I have looked at some arrow charts and I think I am on the right track but would like to get some confirmation from others with more experience than myself.  I want to order some surewood shafts and I think I need 75-80# spine.  My set up is a Caribow Peragrin R/D longbow.  I draw about 30" and the bow is about 57# at that draw.  I want to use a 160 or 190 grain broadhead.  I believe the shelf is cut past center.  Any input would be greatly appreciated. Thanks. Jonathan

That would be right at 160 gr and 31 inch arrows and Dacron . If shooting FF you will need to step up to 80-85. You would need 90# shafts at 190gr.

If the shelf is cut past center, the bow will handle 90# spines, though I doubt they'll be needed. I think 75-80# will work fine with either head and a fast flite string.  Might try a test kit if Surewood offers one.  

Not too difficult to find 75-80# in 11/32 doug fir.  It's less common in spine weights above that at 11/32.  And, if you go to a thicker 23/64 shaft, which has the same effect of building out the side plate on your bow due to the larger diameter of the arrow, you may be able to  drop down 5# or so in spine.

Test kit.....dont waste your money guessing. Its the only way to be sure you buy the right dozen IMHO. What works for one bow wont work for the next, even when the spec's line up. I find long wood arrows to be extra finicky anyhow. I shoot 31" shafts @ 29.5draw.

I have gotten 90/95 in 11/32 from Surewood. I agree with Orion the test kit is essential for you. 75/80 will likely be your minimum.

The depth of the shelf cut has a big effect on spine needs.  I looked at the Caribow site and it doesn't say and the pics don't show it.  If the side plate brings you to center and you shoot a 31" arrow, I figure 85-89 for a 160 point and 90-94 for a 190 point.  Surewood will likely have 11/32 in both spines, but they will be limited in supply.  I would recommend the 23/64 as you will be able to match weights in the future much easier.  Don't worry about the diameter difference and spine.  It is less than .016" dia so you are only moving the arrow out less than .008"; a pound diff at most.  The formulas will get you close with spine, but the test kit really is a good idea.  Consider it an investment and you will always have these arrows to test with in the future.  Try to find access to a spine tester so you can mark each shaft with its true spine.  You can also tune your bow to a slightly weak arrow by building out the side plate just a bit.  Works great.

Study up on paper tuning; I find at a great way to really nail down the best spine range.

Jonathan,

I shoot a Caribow Peregrine with woodies. I would recommend you use Stu Millers' Dynamic spine calculator. It was a GREAT help for me. I am 0,2 accurate in it and my arrows fly unbelievable good! The Peregrine is cut 1/16 past center, and with a bevertail strikeplate it will come around zero centercut. This is important information in Stu's calculator. As bow you can select "generic recurve" because the Peregrine behaves more like a recurve. Remember garbage in = garbage out!

You can download it here:       http://www.heilakka.com/stumiller/    

Don't believe the speed, Stu is a bit optimistic here. For the rest he is dead on!

If you have any questions, contact me!

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QuoteOriginally posted by Fletcher:
The depth of the shelf cut has a big effect on spine needs.  I looked at the Caribow site and it doesn't say and the pics don't show it.  If the side plate brings you to center and you shoot a 31" arrow, I figure 85-89 for a 160 point and 90-94 for a 190 point.  Surewood will likely have 11/32 in both spines, but they will be limited in supply.  I would recommend the 23/64 as you will be able to match weights in the future much easier.  Don't worry about the diameter difference and spine.  It is less than .016" dia so you are only moving the arrow out less than .008"; a pound diff at most.  The formulas will get you close with spine, but the test kit really is a good idea.  Consider it an investment and you will always have these arrows to test with in the future.  Try to find access to a spine tester so you can mark each shaft with its true spine.  You can also tune your bow to a slightly weak arrow by building out the side plate just a bit.  Works great.

That's great advice. The cut of the shelf definitely makes a difference.

I have two bows with exactly the same poundage but one has more mass to the riser and the shelf isn't cut as deep. That created a variance of one whole spine size. That factor alone.