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Spine relative to length
Equipment
Contributors to this thread:
ohiohunter 02-Aug-21
WV Mountaineer 02-Aug-21
skookumjt 02-Aug-21
ohiohunter 03-Aug-21
BUCKeye 03-Aug-21
HDE 03-Aug-21
sticksender 03-Aug-21
ohiohunter 03-Aug-21
Pat Lefemine 03-Aug-21
ohiohunter 03-Aug-21
From: ohiohunter
02-Aug-21
My logic tells me the a shorter arrow will be stiffer than a longer arrow of the same deflection, right? But how much? At what point does a 340 equal a 300, or will it ever (in a usable length)?

I shoot 340’s and could stand to cut them a little more leaving them about 26”, which allows me to add an extra 25gr up front and keep about the same overall weight.

02-Aug-21
I don’t think on carbon it matters much once you’ve obtained enough spine to shoot your arrow of choice. Over spined out of a center shot bow never seemed to hurt much. At least by the time I cut my 340’s to 27”.

I don’t have any idea how much spine is affected by length in carbons. I just know it’s hard to see bad results due to being too stiff out of a modern compound bow. Underpinned is different.

From: skookumjt
02-Aug-21
All of those changes are taken into account in the spine charts. Put those inputs in along with your draw length, arrow length, etc and you will get what you need. Cutting the arrow will make it stiffer. Adding weight to the front will make it weaker.

From: ohiohunter
03-Aug-21
Good ol spine charts, I pretty much forgot they existed. They were always on display at local shops (poster or counter mat), I cannot say I’ve seen one at any shop in quite sometime. I think the online Easton hunting chart assumes 100gr tip. Part of the reason I posted is Bc a local shop guy said “spine is spine, doesn’t matter the length”, I wrinkled my brow and ignored the statement but for some reason it lingered in my subconscious.

From: BUCKeye
03-Aug-21
Spine chart gets me the ballpark. To dial it in, I shoot each arrow bareshaft before fletching. Out of a dozen arrows I end up with slight variations in length and insert weight to get them all spined the same. I shoot a finicky finger bow and my setup is more sensitive to spine than most.

James- I miss the days of studying the Easton chart at Relos...that chart held critical info for a kid about to spend 2 weeks savings on a dozen gamegetters or really splurge on super slams.

From: HDE
03-Aug-21
Length alone deals with static spine.

Added weight upfront deals with dynamic spine.

Regardless, a shorter arrow will be more stiff no matter what.

From: sticksender
03-Aug-21
Ohio, your shop guy is actually kinda right, insofar as the published deflection RATING of a particular shaft size doesn’t vary with length. Since the deflection RATING comes from placing a standardized test weight on 28 inches of suspended shaft. Of course actual static deflection would increase or decrease for different shaft lengths. And then, as mentioned above, there are DYNAMIC factors affecting stiffness behavior. Such as point weight.

From: ohiohunter
03-Aug-21
FINGERS! How the hell you been man!

Stick, right. But in all reality we only care about dynamic spine as a resting arrow draws no blood (except the handler’s). So I guess what would be nice to see is a chart, or to keep with the times a program, that would illustrate spine relative to heavier point weight. Granted this would probably only appeal to a small percent of archers while the others just slap a 100gr tip on their fmj for a whopping 2% foc.

From: Pat Lefemine
03-Aug-21
Spine charts are always off for me, they all say I need a 350 but my best flight is with 250’s. Nothing fancy on the front end just a 100gr 3-blade fixed head. Agree that they should be a rough guide but have to wonder how many archers know that? I bet lots there’s tens of thousands of guys shooting suboptimal spines because that’s what the chart says, or some pro shop guy recommended it.

Suboptimal spine = less forgiving = more bad hits at crunch time.

From: ohiohunter
03-Aug-21
Agreed, especially with today’s hard eccentrics. I think most of us here can vouch for some very ignorant shop guidance. It kills me when people I know take their LBS word as gospel… to each his own… knowing is half the battle.

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