Rangeball

With their being so much disparity between similar draw weight bows available, with IBO ranges from 270-350ish, it would seem to make much more sense to select arrow spine based on the energy output translated into fps.

For instance, an 80# liberty will zip an arrow within a few fps of a 70# patriot. The same arrow should spine for both bows based on the energy the arrow is receiving, but current spine charts are likely to recommend stiffer shafts based on the 80# draw of the liberty.

I can't see a reason why this wouldn't make much more sense... yet

JeffB

how would you compensate for poundage?

If you just spine for a speed rating..say 275 FPS... what if it's a 55 pound bow shooting 275 FPS,and what if it's a 90 pound bow shooting 275 FPS? They obviously will require different spine values.

confucious

I'm stepping way out of my knowledge here, but what the heck...Given the same weight arrow, if a 55# and 80# were shooting the same speed, wouldn't they create the same amount of energy thus requiring the same spine?
The 80# would be have to be hugely inefficient or the 55# incredibly efficient but both should be sending the same amount of energy through the shaft.

That said I think it would be very handy to have arrows separated by speed, but I also think that there are too many variables that people smarter than I need to figure in to make it work.

Rack-attack

This is the reason Easton has 3 different cam types listed on their charts.

The harder the cam the more speed the stiffer the spine.

With Carbons it really doesnt matter[:'(]

there are not enough diff spines.

Whats the diff between 55 to 75 pounds or,
270 to 315 fps.

One spine covers (so they say) everything under the sun

Deleted User

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JeffB

Thats all fine and dandy if we are talking about the same length arrow with the same point weight and the same weight and a 50 pound bow shooting the same as 80 pound bow.

Now cut off 4 inches...you've changed the spine and the speed...how do you account for it in an arrow chart?

You would still have to reverse engineer poundage/spine/length back into the chart.

Straightarrow

The biggest problem I see would be weight distribution, which effects spine in different ways. For instance, one arrow might have a heavier tip, which weakens spine, but shoots the same speed as the same weight arrow that has more weight on the nock end.

I think archers would be better off if they didn't assume such a broad spine range as what the manufacturers give (especially on carbons). Shoot slightly overspined arrows and you will see a lot fewer problems with your carbon arrows, in my opinion. You can always add tip weight, and/or increase draw weight if you want to tune the spine for the absolute best flight.

Rangeball

Jeff, I don't have a clue, I'm just making this up as I go along...

But, it seems in your example that yes you would have changed speed, so at the new length it wouldn't be recommended for that speed. You'd still need to know the arrow length on the chart, just use fps instead of weight to select spine.

Just trying to put several random thoughts into one or two intelligible sentences...

Cougar Mag

Take an 80 lb. bow that is less efficient than a 70 lb. bow, and for arguments's sake they shoot the same through a chronograph. It does not really matter that they shoot the same speed, because shooting the same arrow out of that 80 lb. bow as the 70 lb. bow increases the likelihood of blowing up that 80 lb. bow. That inefficient 80 lb. bow is wasting some of its energy already....don't compound it by shooting too light an arrow or an underspined arrow.

This speed thing is highly overrated when converting to kinetic energy. Check some tables out on other sites or do the math yourself. In almost every case, as the arrow used becomes heavier and stiffer, kinetic energy increases up to a certain point!!!

We should be thankful there are so many spines we can shoot. I would hate to think I could shoot the same spine of arrow as someone shooting 10-15 lbs. less!!!

Jeepnut

Well, I for one would be screwed since I don't have a chrono. Maybe you should market this idea to Easton, Range. If they started making chronographs, and then switched their tables to go by fps, I would have to buy an Easton Crhono to find out which arrows I needed.