Wood Spine Gurus... I have a ?

[Bud B.]

If I have an arrow 60-65 spine that's BOP 31 5/8" long that shoots well out of my longbow, how much static spine would I need drop if I wanted a 28" arrow? Right now I have alot of overhang and I want to shorten the arrows, but, I know thw 60-65s would be way to stiff with that much cut off. I was thinking 50-55 would get me in the right area for a 29" and then cut down to tune using the same point weight I have now of 145gr.


The bow is 64 @ 28. I pull it to around 27.

I know there's a theoretical way to figure it but I also know what should work might not. Just wanting a ballpark. Probably going with Surewoods. Thought I'd get some input here and from the Surewood folks. Cutting 2 5/8 inch off the length might even make it need a lower static spine that 50-55. It ain't to center and my best guess is it's 3/16" from center cut with no sideplate. Shooting off the riser wood at the moment with it.

[Fletcher]

It can vary with draw weight but I figure 4-5 lb per inch.  That would put you at a 50-54 for a 29" BOP; 45-49 for 28".  That might be right depending on the bow and depth of cut, but it seems low for most longbows.  Have you shot the 60-65 thru paper to see how well matched it really is?  For most shooters, a Hill style with 3/16 out from center will shoot about 3-5 lb below bow weight with a 28" BOP and 125 gr point.

[Hud]

If your draw length is 27, your probably around 60 - 61#. Answer: your current arrow setup is 47- 52# spine. Figured 28" - 30.6" = 2.6 x 5 = 13 lbs. Your spine is approx. 47 - 52# (60# - 13# = 47#). This is light unless your using 100 grain, or less pt. wt. because your shooting around 60#. Is the bow a longbow, selfbow, or something similar?

Spine on wood is almost always on 26" centers, by AMO Standards. What is critical is the style of the bow, Longbow, R&D, recurve, the amount of center cut, weight of point, and the type of string.

Example: For a glass laminated Longbow, with a   B50 string I would start:
 60-65 with std string, 125 gr point.
 if the arrow is weak (shoots left for a right hander) try a stiffer spine. if it is too stiff add pt. wt. 145 gr. or 160 gr.

Generally, add or subtract 5# in spine for every
1 inch difference in draw length above or below 28".
Starting with a Base 125 gr pt. then 5# per 25 Gr. in pt wt.
5 lbs for a Fast Flight string.

If your shooting an R&D, the starting wt is maybe 10 - 15# greater.

Several sponsors, Elite Arrow, 3 Rivers to mention a couple have info. on their website on this subject.

[Bud B.]

Thanks guys. Both those answers were the type explanation(s) I was looking for. I appreciate you both taking the time to type it out.

I have some arrows 50-55 (no spine tester but they were bought as 50-55) and I'll try with one of those at 29" with a 125 point.

The bow is a Hill(ish) style SF - maple lams with fiberglass back/belly.

[Bud B.]

Took the 50-55s (4 of 'em) down to 28" BOP and used a 145gr point. Never seen wood arrows fly so well out of this bow.

I questioned going down so low thinking the spine might be too weak and have a risk of breakage. But if the flight tells the answer, I lucked up and got it right.

Thanks for the answers. They helped be with a boost to at least try what I did.

[Bud B.]

I just plugged in what I had to check it on Stu's chart.

 

[Kelly]

Have you cut that arrow down and see how it shoots?

Think it will still fly pretty good at say 28.5" BOP length.

I am of the belief that when an archer uses an arrows drastically longer than their draw it doesn't effect the spine as much as another archer using the same length arrow but draws it within 1/2" of its length. In the latter instance spine is way more critical than in yours.

[Kelly]

As an example, I can shoot spines of 40-60 out of my 35 to 45# Sunset Hills and Schulz longbows.

By the same token I can shoot 15-40# variance in spines out of my recurves too.

Spine is not as critical as some make it to be. There is a good reason why carbons are made in only 3 or 4 different spines.