (usually are) only slight from one brace height to another. You may have to shoot a lot over the course of a lot of changes to find that "sweet spot", but once you do you will appreciate it.

Rick

[RickBarbee]

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

[DRT]

Did you ever see Better off dead? That sounds just like the punch line in the movie. The star states I don't know what to do. Twice he's told "Go this way really fast. If something gets in your way, turn."

Same thing with this. If you don't start out with an arrow set up that is close to right then you'll never be able to reasonably find that peak performance. It's fine to paper tune and bare shaft tune and have spine testers and what not. From what I've gathered most don't.

A wise man told me if I get arrows that shoot well for me and my field points and broadheads hit in about the same spot I'm doing good.

8 months into this obsession I'm just recently able to realize my subtle form issues and the havoc they reek on my shooting. Up until now I have not believed it possible to even try to paper tune.

Brace height is critical no doubt. But when the manufacturer gives to a 3/4" or more in window for that setting that's a pretty vague guideline to try to work through.

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[spidermonkey]

Good info Rick! But I'm curious, will highest pre-load/highest speed be where your bow is at its best "shootability"? As in; quietest, most forgiving in subtle bouts of bad form, etc? This is probably just coming from my thinkin of "faster is not always necessarily better..." If that makes any sense at all! Thanks again for some good intel. Good Huntin, and God Bless, Rusty

[DRT]

So actually raising your brace height is shortening your power stroke of your string correct? A lower brace height puts the arrow on the string slightly longer and since it leaves the string closer to the riser/shelf that's why the angle of deflection increases?

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[RickBarbee]

Good info Rick! But I'm curious, will highest pre-load/highest speed be where your bow is at its best "shootability"? As in; quietest, most forgiving in subtle bouts of bad form, etc? This is probably just coming from my thinkin of "faster is not always necessarily better..." If that makes any sense at all! Thanks again for some good intel. Good Huntin, and God Bless, Rusty

Yes sir. It is where you will experience the best from all aspects.

The point of highest preload is also the point at which the string speed is fastest as it returns to brace when shot. Anything above, or below that point results in the arrow leaving the string at a slower speed, thus a slower arrow.

Rick

[RickBarbee]

So actually raising your brace height is shortening your power stroke of your string correct? A lower brace height puts the arrow on the string slightly longer and since it leaves the string closer to the riser/shelf that's why the angle of deflection increases?

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Yes

Rick

[DRT]

So shooting an arrow that is marginally on the weak side that maximizes your power stroke length should give you optimum speed?

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[DRT]

For instance if I input my bow info in on the spine calculator and then look at arrow build specs if I should be within two pounds I should look at being a pound or two light on the arrow spine vs the bow spine?

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[DRT]

Sorry about all the questions this kind of lit something up for me.

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[spidermonkey]

Rick, I had already read/heard of this somewhere before, can't remember where? Prob from you, who knows! I know how to do the "in depths" of tuning my trad bows, but usually revert to the "seeing nothin but the nock" method for whatever reason. I will shoot at longer distances at a large backstop, concentrating on exact form, release, and not worrying about having to hit an exact spot. And yes I will "look" at the flight of the arrow. Also will have somebody other than me watch as well for anything I may not see. I will always do my dead level best at finding my absolute best spot for my brace height. As far as quiet, forgiving, and best speed. But, with that being said, I dang shore aint no William Tell. I realize all i just said really aint in line with your post, sorry, just got going with the ol diarrhea of the mouth! Long story short, you really got these rusted up gears turnin in this noggin! Good Huntin, and God Bless, Rusty