Brace height to String Length relationship.

dvd8n

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I have a string which is (unwound) pretty near the top of my brace height range.

About how much longer do I need to make a string (ballpark, I know it's impossible to be be precise) to drop the brace height by an inch so that I can play with the brace height.

I don't do this stuff often enough myself to have a feel for it.
 

sreynolds

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Use geometry (Pythagoras) to approximate the relationship between string length and brace height.
(I've written the math out here in a wordy way since I don't seem to have the proper font to represent exponents.)
If A is half the length of your string and B is your brace height, then Pythagora tells us that A-squared plus B-squared equals C-squared.
Calculate C-squared (C will be approximately half of your AMO bow length) using the current brace height and string length.
Then, keeping C constant, subtract 1 from B and solve for A to get your new string length.
A equals squareroot of (C-squared minus B-squared)
 

dvd8n

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I've actually tried to do that in the past and didn't have a lot of success.

I decided that it it was because the hypotenuse wasn't constant and effective string length unpredictable due to the limbs flexing and the recurves uncurling.

Or it could have been my cr@p maths :covereyes
 

flint666

Member
Dont overcomplicate things , get a ball of string tie a loop in the end and use this to string the bow, tighten string untill desired brace hight is reached . Mesure length of string compare to length of old string and note difference get new string made to new length. Job done
 

sreynolds

New member
Dont overcomplicate things , get a ball of string tie a loop in the end and use this to string the bow, tighten string untill desired brace hight is reached . Mesure length of string compare to length of old string and note difference get new string made to new length. Job done
Flint, making things too easy :)
Just to get you in the ballpark, you're probably going to be looking at a string about 1/2 inch longer than the string you have.
 

Rik

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I have a string which is (unwound) pretty near the top of my brace height range.

About how much longer do I need to make a string (ballpark, I know it's impossible to be be precise) to drop the brace height by an inch so that I can play with the brace height.

I don't do this stuff often enough myself to have a feel for it.
Simple estimate: string your bow, measure the string length. Measure the bh.
Add 20 twists. Re-string. Measure the string length again. Measure the bh again.
That gives you an approximation of how bh changes with length on your setup.

As a very rough estimate, take it as 2:1 ratio. 1 cm of string length equals 2cm of bh. But that's really "rule of thumb" territory.
 

lbp121

Member
Rough guide for recurve would be 1/2" longer string gives about 3/4" lower brace. Or you get a long string with a regular loop one end and use an adjustable bowyers knot on the other to make a temporary string to measure.
 

dvd8n

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Thanks for all the suggestions. I ended up making it a third of an inch longer which dropped it an inch which was more than I wanted but I can live with it :)
 
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