Another Stu Miller calculator question

[rod251]

I've always used Stu's old calculator, the one without specific bow models, with great results.  With the proper data entered, matching arrows to bows is easy.  Well now I've downloaded the latest version that lets you enter your bow model.  I have a 45# Samick Red Stag, and when I enter all fields for the bow and the arrows, it reads the same as the old calculator, and the arrows spine correctly for the bow both in the program and when actually shooting.

Here's where I get confused.  I have a 40# Samick Sage on the way so I plugged its numbers in to see how far off the arrows for my Red Stag would be in spine.  Since the new bow is 5 lbs lighter, I assumed the calculator would tell me they are stiff.  Nope.  According to Stu, the 40# Sage requires almost 10 lbs. more dynamic spine than the 45# Red Stag.  What gives?  I entered both with a 28" draw rating, and entered my 26" actual draw length.  I entered the same strike plate thickness, and the calculator entered the same centershot on both bows.  The only differences in the bows is that the Sage has a 2" longer AMO length and is a takedown, where the Red Stag is a one-piece.  They both have recommended brace heights around 8".  The only other possible performance difference I can think of is the limb core material, but I'm not sure what each bow is made of.  I appears they both have hard maple limb cores, but I'm not certain.  Can someone with more knowledge enlighten me?  I'm having a hard time believing that a bow which is very similar to another bow, yet 5 lbs lighter, would require 10 lbs more arrow spine.  Thanks for reading my rambling.      

[Rob DiStefano]

i see lots of issues with "arrow calculators" and one is, are you SURE you know EXACTLY what yer bow's holding weight is at yer draw length?  the other, and more poignant, is that it's just far too plebeian generic a methodology for a medium that's fraught with unique ambiguities.

[L82HUNT]

Originally posted by Rob DiStefano:
 the other, and more poignant, is that it's just far too plebeian generic a methodology for a medium that's fraught with unique ambiguities.

I have no ideal what that means!!      

[Rob DiStefano]

Originally posted by L82HUNT:
 

quote:Originally posted by Rob DiStefano:
 the other, and more poignant, is that it's just far too plebeian generic a methodology for a medium that's fraught with unique ambiguities.

I have no ideal what that means!!      

[Ground Hunter]

Well just keep the pointy end forward - your half way there.

[rod251]

I know arrow calculators aren't the final word in tuning.  Nothing beats getting out in the yard and flingin' arrows at a target.  But what I'm asking is, with equal values being entered into the program, why would it say a 40 lb bow needs a stiffer arrow than a 45 lb bow?

[Rob DiStefano]

Originally posted by rod251:
I know arrow calculators aren't the final word in tuning.  Nothing beats getting out in the yard and flingin' arrows at a target.  But what I'm asking is, with equal values being entered into the program, why would it say a 40 lb bow needs a stiffer arrow than a 45 lb bow?

because software is based on formulaic pre-parsed input = "guesstimate".  it's all common sense guesswork, with a hefty emphasis on "guess".

[rod251]

Rob, I'm pickin' up what you're layin' down. But I think the problems you speak of are more along the lines of, "program tells archer use XXX arrow, archer shoots XXX arrow out of bow, XXX arrow flies like crap." What I'm talking about is strictly a software issue. When asked for my actual draw length, I entered 26" for both bows. The centershot entered for both bows was -1/8".  The strike plate thickness was the same on both bows. The draw weight rating for both bows was Xlbs@28". The only thing entered differently was the difference in draw weights. Why would this program tell me a lighter bow needs a stiffer arrow? That's what has me stumped.

[Rob DiStefano]

like i said, it's all in the programming and no one can answer yer question unless the code can be viewed by someone who can understand it all.  you need to contact the programmer.

[rod251]

Originally posted by Rob DiStefano:
like i said, it's all in the programming and no one can answer yer question unless the code can be viewed by someone who can understand it all.  you need to contact the programmer.

I guess so.  It would seem that the formula would be linear, spine increasing as rated poundage goes up.  Oh well, it'll all come out in the wash this weekend when I have the bow in hand.  Thanks for all the replies!

[Rob DiStefano]

maybe you found a bug in the code.  all the better to report it to the programmer!

[xtrema312]

Sound like a glitch. I have seen some variations, biu not that bad. The one that has me puzzled now is why do I consistently need 20# weak to shoot 400 spine carbon, but when I got some 3555's and set them up I am way weak and it looks like the calculator is real close.  

[rod251]

Email sent.  We will see how this plays out.

[Rob DiStefano]

i know a few things about computer code.  when you think of all the variables a spine calculator program requires, you'll realize why it will fail somewhere along the way for some folks.

[rod251]

I'll have to take your word for it, because if you combine all I know about computer code with a dollar bill, you'll have exactly $1.    :D

[Rob DiStefano]

Originally posted by rod251:
I'll have to take your word for it, because if you combine all I know about computer code with a dollar bill, you'll have exactly $1.     :D  

I remember the good old days with the Easton chart. The chart says try a 2016 cut to length with your choice of head on it. Too stiff? Try a 1918. Still too stiff? A 1916 or an 1818 will be right on. It may seem like a lot, but if you had a good archery shop to work with, it was easy.

[Night Wing]

The old Easton spine charts of the 60's and 70's were much better than the chart Easton now puts out. The chart now is way off (too stiff) for their aluminum arrow choices.

As an example. With my 42# recurve shooting a 32" BOP aluminum arrow tipped with a 75 grain point weight, the present Easton chart says I should be shooting a 2215 aluminum arrow. My 42# recurve doesn't like this arrow length/point weight setup. It likes a 32" BOP, 2212 aluminum arrow tipped with a 75 grain point weight which isn't even listed as a choice.

Example #2. With my 37# recurve shooting the same 32" BOP length aluminum arrow and 75 grain point weight, the present Easton chart says I should be shooting a 2312 aluminum arrow. But, this bow doesn't like this aluminum arrow length/point weight setup either. This bow also likes a 32" BOP, 2212 aluminum arrow with the same 75 grain point weight and again, the 2212 isn't listed.

Stu's calculator has correctly given me many different aluminum arrow spine choices from a light arrow setup all the way up to a very heavy arrow setup for both of my light poundage recurves.

[Rob DiStefano]

with any arrow spine/selection software, there will ALWAYS be a measure of 'hit or miss'.  it's absolutely impossible to code for all of the hundreds of thousands of interactive possibilities of arrow, bow and archer.  that road is fraught with moon crater sized pot holes.  wish it was different, but i know better.  

so, for some folks the code works great, for others it works sometimes, and for others it could never work.  still no substitute for hand's on testing ...

[Swamp Yankee]

Guess I'm on of the few who have a couple of "dead to nuts" setups that Stu's calculator agrees with using 0 as the Personal Form Factor.  Seems to me if the calculator almost always tells you to use a too stiff an arrow, perhaps playing with the form factor might be a way to "calibrate" the calculater to your particular shooting style.