# Draw weight v.s bow mass



## lksseven (Mar 21, 2010)

"Because they're just that good." Not meant as a smart ***** response


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## theminoritydude (Feb 11, 2013)

Have you weighed their risers and their stabilizers?


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## Stash (Jun 1, 2002)

Why would it “seem logical” that there would be a direct correlation between bow mass and draw weight?

Archers who know what they are doing will try just about every reasonable stabilizer configuration to see what actually holds steadiest and feels best _*for them*_ regardless of what “should” work best. And it’s purely subjective, and not quantifiable.


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## PregnantGuppy (Jan 15, 2011)

Stash said:


> Why would it “seem logical” that there would be a direct correlation between bow mass and draw weight?
> 
> Archers who know what they are doing will try just about every reasonable stabilizer configuration to see what actually holds steadiest and feels best _*for them*_ regardless of what “should” work best. And it’s purely subjective, and not quantifiable.


Because they interplay with each other. The slight vertical component of the draw force acting on the shoulder's pivot point is counter-acted by the mass weight of the bow. So in theory, more draw weight means the bow needs to be loaded more to balance out, or you end up with extra strain on the shoulder.

That being said, I agree with your latter point more. Ultimately, that correlation is an idealization of how things should be, and people should instead just play a bit and figure out what works best. Clearly that is what the Korean ladies did, and it definitely seems to work for them, just as the heavier setups work for the other archers that were used as examples in the OP.


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## Vittorio (Jul 17, 2003)

Mauro Nespoli has won World Cup Gold in Salt Lake shooting 64# on fingers. Who does not trust, can have a look to the measured speed of 239 Km/h for his arrows. X10 325, 120 gr tungsten point. 
His bow is so heavy that I think not so many archers can even rise it, not to mention to keep it steady on target.

Yes, there is a a direct relationship between poundage and mass weight. But of course it is influenced by the balance of forces at full draw that depends from many other parameters, like grip shape (high grip --> lighter bow) front shoulder position ( high shoulder, again lighter bow), weight distributionon of the stabilizers (not related to the weight on top of them , only, but also to the pure mass of the rods), and finally but not last by the shooting technique: a puller needs much more weight than a pusher to keep (average) the bow on the line at release. 

So, after the usual static balance test (can I aim steadly at full draw?), other parmeters come to play: can I still aim steadly when I try to get out flom cliker? And, if my release id everything but good, is stil the bow helping me (= is it a bit forgiving) on my average mistake? 

At the end what you reach is a compromise between the various basic needs and your average mistakes to compensate. You can't anyhow make a bow too heavy if you want to contine to shoot high grip in push- pull or pushing (Korean girls as average, Thomas Chirault ), but you can't make it too light if you want to be a pure puller (Brady Ellison). 

There are not independent variables in a set up, this has to be very clear every time, and you get something from one side only loosing something on other sides. But, when the wind comes on the shooting line, power and weight do matter.


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## Gregjlongbow (Jun 15, 2016)

Vittorio said:


> Mauro Nespoli has won World Cup Gold in Salt Lake shooting 64# on fingers. Who does not trust, can have a look to the measured speed of 239 Km/h for his arrows. X10 325, 120 gr tungsten point.
> His bow is so heavy that I think not so many archers can even rise it, not to mention to keep it steady on target.
> 
> Yes, there is a a direct relationship between poundage and mass weight. But of course it is influenced by the balance of forces at full draw that depends from many other parameters, like grip shape (high grip --> lighter bow) front shoulder position ( high shoulder, again lighter bow), weight distributionon of the stabilizers (not related to the weight on top of them , only, but also to the pure mass of the rods), and finally but not last by the shooting technique: a puller needs much more weight than a pusher to keep (average) the bow on the line at release.
> ...


Yes. In setting up a bow there are no independent variables. A change anywhere can cause a change somewhere else, and the need to adjust other parameters. 

I’ve r gently got up in draw weight, and down in mass weight and I’m really happy with the feel and the results. Once you go through objective measures, just go by feel. 


Sent from my iPhone using Tapatalk


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## Stash (Jun 1, 2002)

I would agree with Vittorio that there IS a relationship between mass weight and draw weight, but not a DIRECT relationship. There is no meaningful formula such as Dw=CxMw where C is a Constant

Generally, archers who can shoot a heavy draw weight are physically strong enough to also hold a heavier mass weight bow, but that is clearly not universal.

So the discussion is purely for entertainment purposes, since the exceptions could easily outnumber the ones that adhere to the relationship.


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## Viper1 (Aug 21, 2003)

FN - 

Let me preface this by saying I couldn't care less what the Koreans, or Chinese or Americans are doing, I care about what I'm doing and what my students are doing. 

That being said, if can do 20 pull-ups with ease, does that automatically imply you can do 20 military presses with your body weight? 

While we'd like to believe that we are all well rounded physically, fact is that most people aren't and different muscles/techniques are used to draw a bow as to hold one up. Each shooter follows a bell-shaped curve of acceptable weights for each. The ratio between the two may or may not be the same for every one.

Viper1 out.


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## Stash (Jun 1, 2002)

One thing we all missed in the OP was regarding the positioning of the center of gravity, which is a whole different thing. 

My own preference, and it seems to be logical and has a basis in physics, is to maximize the moment of inertia (pardon if I'm not using the term properly) by putting the center of mass of the bow (whatever the total mass actually is) as far away from the pivot point (shoulder) as possible, without allowing the result of releasing the bow on the shot (the "swing") to affect the follow through. 

This does seem to be more universal, at least among top recurve archers and especially top women recurve archers. 

Curiously, the trend for compound archers is the opposite. Heavy back bars which balance the bow neutrally on release are overwhelmingly popular these days.


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## theminoritydude (Feb 11, 2013)

What would the limit of that distance be?


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## damiaan (Feb 17, 2014)

theminoritydude said:


> What would the limit of that distance be?


the point at which the total C.O.G. is in out from underneath the archers footprint... the archer would just topple over!
shoulder might give up beforehand though


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## theminoritydude (Feb 11, 2013)

damiaan said:


> the point at which the total C.O.G. is in out from underneath the archers footprint... the archer would just topple over!


That would be everyone. Unless you’re close to doing a split.


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## toxoph (Mar 24, 2005)




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## Maggiemaebe (Jan 10, 2017)

toxoph said:


> View attachment 6525125


Ouch! Who would have thought?


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## Stash (Jun 1, 2002)

theminoritydude said:


> What would the limit of that distance be?


Again, varies with personal preference. You don't want the bow swinging around wildly and having the lower limb hit you or twist your wrist off.

It is just a matter of inches for the C of M from neutral to extreme, and a single weight too many at the end of a long rod can make your followthrough uncomfortable.


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## damiaan (Feb 17, 2014)

Vittorio said:


> Mauro Nespoli has won World Cup Gold in Salt Lake shooting 64# on fingers. Who does not trust, can have a look to the measured speed of 239 Km/h for his arrows. X10 325, 120 gr tungsten point.
> His bow is so heavy that I think not so many archers can even rise it, not to mention to keep it steady on target.
> 
> Yes, there is a a direct relationship between poundage and mass weight. But of course it is influenced by the balance of forces at full draw that depends from many other parameters, like grip shape (high grip --> lighter bow) front shoulder position ( high shoulder, again lighter bow), weight distributionon of the stabilizers (not related to the weight on top of them , only, but also to the pure mass of the rods), and finally but not last by the shooting technique: a puller needs much more weight than a pusher to keep (average) the bow on the line at release.
> ...


How does Mauro remain injury free at such a high draw weight?


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## OCBrent (Sep 27, 2007)

The Formula is:

Bow Draw weight / 7.6 = Bow Mass Weight

http://www.tap46home.plus.com/mechanics/bowload.htm

Or at least a ballpark place to start. 

But there is absolutely a relationship between your Draw weight and the effective downward/upward force experienced at your bowhand. If you don't see it from Joe's description here, Ray Axford in "Archery Anatomy" goes into more detail.

If something different gives you a higher score, go with that.


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## chrstphr (Nov 23, 2005)

OCBrent said:


> The Formula is:
> 
> Bow Draw weight / 7.6 = Bow Mass Weight
> 
> ...


i also go by this formula. 


Chris


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## Stash (Jun 1, 2002)

OCBrent said:


> If something different gives you a higher score, go with that.


Probably the best single piece of archery equipment advice ever posted on AT


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## PregnantGuppy (Jan 15, 2011)

Stash said:


> My own preference, and it seems to be logical and has a basis in physics, is to maximize the moment of inertia (pardon if I'm not using the term properly) by putting the center of mass of the bow (whatever the total mass actually is) as far away from the pivot point (shoulder) as possible, without allowing the result of releasing the bow on the shot (the "swing") to affect the follow through.


Just to clarify on the physics, moment of inertia is not necessarily maximized by moving out the center of gravity. It definitely increases it, but it is more largely affected by the distribution of the mass rather than its point of cocnentration. That's the whole point behind putting mass 30 inches away from the handle.


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## bahboric (Aug 22, 2013)

OCBrent said:


> The Formula is:
> 
> Bow Draw weight / 7.6 = Bow Mass Weight


I wonder if this formula is way off for low poundage. So, for example, a 35lb draw would need a 4.6lb bow according to this formula. I don't think one could have a typical long rod and side rods and be even close to this formula. And it would be worse as one went lower in poundage. If one is shooting a typical aluminum riser, I'd guess the bow weights are closer to 6lbs (I should go measure mine).


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## theminoritydude (Feb 11, 2013)

toxoph said:


> View attachment 6525125


I am impressed.


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## theminoritydude (Feb 11, 2013)

Stash said:


> Again, varies with personal preference. You don't want the bow swinging around wildly and having the lower limb hit you or twist your wrist off.
> 
> It is just a matter of inches for the C of M from neutral to extreme, and a single weight too many at the end of a long rod can make your followthrough uncomfortable.


Here’s the thing: As counter intuitive as it may be, the rate of angular rotation during the “flip”, is lower for a setup with a center of mass that’s further outward/forward. Basic pendulum principle. The caveat lies in the rotational inertia in the vertical plane, but for two setups with similar vertical mass distributions, the setup with a center of mass that is closer to the archer, tends to flip faster.

Applying the law of conservation of energy, the bow is not expected to flip more than 180 degrees, unless it is given extra push above its center of mass from the hand, which is something a number of archers do, but its effect is minimal.

There is a limit to how far the center of mass should be. It’s based on how a See-Saw works (two loads and a pivot, and in the more advanced way perspective their roles interchange).


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## Stash (Jun 1, 2002)

PregnantGuppy said:


> Just to clarify on the physics, moment of inertia is not necessarily maximized by moving out the center of gravity. It definitely increases it, but it is more largely affected by the distribution of the mass rather than its point of cocnentration. That's the whole point behind putting mass 30 inches away from the handle.


I was referring to the entire bow’s C of M in relation to the archer’s arm/shoulder, not the distribution of weights about the C of M of the bow itself. This is in relation to steadiness of aim, not stabilization of the bow upon release. Two entirely different things.


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## Stash (Jun 1, 2002)

theminoritydude said:


> Here’s the thing: As counter intuitive as it may be, the rate of angular rotation during the “flip”, is lower for a setup with a center of mass that’s further outward/forward. Basic pendulum principle. The caveat lies in the rotational inertia in the vertical plane, but for two setups with similar vertical mass distributions, the setup with a center of mass that is closer to the archer, tends to flip faster.
> 
> Applying the law of conservation of energy, the bow is not expected to flip more than 180 degrees, unless it is given extra push above its center of mass from the hand, which is something a number of archers do, but its effect is minimal.
> 
> There is a limit to how far the center of mass should be. It’s based on how a See-Saw works (two loads and a pivot, and in the more advanced way perspective their roles interchange).


It’s not the rate of angular rotation that is the concern, but the actual amount of the flip. Take a bow with a single long rod and single light weight at the end. Easily managed, and a common starter setup. Then take the same bow and add 10 weights to the end of the rod. Completely unshootable.


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## theminoritydude (Feb 11, 2013)

As I have said, the actual amount of “flip” is limited by conservation of energy, unless extra energy has been added during the initial stage, in the form of a push vertically above the mass center.

Have you actually tried adding.....15oz to the long stabilizer? I’m not advocating doing that for practice, but as a demonstration of those physics principles I have mentioned.


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## Vittorio (Jul 17, 2003)

damiaan said:


> How does Mauro remain injury free at such a high draw weight?


Mauro does a lot of gymn even during the season, to be able to handle such a poundage. Went from 60# to 64# a the beginning of this outdoor season, but he has experimnted up to 70#, already.

People tends to think that what has been done in the past will also be done in future for archery, and that there are absolute limits in many things
Of course, said limits do not exist, apart in our customs and mind.

Bow poundage, if properly transferred to the arrow, gives a lot of advantege in medium windy conditions, and some advantage in all other conditions. Mauro handling 64# today is nothing strange, if you remeber Manus Petterson shooting 56# in 1996. 

With medium wind effective the arrow flight, only, but not so much effecting archer on the line , a 64# archer has an incredible advantge over a 48# archer. being both at same level in calm wether. Seen this year Mauro defeating Michele and Max Mandia a couple of time exactly for this reason only. The result of the Gold match in Salt Lake was written on the limbs of the contenders. 

What is strange is that no other archer has followed this trend, yet. It is an obvious trend, and human limits in this are still unknown.


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## ForeverNewbie (Feb 21, 2018)

Thank you all for your reply and discussion, here is mine (a bit lengthy though)



lksseven said:


> "Because they're just that good." Not meant as a smart ***** response


Will you be so kind to elaborate the logic/reason that the Korean lady use lighter setup because they are good at certain aspect (techniques, equipment tuning, or physical trait, ect.)? Thank you in advance. 



theminoritydude said:


> Have you weighed their risers and their stabilizers?


Unfortunately I have no access to their personal belonging. However, thorough examine the photos, while the Korean ladies use riser with wide array of weight like others, from 1250 g CXT to 1350 g GMX, they almost exclusively use HMC Plus, which I believe is also on the lighter side of the spectrum.



Viper1 said:


> FN -
> Let me preface this by saying I couldn't care less what the Koreans, or Chinese or Americans are doing, I care about what I'm doing and what my students are doing.
> That being said, if can do 20 pull-ups with ease, does that automatically imply you can do 20 military presses with your body weight?
> While we'd like to believe that we are all well rounded physically, fact is that most people aren't and different muscles/techniques are used to draw a bow as to hold one up. Each shooter follows a bell-shaped curve of acceptable weights for each. The ratio between the two may or may not be the same for every one.
> Viper1 out.


I agree with you that most human are not in a symmetric shape with perfect technique that requires a bit fine adjustment for each individual.
However, it requires an foundation of logic for these adjustments.
The common claim I heard a lot is "whatever works for you is the way to go," however, how one knows if something is going to work without knowing why?
One can certainly find out what would work through buying every products in the market and trying every possible combination without a logic behind, I am just too broke and too busy for this path. 
When seeing a group of top performing athletes trained by a given system all favour a particular type of equipment setup delivering excellent results consistently, I would like to understand why they make such choice deviate from others.
Will be very appreciated to hear your rationale about this topic. 



OCBrent said:


> http://www.tap46home.plus.com/mechanics/bowload.htm





Vittorio said:


> Mauro Nespoli has won World Cup Gold in Salt Lake shooting 64# on fingers. Who does not trust, can have a look to the measured speed of 239 Km/h for his arrows. X10 325, 120 gr tungsten point.
> His bow is so heavy that I think not so many archers can even rise it, not to mention to keep it steady on target.
> 
> Yes, there is a a direct relationship between poundage and mass weight. But of course it is influenced by the balance of forces at full draw that depends from many other parameters, like grip shape (high grip --> lighter bow) front shoulder position ( high shoulder, again lighter bow), weight distributionon of the stabilizers (not related to the weight on top of them , only, but also to the pure mass of the rods), and finally but not last by the shooting technique: a puller needs much more weight than a pusher to keep (average) the bow on the line at release.
> ...


Thank you for filling the gap, Vittorio. The "perceived" push-pull (forward-backward) ratio an archer has when going through the clicker is something I missed.
In addition, the shoulder and grip heights and stabilizer mess affecting the preferred bow mass you mentioned aligned with the purposed model in the link above makes the statement very convincing.
(I believe you reached the conclusion independently from the author of the linked page.)
Thank you again for sharing your insight.


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## PregnantGuppy (Jan 15, 2011)

Stash said:


> I was referring to the entire bow’s C of M in relation to the archer’s arm/shoulder, not the distribution of weights about the C of M of the bow itself. This is in relation to steadiness of aim, not stabilization of the bow upon release. Two entirely different things.


They're not that different. Moment of inertia is moment of inertia, regardless of what we are measuring it for. As I said before, moving the center of mass is obviously going to increase your moment of inertia, but so is extending all stabilizers, even if the center of mass is kept constant


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## jmvargas (Oct 21, 2004)

i estimate the poundage these archers are pulling by the position of the sight bar..

nespoli's looks like it's about halfway down or just short of halfway..

the malaysians and taiwanese looks like theirs is just beyond the halfway point..

most of the ladies are 3/4 down or lower..

if nespoli is pulling 64# is it safe to assume the malaysians and taiwanese are pulling close to 60#???


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## waxyjaywalker (Apr 10, 2013)

jmvargas said:


> i estimate the poundage these archers are pulling by the position of the sight bar..


The mounting of the elevation rail on the extension bar for Nespoli looks to be one hole below the middle, while for tan ya ting, for example, one or 2 holes above. So although they may be similar in height on the elevation bar, Nespoli probably has 1/2, 3/4 inch higher sight pin location. Besides, elevation setting on the sight is so dependent on the face-structure and anchor of the particular archer, it's probably not a good indication of pounds on the finger...


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## theminoritydude (Feb 11, 2013)

That’s a very inaccurate way to ascertain now poundage. Sight mount on the Titan EX is slightly different too.


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## chrstphr (Nov 23, 2005)

jmvargas said:


> i estimate the poundage these archers are pulling by the position of the sight bar..
> 
> nespoli's looks like it's about halfway down or just short of halfway..
> 
> ...



Also their arrows are lighter. 

Many of the ladies on the circuit shoot 38 pounds or so. They tend to shoot a 700 X10. I shoot the same poundage but i shoot a 550 spine, sometimes 500. My arrow is heavier and thus i have lower sight marks. 

Sometimes the archers are not shooting the same spine at a similar poundage so looking at the sight can be misleading.

Chris


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## jmvargas (Oct 21, 2004)

theminoritydude said:


> That’s a very inaccurate way to ascertain now poundage. Sight mount on the Titan EX is slightly different too.


he he!..i realise that and i know i'm just making a guess..

anyway the lower it is the weaker the poundage USUALLY is..

in any case does anyone know what poundages the malaysians and taiwanese are pulling?...

i'm guessing high 40s at the very least but most probably in the 50s---which is still awesome for me..


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## Vittorio (Jul 17, 2003)

I have met Mauro Nespoli yesterday at the arrival of the italian team in Milano and asked directly to him. My records have to be updated: he told me the Green bow he was using in the final match was set over 66# already. 

By the way, it seems the a lot of archers are already in the high 50s on the World cup fields.


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## ForeverNewbie (Feb 21, 2018)

In World Archery's website, Mauro Nespoli's draw weight is 52 pound.
https://worldarchery.org/athlete/5796/mauro-nespoli

I believe in Vittorio's information, so this suggests WA measures the poundage as AMO measurement instead of OTF.
Is this assumption correct?


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## Vittorio (Jul 17, 2003)

ForeverNewbie said:


> In World Archery's website, Mauro Nespoli's draw weight is 52 pound.
> https://worldarchery.org/athlete/5796/mauro-nespoli
> 
> I believe in Vittorio's information, so this suggests WA measures the poundage as AMO measurement instead of OTF.
> Is this assumption correct?


WA does not measure poundages at all. They simply register what archers declare when and if asked. This generates a lot of confusion, as quite often they answer using marked limbs poundage instead of off the fingers one. 

For sure Mauro has also shot 52#, sometime in the past, or his limbs are marked 52# ? I will ask.


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## PregnantGuppy (Jan 15, 2011)

Vittorio said:


> WA does not measure poundages at all. They simply register what archers declare when and if asked. This generates a lot of confusion, as quite often they answer using marked limbs poundage instead of off the fingers one.
> 
> For sure Mauro has also shot 52#, sometime in the past, or his limbs are marked 52# ? I will ask.


Wouldn't be surprised if they're marked 52# limbs. With a 31" draw length that WA claims Mauro has, that could easily work out to over 60# OTF.


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## jmvargas (Oct 21, 2004)

if nespoli is now pulling heavier weights than the compounders is he also now approaching or even exceeding their arrow velocities??

i heard the compound transfers its energy to the arrow more efficiently vs a recurve but don't really understand why..


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## theminoritydude (Feb 11, 2013)

Aggregate mass movement. A large part of the limbs' mass transit from point to point. Also depending on the type of cam, given the overall longer cast of compounds, that all adds up to the performance.


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## PregnantGuppy (Jan 15, 2011)

jmvargas said:


> if nespoli is now pulling heavier weights than the compounders is he also now approaching or even exceeding their arrow velocities??
> 
> i heard the compound transfers its energy to the arrow more efficiently vs a recurve but don't really understand why..


It's not really about efficiency. The biggest difference is draw force curve, or otherwise the distribution of the draw weight throughout the draw.

Let me use an example. This site has a draw force curve comparison at the bottom for a compound, a recurve, and a longbow. The big thing to notice is that the draw force curve of the compound is massively different from the other two. In particular, the energy stored in the bow can be shown with calculus to be proportional to the area under the curve for each bow. Even if we scaled down the compound to the same peak weight, it works out to having less area, and therefore less energy.

Furthermore, if you click around on that site you'll notice that they use a very old compound for this example. Modern compounds can manipulate the draw force curve to create even more area under the curve, and therefore more energy and more speed. The trade-off is that the beginning and end of the draw cycle then become very steep on the graph, which is what we would usually call a harsh draw cycle.


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## Viper1 (Aug 21, 2003)

FN - 



> One can certainly find out what would work through buying every products in the market and trying every possible combination without a logic behind, I am just too broke and too busy for this path.


Getting back to YOUR question. It's simpler than you think. 
You start with a generic set up, meaning a long rod with about 6 ounces of weight up front and shoot.
After a while, you'll get a feeling for what the bow is doing or not doing. 
You, or a coach/fellow shooter should be able to figure out what has to be added or change for you to get the desired response. 
Will you ever buy some thing you don't need or like? Sure, but as your experience grows the randomness will lessen. 



> When seeing a group of top performing athletes trained by a given system all favour a particular type of equipment setup delivering excellent results consistently, I would like to understand why they make such choice deviate from others.


Problem is you don't see that, or rather you'll see a different group doing something different and getting the same results. Weights of bow can vary by as much as 20#, and stabilizer combinations are all over the board. Yes Virginia, there are even a few top level shooters who don't always use v-bars. Next you are NOT a top performing athlete (yet), so what they are doing or getting away with after years or decades of daily practice may not be close to what's right for you. Lastly, and bluntly, please remember that a lot of top athletes are sponsored. They don't pay for their gear and are even sometimes told what to use. 

In traditional archery the most common problem with new shooters is being over bowed, with OR, it's new guys wanting what "Brady" uses. 

Viper1 out.


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## theminoritydude (Feb 11, 2013)

PregnantGuppy said:


> It's not really about efficiency. The biggest difference is draw force curve, or otherwise the distribution of the draw weight throughout the draw.
> 
> Let me use an example. This site has a draw force curve comparison at the bottom for a compound, a recurve, and a longbow. The big thing to notice is that the draw force curve of the compound is massively different from the other two. In particular, the energy stored in the bow can be shown with calculus to be proportional to the area under the curve for each bow. Even if we scaled down the compound to the same peak weight, it works out to having less area, and therefore less energy.
> 
> Furthermore, if you click around on that site you'll notice that they use a very old compound for this example. Modern compounds can manipulate the draw force curve to create even more area under the curve, and therefore more energy and more speed. The trade-off is that the beginning and end of the draw cycle then become very steep on the graph, which is what we would usually call a harsh draw cycle.


The integration of the DFC, the area under the graph does accurately quantify the amount of energy stored, but it does not paint the total picture of what jmvargas is talking about - the exit velocity. Stored energy is just that, potential energy waiting to be transformed into kinetic energy. The manner in which the transfer takes place, is the issue here. Of course having a large potential energy store to draw from is an advantage, but the magic of compound lies in the efficient transfer of energy to the arrow, and not somewhere else.


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## ForeverNewbie (Feb 21, 2018)

Vittorio said:


> WA does not measure poundages at all. They simply register what archers declare when and if asked. This generates a lot of confusion, as quite often they answer using marked limbs poundage instead of off the fingers one.


Thank you, Vittorio. This piece of information is an eye opener. 
I used to think they change/update the info based on measurement every year because I remember the commentator mentioned Ki bobae's draw weight as 44 lbs in Shanghai in 2015 but now listed as 41.7 lbs. 
I will need to change my premise of this thread completely then since the info concerning the draw weight in WA website is merely statements but measurements.


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## jmvargas (Oct 21, 2004)

theminoritydude said:


> The integration of the DFC, the area under the graph does accurately quantify the amount of energy stored, but it does not paint the total picture of what jmvargas is talking about - the exit velocity. Stored energy is just that, potential energy waiting to be transformed into kinetic energy. The manner in which the transfer takes place, is the issue here. Of course having a large potential energy store to draw from is an advantage, but the magic of compound lies in the efficient transfer of energy to the arrow, and not somewhere else.



thank you for all the explanations to my concern..

..it's a bit clearer to me now----i think.


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## PregnantGuppy (Jan 15, 2011)

theminoritydude said:


> The integration of the DFC, the area under the graph does accurately quantify the amount of energy stored, but it does not paint the total picture of what jmvargas is talking about - the exit velocity. Stored energy is just that, potential energy waiting to be transformed into kinetic energy. The manner in which the transfer takes place, is the issue here. Of course having a large potential energy store to draw from is an advantage, but the magic of compound lies in the efficient transfer of energy to the arrow, and not somewhere else.


You made me curious enough to crunch the numbers. I used the data on the link I posted before to get this. The bows they use are very old by today's standards, so things might be a bit different nowadays, but it should provide an interesting starting point. I calculated speed by using the last two data points on the position vs time data, kinetic energy using the standard formula, and potential energy by using a trapezoidal approximation of the integral using the draw weight vs draw data.

Compound Speed: 62.07 m/s
Compound Peak Draw Weight: 303 N (~68.1 lbs)
Compound Arrow Mass: 0.0374 kg
Compound KE: 72.0 J
Compound PE: 97.72 J
Compound Efficiency: 74.1%

Recurve Speed: 47.0 m/s
Recurve Peak Draw Weight: 202 N (~45.4 lbs)
Recurve Arrow Mass: 0.031 kg
Recurve KE: 34.2 J
Recurve PE: 58.86 J
Recurve Efficiency: 58.1%

So clearly, there is indeed a significant difference in the efficiency of the compound versus the recurve. However, it doesn't account for the majority of the speed difference. If we just scale up the recurve to the same draw weight and same arrow weight, we get a theoretical speed of about 52 m/s. But then if we magically give it the same efficiency as the compound while keeping the draw force curve (and therefore potential energy) the same, we only get to a theoretical 57.5 m/s. So we're only accounting for about half the speed difference with just efficiency, meaning that there have to be other factors at play, such as the increased potential energy storage.

In conclusion, it seems no one factor is solely responsible for the speed difference in compound bows. It's a combination of a lot of factors together, all making some partial contribution to the speed. Again, this could be very different for modern bows, specially since this example is a very old model, but I unfortunately don't have data for that.


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## theminoritydude (Feb 11, 2013)

This is getting fun.

I have no doubt that your numbers check out. You wish to explain that increase in efficiency using compound, you can find it in my previous post about aggregate mass displacement. 

Moving mass requires energy. Besides the arrow, the other major component that uses the potential energy is the pair of limbs, and in the case of compound, the limbs and the cams. 

Lacking the instruments required to quantify the kinetic energies of both of these equipments, it is difficult for me to offer a side by side comparison. But I reckon the moving mass of a pair of Olympic recurve limbs to be higher, and at a higher final velocity, than the limbs of a compound of similar stored potential energy. The rest of that (awesome) speed comes from the reeling of the string via the cams, kinetic energy drawn from the stored energy approximated to 1 X MV squared where M equals mass of each cam, plus the rotational kinetic energy about the axel of each cam. For an efficient transfer of energy from bow to arrow, the aggregate moving mass of these components have to be relatively light, which is the case of modern compound bows. If you weighed a cam made of aluminum, you’ll know how light they are, compared to limbs.

Which is also the reason why compounds don’t seem to flutter so much or make as much noise than recurve. Because most of that energy is transferred to the arrow, and ends up as drag and impact force on the target.


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## waxyjaywalker (Apr 10, 2013)

While we're getting into the mechanics; I just wonder how much energy gets wasted as frictional heat (from rubbing the leather before string departs) and material compression (leather compression & moving our finger meat around) for a finger+tab release. Intuitively, I'd say it can't be _that _much. But if there's ever a model to reflect the different hook mechanisms, I won't be surprised the mechanical release is orders of magnitude more efficient than a finger release.


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## PregnantGuppy (Jan 15, 2011)

theminoritydude said:


> This is getting fun.
> 
> I have no doubt that your numbers check out. You wish to explain that increase in efficiency using compound, you can find it in my previous post about aggregate mass displacement.
> 
> ...


Indeed, that is the conclusion i came to. I did initially doubt that cams could be light enough to make the bow more efficient, but the more I think about it it does make sense; aluminium is just a very good material for this. Let's also remember that these numbers come from a very old style compound, using steel cables and primitive cams. No doubt more modern designs can improve on its efficiency gains even more, and adding the extra energy stored you can completely explain the extra speed.



> While we're getting into the mechanics; I just wonder how much energy gets wasted as frictional heat (from rubbing the leather before string departs) and material compression (leather compression & moving our finger meat around) for a finger+tab release. Intuitively, I'd say it can't be that much. But if there's ever a model to reflect the different hook mechanisms, I won't be surprised the mechanical release is orders of magnitude more efficient than a finger release.


I would also initially have guessed that it makes little difference. But given how much of an efficiency differene the additon of the cams made, I am starting to doubt that. To be fair, though, all of these numbers were obtained using a mechanical release, so we have no data for comparison. Really wish i had the time and resources to get that date. It's not something that I expect can help me shoot better, but I'm just too curious


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