Draw length vs Spine

[Rick Butler]

This is something I've pondered for a long time and figured it was time to ask the experts.

   Say you have an arrow(cedar shaft) that falls in the 45-50 spine range and it's cut at 28". Your bow is 47 lbs. at 28"
but you're only drawing it 26.5" So really you're only pulling 42.5 lbs.
  My question is at the shorter draw would this actually create a stiffer arrow?

[WESTBROOK]

No, the arrow is the same, you changed the bow by drawing less than 28". Your only drawing 42.5#

But the same result, your arrow is now a little stiff.

Eric

[Whip]

No, the shorter draw doesn't create a stiffer arrow.  But you have an extra 1-1/2" of shaft, and if you cut that off it will create a stiffer arrow.  

I'll give this a try - hope that I make sense, and that I've got it right....

Actual arrow spine is measured by hanging a weight in the center of a shaft supported at each end 26" apart for all arrows regardless of length.  

Most arrow charts assume that you are using a 28" arrow.  So two arrows that each spine the same might act very different if they are different lengths.  The longer arrow will act weaker.  

Cut an arrow shorter than 28" and it will act stiffer.  Leave it longer and it will act weaker.  Both of those are true regardless of your actual draw length.

Increasing your draw length of course increases the draw weight, which then requires a stiffer shaft.  It also increases the "power stroke" of the bow, and that will have some impact on arrow requirements as well.  

Check out and play around with Stu's Calculator to get a good idea on how all the different variables interact with each other.

[Bjorn]

Well done Whip!      

[moebow]

The arrow will act like it is stiffer since it is now being pushed by 42# rather than 47#.

[Caughtandhobble]

I am no expert my friend but you are correct. In the situation listed above the spine would most certainly be stiffer.

The draw length, arrow length, draw weight, type of string, point weight (I'm sure I'm missing something) all affect the spine of the arrow.

[Rick Butler]

Thanks guys. Whip,for whatever reason my computer won't let me access Stu's Calculator.  I've tried numerous times.
  So the actual length an arrow is drawn to does'nt affect the actual spine of the arrow but cutting the arrow down or leaving it longer will, right?

[Rick Butler]

Moebow and caughtandhobble, I did'nt see your posts.

[bowhuntingrn]

If you can download Stu's calculator, but not get it to open for you, it may be because it requires an excel type program to open. If you don't have excel, like me, you can go to openoffice.org and download their software for free. This will allow you to use the calculator. Hope this helps 'cause it's sure a handy tool to have.

[Rick Butler]

Thanks Cory that worked.  I'm pretty much a caveman when it comes to computer programs.  Thanks everyone else for your input.

[Jeff Strubberg]

Did you ever break a pencil when you were a kid by weaving it through your fingers, then slapping your hand against something?

Pretty easy to do with a long pencil. Try it with a short one and you end up with bruises instead of a broken pencil.  

Longer shafts act weaker because you are applying a longer lever to the center of the shaft to create bend.  Longer draw length compounds the problem because, as the folks above have said, you now also have a more efficient, higher poundage bow.