# Arrow Spine: Cause and Effect



## silhouette13 (Feb 26, 2007)

good post. would less speed be lost with a "properly" spined arrow over the excessive cycling on a too weak shaft? say a 500 ligt speed at 27.5" 100 gr tip gnocks and 1.75 vanes. weights about 307 grains...a 400 lightspeed with supernock, 80 gr same vanes weigh say 306 grains...the 500 is underspined (barely) which is "ok" by the chart till 27.5 then it bumps to 400. so a 400 with 80 gr is stiffer, and again stiffness is added bu point reduction.... would the energy loss of bending thru the stabilizing cycle be reduced with a faster recovering arrow? all theorhetical here....just interested in learing whys hows and cause and effect "truths"


----------



## Strodav (Apr 25, 2012)

Good post and I agree with 90% of it. Over the years I have been given conflicting advice to use under or over spined arrows for target. Did an experiment last year, you should to know I'm a Six Sigma Black Belt, which is a practical statistician. Made up 3 sets of 5 of the same arrows in different spines. Used VAP V3s in 300, 400, and 500 spine. All are the same length, but the weight varies because the gr / in of the carbon varies with spine, so the speed out of the bow was different, but kept the FOC very close to the same. Shot them from my well tuned Alpha Elite at 20, 30, 40 and 50 yards. Shot a lot of arrows to get a statistically significant sample at all distances and measured the group sizes by taking out the flier (if any) and measuring the largest distance between the remaining 4 arrows. Threw out and redid trials where I didn't shoot well. Test took several days to finish. For that bow and those arrows could not find a statistically significant difference in group size, but did see a change in the point of impact as expected. Of course, you can correct for POI by sighting in for that arrow. I've come to the conclusion that spine is not as critical for a target setup as I was led to believe. I believe correct spine is critical to traditional bows, finger shooters and maybe early compound bows, and that lore has followed along the time line to modern compound bows where it is not as critical as it once was.

I don't know why, but I haven't had the types of problems with broad heads that I've seen others report. Maybe it's because I tune my Carbon Matrix only for broad heads, using "optimal spined" arrows and have never had a problem grouping well out to 60 yds, even though I probably wouldn't need to take a shot out past 30 yds hunting deer in the Midwest from a tree stand.


----------



## GRIMWALD (Sep 28, 2012)

Strodav said:


> Good post and I agree with 90% of it. Over the years I have been given conflicting advice to use under or over spined arrows for target. Did an experiment last year, you should to know I'm a Six Sigma Black Belt, which is a practical statistician. Made up 3 sets of 5 of the same arrows in different spines. Used VAP V3s in 300, 400, and 500 spine. All are the same length, but the weight varies because the gr / in of the carbon varies with spine, so the speed out of the bow was different, but kept the FOC very close to the same. Shot them from my well tuned Alpha Elite at 20, 30, 40 and 50 yards. Shot a lot of arrows to get a statistically significant sample at all distances and measured the group sizes by taking out the flier (if any) and measuring the largest distance between the remaining 4 arrows. Threw out and redid trials where I didn't shoot well. Test took several days to finish. For that bow and those arrows could not find a statistically significant difference in group size, but did see a change in the point of impact as expected. Of course, you can correct for POI by sighting in for that arrow. I've come to the conclusion that spine is not as critical for a target setup as I was led to believe. I believe correct spine is critical to traditional bows, finger shooters and maybe early compound bows, and that lore has followed along the time line to modern compound bows where it is not as critical as it once was.
> 
> I don't know why, but I haven't had the types of problems with broad heads that I've seen others report. Maybe it's because I tune my Carbon Matrix only for broad heads, using "optimal spined" arrows and have never had a problem grouping well out to 60 yds, even though I probably wouldn't need to take a shot out past 30 yds hunting deer in the Midwest from a tree stand.



My comment is a little off topic but your comment sparked a memory of an article I came across about a year ago and thought it may be of interest to you.
Checkout bullet point number 12

http://technicalarchery.com/

GRIM


----------



## beaverman (Jun 21, 2008)

Strodav said:


> Good post and I agree with 90% of it. Over the years I have been given conflicting advice to use under or over spined arrows for target. Did an experiment last year, you should to know I'm a Six Sigma Black Belt, which is a practical statistician. Made up 3 sets of 5 of the same arrows in different spines. Used VAP V3s in 300, 400, and 500 spine. All are the same length, but the weight varies because the gr / in of the carbon varies with spine, so the speed out of the bow was different, but kept the FOC very close to the same. Shot them from my well tuned Alpha Elite at 20, 30, 40 and 50 yards. Shot a lot of arrows to get a statistically significant sample at all distances and measured the group sizes by taking out the flier (if any) and measuring the largest distance between the remaining 4 arrows. Threw out and redid trials where I didn't shoot well. Test took several days to finish. For that bow and those arrows could not find a statistically significant difference in group size, but did see a change in the point of impact as expected. Of course, you can correct for POI by sighting in for that arrow. I've come to the conclusion that spine is not as critical for a target setup as I was led to believe. I believe correct spine is critical to traditional bows, finger shooters and maybe early compound bows, and that lore has followed along the time line to modern compound bows where it is not as critical as it once was.
> 
> I don't know why, but I haven't had the types of problems with broad heads that I've seen others report. Maybe it's because I tune my Carbon Matrix only for broad heads, using "optimal spined" arrows and have never had a problem grouping well out to 60 yds, even though I probably wouldn't need to take a shot out past 30 yds hunting deer in the Midwest from a tree stand.


Did you conduct the test with broadheads or field points?


----------



## Deezlin (Feb 5, 2004)

silhouette13 said:


> good post. would less speed be lost with a "properly" spined arrow over the excessive cycling on a too weak shaft? say a 500 ligt speed at 27.5" 100 gr tip gnocks and 1.75 vanes. weights about 307 grains...a 400 lightspeed with supernock, 80 gr same vanes weigh say 306 grains...the 500 is underspined (barely) which is "" by the chart till 27.5 then it bumps to 400. so a 400 with 80 gr is stiffer, and again stiffness is added bu point reduction.... would the energy loss of bending thru the stabilizing cycle be reduced with a faster recovering arrow? all theorhetical here....just interested in learing whys hows and cause and effect "truths"


I did a little experimented. A properly spined arrow flys a little faster. What I found is the weaker spined arrow absorbs slight increases in string speed.


----------



## Rhasenbusch (Jul 3, 2021)

Deezlin said:


> This subject seems to be popping up quite a bit. I recently fell into a shooting slump because of slightly underspined arrows.
> 
> What is spine. Spine is a physical measure of deflection over a prescribed span. An arrow shaft is place on the spine tester supported with supports under the shaft at 28", I believe. Then a specific weight is placed at the center of the shaft and the deflection is measured. This deflection is measured in thousands. There for a 500 shaft has .500 deflection or 1/2" inch. There are some other shaft descriptions on the market which either describe the construction or physical dia. Other companies have devised a number that makes more sense to the consumer, but in general, I think these variations have confused the consumer more than it has helped.
> 
> ...


This is good info, thank you very much. 
Well written!


----------

