TAP seems to pick arrow spines a little on the STIFF side. Please Help???

[Mike Trump]

When comparing my bow setup and calculated spine match to Easton's arrow chart, TAP seems to always rate Easton's choice on the really weak side. *This of course gets much better as I change from a hard cam to a medium cam and finally to the round wheel setting. *Whereas, the round wheel setting is a perfect match with what Easton's charts seem to indicate. *Who is right? *Here's my setup:

Calculate Everything mode (using custom BPF specs)
2003 Hoyt UltraTec
Speed = 256
Brace = 7.00
AMO = 28.75
Draw Weight = 68
Arrow Weight = 461

This establishes a 1.2604 BPF factor.

Now, I would like to drop my poundage down to 65 lbs instead and shoot a 27.5 inch Easton Fatboy 400 shaft with 100 grain screw-in points. *So, I updated the Input Data screen to show the following:

Calculate Everything = yes
Feathers = yes
3 fletches
4 inches long
.5625 inches high
28 inch arrow length (really a 27.5, but the program seems to add a half an inch for some reason)
0.366 diameter
385.125 arrow weight
and I adjusted the draw weight down to 65 lbs.

When I run this thru the spine calculator it says that my bow is 8.1 lbs too heavy for a 27.5 inch Easton Fatboy 400 with a 100 grain screw in tip. *Even on the medium cam setting, TAP shows that I still am 6.1 lbs over drawn. *However, by Easton's charts, a 65 lb hard cam bow would be perfect using a 400. *What gives???

Thanks,
Mike

[Mike Trump]

Also, I guess I need to know how TAP views the Hoyt Cam 1/2. Is it really a hard cam, or is it a medium cam instead?

Thanks.
Mike

PS - I really do like the program. I just need to understand why it's so different from published arrow charts.

[TAP]

Mike-

GREAT questions.....

First of all I will answer why the 'charts' do not match TAP. They can't possibly!!! :D

Charts use some basic adders and subtracters to establish a adjusted weight for your bow....TAP uses a very proprietary algorythm that has been in development for over 7 years. Tap takes the bows REAL performance into effect to select shafts where charts group ALL similar bows into catagories and then makes a recommendation from there.

Usually and I use that pretty loosely the Easton Chart will be pretty close to TAP.......In your case however I would go with what TAP recommends here's why...

The performance factor is what truly chooses an arrow, TAP only uses the cam type as a guide to get going so to speak. The Easton chart would have your bow at approximately 70 lbs adjusted weight.....(4 pounds for 138 grains in the tips, and another pound for the 1" overdraw which is pretty typical....) Now that puts in the T11-T12 category which is pretty close to what TAP is telling you. This is why a program like TAP is so useful! You get see GRAPHICALLY what a chart can't do.

The cam & half is definately a HARD cam for a starting point.......From there the BPF takes over.

I hope I have answered your question.....

[Mike Trump]

Thanks Tony.

Just one point of clarification. I really don't consider my seutp to be in an overdraw situation. My arrow contact point is directly above the handle pivot point. Therefore, I do not see any need to include the overdraw measurement in the calculation. If I'm wrong, please let me know.

Also, given my setup posted above, which arrow would you choose?

1.) Easton Fatboy 400 where my draw is 8.1 lbs too heavy?
or
2.) Easton Fatboy 340 where my draw is 4.2 lbs too light?

Niether are perfect. Which is better?

Thanks for your time!
Mike

[TAP]

Your overdraw calc is fine.....makes perfect sense to me. I just assume a 1" based purely on most setups being behind the grip just a tad..:)

Play with TAP a bit and see if you can lighten the tip of the 400 enough to get green. OR lenghten or add tip weight to the 340 till you get green.

Usually I would opt myself for the stiffer arrow, but a little tuning can get an arrow the plots ON THE CHART shooting!

[Mike Trump]

Thanks Tony! I'll keep playing with it. Love the program.

later,
mike