Just an FYI:

The modern manufacturer's deflection ratings are done on the ASTM chart, and derived by checking the deflection on a 28" center with a 1.94# weight.

When spine is checked using the AMO standard (26" center with 2# weight) it will always show a higher spine than the ASTM.

EXAMPLE: I have some shafts that ASTM spine as .300, and they are dead on. When checking their spine on a spine tester using the AMO formula, they have a .250 deflection.

To see what the ASTM charts actually are in AMO spine, you can use the conversion formula of ASTM deflection X .825.

Example: ASTM spine defletion of .300 X .825 = AMO spine deflection of .247

Shafts from different manufacturers, and different materials will vary some, so the conversion formula is not perfect, but it will get you close enough to make accurate shaft selections when viewing the manufacturers spine charts.

Here also is an AMO spine deflection chart.

Hope that helps some.

Rick

I wish my printer would work,thanks Rick

Rick: Now the question is does that give you the spine for a 28" arrow or 29" arrow. The AMO chart gives you the spine for a 28" arrow when suspended between 26" centers. Bob

Bob, I really don't understand what you are asking.

This is simply the "static" spine for shafts using the ASTM formula, or an AMO formula.

In my observation, the static spine does not change due to extra length beyond what the point to point measurement has to be for which ever measurement you are using.

Dynamic spine is a whole different ball of wax, and will change dramatically once user input of build of the arrow becomes involved.

If you have other formulas, or input I for one would very much appreciate you sharing them.

Rick

Rick: With the AMO standard. the arrow is measured between 26" centers giving you the deflection or spine is for a 28" arrow. The ASTM standard measures between 28" centers, is that deflection for a 28" arrow or a 29" arrow. Static spine still has an arrow length standard. Bob

Got ya Bob.

I never knew that.

I always just took the calculation given, and in knowing that the length matters, as well as other things, I just worked from there.

Very good info. 8^)

Thanks !!!

Now, can you tell us how much the spine will change for every inch above, or below those figures? A chart for that would be a nice addition to this topic.

Rick

A lot of things get lost with the passage time. I remember exactly what Bob refers to but just forgot about that part of it. The spine was predicated on a 28" arrow. I don't even know if the ASTM measure takes that into consideration. That said, it really is all about the dynamic spine anyway so that quickly loses its meaning in the gozintos.

Rick or George:

Seeing that many carbon arrows list their spine as 350, 400, 500, 600, and for lighter weight bows, 800, 900 and 1000, when I look at the chart, my simple mind seems to see that these numbers are derived by eliminating the decimal point from the number.

Would this be a "fairly correct" assumption?

I do know I'm going to print this chart off as soon as I get to the work computer tomorrow.

Harry, your assumption is right with gold tip and Easton. It goes out the window with carbon express. With CEs, the higher the number, the stiffer the spine.

Steve

Steve, THANKS! As for Carbon Express Predators, their "800" spine version is an arrow for lighter weight bows; I traded for a couple and they're are almost "magic" for my 31#-33# bows. Perhaps the Predator is an anomaly within the C.E. brand.

I didn't grow up with carbons, so they are still quite foreign to me and how I go about arrows.....

They have some numbered 700, 800 and 900, and they are right for their spine. The 150 is close to .500, the 250 is around .400 and the 350 is .340 if memory serves me correctly.

George: I disagree with your statement,"That said, it really is all about the dynamic spine anyway so that quickly loses its meaning in the gozintos." There has to be a starting point for length with the deflection. With the AMO standard you know that a .520 deflection is for a 28" arrow that converted to pounds is 50#@28". If you didn't know that arrow length you would never know that if that shaft is cut to 29" it would be 45#, as for every inch longer the shaft looses 5# of spine. Bob

Let me add something else. The AMO standard is based of a mathematical formula; 26" centers and a 2# weight gives you a deflection number in thousands of an inch, that number divided into 26 = bow wt. for a 28" arrow.

The ATA standard is based on; oh gee I just weighed our weight and its only 1.94# instead of 2#, so rather than admit we have had a slight variation in our weight all these years, lets change the standard and base it on a 1.94# weight & "No formula" no one will know the difference! And we will save face. By coincidence all this happened while Jim Easton was president of ATA!!!!!

This is where we need a sticky thread! Excelent information! Thank you, Rick, and Bob!

Rob..

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