Your Bracing Height?

Was: Bracing height and string length


From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Your Bracing Height? (Was: Bracing height and string length)
Date: 3 Nov 1995 11:06:59 GMT


Slightly off the original subject matter...what factors does changing
the bracing height influence?

1: Tiller?
2: Nocking Point?
3: Initial Draw Weight?
4: Full Draw Draw weight?
5: Type of nocking point?
Others that you want to mention???

I reckon #3 is easy enough, yes, higher bracing height = higher initial
draw (ie the effort it takes to move the string in the first place)

#4 is very hazy, you are still only drawing the bow the same distance
but the string is effectively a different length and the bending in the
limb is slightly different....does higher BH = Higher draw weight?
Certainly it usually makes arrows perform weaker (higher impulse energy?)

#1 I reckon depends on your bow and how much you change the BH. Like i
said before mine doesn't appear to change....does yours?

#2 again with my bow it doesn't appear to but that doesn't mean that it doesn't!

#5 well if you change from a few wispy bits of superglue and thread to
two great big metal nocking points then surely it's going to change your
setup? However is ideal BH one of the things it changes?
(This brings on the note that if you tune your bow with floss or tape
nocking points and then stick on damn great big nock sets it isn't going
to shoot the same!)

OK that's about it for now, just trying to stir up a little discussion.


John Dickson,(aka Stretch)    

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From: David Bruce <dib@dra.hmg.gb>
Subject: Re: Bracing height and string length
Date: 3 Nov 1995 13:31:01 GMT


jdickson@festival.ed.ac.uk (John Dickson) wrote:
>melin@cm5cofis.gmd.de (Stephan Melin) writes:
>>Doesn't the correct position of the nocking point also depend on the bracing
>>height?
>
>Probably but how much? What are the main factors that influence your
>nocking point? Ok it varies a lot from archer to archer, but mine are
>bow tiller and finger position on string (and nock type but we'll assume
>that's constant!)

I assume that Marcel changes his bracing height by twisting the string.
When you do this the nocking point is going to stay the same proportion
above centre, but not necessarily the same distance.
(I've not measured it, but I guess this is a fairly small effect.
Nevertheless, it might be significant, which is why Marcel said to check.)

    David Bruce

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From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Bracing height and string length
Date: 3 Nov 1995 15:02:38 GMT


David Bruce <dib@dra.hmg.gb> writes:

>jdickson@festival.ed.ac.uk (John Dickson) wrote:
>>melin@cm5cofis.gmd.de (Stephan Melin) writes:
>>>Doesn't the correct position of the nocking point also depend on the bracing
>>>height?
>>
>>Probably but how much? What are the main factors that influence your
>>nocking point? Ok it varies a lot from archer to archer, but mine are
>>bow tiller and finger position on string (and nock type but we'll assume
>>that's constant!)

>I assume that Marcel changes his bracing height by twisting the string.
>When you do this the nocking point is going to stay the same proportion
>above centre, but not necessarily the same distance.
>(I've not measured it, but I guess this is a fairly small effect.
>Nevertheless, it might be significant, which is why Marcel said to check.)

Now that's a completely different way of looking at what Stephan said! I
assumed he meant the correct position for your nocking point may change
eg if you shoot off 9" your n-pt may be 6mm above square (when tuned); if
you shoot off 9.5" your n-pt may be 4mm above square when tuned.

My n-pt moves up about 0.5-1mm when I move from minimum b-H to maximum
B-H (9.25" - 9.75"). So not much, and thats with a string that is maybe
a bit too twisted at the top of the range.

You are certainly right to emphasise the point that if you are going to
use Marcels test you must make sure you check the n-pt each time you
change the B-H. 

(BTW when I say *factors which influence your n-pt* I mean where you put
your n-pt when the bow is tuned)

John Dickson,(aka Stretch) 

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From: vittorio.brizzi@bo.nettuno.it (Vittorio Brizzi)
Subject: Re: Your Bracing Height? (Was: Bracing height and string length)
Date: Sun, 05 Nov 1995 12:24:08 GMT


jdickson@festival.ed.ac.uk (John Dickson) wrote:

>Slightly off the original subject matter...what factors does changing
>the bracing height influence?

>1: Tiller?
No
>2: Nocking Point?
No
>3: Initial Draw Weight?
Yes, increasing BH the initial draw weight can increase little because
the bow is pre-charged
>4: Full Draw Draw weight?
Yes, Increasing BH the limbs are more stressed at full draw
>5: Type of nocking point?
No
>Others that you want to mention???
Arrow velocity: the speed of your arrow decrease because the total
amount of energy stored in the full draw bow decrease.
The run of the string decrease with more bracing.

>I reckon #3 is easy enough, yes, higher bracing height = higher initial
>draw (ie the effort it takes to move the string in the first place)

>#4 is very hazy, you are still only drawing the bow the same distance
>but the string is effectively a different length and the bending in the
>limb is slightly different....does higher BH = Higher draw weight?
>Certainly it usually makes arrows perform weaker (higher impulse energy?)
Is possible that you must use a stiffer spined arrow with a higher
bracing, because the initial impulse become harder. This if you are in
a "limit"condition.

>#1 I reckon depends on your bow and how much you change the BH. Like i
>said before mine doesn't appear to change....does yours?
Me too

>#2 again with my bow it doesn't appear to but that doesn't mean that it
doesn't!
With more bracing the nocking position is less sensitive. The
bow-arrow setup is more tolerant

>#5 well if you change from a few wispy bits of superglue and thread to
>two great big metal nocking points then surely it's going to change your
>setup? However is ideal BH one of the things it changes?
>(This brings on the note that if you tune your bow with floss or tape
>nocking points and then stick on damn great big nock sets it isn't going
>to shoot the same!)
In my experiment, a little weight increasing on nocking point increase
virtual mass of the dinamic components of bow-arrow. It is a little
ecreasing factor of arrow speed.

>OK that's about it for now, just trying to stir up a little discussion.

>                               John
>--
>John Dickson,(aka Stretch)    

Vittorio Brizzi

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From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Your Bracing Height? (Was: Bracing height and string length)
Date: 6 Nov 1995 10:01:51 GMT


vittorio.brizzi@bo.nettuno.it (Vittorio Brizzi) writes:

>jdickson@festival.ed.ac.uk (John Dickson) wrote:

>>Slightly off the original subject matter...what factors does changing
>>the bracing height influence?

<SNIP, lots of points we agree on>

>>Others that you want to mention???
>Arrow velocity: the speed of your arrow decrease because the total
>amount of energy stored in the full draw bow decrease.
>The run of the string decrease with more bracing.

Yes technically the string stays in contact with the nock longer and has
the opportunity to transfer more kinetic energy, in practice however I
don't feel that lower bracing height always guarantees more speed.

For starters you need to consider the limb design, yes the bow has
higher pre-loading but it also has higher full draw weight. Surely the
speed will only increase with lower B-H if the pre-loading outweighs the
full draw weight reduction? I believe that my bow is faster at a higher
B-H than it is at a lower one. The shot is a lot smoother and far more
of the energy is converted to arrow speed and less into noise and
vibration.
  
I know that your stabilisers and other accessories which damp the
reaction of the bow don't actually do much until the arrow is off
the string so they shouldn't really affect the speed.

Another thing that affects the speed of the arrow is the quality of
the energy transfer. If the bow is smoother at a higher B-H then the
energy transfer will be more efficient because the arrow is accelerated
smoothly from the bow.

So, I'll agree that Bracing Height affects your bow speed but whether it
makes your bow faster or slower depends on the archer/bow setup and
design (although most archers are of similar design B) )

All these points are only addressing Recurve bows (as far as I'm
concerned) I really wouldn't know about Wheelies.

                                
John Dickson,(aka Stretch)   

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