Will the length of the broadhead effect spine?

[Mint]

I've noticed shooting Simmons broadheads like the intercepter I can go a little lighter in point weight and I'm wondering since it is a long broadhead it is weakening the spine a little or is it something else?

[Orion]

Theoretically, it's moving more weight further out on the end of the shaft, so it would weaken the shaft slightly.  Practically, not enough to make a difference. 

[McDave]

I agree with Orion.  Only the part of the broadhead that sticks out further than a field point of the same weight will affect spine more than the field point itself.  The amount of the broadhead sticking out to the sides has no more effect on spine than a field point of the same weight.  So unless you have an extremely long broadhead, the effect should be negligible.

[BAbassangler]

A tip I just learned on here...make a broadhead "bareshaft" with the fletching cut down to 1/8", to check the tune.

[Stringwacker]

Absolutely.

Not only is the weight moved a little further out but the overall arrow length is longer. Look at it this way, if you had two arrows with the identical field tip weight; the longer shaft will shoot weaker. Shorter arrows will act stiffer all things being equal.

My own test with broadheads on 1/8" feathers (on stripped quills) usually shows the broadhead needs about 20 grains less weight to bareshaft the same as a field point 20 grains heavier. Vented heads for reasons I don't know shoot a little more stiff than non-vented heads. Maybe a different bow weight or draw dynamic would change that; but this is how it works for me.

As was mentioned before... this is minor variantion that is unlikely to effect the good flight characteristics of a feathered shaft. But those who want a tuned arrow to the highest degree possible might be interested in knowing.

[Tajue17]

A tip I just learned on here...make a broadhead "bareshaft" with the fletching cut down to 1/8", to check the tune.

I have to try that...

[Pat B]

I learned this many years ago from my friend and TG member Art Butner(artcher1). Art was an expert in arrow making from simple cane and hardwood shoot arrows to commercial or homemade doweled and split shafting.
The spine weight given on a particular bare shaft is for a complete arrow of 28" with a 125 grain point up front. At least this is for wood arrows. I'm, not familiar with carbon or aluminum arrow shafts. You can change the actual spine by adding or subtracting length and adding or subtracting tip weight. By shortening the length you increase the dynamic spine value of the arrow and by increasing the length you decrease the dynamic spine value by 25# per inch. By increasing the head weight you decrease the dynamic spine value of the arrow and by decreasing the weight of the head you increase the dynamic spine value by 25# for each 25 grains of point weight.

[BAbassangler]

25# for each 25 grains of point weight.

Even I can do that math...I'm switching to wood!

[Orion]

 "by decreasing the weight of the head you increase the dynamic spine value by 25# for each 25 grains of point weight." Nope. Must be a typo there somewhere. 

[BAbassangler]

Sorry, just mean it's a grain/lb...easy math.  Al and carbon; each shaft is different, and I haven't had one yet be 1:1

[Pat B]

Yeah, Orion, my 75 year old, A.D.D, addled brain gets those values mixed up.Glad you caught that.

[Arctic Hunter]

I've often wondered this too. I've always noticed that bigger broadheads generally have a greater effect on arrow flight. But I always wondered if it was a consequence of spine or the aerodynamic properties of the particular head. I heard a very accomplished compound shooter say that it has a big effect on spine, and therefore his accuracy. It probably makes more of a difference if you're tuned right on the edge of being weak anyway.

I think this year I'm going to do more testing and playing around with big broadheads. I have a bunch of 2" feathers that I will likely never use. I'll cut them down to some shark's teeth size and shoot broadheads to see what the results are.

I need something to do until bear season anyway.

[BAbassangler]

TG, not far behind buddy!
Mr. Arctic, I'm thinking unless you have engineers' software, and experience in rocket science, best not to loose sleep and just start experimenting...I should take my own advice.
I have some No Mercy single bevels, that seemed to wander a bit when matched with my 5mm shafts and 4" Trad-Vanes.  Fly perfect on 6.5mm shafts with 5" feathers...need to put this hobby down for a bit (I tell myself), and wait to try the 5mm with feathers to see if there's a middle ground.
Jeff Phillips from YouTube says 6.5mm are more forgiving and better suited to big heads; I'll roll with that for now.

[Wudstix]

Pat that is probably why I can push 175-230 grain broadhead combos from my 64-67# bows with 70-75# spine.  Occasionally, I bump up to 80# spine.  But most of my shafts are tapered and footed.

[Pat B]

Michael, tapered shafts add another variable to the mix. With cane and hardwood shoot shafts the natural taper can make the arrow shootable from bows up to 10# difference in draw weight. It probably is similar with tapered doweled shafts like you have. I have a set of hand tapered ash shafts that I've shot from bows from 55#(my old draw weight) to 45#(my new draw weight).

[Wudstix]

My tapered and footed arrows allow me to shoot from 60-67# D/R longbows and 67# Big River recurve with 190 grain heads (avg).  They fly well.