Spine calculation

[TylerTheTerrible]

I got a new bow and looking for new arrows as my poundage is higher. However, looking at different manufacturer calculators, I'm getting significantly different results. I'm shooting a 30 inch arrow at 60lbs with a 343 ibo with a index release. Bow's brace height is 6 inches. I'm open to shooting a 100 or 125 grain broad head depending on GPI, etc.

Using the Easton chart, I'm getting a recommendation of 240 - 260 spine.

Using the Victory calculator, I'm getting a suggestion of ~350 spine depending on the exact weight of arrow components.

What spine would you go with? I'm under the impression, that the spines are all measured (nearly if not exactly) the same way and should not be manufacturer specific.

 

[Rob5589]

I would lean toward a .300, depending on how much weight you have up front. With that long of a shaft, a .250 is totally plausible a good amount of weight in front.

What is your draw length, out of curiosity?

 

[TylerTheTerrible]

I would lean toward a .300, depending on how much weight you have up front. With that long of a shaft, a .250 is totally plausible a good amount of weight in front.

What is your draw length, out of curiosity?

That's what I was leaning towards. 30 inch draw length.. Depending on your school of thought I could probably add or subtract ~1 inch of arrow length. Without a point, the arrow is just about even with the front of the riser when at full draw.

 

[Rob5589]

That changes things. A .300 should work with ave wt up front. A .340 is also a possibility. You need to decide how much wt up front you want to run, what kind of foc are you looking for, etc. Gold Tip has a calculator that I use and works well.

 

[Vandal 44]

I think you would be fine with a 300 spine arrow cut to 29 inches carbon to carbon, with inserts weighing up to 50 grains and a 125 grain BH. If you start going over 175 grain point weight you may need to move up to a stiffer spine


Sent from my iPhone using Tapatalk

 

[Hoot]

It also depends on your bows cam system, but I would tend to agree with the above. I'd imagine, unless your bow has a real hard cam, you'll probably get a .340 to tune the best.

 

[5 shot group]

(edited to remove incorrect info)

 

[Jimbob]

View attachment 187973

60lbs
30" arrow
100gr Point
Standard insert / blazers / nock


View attachment 187977

Same as above, but a 300 spine

My software (computer version and iPhone version) is giving very different results from you. I get different weights, different speed and different spine match.

Are you using 30" draw?

 

[Jimbob]

30"draw 60lb bow 343 ibo 6" brace 85% let off

I would look for an arrow close to these specs. I used 125 grain point to gain a little FOC and weight for the 340. You could switch to a 100 grain point on the 340 arrow and it would spine better but then you are losing FOC and total arrow weight. To get the 340 to work you need to cut it pretty short to stiffen it up.

standard insert nock and blazer vanes 125 grain point

Easton 340 at 28"

Easton 300 at 30"

 

[5 shot group]

My software (computer version and iPhone version) is giving very different results from you. I get different weights, different speed and different spine match.

Are you using 30" draw?

I must not of been. I re-ran it and got about the same as you. I'm gonna edit that post (oops )

 

[roursbourn]

The Gold Tip website has spine charts for 100, 125, and 150gr point weight. Essentially adding 25gr in point weight is equivalent to adding 5lbs in draw weight. For example if you wanted to shoot 60 lbs with 150gr point the spine would need to be the same as a 70lb with 100gr point.

 

[roursbourn]

The 25gr/5lb rule can be extrapolated out but be careful about pushing the limits. Shattered shafts aren’t fun