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Phoenix, AZ
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After resolving my issues with limb alignment, I noticed that I'm now unable to tune my ACE 570's at 44#. My draw length is 28 1/2 and normally the Easton Chart has always been on the stiff side for me. Now I'm finding the opposite is true. The only differences is that I'm now shooting wood core F7's and a Fast Flight Plus string. I haven't really shot my HPX allot, but do many of you find that you need to go up a spine shooting a HPX? Right now it appears that I need to shoot ACE 520's to get a proper tune. Btw, I have always used a 120 grain point. Ant suggestions or comments?
 

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I am shooting two spines weaker from what Easton recommends with my HPX/F7 foam limbs. I use to go by what the chart recommended but found them to stiff.
 

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Yes, I've heard it very common that the more aggressive geometry of the hpx requires archers to move one spine stiffer. The HPX has less deflex (and therefore a lower brace height) than other bows. I gather that this means more of a power stroke, which means more time for energy to be transferred into the arrow, which means an arrow that will act weaker.
 

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In my experience, I have not run into any accomplished shooters who required a shaft spine change after going to the HPX. Not one.
 

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Maybe its just us non-accomplished shooters then? Haha. I recently went from a Horizon to an Ion-X and I actually moved to a weaker shaft, but that's just me. A teammate of mine moved from a samick to an hpx of the same on-finger poundage and had to get a 1 spine stiffer shaft.

I guess the moral of the story is: expect your tuning to change whenever you change equipment.
 

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Archery Dude
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Bob, I'm no 'accomplished' shooter. But, I experienced a spine change when I moved to an HPX and F7 limbs. I currently shoot 550 X10's on 42lbs at 28" (8125 string) - that's pretty consistent with 520's at your poundage and draw length.
 

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After resolving my issues with limb alignment, I noticed that I'm now unable to tune my ACE 570's at 44#. My draw length is 28 1/2 and normally the Easton Chart has always been on the stiff side for me. Now I'm finding the opposite is true. The only differences is that I'm now shooting wood core F7's and a Fast Flight Plus string. I haven't really shot my HPX allot, but do many of you find that you need to go up a spine shooting a HPX? Right now it appears that I need to shoot ACE 520's to get a proper tune. Btw, I have always used a 120 grain point. Ant suggestions or comments?
ACE arrows are lighter so you might be able to use a 100 grain point. That will get you three pounds of spine equivalent. Consider running your brace height lower than you did on your GMX if you're not already doing that. Nobody likes to run a low brace height on the HPX, but it was designed for that and the manual recommends a lower brace height.

You can also tame your HPX by going to a fatter string. My 37 lb HPX / Border Hex6 BB2 combination is much quieter and tunes a slightly softer arrow with a 16 strand D97 string compared with 14 strands of D97 or 18 strands of 8190.

What about switching to vanes if you are using spin-wings? They might be heavier, but not as much as going a whole spine stiffer on your arrow.
 

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Nobody likes to run a low brace height on the HPX, but it was designed for that and the manual recommends a lower brace height.
Keep in mind that it should still fall within Hoyt's recommended range, which for the hpx and ion-x is considerably less than other bows of similar lengths.
 
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