Arrow Spine and Weight

[Ssamac]

OK Here's topic that will probably have a lot of opinions. How do you determine the correct arrow spine for a particular bow? Also, is the weight of the arrow part of the equation or is that a separate calculation?

That said, I understand that as you shorten an arrow, the spine gets stiffer and the weight goes down. Once again, how do you determine the right combination for a particular bow?

Obviously, I have some arrows for 45 and 55# bows and am now shooting a 25# as well as my youngest son shooting a 25# and need to reassess the whole thing moving forward.

Thanks
sam

[Bjorn]

Go to either the Morrison web-site or acsbows.com and look for the tuning sections there. You will have it down in no time.
I used both sites for my son and myself.

[Bard1]

good links above.  But to address it a bit more (and there are much more experianced archers on here then I) finding the correct spine for a bow is part of the tuning process.  People on here will be able to pretty well tell you the arrow spine you should start with depending on the bow.  From there it's a matter of figuring out the right weight tip you need at the length of arrow.  Your correct that a shorter shaft = stiffer spine.  Don't forget that the heavier tip=softer spine.  In effect tuning an arrow to a bow is both a science and an art, but it comes down to trial and error.  
Derek

[Shawn Leonard]

Go to  www.arrowsbykelly.com  and check out his spine charts they will get ya darn close. I get close and as others said I experiment a bit with point weight. Shawn

[Ssamac]

I'll check out the sites. Thanks guys. Still trying to think through how a heavier point makes the spine "softer". I'll get that sooner or later.

So how do I translate the numbers on my arrows, ie, Easton 2017 etc. to a spine and a weight? Also, what about woodies with no numbers written on them?

Sam

[stump man]

is the weight of the arrow part of the equation or is that a separate calculation?

ss:
  A short story and experience of mine may help.   Getting close to hunting season one year it was time to switch the arrows I had been shooting from field points to broad heads.  I could not get them to fly worth a hoot, they had been flying ok with field points.  With some experimentation   I found they flew ok if I overdrew them an inch or so.  I didn’t have shafts on hand of any other spine range but I did have a good quantity of the same spine and it was down to crunch time (the 70’s. I bought by the thousand from Acme).  So I weighed and picked out a dozen of the heaviest I had on hand, an increase of 50 grains from those which I was having troubles with, and fletched them up.  Problem solved! They flew great!!  And I’m sure I went afield and harvested a monster that year!
  In conclusion the originals were actually heavy in spine hence, they flew great when overdrawn, but increasing  in mass weight “settled them down” also.  So I have to conclude that yes, “mass weight is part of the equation”.
A separate calculation?, perhaps..especially if borderline on spine wt.   Note : I could have solved the above problem by dropping down 5 lbs in spine weight but I didn’t have them on hand at the time.  
 Best advice I can give is use the charts and get yourself close with spine weight.  Buy a test pak 5 lbs under thru 5 lbs over and know your mass weight.  Final tuning with mass weight is a viable option and unless you know what it is it's hard to use it one way or the other.  And don’t wait until the last few days to mount your broadheads to see if they fly the same as your practice points .

my .02 worth
Stump

[Ssamac]

arrows by kelly is great. interestingly enough, all the chart start at 30 or 35# @28. You can only assume that the lightest weight at 30#, the 1616 aluminum, is what you need for a 25#.
The conversion to know what a carbon shaft is related to a 1616 aluminum is non existant. And measuring wood to alum or carbon does not exist. Also, they don't write the spine on wood shafts, so you never really know unless you weigh them and test the bend. I guess it's as much an art as a science.

sam

[Ssamac]

So what about the bow string? 12 strand vs 16 strand vs twisted vs fast flight? How does that affect the tuning? How come archery stores don't carry lighter weight shafts even though they have lighter bows?

Sam