# Arrow Spine Charts vs. FPS



## shine (May 8, 2010)

Been having problems tuning my arrows for broad heads again this year. Using the same arrows - Trophy Ridge Blast 400s. Shooting a Destroyer 340 - my results point to “weak spine reaction” - broad heads tracking right and catch up is way off center.

According to the arrow chart, I should be shooting a 400 since I am at 28” draw and 58#. That said, my arrow speed is around 280 fps. My old bow shot these 400s around 240 fps. Question: should arrow spine be based on bow weight or bow speed, especially with the wide speed disparities on the market today? Doing the math, I would have to go above 70# to get my old bow to shoot 280 fps.


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## Ches (Aug 3, 2009)

Not sure, but I think it has to do with cam type. Some are more aggresive or hard, I would think a 340 would fit into this.


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## nomad11 (Apr 14, 2006)

I will say...you don't know the speed until you buy it and shoot it...unless you're the lucky someone that shoots the industry standard drawlength. With that you can build an IBO arrow and get what is advertised in the specs....maybe. For those of us with a D/L that is different..who knows. Best we can do is get input from others similar to us or use the arrow manufacturer charts or on-line calculators. No absolutes. In these cases (charts/calculators) recommendations are based on D/L, cam, draw weight and a few other items.....but again, no guarantees. Problem is....if given a 20yr old bow at 58#, 28" draw and medium cam and 1yr old bow at 58#, 28" draw and somewhat medium cam....one could get the same answer. Yet the latter is so much more efficient (40 fps more efficient in your case) today that now your old arrows are not applicable. You may be in such a situation.

Other than gaining 40fps...what is the problem? I gotta figure in gaining that much energy it will change your arrow stiffness. Maybe to the point the old arrows are no longer applicable.


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## canse (Sep 9, 2008)

when I´m in this situation usually play with some ballistic program but based on the velocity recorded on MY bow and MY arrows instead of just poundage because of de same reason you stated above.:wink:
Canse


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## GregBS (Oct 30, 2010)

Recently, there has been a new classification of cam, the Extra Hard. Almost all of Bowtech's bows fall into this category. The charts don't account for this but it usually means you must go stiffer than the chart recommends. Charts are only billed as a starting point anyways.

Example:

My D340
64#
29" DL
28" Arrow
100gr tip

Easton's recommendation is a .400 spine arrow. That's complete bunk as 'On Target' has that spine FAR too weak for me. I shoot 27.5" .340 spine arrows perfectly with bare shafts grouping with arrows at 20 yards.

Playing with OT2, a 28" .340 arrow w/ 100gr point is just about perfect for your bow.


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