Spine adjustment?
 

There is a lot of talk about the importance of correct spine, yet I rarely see this sharacteristic published in manufacturers data. Is this just grains / inch. I thought that was weight. If I need to increase my spine, do I just increase my grains / inch. If not do most web sights advertise individual arrow spines or is this something you measure on your own.

Also, when an arrow manufacturer adverstises + / - 2 grains per dozen. Does that mean 2 grains per inch per arrow or if you weigh a single entire arrow, it may be off two grains per inch from a second arrow. If my calculation are correct, a 30 inch arow could be off 60 grains in total weight. That seems like a lot. What tolerance should I be striving for?

RE: Spine adjustment?
 

Each arrow manufacture has their own standard for measuring spine. Take Beman for example. 340's are stiffer than 400's. You just have to look at a arrow chart. Generally arrows that are stiffer are heavier. This is simply a rule of thumb. +- 2 grains is for the entire arrow. 2 grains means almost nothing, it's not worth worrying about unless you are a target archer that is really really good.

RE: Spine adjustment?
 

As I thought about that question i realized it was alttle silly. Obviously arrows would have to be closer tolerance than 60 grains. So if you have a 240 grain arrow, then out of a dozen some may be as low as 238 and some 242, right?

RE: Spine adjustment?
 

Why does changing the length of an arrow or tip weight change spine? Obviously it must have some correlation with total arrow weight.

RE: Spine adjustment?
 

Because you are changing the stiffness of the arrow.Putting on a heavier brodhead will make the arrow less stiff,and conversely adding a lighter weight broadhead will make the arrow stiffer.

RE: Spine adjustment?
 

Ok when a manufacture puts their number on the arrows say beman with the 340's they measure static spine. They put a wieght on the arrow and how much the arrow bends, determines the static spine.

When you shot that 340 out of a bow that is dynamic spine. When you shot your arrow bends (Pretty dramatic if you have never seen this). Think of it this way, if you take your pincil and break it in half it breaks pretty easy right? Now do it again. It gets harder and harder to break. The same way with an arrow the shorter the arrow is the harder it is to bend. The same way with point weight think of a long pole picking up a weight. The heavier the weight the more bend you will get in the pole.

Here is the great things about length and arrow spine. I have a custom PSE bow I put hoyt command cams on. I tuned the bow to Beman 300's full length. I also tuned it with 400's that were as short as I could go. So the lengths alone allowed me to tune the bow to 3 arrows. 300,340,400.

Maybe someone can explain this better than me, it's kind of hard to explain. Keep the questions coming

RE: Spine adjustment?
 

Thanks for the analogy, that clears things up. Can I expect a dozen "middle of the line" arrows to have fairly consistent spine?

RE: Spine adjustment?
 

Ewolf,

What are your feeling on carbon aluminum composite arrows?

RE: Spine adjustment?
 

Thanks for putting that into perspective ewolf, I never did really understand that. So, I guess my 26 1/4 inch 2117 with a 100 grain head, is PRETTY stiff for a 55 lbs bow.

RE: Spine adjustment?
 

Nah, I think you did a pretty good job ewolf. I would only clear up the other question. Grains per inch has nothing to do with an arrows spine. All it determines is the arrows aoverall weight when you're done cutting it to length. What determines an arrow's spine is a combination of diameter and wall thickness. Large diameter, thin walled shafts can have the same spine as a small diameter, thick walled shaft---the difference being that the thin walled shaft will usually be lighter in wiehgt (grains per inch).