The
following is a summary of an article written by Doug Besherse (see link)
entitled "Picking The Correct Arrow Spine For Longbows & Recurves".
Type of string:
The advance low or no stretch
strings will have the greatest effect on spine. With the use of the advanced
strings on average you will need to increase spine weight by #15 on wood and two
shaft sizes on aluminum arrows.
Weight of Broadhead:
110grain to 140grain - no
adjustment.
100grain - lower #5 in wood or 1 size on aluminum.
150grain - increase #5 in wood, 1 size on aluminum.
190grain - increase #10 in wood, 2 sizes on aluminum.
Arrow Length:
"The average guy
shoots a 28 1/2" arrow, for every 2" over that you will need to
increase the spine weight by 5# in wood or by 1 size in aluminum. For every
2" under that you will need to decrease that same amount."
Off set in the riser:
You can shoot a stiffer
arrow out of a more center shot bow and you have to shoot a weaker arrow out of
a bow with more off set. For longbows shoot one step weaker in spine than the
average center shot recurve.
Other Notables:
- Bigger feathers have the effect of stiffening
the shaft.
- Crown dipping has a stiffening effect on
arrows.
- String silencers add weight to the string and
slow it down, which has a stiffening effect on the arrow.
- Bow quivers that slides on the limbs of the
bow will make it necessary to go down one step in spine.