spine calculator

Gooserbat · October 16, 2014, 10:30:00 PM

Okay I've used both stu's and 3 rivers and both say my bow needs around 76# arrows. My arrows work out to 46#. Anyone else have this kind of results?

bigbadjon · October 16, 2014, 10:59:00 PM

While not that extreme, I think most spine calculators recommend an stiffer than needed shaft.

Flying Dutchman · October 17, 2014, 01:02:00 AM

I never had. When you have such a big difference, my guess is you plug in something wrong?

slowbowjoe · October 17, 2014, 04:45:00 AM

My (wood) arrows are pretty far off from their numbers, like 15-20#.
Like 'Dutchman notes, it can sometimes be an error in entry.
Personally, I don't rely on the calculator. It's an interesting and helpful tool which I understand works very well for many other folks though.
Not saying it's "wrong" by any means, just doesn't work for my set up.

dbd870 · October 17, 2014, 07:47:00 AM

That's why Stu has a personal form factor in his. According to his I should be using 2016's but I've had several trad shooters comment how well my 1916's fly so his did recommend a little stiffer shaft than is working for me; however the difference wasn't that much!

coldwinterlake · October 17, 2014, 08:50:00 AM

The calculator is suggesting 340 spine for me. I've tried that and actually I can shoot this spine. Still 500 or 400 would be better I think. I've stopped using this calculator. Doesn't seem to work well enough for me.
I've tried to put in similar number as some of us here is using. Lets say 125gr head, 100gr insert and 31" lenght GT 3555 arrows. My bows dynamic spine is 80.2# and arrows 34.8#.
If I put only the default insert, 125gr point, 3x5" feathers, 5575 shaft 31" the dynamic spine of the arrow is 60.4# and bows the same 80.2#.
I don't get it.
Maybe I'm doing something wrong with it :D

Bladepeek · October 17, 2014, 10:42:00 AM

Coldwinterlake, I'm not going to suggest Stu's calculator will work for you, but your statement has me a bit confused. In your examples, your bow stays the same regardless of what arrow info you put in. It should. Nothing has changed on the bow - only the arrow.

I question the 80.2# bow reading unless you really are pulling one heck of a draw, and if you are, neither of those arrow setups are going to work for you. My guess, and it's just a guess, is you have put some bogus info in for your bow. The calculator is very sensitive to actual draw weight at the indicated draw length, your true draw length and the distance from center cut (+ or -). Substituting fast flight for dacron string will have an effect, but not that great.

Unless you are shooting a bow rated at 70# or higher at 28 " and drawing it REALLY long (like 30" or more), I really question that 80.2# reading.

Gooserbat · October 17, 2014, 12:01:00 PM

Here is my bows specs Tall Tines 55@30 I pull closer to 30.25 and so I plugged in 30.3" and 56#. There is no Tall Tines listed so I've tried with bows of similar performance, (Black Widow, Bob Lee, Silvertip) and I've been very careful to include the striker and proper string. Always comes out 74-77# I am shooting Easton aftermath arrows and they are basically Easton ST Excels (.1 gpi different and the same diameter.) I also am using 75 gr Easton inserts and I doubt the extra .375 of insert length would stiffen my arrows that much.

Wheels2 · October 17, 2014, 12:38:00 PM

I am around 15# under the calculator with aluminum and carbons. Even more with cedars.
It is a guide, not the gospel on arrow selection.
On my hunting bow, I am getting the best flight from a XX75 2016. I can shoot .400 and .500 carbons but fletched .400s will occasionally have a bit of right tail kick. Both .500 and .400 bare shafts really have a right tail kick with the .400s being very pronounced.

Best arrow calculator is to borrow some from friends and try them.

Bobaru · October 17, 2014, 02:06:00 PM

from the best I know, 3Rivers calculator is Stu's calculator.

Most of my bows are very close - form factor of zero to -2.

But, one of my bows was simply off the charts! Don't know why. ... In the end, bare shaft tuning is what counts.

Bladepeek · October 17, 2014, 04:45:00 PM

Gooserbat, you're right. Given your bow specs and draw length, I come up with the same dynamic bow weight. I think what we are seeing is just how much carbons are affected by length. Cut that arrow back to 30" in the chart and watch how it stiffens up.

Obviously, with your draw length, you are going to have to shoot 31" or longer, so that's not an option and you may have to go with a stiffer arrow yet if you want much weight up front at all.

Sure glad I'm just a little guy with a 28" draw. Sure makes life simpler

Gooserbat · October 17, 2014, 04:53:00 PM

Bladepeek, I started out wanting to shoot a 75 gr insert and a 125 point, however I settled on a 200 gr point in order to get the arrows to tune. Now that extra weight isn't all bad.

yeager · October 18, 2014, 11:30:00 PM

I've used Stu's calculator for both mine and my wife's bows, and they have been spot on for me each time. Can't say anything negative about his work!

coldwinterlake · October 19, 2014, 08:01:00 AM

"I question the 80.2# bow reading unless you really are pulling one heck of a draw, and if you are, neither of those arrow setups are going to work for you. My guess, and it's just a guess, is you have put some bogus info in for your bow. The calculator is very sensitive to actual draw weight at the indicated draw length, your true draw length and the distance from center cut (+ or -). Substituting fast flight for dacron string will have an effect, but not that great."

I know it sounds crazy but as you can see in this printscreen that's the reading this calculator gives me. I'm drawing 29.5" with 0.1875 cut past center and 8 strand string. Tell me what I'm doing wrong?

Bladepeek · October 19, 2014, 04:51:00 PM

coldwinterlake, I don't think you are necessarily doing any thing wrong. I think it's that long draw of yours that is creating the big difference. I think the arrow spines are based on a 28" draw. Stretch that arrow out to 31" or 32" and it starts getting pretty "whippy" regardless of the spine rating.

I'm only drawing 28" now and can pretty much go with either 500 or 600 spine depending on point weight with a 29.5" arrow length, but when I was shooting right handed and my form was different I was drawing 29". I had to shoot a pretty stiff arrow just for that additional 1" and you're stretching it 1.5".

What are you seeing when you shoot the various setups you described? If the 340 spine works for you and the 500 does not, I think perhaps the calculator is working pretty well for you. If the 340 flies stiff, then maybe you need to go with a 400 spine and shorten it as much as possible (30.5", 30.75"?) If you have an arrow that flies really well for you, you can adjust your bow inputs or the personal form factor on Stu's calculator to make the two match up and then use that to figure different arrow setups. Like I said before, I'm sure glad I'm an average sized guy

coldwinterlake · October 20, 2014, 06:45:00 AM

I used to shoot 45#@28, 68" reflexed longbow for a very long time. I just bought some 2016s and cut them to 31" without a further thought. The flew like darts and I didn't pay much attention to arrow tuning during that time.
Now when I have several bows and I primarily shoot recurves I have started to dig into this stuff.
A month ago I ordered Gamegetter 340s (according to Stu's calculator) and used some epoxy to glue 50gr weight to the default insert. Those arrows seemed to fly nicely and very quietly.
I'm prone to breaking and bending arrows (usually 4 during one 3D session) even i DON'T hit anything hard, so I want to use carbon for now on. Also this "extra weight" thing I used was too weak for high speed impacts and they would break off. I need heavy inserts to aluminum arrows (I cant' find them anywhere from Finland) or I need a proper carbon arrows, which I'm not familiar with. I got confused when reading the "debate" about carbon dynamic spines being different from static spines. I'm getting more headache when I read here which kind of combos people are using. I tried to shoot 32" GT 3555 with 125gr points and 5" flecthigs yesterday... Sounded like dry fire and totally crappy flight

If I put a 100gr insert to it I'm going to miss the hole target :D
I know I could be totally happy without a perfectly tuned arrow but it would be nice to understand these things without spending all my money on different arrows (Which cost like 100€ per dozen here)and still have only average flight. :D
I know this thing gets so much easier when I finally get one carbon setup correct.

coldwinterlake · October 20, 2014, 06:48:00 AM

Camohunter 2117s (400 spine) flies better but it's too light arrow setup. Is there somekind of weight system to aluminum arrows? The best flight I've had was with those Gamegetter 340s but only with this homemade extra weight thing

Bladepeek · October 20, 2014, 10:54:00 AM

Coldwinterlake, I don't know what kind of insert you are using on the Gamegetter 340s, but I'm guessing if they are not threaded all the way through, you could drill them out and tap with an 8x32 tap so you can screw weights into the rear of the insert. Gold Tip (which I shoot) makes 20gr and 50gr weights that would then screw into the rear of the inserts. My 3555s like around 175gr up front so I use 50gr weights on the standard GT insert (around 11gr) and a 125gr field point. For my hunting arrows, I leave the 50gr weight out and use 160gr broadheads. The weights can be screwed into each other so you could screw a 20gr into the rear of the 50gr for a total of 70gr, or stack 2 50gr for 100gr weight.

I believe you probably could do something similar. Those screw-in weights just don't come loose, especially if you wipe a dab of beeswax on the threads before tightening them. You will need the long allen wrench tool to insert/remove them from the rear once you glue the insert in the arrow.

Just something to consider.

coldwinterlake · November 17, 2014, 08:01:00 AM

Okay, I have now another question. I just received CX Heritage 250s (.391 spine)and installed 100gr brass inserts into them and I'm using 125gr points in them. I have so far shot only full lenght arrows (32.75")and with fletchings those arrows seem to be weak (they hit on the left side of my target, LH shooter). The questions is concerning bare shafts.
When I shoot these arrows without fletching, they don't even fly! First 2 yards they fly "straight" and then they make impossible curves and hit on the left and nock is pointing either left or right. They are like totally out of control. Is this caused by the arrow lenght, because they are really long. I don't think they are actually WAY too weak but the flight is so erratic I'm confused :D Just want an opinion before I start cutting them. My draw lenght is 29.5", the bow is Martin hunter 50# (I don't know the actual poundage)and I'm using SBD 8 strand string with otter fur silencers. Nocking point is 1/2" above the shelf and the shelf is cut -0.1875" past center.