Spine?

[mspink]

Hey guys was wondering if you could help me out? So I've been making arrows that fly perfectly at 55 lb spine but they are only 27 1/2 inches long. My question is if I want to shoot arrows that are 29" then should the spine be a tad weaker or stiffer? Please let me hear ur thoughts and thank you!

[Pat B]

On store bought shafts the spine is for a 28" arrow with a 125 gr head. Longer arrows will decrease the effective spine by 5# per inch. Shorter arrows will increase the effective spine by 5# per inch.

[DarkSoul]

Exactly. So you'll be needing about 60# spine-weight for a 29" arrow. The spine does not change when the shaft gets longer (the spine is always measure as deflection between two point 26" apart), but since the shaft is longer, it will deflect more around the bow handle. This increase in deflection is avoided by choosing a shaft with a higher spine. Store bought shafts have their spine indicated at 28" of arrow length. For every inch you want the arrow to be longer, add 5# in spine weight.

[iowabow]

Exactly. So you'll be needing about 60# spine-weight for a 29" arrow. The spine does not change when the shaft gets longer (the spine is always measure as deflection between two point 26" apart), but since the shaft is longer, it will deflect more around the bow handle. This increase in deflection is avoided by choosing a shaft with a higher spine. Store bought shafts have their spine indicated at 28" of arrow length. For every inch you want the arrow to be longer, add 5# in spine weight.

Also voided by decrease in point wt

[Tom Leemans]

And this is why I make a bunch of cane shafts, and use the ones that fly the best. The odd balls are used for shots a squirrels and such.