Drawlength and powerstroke

[Margly]

Hi!
Is there a calculator somewhere on the web that can tell you about powerstroke?

Thinking about following:
If you pull a bow 55# with 28" of drawlength what # of bowweight would make an equal when you pull 31"  

[COLongbow]

Interesting question, I've wondered about that as well. I draw 29.5 and wonder what poundage advantage I have because of it. In other words, if I shoot 47 lbs at 29.5, whould my arrow speed equal 50 lbs at 28? (just an example, and of course all other factors being equal)

[jamesh76]

Interesting. I have often though of this and a comparison to performance of the different draw lenghts.  But I am not sure it would ever even matter considering I draw 27 1/2" and can't change it.

I do not know if you will find a calculator though.

[Troy Breeding]

The old rule used to be 1" of draw was equal to 5# if bow weight in reguards to powerstroke.

Not sure if it still holds true.

Troy

[Margly]

Hmm
5# pr " sounds much?

[Troy Breeding]

Thats way I said, not sure if it holds true today.

I do know I've tested the speed difference by basing everything on 10 GPP.

ie: bow pulling 50# at 27" using a 500gr arrow, 53# at 28" using a 530gr arrow and 56# at 29" using a 560gr arrow. When drawn below 28" the increase in speed was only 2-3 FPS. From 28 to 29 it made alittle bigger jump, 4#.

Somewhere down the line you are going to hit a peek. I'd guess to say it would come once the bow starts to stack.

Troy

[Margly]

Inreresting numbers!

But if we as a thumb rule could say something ?
And that it not should take in to consideration the different effency from different bows then what would that number be?

Maybe 2-3# pr"?

So if you shoot a 50@28 I would get the same effect out of a 41-44@31?

[Margly]

Or in the other direction:
50 @28 would give me 56-59@31 in effency?

[Sixby]

If a bow gains 2 1/2 lb per inch of draw with no stack then the pickup would be three times that amount. it would be equal to About a 63 lb bow.

This is why I worked toward a rear mounted bow with a 7 in brace instead of 8 1/2 or nine inches.

God bless you, Steve

[Margly]

So the difference would be 13#?

[Troy Breeding]

Lordy, all these numbers are making my noggin spin....  Been away from it toooooo long.

I do know you can increase you speed alittle bit by dropping your brace heigth. Guess you can say this is due to the arrow staying on the string longer. I found this out while shooting thru the chronie up close. However, when I backed off to say 20 yds and shot thru the chronie the speed would often be slower with the lower brace compared to the raised brace. I figured this had to do with the tuning being off. Never took the time to retune to the lower brace. Didn't like the way the string would eat on my arm at the lower brace

Troy

[tiur]

Hi, 2 - 3 lbs per inch would be a good average but with a 31 " draw all you have to worry about is getting long enough arras LOL.

Asgeir

[Sixby]

Troy I hear ya about the brace. However 7 inches is not an excessively low brace . Ishoot with no armguard with no problems. Most d and r longbows brace about that height but for some reason people seem to have trouble getting good stability with the recurves without a deeper brace.
Margley It depends on the increase in lb you have per inch. If your bow increases 3 lb per inch and you have a 44 lb bow at 28 inches and you draw it 31 inches then your bow would add about 9 lbs . that would make it the equivilant of a 53 lb bow at 28 inches , give or take a lb or 2....

faster arrows have flatter trajectories than slower arrows of the same weight and aerodynamics. In other words if you shoot the same arrow then you will get a flatter trajectory if it is moving faster. If you are hitting lower with the faster arrow it would probably be a nock point change causing it.

God bless you all, Steve

[Bill Carlsen]

I know from my experience with DAS ILF limbs that the preload is more important than a given weight at a determined draw length. For example, my wife shoots 46#  @ 26". Two years ago she had trouble with her thyroid, lost strength and was unable to shoot 46#. I lowered the weight on the limbs to about 42# but the performance lost was significant because of the loss of pre load. I got a lower weight set of the same limbs, same length, and set them for 42# @ 26". Because the preload on the new limbs was increased  in order to get to 42# she was able to redeem the performance she lost with the same set of limbs, set at 42# but with much less preload. So, one set of limbs at 42# was significantly better performance-wise than the 42# limbs with less preload. I know that was redundant but I think limb design has a lot to do with performance and one bow of equal weight at 28" may actually outshoot a bow of equal weight at 31".

[COLongbow]

Sixby,  that's good information, thank you.
I look forward to hearing from other skilled bowyers.

Those of us with longer draws, but who choose a slightly lower draw weight, want to know!

[Troy Breeding]

I used to think fellows with short draws had it made.

Now that I understand things better I found that short draws are a cursed.

I have a 29-29.25" draw and find I can shoot lower poundage and still get the same preformance as my friends that have short draws and heavy weight bows.

My only problem is with the arrow.

Troy

[Dodger]

Margly,

I am unaware of any such online calculator. However, to calculate draw weight at a given draw length, divide the draw weight at 28" by (28 minus brace height) to arrive at the weight that you would need to add or subtract for each inch or part thereof above or below 28". Once you get this figure, it's simple math to find out what draw weight bow is required at a given draw length to arrive at your desired draw weight.

Dodger

[sticksnstones]

I was told 3# per inch as a rule of thumb when going over 28". I checked it before on a R/D longbow and again tonight on a recurve and it came out on the money. My 49#@28" came in at 58#@31", exactly 9 pounds at 3". Brace height set to recommended height. YMMV.

[ChuckC]

I am thinking that there are too many "other" things to consider to be able to calculate this out in a forum setting.

it comes down to. . .  whatever speed your bow puts an arrow down range at,  thats what it does.  

Shoot it thru a chronograph, shoot other bows using the same arrow, which ever one shoots fastest has the best performance FOR YOU. Make it shoot a good clean arrow and you got you a winner.  Done !
ChuckC

[LimBender]

What Bill Carlsen says makes sense, and is part of why it would seem to be better to shoot a bow designed for a 26" dl than try to achieve the same weight in a 29" dl (using more #).  Yes, it is the same holding weight at total 26" dl, but the 29" limb may not be working as hard throughout the draw or designed as efficiently for the 26" draw.  

Just something to chew on with custom bows, but in most cases (like 1-2" draw) probably won't make much difference.

BH doesn't seem to be a big deal in the stickbow world, but seems like having 1 - 2" less bh would lead to a slightly faster, less forgiving bow (all other things being equal).