Arrow spine, carbon to wood

[ny state land]

I am shooting 47-50, 28” arrows. I am looking to get some carbons tuned. I have some 500 spine 29.5”. So the real question is.
, if I put a wood arrow on a spine tester and it’s 48 spine. What would a .500 spine read? Is not that simple or do I have to factor the length in as well?

[Orion]

It's not that simple.  Wood arrows are spined with a 2# weight with balance posts 26 inches apart.  Easton's method of spining carbon uses a 1.93# weight and support posts 28 inches apart.  The latter gives a lighter reading.  According to a chart I have that I got off the internet a while back from Ranger Archery.com, a 48# spine yields a .54 deflection using the 2# weight and .66 using the Easton method. A .500 spine using the Easton method equals about 63#

In short, it suggests you should be going with a .600 shaft in carbon or even lighter.  That being said, there are a lot of other factors involved.  If you have some .500s, give them a try.  They might work. May need to add a little more weight up front.     

[ny state land]

Thanks Jerry,
If I am understanding you correctly it’s currently about 8lbs too much spine. That makes a lot of sense on how they were flying. I have all kinds of weights so I’ll dive in. I guess the real answer I was looking for is if any ever put them but on the same tester and logged the results?

[LookMomNoSights]

It's not that simple.  Wood arrows are spined with a 2# weight with balance posts 26 inches apart.  Easton's method of spining carbon uses a 1.93# weight and support posts 28 inches apart.  The latter gives a lighter reading.  According to a chart I have that I got off the internet a while back from Ranger Archery.com, a 48# spine yields a .54 deflection using the 2# weight and .66 using the Easton method. A .500 spine using the Easton method equals about 63#

In short, it suggests you should be going with a .600 shaft in carbon or even lighter.  That being said, there are a lot of other factors involved.  If you have some .500s, give them a try.  They might work. May need to add a little more weight up front.   

Great info here.   My 2 cents,  I believe you will absolutely be able to get the 500's to work with a bit of added length and some front weight as Orion said.  Not sure of your draw length and bow specs but what you did tell us,  I'm not far off from you .......... I draw 27", 46#,   shoot a 29" wood arrow spined 55-60 range (closer to the 60 when hand spined sorted) with 125 - 145 field point/broadhead and my carbons are 500 spine, 29.5" with 200gr field point/235 gr 3 blade adapter combo. 2 different arrow lengths with different points all around,  but identical perfect flight/trajectory/cast from one shot to the next, wood or carbon, I can grab either or mix em all up and get after it, zero change in point of impact.

[Tajue17]

I agree the spine comparisons don't work when comparing wood with carbon I think its arrow diameter, points and insert weights and yes even nock pinch on the serving,, and arrow recovery is much faster with carbons so using a deflection number on woods is useless in my experience.   

I have a couple bows that bare shaft a 29' .500 spine dark timbers perfect at my draw of 27 1/2,  those same bows shoot 28" 55/60 11/32 wood arrows pretty darn good with big 2 blade broad heads.   carbons always hit higher so I put a couple lengths of weed wacker line inside them which doesn't effect spine and that brings the POI down to where the woods are so then I can shoot both together with no problems. 

[Kirkll]

Something else to consider that you rarely hear about when it comes to carbon shaft spine deflection…. Rotating a carbon shaft at 90 degree increments and testing them will shock you how much difference there is…worse than woodies in some economical shafts… blems are all over the map….. but even high quality shafts have a weak and strong side to them.

 also the spine deflection from one shaft to the next in the same dozen arrows can vary a lot.  The plus or minus on straightness is much more consistent on carbon shafts, but the spine differences just rotating the shaft is an eye opener….  Kirk

[ny state land]

Thanks guys!  Wow great information. Kirk, holy crap, makes me wonder about even shooting them!

[Orion]

Good point Kirk.  I roll my carbon shafts in my hands just like I do my woodies to find the stiffest spine orientation before nocking and fletching.  For those who are interested in how to do it, I place the front of the shaft on a hard surface with the shaft angled about 45 degrees and the opposite end in the palm of my right hand.  I use my left hand to apply pressure to the shaft and roll it back and forth in my palm.  It's very easy to feel the stiffer orientation.  I mark it and then locate the nock accordingly.   

[Kirkll]

Thanks guys!  Wow great information. Kirk, holy crap, makes me wonder about even shooting them!

All carbon shafts are not created equally…. I first heard about this from a competition shooter who was balancing out his shafts and getting a new set dialed in. He told me that that the first thing he does is test the spine and match them up for consistency with the stiff side toward the shelf. Then he tunes the arrows with length and tip weight. Then does his fletching.   Doing this saves having to bare shaft tune each arrow.

So just for fun I got out a bunch of different type carbon shafts and started checking them…. I was shocked at the difference.  Made me understand why I was getting a few fliers here and there on a new batch of arrows….. I won’t ever buy blem shafts again either….   

Then again…. You can do it the old fashioned way and build a dozen arrows and shoot ‘em…. The ones that don’t shoot well, you break em over your knee, then go hunting…. 


Kirk

[Maclean]

Kirk,   thanks for the insight on carbon shafts. I've always mistakenly assumed that carbon shafts were uniform in their construction and therefore without a weak or strong side. This is a real eye opener.

[M60gunner]

Years ago we were testing a new spine tester going on the market. That’s when we discovered carbon arrows are not uniform around the shaft. Since then I put them in my spine tester to find the weak side. Another issue I have with carbon manufacturers is each one seems to define spine numbers differently. A 500 spine Gold Tip maybe 35#-55# but a Victory is 30#-50#. For a newbie I can imagine it can be mind boggling. They should have left the weight definition and skipped the spine thing. We had newbies show up with 30# bows and 300 spine arrows.