Spine? IBO ABO? etc...?

[salukipv1]

I think I saw it mentioned on here before how to calculate the ideal/best spine etc...for your setup?

I'm not new to archery, but new to all these figures and numbers and what is best etc...

My draw length is 28"
current draw weight 63lbs, would like to become comfortable at 70lbs.
shooting 100gr broadheads.

have a few different arrow setups
don't know exact arrow weights...
1 set is 10gr/in estimated wt... 418grs
2 set is 7.9gr/in.................... 353
3 set is 6.4gr/in................... 307grs

Mainly trying to figure out if I could tweak my setup to shoot even tigher groups by determing an ideal BH weight, and or ideal spine/arrow weight etc...

Is spine just arrow shaft diamter? and what is spine used to determine...?

Thanks.

[brucelanthier]

Spine is theamount of flex or bendof an arrow shaft under certain conditions. When you shoot the arrow it flexes as it leaves the string. If it flexes the correct amount then you have a correctly spined arrow and it will shoot best. If it doesn't flex enough then it is too stiff, too much flexing and it is too weak and either one too stiff or too weak is not ideal. A hunting arrow is usually set up with a slightly stiffer spine than a target arrow.

Someone can look up your info if you list your bow model and its' current setup and your arrow model with its' length and tip weight along with fletches.

[davepjr71]

Just to add to bruce's good post.

Shaft diameter has a small part to do with the spine. There are very skinny arrows that have stiff spine and very fat arrows that have weak spines. It all depends on the thickness between the inside and outside diameter, the overall diameter, and shaft material and design. Even arrow weight between manufacturers may vary.

If all 3 arrow you listed are the same exact arrow manufacturer/model the heaviest one will probably be the one with the stiffest spine.

As bruce stated supply your bow manufacturer, the arrow manufacturer/model that you have, the arrow length you intend to use and we can help you out.

[salukipv1]

Carbon tech arrows, whitetails, rhinos, cheetahs,plan to use whitetails or rhinos for hunting
most likely whitetails Spine for all 3 is listed at .400?

Arrow Shaft lenght: 28"
NAP quickspin ST speed hunters
Matthews drenalin 70#, 28" draw, current weight 63#

100gr broadheads, muzzy 3 blade, not mx3, also have rage 2 blade 100gr

[brucelanthier]

It looks as if you are marginally weak spine with that setup. Not awful but marginally stiff would be better. If you are going to get up to 70#'s you may want to look at the whitetails, rhino's and cheetahs with a .300 spine. You may also want to look at some other arrows in the .360 spine range, easton, carbon express, gold tips, etc.

Edit: Forgot to chnage the DL to 28" but you are still slightly weak.

[davepjr71]

If you are shooting the Drenalin with 80% let off your spine should be ok with any of those arrows up to 70 lbs. You may want to use a wrap though to stiffen the spine a little. Try to remember when looking at this that the spine is probably a little stiffer than what is shown. The program uses IBO speed and every bow's IBO differs depending on DL and the actual performance of the bow. Your bow's IBO will not be 320 FPS as listed by manufacturer because that IBO is for a 30" draw length unless otherwise specified.

You need the speed of a known arrow shot from your bow to adjust theIBO speed for your bow and a program like Archer's Advantage to figure out the exact spine. OT2 does not compensate for slower IBO's. So, ifthe program showsthe spine on the low side it is probably actually in the middle or slightly high. I've used this method with this program and have no issues with my arrows.

[salukipv1]

65% let off, drenalin

so lower spine # equals a stiffer arrow? higher spine # weaker/less stiff?

I'm typically at 63lbs, but if I shot more I know 70# wouldn't be a problem, so looking to get there. Always planning to shoot 100gr too, dont think I'll ever shoot 125grs, maybe for something large, but doubtful.

Thanks for the info

[davepjr71]

ORIGINAL: salukipv1

65% let off, drenalin

so lower spine # equals a stiffer arrow? higher spine # weaker/less stiff?

I'm typically at 63lbs, but if I shot more I know 70# wouldn't be a problem, so looking to get there. Always planning to shoot 100gr too, dont think I'll ever shoot 125grs, maybe for something large, but doubtful.

Thanks for the info

Then the arrows are definitely underspined. Go with what bruce listed in the .360 range.

[TFOX]

ORIGINAL: davepjr71

If you are shooting the Drenalin with 80% let off your spine should be ok with any of those arrows up to 70 lbs. You may want to use a wrap though to stiffen the spine a little. Try to remember when looking at this that the spine is probably a little stiffer than what is shown. The program uses IBO speed and every bow's IBO differs depending on DL and the actual performance of the bow. Your bow's IBO will not be 320 FPS as listed by manufacturer because that IBO is for a 30" draw length unless otherwise specified.

You need the speed of a known arrow shot from your bow to adjust theIBO speed for your bow and a program like Archer's Advantage to figure out the exact spine. OT2 does not compensate for slower IBO's. So, ifthe program showsthe spine on the low side it is probably actually in the middle or slightly high. I've used this method with this program and have no issues with my arrows.

Actually Dave,I have found how to correctly adjust the speed of the program so it can be calibrated on OT2.OT2 does not use IBO,it uses cam style so when you get your exact speed,slide the performance scale down on the setup page(I believe) and then click over to the spine page untill you get it to show the correct speed for your setup.IT IS A PAIN but this is the correct way to calibrate it.It doesn't show the speed change when you do it on the same page,you must click over before it sets it.

Hope this makes sense.

[salukipv1]

What program are you guys using? Is it free?