Bow measurement confusion

Bertiee

New member
I've been shooting for a while and I'm trying to understand bows a bit better. My current one is fairly low end and I got it from an archery shop who did all the measuring and sizing with me and I just let them get on with it. My knowledge is on the level of 'pull the string back, watch the arrow go' but I'd like to expand it a bit so I can look into increasing my draw weight.

My current limbs (Core Ignite short) say this on them:

25H 68-28
23H 66-30

Now my understanding was that this means if you put them on a 25" riser (which I have) and then measure from tip to tip (unstrung) then the bow length would be 68". However when I measure it I get 64". I'm fairly sure I can use a tape measure correctly and even if I'd measured the riser incorrectly I'd still be 2" out! Can someone explain what I'm misunderstanding please?

Thanks!
 

Rik

Supporter
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It's not quite so simple...
The standard for a conventional profile of limb says it is a 68" bow, if it braces correctly with a 65" string. Length is 3" longer than a "standard" string.
If you're looking at a non-conventional profile (long-bow type, or super recurve) then that doesn't apply, you have to go by how the manufacturer designates things.

Basically, bow length is a convention, rather than something you directly measure
 

geoffretired

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I have a vague notion that the limbs are measured following the curve; that would add something to the shortness noticed by Bertiee.
 

dvd8n

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My understanding is that it all goes back to the longbow. A longbow is a straight stick and easy to measure. When you went to a shop for a string your tell them your bow length and they'd give you a string 3" shorter and it'd brace ok.

When recurves became a thing they were a lot harder to measure and string length not so predictable so manufacturers gave them a nominal length that was 3" longer than the string that they needed. This meant that when the you asked for a string and were asked your bow length you'd still get a string length that would brace correctly.

That may be apocryphal...
 

Rik

Supporter
Supporter
My understanding is that it all goes back to the longbow. A longbow is a straight stick and easy to measure. When you went to a shop for a string your tell them your bow length and they'd give you a string 3" shorter and it'd brace ok.

When recurves became a thing they were a lot harder to measure and string length not so predictable so manufacturers gave them a nominal length that was 3" longer than the string that they needed. This meant that when the you asked for a string and were asked your bow length you'd still get a string length that would brace correctly.

That may be apocryphal...
I think that's exactly it. That's why the AMO standards were worded that way: so that you could just order a string by specifying the bow length, or if you knew the bow length, that would tell you how long the string should be.

Hampered a bit by the way mixing and matching kit means nothing ever exactly follows the rules...
 

Stretch

Active member
I agree with Geoff. Different manufacturers do it differently But basically it means running the measure along the curve of the limb - whether that it tip or string groove seems to vary. Also I think they then measure dovetail to dovetail to get the riser length (so ignoring the profile). So a Super Recurve 70” looks a lot shorter than a “normal” 70” and so on.

Rediculously long (75”), Absurdly long (74”),Really Long (72”), Quite Long (70”), Nearly Long (68”), Not very long (66”), Not long (64”), Unlong (anything else) might be more helpful.

So many factors in choosing bow length - arrow length is primary but dependent on your hook you might need to go up or down for nock pinch. Also length of nose/anchor location. Bow speed. And of course testosterone levels.

Stretch
 
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Bertiee

New member
It's not quite so simple...
Glad to hear I haven't failed dismally at measuring and maths!

I agree with Geoff. Different manufacturers do it differently But basically it means running the measure along the curve of the limb - whether that it tip or string groove seems to vary. Also I think they then measure dovetail to dovetail to get the riser length (so ignoring the profile).
That would certainly make more sense as going to the groove I get 68".

My follow up question is how this all relates to draw length. Based on what I can find online with my draw being around 27-28" I'd use a 66-68 bow which is what I have at the moment. With the variations in size that have been mentioned and the fact that this estimation uses a range anyway is there (a) any particular way for me to identify what's my best draw length and (b) if my bow length is a couple of inches out am I really going to notice with my limited amount of experience?

Thanks for all the replies
 

geoffretired

Supporter
Supporter
My thinking is, that in days past, having a short bow and long draw length would be a recipe for a breakage. Having a long bow and a short draw length, would mean the bow wasn't being drawn far enough to get the best from it.
With modern glues and materials, I think the shorter bows would survive being drawn a bit further than necessary. Longer bow would still give less than ideal performance with a short draw.
It is worth noting that a short bow gives a more acute angle of the string at full draw; so fingers may feel more pinched together than on a longer one.
 

KidCurry

Well-known member
AIUK Saviour
I have a 29" draw. I have two bows that I shoot for score at 68" and one cheap-as-chips bow that is 66", principally to shoot indoors (my landing) without filling the ceiling with holes. I would be hard pushed to tell the difference between the two bow lengths and both shoot perfectly okay.
 

Bertiee

New member
I have a 29" draw. I have two bows that I shoot for score at 68" and one cheap-as-chips bow that is 66", principally to shoot indoors (my landing) without filling the ceiling with holes. I would be hard pushed to tell the difference between the two bow lengths and both shoot perfectly okay.
Useful to know, although I'm wondering what you shoot at on your landing!
 

mk1

It's an X
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Glad to hear I haven't failed dismally at measuring and maths!



That would certainly make more sense as going to the groove I get 68".

My follow up question is how this all relates to draw length. Based on what I can find online with my draw being around 27-28" I'd use a 66-68 bow which is what I have at the moment. With the variations in size that have been mentioned and the fact that this estimation uses a range anyway is there (a) any particular way for me to identify what's my best draw length and (b) if my bow length is a couple of inches out am I really going to notice with my limited amount of experience?

Thanks for all the replies
It's all do do with whether you are under drawing or over drawing the bow. When you draw back a bow you bend the limbs - that is self evident I know - but for a set of limbs there will be an optimal range, below that you will not store enough energy and above that there will be decreased benefit and also undue stress and possible stacking (and I realise modern limbs are built like tanks) and limbs oscillate when let go so you can introduce more torque. If you take the premise that you want the maximum power from the lightest limbs suitable for you then you need also to take account of finger pinch; so someone with chunky fingers may have to go up length ahead of someone with slim fingers.

There are lots of articles availebl about this I've dug up a paper by Joe Tapely who was active in studying and writing about archery mechamics some decades ago TOPICS ON ARCHERY MECHANICS . If you go down to The Draw Force Curve section on page 13 of this paper - http://witchfordarchers.drmsite.com/resources/Archery Mechanics.pdf - you can read to your heart's content.
 

Bertiee

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munchkin

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It's all do do with whether you are under drawing or over drawing the bow. When you draw back a bow you bend the limbs - that is self evident I know - but for a set of limbs there will be an optimal range, below that you will not store enough energy and above that there will be decreased benefit and also undue stress and possible stacking (and I realise modern limbs are built like tanks) and limbs oscillate when let go so you can introduce more torque. If you take the premise that you want the maximum power from the lightest limbs suitable for you then you need also to take account of finger pinch; so someone with chunky fingers may have to go up length ahead of someone with slim fingers.

There are lots of articles availebl about this I've dug up a paper by Joe Tapely who was active in studying and writing about archery mechamics some decades ago TOPICS ON ARCHERY MECHANICS . If you go down to The Draw Force Curve section on page 13 of this paper - http://witchfordarchers.drmsite.com/resources/Archery Mechanics.pdf - you can read to your heart's content.
Oh my word this takes me back and definitely makes me feel old!
A 64in bow comes up to my eyes/forehead when strung, a 66in bow comes up to the top of my head, and a 68in bow is taller than me (all when standing the bottom limb tip on my shoe). That's how I tell bows apart....
 
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