Is it true? Does a one inch longer draw impart energy of a 6-10 lb heavier bow?

[WDELongbow]

I saw something online about how - all things being equal - increasing your draw length by one inch is equivalent to increasing draw weight by 6-10 lbs. That of course would be for shooting arrows of equivalent weight. This was said (confidently) by one of the so-called "experts".

Is that true? I get it; increasing the power stroke. But one inch increase in draw length being worth 6-10 lbs in bow weight at the lessor draw length? Almost hard to believe.

The other day I was shooting a 46 lbs @ 28" longbow (my draw is typically around 26" with bows labeled 55-65 lbs @ 28"). I would be pulling around 40-41 lbs @ 26" with this bow. But, with this lighter bow, I could comfortably draw to 27.5". That's a 1.5" increase in draw length! Given the expert's statement, at a 27.5" draw I should now get arrow velocity of a bow 9-15 lbs heavier. To sum it up ... me shooting that lighter longbow at 27.5" draw would be equivalent to me shooting about a 50-55 lbs bow at 26".

Basically ZERO gain from shooting the heavier bow in this situation. Is this true?

Update/change: I know actual draw weight increases 2-3 lbs per inch. I'm referring to the energy imparted to arrow. See my comment in my reply below. Basically asking if shooting say 45 lbs at 27.5" would be equivalent to shooting something significantly heavier at 26". The longer power stroke imparts more energy to the arrow. Appears to me there is like a zone where you are better off shooting a lower weight bow if you can shoot that bow with a longer draw length.

For example, one bow 50 lbs at 28", and another bow (same design, same arrow) 50 lbs at 30". The bow with 30" draw should outshoot the bow with 28" draw. Question I'm asking is how much.

[Maclean]

Not sure where you heard that.  Typically it's in the 2 to 3 lb. range.

[Orion]

Anyone can create a U-tube video.  That doesn't make them an expert.  An inch of draw length will add 2-3# of draw weight for a mid-weight draw bow. The one-inch longer power stroke will also impart more energy to the arrow because it is on the string longer, but not 5-7# worth of draw weight, maybe the equivalent of another pound or two in draw weight. 3-5# per inch, I'd accept, not 6-10#.

[WDELongbow]

I mis-stated (I think). I know that the actual draw weight increases 2-3 lbs per inch.

I was speaking to the energy imparted to the arrow. At a longer draw length (at equivalent draw weight) much more energy is imparted to the arrow (supposedly). For example, a 40 lbs bow at 30" should outshoot a 40 lb bow at 28", given same arrow. But does it outshoot by an amount equal to 6-10 lbs of increased weight at the lessor draw.

[Orion]

I think you stated it correctly.  Yes, the longer draw at the same weight will transfer more energy to the arrow, but not at the rate of the equivalent of 6-10# of draw weight per one inch of draw length. 

How is your "expert" measuring/computing this stat?  Is he using the same arrow grains per pound for each bow set up?  Measuring fps and converting it to pounds of bow weight?  I read somewhere that every pound of additional bow weight past 28 inches adds about 1 1/2 to 2 fps, but I can't verify that.

[30coupe]

I have heard the longer draw means more energy imparted on the arrow because it is on the string longer. While this is undoubtedly true, I doubt that the difference is really all that significant. Think about how long it takes the string to travel that extra inch. Not very darn long! The extra 2-3 pounds of draw weight gained will be far more significant than the distance traveled. I seriously doubt that a 40# @ 29" bow will show all that much of a gain over a 40# @ 28" if each is drawn to spec.

That's my $.02 worth and worth every penny. 

[Michael Guran]

Yeah I agree with 30coupe.  48lbs should be 48lbs—whether it’s 48 @ 28 or 48 @ 26, they should be the same if drawn to there respective draw lengths…

[elkken]

I'm sure some where here in the archives is a formula to calculate foot pounds of energy, that I think would answer your question. I do think your expert has overstated the gain.

[Steelhead]

On the same bow it will be on the string longer as stated.

The limbs will be bending more as well storing more energy.

I doubt the 1 inch difference between 28 and 29 inched draw length equals a  6 to 10 pound difference though.

[Nosight]

Formula for conetic energy is
Mass x speed x speed  divided by 450420
To get the answer one is looking for you need those numbers
I have aged with this for awhile and for.me the gain in conetic energy by adding 1 inch of draw for me increased my draw weight by 2.5 pounds and I. Turn increased conetic energy by 3 tenths of pound
If this y tube expert says it's almost 10 pounds I would like to see his math
Hope this helps

[GregD]

If we had two guys shooting 500 grain arrows, identical bows one guy draws 50@26 and the other guy draws 50@30” would they chronograph the same or would the longer draw be faster? Aside from that I would try to figure out what you are doing form wise that your draw length is changing with different weight bows. Are you overbowed at you normal weights?

[Cari-bow]

WDELongbow
This is good question and I've heard it stated differently but with similar numbers.
I just came from a test with a shooting machine. I used 2 bows, 1 50#@28" the other 50#@27". Had heavy arrows on the first test . Bow 50#@28" shot 4 ft per sec faster then 50#@27". Changed to lighter  arrow (-150 grs.) The same results 4 ft per sec faster.

With either bow if I dropped the draw length by 1 inch I would lose 8 ft per sec with the heavy arrows.  With the lighter arrow it dropped 10 ft per sec with 1 inch less draw.

This has been a question for me ( if one has a longer draw how much less weight can you get away with)? It's not that I can change my draw length but I deal with customers with longer draws then myself. This gives me a more concrete answer. I always knew the advantage  lay with longer draws.

[Stringwacker]

I guess I will be that one guy who has a different thought. I used to play with bows and cronographs all the time. At my normal 27" draw length, with a 72 pound bow at the time, I determined that an extra pound of draw (all things being equal) would be worth about 1 FPS at my draw length.

But, an extra inch of draw was worth about 7 ft per second at my poundage and arrow weight. (all things being equal) Not sure if that would incrementally hold true for even longer draws (and different bow weights) as I couldn't overdraw but one inch.

I've always been amazed how much performance a longer draw archer gets out of the same bow weight. Actual draw weight is the same regardless of the inches pulled to get it there. BUT....the guy that pulls the longer draw length gets the benefit of the longer power stroke so the same can't be said about bow performance in terms of arrow speed.

[Squirrel Hunter]

Basic physics: with a typical bow in the 50 lb range and a 9-10 gpp arrow, an extra inch of draw will store more energy, resulting in about 4 fps more speed. That’s equivalent to a bow 3 lbs heavier.

It will also increase draw weight 2-3 lbs, as has been said, so you could say you’re getting the effect of a 6 lb heavier bow, but that’s misleading because you really are, at that point, shooting a heavier bow..

[Stringwacker]

WDELongbow
This is good question and I've heard it stated differently but with similar numbers.
I just came from a test with a shooting machine. I used 2 bows, 1 50#@28" the other 50#@27". Had heavy arrows on the first test . Bow 50#@28" shot 4 ft per sec faster then 50#@27". Changed to lighter  arrow (-150 grs.) The same results 4 ft per sec faster.

With either bow if I dropped the draw length by 1 inch I would lose 8 ft per sec with the heavy arrows.  With the lighter arrow it dropped 10 ft per sec with 1 inch less draw.

This has been a question for me ( if one has a longer draw how much less weight can you get away with)? It's not that I can change my draw length but I deal with customers with longer draws then myself. This gives me a more concrete answer. I always knew the advantage  lay with longer draws.

I think this post is so informative as its recent, uses identical bows with the same draw weight, and is shot from a machine.

In this case, the test involved bows with the only stated difference being that one bow had a bow weight (50lbs) at 28"..... vs 27" (50lbs) with the other. With the same amount of stored energy, the bow that had the longer draw length (at the same bow weight) shot 4 FPS faster. This can only be credited to the longer power stoke of the 28" drawn bow, I assume?

If you took the 50lb bow at 27" and drew it to 28" you would have the effect of the longer power stroke (4fps)...and the increasing drawn weight of the bow (3 lbs). I could see how you could get 6 to 10 FPS more by drawing one bow an extra inch.

The other thing of interest was if he took either bow and dropped the draw to one inch less; he was losing 8 to 10 FPS with likely only a 3 or 4 pound reduction in actual bow weight. In this case the speed likely mirrored the results of a shorter power stroke...and a bow weight reduction added together.

[mj seratt]

Dan Quillion said that by increasing the draw length by an inch, it  increased improved performance like a 10 pound increase in bow weight.  I may not be totally accurate here, but I'm sure someone will be along to set it straight.

Murray

[azhunter]

From what I have seen with a few guys with a shooting machine testing different draw lengths said there was about an average gain of 7 feet per second with each additional inch of draw length. What that compares to in terms of the added poundage needed to gain 7 feet per second I have no idea.

[McDave]

Another factor that ought to be considered is the effect on accuracy of a 1” increase in draw length using the same bow, resulting in a 2-3 pound increase in draw weight.  If a 1” increase in draw length is a byproduct of improving form, then we have three factors working for us: the increase in stored energy, the increase in poundage, and the increase in accuracy. 

This is often the case when someone who has been drawing to full draw and shooting fairly well goes the extra step from full draw to transfer to hold before shooting.  Or, as Terry would say more simply, achieves better alignment.  The transfer to hold step achieves better bone on bone alignment along with an increase of up to an inch in draw length.  This makes it easier to hold the 2-3 additional pounds than it was before the transfer to hold 2-3 pounds less, and thus increases accuracy.

OTOH, if one simply muscles the bow back another inch, the increase in velocity simply makes it possible to miss by a greater distance with a faster arrow.

[Cari-bow]

In my test the increase of 1" of draw increased the ft per sec by 8 ft with 13.36 grs per inch.
With 10.4 grs per inch the increase was 9-10 ft p8er sec.

I think that having proper form is the most important.  If that increases one's draw length big dividends are achieved even with less draw weight.

Not sure the goal for everyone is to increase one's draw. For me it's that when someone says they   a longer draw (say 29.5") and they feel they want to drop down in poundage I now have some numbers to verify they could.

[tecum-tha]

The energy stored in a bow is the area below the force draw curve.
Assuming you use a bow that has lets say 8" of brace height and you draw it 26" and you draw another bow with the same brace height 27" and you have a F-D curve which does not have a huge belly in the early draw, but more linear like a longbow. Let's say we have a bow that pulls 50#@26 and a bow with 50#@27".
The area for a linear curve is 1/2x(26x50)=650 inch-lbs
For the second bow this is  1/2x(27 x50) = 675 inch lbs
If the 26" draw is your 100%, you gained 3.85% of energy @27" and 7.7%@28".
Now, if you shoot an arrow with the same gpp, the arrow with the longer draw will be faster.
You can only store more energy in a bow by drawing longer or drawing more pounds or both.
Now, in Asiatic archery they gain more energy storage by drawing further. Extremes are Japanese bows and Manchu bows.

If you draw rather short, high early energy storage is important to store the max amount of energy. But for a lot of people that does not feel smooth.
The percentage of energy gained will be smaller, when you draw longer with these early energy storage bows, because the area under the FD curve will be larger in relation to a linear F-D curve.

If one wants to compare things, one cannot compare things successfully when alternating more than one variable. The results will be unconclusive.