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Discussion Starter #1
As above, what effect does point weight have on spine.

As an example my current arrow, 500 spine and 30 inches, is good up to 50lbs.

7277016

(This an advert for my arrow - the nock and points come as a set - it's not part of the spine chart description)

Is that assuming a certain point weight?

If I went from 100grains point weight to 150 grains, what effect would that have on the max draw weight?
 

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Slinging Arrows
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Adding weight to the front of the arrow weakens the spine and any weight added to the nock of the arrow stiffens the arrow.

I would run your number in a spine program and see what happens when you change the variables.
 
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Generally speaking arrow manufacturers use the 100gr point to set up their charts. A heavier tip will cause the spine to act weaker, a lighter tip causes the spine to act stiffer.
 

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Back Yard Champion
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30" arrow, 100 gr point, .500" spine, and 50 pounds - I think you're pushing the limit. Your draw length is needed and what cam, med, hard?
 

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Where would I find this software?

There are other similar programs as well (e.g. Archer's Advantage) but SFA is the most accurate one I've used
 

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If you call them up they will normally have the info or offer the full chart with all the instructions.
 

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Discussion Starter #9
30" arrow, 100 gr point, .500" spine, and 50 pounds - I think you're pushing the limit. Your draw length is needed and what cam, med, hard?
Can you please explain.

The chart says up to 50lbs if 500 and 30 inches.

The chart does not call for draw length. Why should it be factored in and where do I find a table / chart that includes draw length?

What do you mean by medium or hard Cam? Is this subjective or based on the bows IBO rating or what?
 

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Draw length only matters in overdraw spine.

Cam is how quick it changes from let off to peak weight.
 

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Back Yard Champion
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Can you please explain.

The chart says up to 50lbs if 500 and 30 inches.

The chart does not call for draw length. Why should it be factored in and where do I find a table / chart that includes draw length?

What do you mean by medium or hard Cam? Is this subjective or based on the bows IBO rating or what?
For one, a short draw length doesn't effect spine as much. Like dsdhunts noted, it's energy imparted on the shaft. Say smooth is maybe 2 points, med is 4 and hard is 6. These values are taken into consideration.
Let off is another value. So is the IBO or ATA rating.
Not having these values and running off the top of my head I show you needing a .400" spine arrow.
 

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(aka lug nut)
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Can you please explain.

The chart says up to 50lbs if 500 and 30 inches.

The chart does not call for draw length. Why should it be factored in and where do I find a table / chart that includes draw length?

What do you mean by medium or hard Cam? Is this subjective or based on the bows IBO rating or what?
So, let's make this super simple.

1) what brand and model of bow?
LONGER draw length, means more power from the bow to the arrow.
24-inch draw length and 50 pounds draw weight, means not much arrow speed.
31-inch draw length and same bow, same 50 lbs draw weight means A LOT MORE arrow speed, so
longer draw length requires more arrow stiffness, a lower arrow spine number.

This is why a chart for arrow selection is completely and utterly USELESS.
 

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Discussion Starter #13
So, let's make this super simple.

1) what brand and model of bow?
LONGER draw length, means more power from the bow to the arrow.
24-inch draw length and 50 pounds draw weight, means not much arrow speed.
31-inch draw length and same bow, same 50 lbs draw weight means A LOT MORE arrow speed, so
longer draw length requires more arrow stiffness, a lower arrow spine number.

This is why a chart for arrow selection is completely and utterly USELESS.
I'm using a PSE Drive 3B with 28.5 inch draw length.
 

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(aka lug nut)
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I'm using a PSE Drive 3B with 28.5 inch draw length.
So, the PSE Drive 3B has a "horsepower rating" of 319 feet per second. Bows are all rated for IBO speed rating,
assuming 70 lbs of draw weight and "30-inches" of draw length. Some bows are faster than yours. Some bows are slower than yours. That's why the chart is ABSOLUTELY useless. The draw length also will increase or decrease the arrow speed. MORE draw length, same draw weight, means MORE arrow speed. LESS draw length and same draw weight, means LESS arrow speed. Another reason the chart is completely useless.

NO, your 500 spine arrow is NOT good for your bow, at YOUR draw weight, and at YOUR draw length. Your arrow tube length at 30-inches (MUCH too long), makes your 500 spine arrow DANGEROUSLY weak...meaning the arrow could SNAP when you fire the arrow....when using the PSE Drive 3B, at 28.5-inches of draw length, and at 50 lbs draw weight, with a 500 spine arrow, that is 30-inches long, with a 100 grain point up front (assuming field point).
 

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(aka lug nut)
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I'm using a PSE Drive 3B with 28.5 inch draw length.
If you insist on using a 30-inch long arrow, when using your PSE Drive 3B compound bow, at 50 lbs of draw weight,
and 28.5 inches of draw length, and if you use the 100 grain screw in field point, the SAFE arrow spine rating for you,
is a 450 spine arrow.

This assumes 100 grain screw in field points, this assumes Blazer vanes, this assume a carbon tube length of
30-inches (just the length of the black tube), this assumes the PSE Drive 3B compound bow, 28.5-inches of draw length and 50 lbs of draw weight.
 

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(aka lug nut)
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I'm using a PSE Drive 3B with 28.5 inch draw length.
Now, if you want to change to a 150 grain field point up front, then, the 400 spine arrow, the tube length needs to be cut down to a raw carbon tube length of 28-inches...this means the black tube needs to measure only 28-inches.

BUT, my draw length is 28.5-inches. How can I use an arrow that only measures 28-inches? A 28.5-inch draw length means the distance from the nock groove to the pivot point of the grip (deepest part of the curve on the grip) measures 26.75-inches. The 28-inch long arrow (length of black tube only) will still be forwards of the deepest part of the grip.

So, 400 spine arrow, black tube length of 30-inches, and a 150 grain point up front, will be safe to use with your PSE Drive 3B compound bow. I assumed the GoldTip Kinetic XT 400 spine arrow, 24.8 grain aluminum insert, 150 grain field point, and Blazer vanes. The black tube length is 30-inches. This 400 spine arrow will be safe to use with your PSE Drive 3B compound bow, at 28.5-inches of draw length, and 50 lbs of draw weight.
 

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(aka lug nut)
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As above, what effect does point weight have on spine.

As an example my current arrow, 500 spine and 30 inches, is good up to 50lbs.

View attachment 7277016
(This an advert for my arrow - the nock and points come as a set - it's not part of the spine chart description)

Is that assuming a certain point weight?

If I went from 100grains point weight to 150 grains, what effect would that have on the max draw weight?
Your PSE Drive 3B compound bow, at 50 lbs of draw weight and 28.5-inches of draw length,
your 500 spine arrow and 30-inches long, with 150 grains of point weight would ONLY be safe to shoot at
37 lbs of draw weight.

Your PSE Drive 3B compound bow, at 50 lbs of draw weight and 28.5-inches of draw length,
your 500 spine arrow and 30-inches long, with 100 grains of point weight would ONLY be safe to shoot at
43 lbs of draw weight. These calculations take into account the SPEED rating of your bow, the draw weight of your bow, the draw length of your bow, the specific weight of the vane, the length of the arrow tube, the insert weight, the point weight. All of these things matter when it comes to calculate the breaking strength of the arrow, when fired out of your PSE Drive 3B compound bow. Your chart is not a good thing to use.
 

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For that set-up and your draw length I'd try a 29" (carbon length) 400 spine arrow with 125-150 grain points.
 

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Discussion Starter #19 (Edited)
Ok. Thanks for all your suggestions.

I downloaded OT2GO Spine from PinWheel on my iPhone - and well it's okay.

Had to pay some in App purchases to get the arrow database and ability to save, but still pretty reasonably priced.

Unfortunately it doesn't have my arrow manufacturer, Accura, in the database, which really means it's not very useful unless I buy arrows from one of their covered manufactures. So that was disappointing.

The arrow configuration is also a bit limited. Yes you can enter arrow length, point weight, point insert weight, shaft OD, Shaft GPI, and Wrap Weight, but nothing for Pin & Nock or Flight Weight - that seems like quite an elementary omission.

What I have noticed when loading in profiles of other arrows with 500 spine, is that they tend to have a smaller GPI.

For example the Easton Carbon One 500 has a GPI of 7.4 (weak spine for my set up), where the Easton Carbon One 410 has a GPI of 8.5 (slightly over spined for my set up).

Now the arrow I'm using, Accura X One Prime Carbon 500, has a GPI of 8.14, so may in fact be suitable for my set up - but of course I can't find it in the database.

It really doesn't help that every manufacture defines spine differently.

Back to OT2GO Spine - it seems like ok software, but not very intuative or user friendly, I had to Google to find some resources, even then. I have not found the definitions for the following:

FPS: Feet Per Second
TAW: Total Arrow Weight (again it hasn't asked for Pin + Nock or Flight)
GR/LB: ?????
KE: Kinetic Energy?
MO: ?????
%FOC: Percentage front of center
 

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Dont get hung up on GPI. That is how much that particular arrow weighs per inch. Does not necessarily correlate to spine strength.
 
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