# Olympic Bow Length



## scolist (Sep 16, 2014)

Can anyone tell me the proper way to measure the length of an Olympic Recurve?

How many twists can I add to my bow string to achieve proper Brace Height?


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## rstgyx (Apr 13, 2013)

Easiest way to measure an OR is via the length of the riser and limbs. 

25" riser + short limbs = 66" bow
25" riser + medium limbs = 68" bow
25" riser + long limbs = 70" bow

27" riser + short limbs = 68" bow
27" riser + medium limbs = 70" bow
27" riser + long limbs = 72" bow


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## RickBac (Sep 18, 2011)

Scolist, that is an interesting question.

The basic guide above give you your bow size. However that does not necessarily give you your string length in the usual method. Bow Length minus 4" give you string length, that does not always work, brace height can be too large and have not twists in the string yet.. We have been doing 3" less then bow length then putting the twists in to get your brace height.


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## dchan (Jun 29, 2004)

RickBac said:


> Scolist, that is an interesting question.
> 
> The basic guide above give you your bow size. However that does not necessarily give you your string length in the usual method. Bow Length minus 4" give you string length, that does not always work, brace height can be too large and have not twists in the string yet.. We have been doing 3" less then bow length then putting the twists in to get your brace height.


Actually the proper method is much more complicated.

from the AMO standard

========================
AMO CONVENTIONAL
BOW LENGTH STANDARD
AMO Bow Length Standard is designated to be three inches longer than AMO
Bow String Master that braces bow at proper String or Brace Height. Bow String
Master will carry only the bow length designation. Example: A Bow String
Master designated as AMO 66” (bow length) will have an actual length under
tension of 63”.
Cable length is determined by placing loops over 1/4” diameter steel pins and
stretching under 100 pound load and measuring from outside of pin to outside of
pin. Tolerance is +-1/16”. End loops of cable will be 1 1/4” long and plastic
coated.
Bow String Master shall have the following material specifications or equivalent:
1/16” 7 x 7 galvanized (Mil-C-1511) or stainless (Mil-C-5424) steel aircraft cable
of 480 lb. test.
A Bow String Master Set shall consist of twenty-five Bow String Masters to
measure bow lengths in one inch increments ranging from 48” to 72”; (i.e. actual
string lengths 45” to 69”).
The AMO prefix to bow lengths in inches means that the bow has been manufac-
tured to a length that properly uses a bow string designated with the identical
AMO marking. (i.e. A bow marked “AMO 60”, 50 lb. will brace to the proper
string height with a string marked “AMO 60”, 45 lb. to 55 lb.

=======================

Copy of this document can be found here

http://peteward.com/AMOStandards.pdf 

and there's a link to it in my sticky thread.


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## Mr. Roboto (Jul 13, 2012)

So how long is a "short" or a "Medium" or a "Long" or a "Extra Long" or a "Extra Short" limb? I have a tape measure at home, I have calipers at home, and I have CMM machines at work, so where does one measure on these limbs to determine length? Someone tell me where to measure.

Is 25 inches on a 25" riser the real geometrical dimension when added to physical measurements from the actual limb? Or is it really 20 inches.

The equations that rstgyx presents are some of the commonly accepted look up chart data. But do they relate to real physical measurements? Not really, especially when there are vague terms like short, medium, long, etc.

Does not Hoyt's new risers and limbs have different key dimensions, and yet, they think people are incapable of handling real numbers so they keep using the same vague terms?

With new "standards" entering the market every year, which then no one follows, shouldn't we instead just get used to using real hard numbers? When putting pieces together from different manufacturers that do things differently, using hard, physically measurable, numbers makes it a whole lot easier to figure out what size string one needs for their new set of hardware.


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## rat4go (Apr 14, 2011)

From the Sky Archery FAQ. Don't know if it helps or becomes confusing but...
Q.

How do you calculate bow length?

A.

The length of the bow is determined by adding the distance between the riser bolts to the length of both limbs.

Bolt Pattern is the length between Limb Bolts.The Bolt Pattern is 5" shorter than the Riser.I.L.F. Limb lengths are: Short 23", Medium 24", and Long 25".Example: 15" Riser + Long Limbs = 60" Bow10" Bolt Pattern + (2 X 25" Limbs) = 60" Bow


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## dchan (Jun 29, 2004)

Mr. Roboto said:


> So how long is a "short" or a "Medium" or a "Long" or a "Extra Long" or a "Extra Short" limb? I have a tape measure at home, I have calipers at home, and I have CMM machines at work, so where does one measure on these limbs to determine length? Someone tell me where to measure.
> 
> Is 25 inches on a 25" riser the real geometrical dimension when added to physical measurements from the actual limb? Or is it really 20 inches.
> 
> ...


While I'm sure there are specifics to the measurements, there are way more people that don't know how to use tools or tape measures properly and add to the fact that there are curves to account for, angles of the limb pockets, etc it would be very hard to explain to the general public how to measure the exact distances.

That being said, the overall length of a "25 inch" riser is just short of 25" If you measure the bolt pattern, it is NOT 5" less than the rated riser length. 
If you take rat4go's information from sky archery as fact, then other things don't add up. I have a medium limb in my hand right now and if you measure it from the center of the limb bolt to the tip of the limb, you would get 24" however if you measure it from the base of string notch to the limb bolt center you would get a different measurement. 

If you take this measurement along the outside of the curve compared to the inside of the curve of the recurve, you would also have discrepancies. Depending on how thick the limb is, and how much angle there where the limb bolt goes through the limb would also change these measurements.

So I agree with Hoyt and other MFG's to tell people riser length = x" as just short of the over all length, and the limb lengths as X short-short-med-long-xlong. and then advertise that an xshort limb on "x inch" riser will create an x inch long bow based on the AMO designation. If a MFG decides to change the geometry such as Kaya or Border does with their limbs, and they calculate where the best "brace height" is for performance, they can build the sizes to match the proper AMO to correspond to the designations of limb length and still come up with an understandable system for the general public.

Every limb I have seen is marked with it's "length". so I don't understand why we really need to know how long that is.

DC


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## scolist (Sep 16, 2014)

Gear in question: SF 25" Forged Riser+ recurve riser and SF Axiom + recurve Long Limbs. Considered as a 70" bow. String is a Cartel Fast Flight Recurve 14st - 70".

In a 2+ hour chat with LAS yesterday, I asked why am I only able to achieve a BH of 8" and that was with approx 50 twists in the string. They gave me a generic response of "just use generic numbers, and you should be okay". Well how do I know that SF used generic numbers in their design? Turns out SF recommends a BH of 22,5-24,5cm (8.85-9.65"). But yet, those are numbers I can't obtain, nor could LAS help me with obtaining them. LAS then gave me this, The 2015 Hoyt Target Recurve Archery manual, and said to read pages 23,24,and 25 where it show a BH of 8.75-9.5". On page 26 the BH for the Prodigy, Progidy XT, Formula HPX, Ion-X, and the GPX, they list a BH of 8.0-8.75".

As a total beginner, I'm not willing to risk having the bow, blow up in my face. So I posted in hopes of some insight and knowledge from those who know.

One more thing.....................I found that if you measure your bow with limbs attached, unstrung, around the outside of your bow, you'll be much closer to knowing the actual bow length.


Thanks,
Scott


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## dchan (Jun 29, 2004)

So if the primary question is how much can you twist that string, A lot more than 50 twists. 50 twists is not even 1 twist per inch. if your string is starting to hold kinks when strung, you have twisted it too much. It may not be ideal but that's how far you can go. Twist away.

If you read the manuals for Formula system Hoyt's and most of the reviews, you would find that most actually state that the BH for those bows is a lower range than "normal" whatever normal is.

A SF Forged + with long limbs (70" bow) you will probably find the sweet spot around 9.00-9.25"

The other thing you will find is those first 50-75 twists seem to not do much, then as you get up there in the 80 twist range one or 2 turns may change your BH by much more. 

How long is your is your string (actually) not the "amo length" which will be about 3.25"-4" shorter than your target bow length.

DC


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## dchan (Jun 29, 2004)

And there's not much chance of that bow blowing up in your face with a very low BH or very high BH. It will feel different and may sound real loud but blow up in your face? unless you dry fire it a few times, odds are almost zero to none.

DC


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## scolist (Sep 16, 2014)

DC 

Thanks for your response

From beginning of loop is 63". Total overall is almost 66.5".


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## dchan (Jun 29, 2004)

Strings should be measured on 2 posts, each 1/4" in diameter. The measurement used is the center of each post. per AMO.

66.5 measured the way it sounds like you did, puts your string probably around 66.25 so probably pretty close.


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## Mr. Roboto (Jul 13, 2012)

scolist said:


> Gear in question: SF 25" Forged Riser+ recurve riser and SF Axiom + recurve Long Limbs. Considered as a 70" bow. String is a Cartel Fast Flight Recurve 14st - 70".
> 
> In a 2+ hour chat with LAS yesterday, I asked why am I only able to achieve a BH of 8" and that was with approx 50 twists in the string. They gave me a generic response of "just use generic numbers, and you should be okay". Well how do I know that SF used generic numbers in their design? Turns out SF recommends a BH of 22,5-24,5cm (8.85-9.65"). But yet, those are numbers I can't obtain, nor could LAS help me with obtaining them. LAS then gave me this, The 2015 Hoyt Target Recurve Archery manual, and said to read pages 23,24,and 25 where it show a BH of 8.75-9.5". On page 26 the BH for the Prodigy, Progidy XT, Formula HPX, Ion-X, and the GPX, they list a BH of 8.0-8.75".
> 
> ...


Exactly.

What is wrong with providing key assembly/mounting dimensions for the hardware so this confusion goes away. People shouldn't have to come to a forum or spend 2 hours talking to the sales rep just to find out how long a string to get. Limbs should be marked with a length from limb bolt to string groove and the riser should be dimensioned from limb bolt to limb bolt. And then when they assemble the bow, a tape measure from string groove to string groove on the back side of the bow should approximately equal to three earlier numbers. Then buy a string that is 3 inches shorter.

People do get smacked in the head when a bow explodes. I have experienced it personally on two different occasions.


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## scolist (Sep 16, 2014)

Dc, The string was measured freehand. But when you measure twists, is that 180deg, or 360deg?


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## dchan (Jun 29, 2004)

I think of one twist as 360. if you did 180 then you have a long way to go. 

AMO says you would stretch the string under tension to measure. quite a bit of tension actually.

as far as bows exploding, in my 35+ years of active shooting, I can count on one hand how many catastrophic failures I've seen or been personally party to. Only one was a metal riser and it was a compound..

All the other failures were twisted limbs releasing the string upon being shot, cut strings due to sharp edges on the limbs or a wood riser that De-laminated. I think one was a stabilizer that broke off at the bolt, one was a dry fire that caused a riser bolt failure.
All other failures I've witnessed were stupid mistakes, by the operator or incorrect setup. None were catastrophic. A few were caught as problems but not exploding as they were caught during routine checks of gear.


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## dchan (Jun 29, 2004)

Mr. Roboto said:


> Exactly.
> 
> What is wrong with providing key assembly/mounting dimensions for the hardware so this confusion goes away. People shouldn't have to come to a forum or spend 2 hours talking to the sales rep just to find out how long a string to get. Limbs should be marked with a length from limb bolt to string groove and the riser should be dimensioned from limb bolt to limb bolt. And then when they assemble the bow, a tape measure from string groove to string groove on the back side of the bow should approximately equal to three earlier numbers. Then buy a string that is 3 inches shorter..


How do you get someone to measure limb bolt to limb bolt when the bolts are not parallel? If you tell them to measure the center of the bolt at the head, and they are not cranked in the same distance, from one riser to the next, that measurement changes. If you tell them to measure from the center of the bolt hole, do they have to remove the bolts and have a special caliper to measure? most bows have limb pockets so you can't see or line up the location to measure from.

Because the the geometry of the limbs are different, (more recurve for border's for instance) and they suggest a lower BH to take advantage of it measuring that distance will not give you proper measurement either.

Where we use 15, 17, 19, 21, 23, 24, 25, 27 as riser standards and most limbs are marked as " _xx" on an XX" "riser or handle"_ " along with the xs, s, m, l, xl being pretty standard, I think we have a pretty good system. Especially since how many different MFG's there are and how many models, and we pretty much can put it right in the ball park 98% of the time.


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## Bob Furman (May 16, 2012)

And now we are back to shooting two sticks attached by a taught string as it should be. What have we now learned?


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## Mr. Roboto (Jul 13, 2012)

I know, its a system that many people are used to using a lookup table to get the total bow length. My point is that a manufacturer that makes the xs, s, m, l, and xl limbs know what the linear length is in mm and in inches between the critical features. The manufacturers also know for their risers the critical dimensions for the riser. The pieces of equipment can be easily marked with the real numbers, the packaging, websites, and all literature can be marked with real engineering numbers. No guess work, no miss understanding, no miss calculating. So if one manufacturer wants to sell a riser that the critical dimensions are 22 inches, and a different manufacturer has a new limb design that is 23.5 inches each, one can easily just add the numbers up to a 69 inch long bow, and the required string would be 66 inches long. The manufacturer doesn't need to provide any special instructions or interpretations of the riser length, and doesn't have to come up with a new limb name like extra-medium.

As more and more companies come on line with their unique hardware and special designs, these vague terms are going to become more of a problem and new vague terms have to be created.

What is interesting is this AMO standard organization doesn't even exist anymore. I am pretty sure that if ISO got involved with the standard, hard numerical dimensions would be required.


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## dchan (Jun 29, 2004)

While we call it "AMO" the organization is now ATA (archery trade association) and they are still around. 

Any mfg can build a bow, limbs or riser of any size. The AMO standard just says they should label it to match the measurements set forth in the standard. Spacing of specific holes like sight mounts are specified as well.


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## Mr. Roboto (Jul 13, 2012)

Have you been to the ATA website lately? It is all about the business marketing and trade shows with regards to archery. I haven't found anything that relates to standards there. It is as if the standards part of the organization has vanished. Most organizations charge outrageous fees to get copies of their standards, but at least they make reference to them on their websites.

I think I have the most recent AMO standard, last revision May, 2000. Unfortunately, it doesn't address the issues I bring up.


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## scolist (Sep 16, 2014)

Well here's what I came up with.

Gear:
SF 25" Forged+ riser
SF 30# Long Axiom+ Limbs
Cartel Fast Flight 14st 70" String.

Using Hoyt's manual, I am six total revolutions out, after bottoming out the limb bolts. I started with 80 twists, and had to come down to 60 twists to achieve a 9" BH. And I adjusted Tiller from that point.

Thank you all for your help!

Scott


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## Warbow (Apr 18, 2006)

Mr. Roboto said:


> Have you been to the ATA website lately? It is all about the business marketing and trade shows with regards to archery. I haven't found anything that relates to standards there. It is as if the standards part of the organization has vanished. Most organizations charge outrageous fees to get copies of their standards, but at least they make reference to them on their websites.
> 
> I think I have the most recent AMO standard, last revision May, 2000. Unfortunately, it doesn't address the issues I bring up.


The By Laws of the AMO/ATA were changed. The technical committee is specifically prohibited from creating "standards". They do, however, now create "guidelines", which are published in the ATA Technical Guidelines manual.

http://www.archerytrade.org/news/tech-guidelines-promise-consistency

I don't know, though, if they've published anything since the first edition in 2009.

I really wish the ATA would reach out to archers with relevant info, not just to manufacturers.


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## dchan (Jun 29, 2004)

and wonder of wonders,

THEY CHARGE FOR COPIES. 30.00 if you are not a member.

Also ASTM was given control of some of the testing "standards" and guess what! They charge too..


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## Warbow (Apr 18, 2006)

dchan said:


> and wonder of wonders,
> 
> THEY CHARGE FOR COPIES. 30.00 if you are not a member.
> 
> Also ASTM was given control of some of the testing "standards" and guess what! They charge too..


Yeah, I don't need to know the specs for making inserts and what not, but ATA draw length, bow length, string length, arrow spine, etc. are all standards that are relevant to end users. ATA spends a lot of msrketing money trying to drive traffic to their Archery 360 and Release Your Wild sites, they should consider posting something that is actually useful, such as the ATA guidelines, and maybe a discussion about their relevance to archers.


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## Mr. Roboto (Jul 13, 2012)

Yeah, its just crazy talk to actually let the customers and end users know the specifics of the hardware they spend a lot of time and money on. It is the mushroom principle.


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## mahgnillig (Aug 3, 2014)

dchan said:


> A SF Forged + with long limbs (70" bow) you will probably find the sweet spot around 9.00-9.25"
> DC


Good info, thanks! This is the combo my hubby is using (SF Forged+ with long limbs), I will let him know to try this as a ball park brace height. I tried tuning mine by sound (started at the minimum recommended and kept adding 5 twists at a time). To be honest, I couldn't tell any difference in sound at all [emoji15]. Is this something best done with a decibel meter? I'm using a 23" SF Forged + with medium limbs. I ended up setting the brace height right in the middle of the manufacturers recommendation (23.5cm), basically because I had no idea what was best.


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## dchan (Jun 29, 2004)

It's actually kind of cool. It will seem like nothing's happening for a while as you slowly increase the brace height and then all of a sudden it's real quiet. Then if you keep going it gets louder again. Then you back off a few twists and you will get back into that sweet spot.

As you learn what you are listening for, you will find that just 1 twist can often make the difference but it's way more subtle at that point.

Hmm. Jen, knows something about skiing, lives near in or near Reno..

You wouldn't happen to be a ski instructor?


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## Fury90flier (Jun 27, 2012)

on her string length...is it AMO length or actual length? It seems that given the number of twists that have been put into the sting, that her string is too long.

maybe I'm missing something...or it's late and I'm tired...so, missing something.


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## dchan (Jun 29, 2004)

23" riser, and medium limbs, 66" bow, average configuration, I would probably be looking to be around 8.75" maybe 8.9" as a starting point for your brace height..

You sure you're at 23.5? I would have expected a 23" SF Forged + would have been 21.5-23.5 for it's range.

and now going through all the documents I can find, 23" risers by SF and Win&win all show 20.5cm-23cm for the range with medium limbs.

DC


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## dchan (Jun 29, 2004)

Fury90flier said:


> on her string length...is it AMO length or actual length? It seems that given the number of twists that have been put into the sting, that her string is too long.
> 
> maybe I'm missing something...or it's late and I'm tired...so, missing something.


yeah the twist count is getting towards the high side but not unreasonable.

PER the Hoyt tuning manual and also my experience, if the string is not "knotting or kinking" as you twist it, you can keep going.. .5-1.5 twists per inch is within reason.


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## Fury90flier (Jun 27, 2012)

scolist said:


> Well here's what I came up with.
> 
> Gear:
> SF 25" Forged+ riser
> ...


what did I miss... riser length is 25"


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## dchan (Jun 29, 2004)

mahgnillig said:


> Good info, thanks! This is the combo my hubby is using (SF Forged+ with long limbs), I will let him know to try this as a ball park brace height. I tried tuning mine by sound (started at the minimum recommended and kept adding 5 twists at a time). To be honest, I couldn't tell any difference in sound at all [emoji15]. Is this something best done with a decibel meter? I'm using a 23" SF Forged + with medium limbs. I ended up setting the brace height right in the middle of the manufacturers recommendation (23.5cm), basically because I had no idea what was best.





Fury90flier said:


> what did I miss... riser length is 25"


we switched gears on you..


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## Fury90flier (Jun 27, 2012)

lol...crap, my wife does the same thing.


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## mahgnillig (Aug 3, 2014)

dchan said:


> Hmm. Jen, knows something about skiing, lives near in or near Reno..
> 
> You wouldn't happen to be a ski instructor?


I would love to be a ski instructor! Maybe when I retire  Right now I'm just an average idiot with too many expensive hobbies  

I will try the brace height tuning again... I just realized the manual I have doesn't differentiate between 25" and 23" risers, so maybe the issue is that I didn't start low enough.


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## Fury90flier (Jun 27, 2012)

The only time you have too many expensive hobbies is if you're married...lol.


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