how to properly get spine

kshort · 07-29-2007, 08:26 PM

do you use the draw length or the length of the arrow??????????
i have heard both and just would like to the right way.....

freakysneeky · 07-29-2007, 09:10 PM

what kind of arrows do you shoot now?what is your draw weight and draw length on your bow?

Straightarrow · 07-30-2007, 04:18 AM

To do it properly, you need both. Unfortunately, mfgr charts don't allow this. I think they assume that you're going to use a similar length arrow for a given drawlength. If you don't, large adjustments have to be made. This is only one reason the charts are near useless. They also don't take into account cam style (which varies greatly), or power stroke which can be 1-2" difference.

The bottom line is, to get it exactly right you have to be willing to do the arrow tuning work and bareshaft testing.

Paul L Mohr · 07-30-2007, 02:09 PM

Most charts ask for arrow length and assume you are using the correct length arrow for your draw length and calculate the draw length from that. Most of the spine software lets you specify an arrow length and a given draw length making them a bit more accurate and versatile.

Paul

Straightarrow · 07-31-2007, 04:22 AM

Quote:

Most charts ask for arrow length and assume you are using the correct length arrow for your draw length and calculate the draw length from that.

That's the problem. The correct arrow length has only a small relationship with draw length. It has more to do with the arrow spine. I'm currently shooting 30.5" arrows out of my compound with a 29" draw length. The arrows I'm going to hunt with this fall are 31.25" long. Out of my longbow, they are 32". If a guy like Arthur wanted to shoot an extreme FOC arrow, he might be forced to shoot a 29" arrow from an overdraw, with his 33" draw length (or whatever it is).

It is possible to get proper spine with an arrow that is approximately the same as your drawlength, but this greatly limits your options. In my opinion, the arrow manfacturers would be far better served to have a calcuator for arrow selection that includes all the factors that affect arrow flight. I have a feeling that they don't want to make it so complicated that people go to their competition who has a simple calcuation, so they dumb-it-down for the masses.