Redneck Bowhunter

Can someone explain to me the differance between static and dynamic spine. It has me a little confused. Also everyone talks about matching total arrow weight to your bow. But how do you now what is the ideal weight. All I have seen from the manufacturer is the minimum recomended weight. How do you know what is ideal for your bow and for hunting?

Bloodsaw

Static spine is the spine of the arrow wile its not moving or flexing, dynamic spine is the spine of the arrow in flighti think, someone correct me if im wrong here, i dont know for sure

davepjr71

You're almost correct. The dynamic spine is the spine based on length of arrow,draw length, draw weight,and arrow component weight for an arrow when shot.

All arrows that are marked the same have the same static spine. i.e. 300 series etc. The static spine is measured using a weight and only gives the stiffness of the arrow when braced across 28".

However, for dynamic spine the a 28" arrow will have a stiffer dynamic spine than a 30" arrow due to it's shorter length. The same arrow with a 100 gr tip will have a stiffer spine than one with a 125 gr. An arrow with a wrap will have a stiffer spine. Any weight added to the rear will stiffen the dynamic spine. Any weight to the from will reduce the spine. The same length arrow shot out of a 30" DL bow will have a weaker spine than shot out of a 28" bow due to the longer power stroke.

What's an ideal arrow weight for hunting is different between a lot of people and opens up a big discussion. However, I can tell you how I choose my set-up and what I like. That doesn't mean it's perfect and there are a lot of ways to choose an arrow.

I decided on a broadhead weight and a draw weight that I expect to be using for hunting. I then used a program like OT2 to narrow my arrow choices down based on an arrow length that I want to use. That actually got me to an arrow that is spined a little stiff (which is recommended for hunting). If the shaft were a little weak I'd add a wrap (which I'm doing) and possibly shorten the shaft if needed. If I needed to I could also go down in draw weight to get the spine a little stiff.

My finished arrow is around 420 grains. a 27" GT XT Hunter 7595 with a 125 grain tip and wraps.

There are guys on here with a ton of experience that can explain it better if I screwed up or missed something.

Redneck Bowhunter

I somewhat understand thanks dave.

Straightarrow

Static spine is the measure of deflection that an arrow has with a 2 lb weight hanging from the middle with end supports 28" apart. For instance, an arrow that says it's 340 means that it deflects .340" with the weight hanging from it. The lower numbers are from arrow that deflect less and are therefore stiffer.

Dynamic spine is the actual deflection that an arrow has when shot out of your bow. Only a relatively small range of defection will fly properly out of a given setup. You want to tune your dynamic spine to match this range. Shortening arrows increases dynamic spine (stiffens them). Lowering draw weight also increases dynamic spine, and lowering tip weight does the same. The reverse of these will weaken spine. Spine tuning an arrow means to adjust these in combination to obtain a good flying arrow for your setup. The logical way to start is to look at the tip weight (FOC) you desire and then work from there. You can easily shoot arrow designed for 90 lb draw weights out of a 60 lb bow, if you know how to weaken the dynamic spine properly.

Paul L Mohr

Static spine is a measurement and should be a controlled specification. It is a way of rating arrows.

Dynamic spine is simply how your bow reacts to a given arrow.

Paul

Redneck Bowhunter

Wow, it just clicked in. Thanks StraightArrow. Just a question though. Should you adjust your bow to the arrow to get correct dynamic spine or the arrow to the bow. This is for an arrow that you have already purchased using the shaft selection guides.

Straightarrow

Hopefully, you haven't cut them or fletched them. That really cuts into your options and ability to tune them to your bow.

Ideally, you figure out an approximate FOC you want to shoot and then buy the shaft that you think will come closest to being stiff enough without cutting much off. You then use a combination of adjusting tip weight, draw weight and arrow length to fine tune it to your bow - done by bareshaft tuning.

Paul, I would have said the it's how your arrow reacts to a given bow.

mjhamel

So in response to some of your guys' replies, what is an optimal FOC for hunting? What are the benefits to have it higher or lower? Also, my total weight for my arrow, including broadhead is around 425 grains. Is this a heavy, medium, light set-up? Sorry for all of the dumb questions. I am a beginner when it comes to tuning a bow and would really like to learn how to do everything myself.

Redneck Bowhunter

The optimal FOC for hunting is from 8% to 12%. The higher the FOC the more the arrow will want to nose dive which increases stability but also decreases effectice range becuase the arrow arcs alot more at longer didtances. There is a suggested min. weight from your bow company for arrow weight, as long as your above that you should be fine.

Yes, I have cut and fletched them. My front of center is 11.1%.