I tune to a weak spine

Lee Lobbestael · August 30, 2019, 06:41:36 AM

Does anyone else shoot a arrow that according to all spine charts is far too weak for their bow? I have a 26.5 inch draw and am shooting a 48# at my draw hybrid long bow, cut to center with a Velcro side plate. The arrows I finally got to tune to my bow are 29" 2016 tributes standard insert with a 250 grain point! I bareshafted them and shot them through paper. According to spine charts that should tune out to a 38pound bow. I have been doing this for 15 years or so so I'm confident that my form is solid. Very strange

Lee Lobbestael · August 30, 2019, 06:43:24 AM

Oh yeah and I'm running a 12 strand d97 Flemish twist

Crooked Stic · August 30, 2019, 07:12:05 AM

A 2016 sounds about right for 48 lbs. but the tip weight sounds heavy. But if it is good for your setup why worry with the chart.

Lee Lobbestael · August 30, 2019, 07:15:44 AM

I'm not to worried about it. More I'm just curious if anyone else has experienced this

Friend · August 30, 2019, 07:37:58 AM

I typically run 15#s under.

Yooper-traveler · August 30, 2019, 08:32:43 AM

2016 is what I would shoot at 45ish pounds, with less weight up front. It's a 530's spine. If your B/S is on it's probably just your grip/release/draw.

I have two hybrid TallTine LBs, one is 64" @41# the other 62" @42#. One tunes out with 600 GT or 1916s, the other is better with 700s which is what my ASL likes @ 36#s.

McDave · August 30, 2019, 09:12:53 AM

I've noticed in my own experiments that increasing point weight seems to have less effect on tuning as point weight increases. For example, there seems to be a greater effect on spine between a 100 and a 125 grain point change on a target arrow than between a 200 and a 225 grain point change on a hunting arrow. It may be that the percentage change in point weight matters more than the actual change in weight. If that is true, to get the same effect on spine of a 25% change in point weight from 100 to 125 grains, you would have to increase a 200 grain point to 250 grains.

Lee Lobbestael · August 30, 2019, 09:25:16 AM

That is interesting! Maybe the more foc you get the faster your arrow corrects

Friend · September 01, 2019, 02:18:38 PM

An Ultra EFOC arrow corrects in 1/2 the distance of a Hi FOC arrow

kennym · September 02, 2019, 07:28:48 AM

Depth of sight window affects the spine a lot too.

smokin joe · September 02, 2019, 08:14:09 AM

In my experiments, I have found that two factors make a ton of difference.

1. As Kenny mentioned, the sight window makes a difference, if it is cut exactly to center versus another bow that has a window cut short of center. If the window is short of center, the bow will require a weaker dynamic spine. In some cases this is quite a bit. I have a recurve that is just a bit short of center and the dynamic spine of a tuned arrow is 13 pounds lighter than the draw weight of the bow.

2. High FOC can have an effect as well. I have a bow that is cut precisely to center, and in making 27% FOC arrows for it, I found that I needed arrows that had a dynamic spine that ended up 8 pounds weaker than the draw weight of the bow. It did not make sense to me at first, but the arrows shoot like laser beams.

I think the spine charts can be a good starting place, but each bow has its own personality and meticulous tuning (in my case bare shaft tuning) will be the best way to arrive at the correct arrow formula. In addition, high FOC will influence the necessary dynamic spine of the finished arrow.